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MG MGB Technical - Replacing the heater matrix

The screen has been misting up as the engine warms. My assumption is the matrix is leaking and needs to be changed.

Obviously the easiest way to change the matrix is to remove the whole heater but that involves the cable to the interior/demist air control. Has anyone experience of changing the matrix by removing the front panel of the heater ? Essential the question is whether it is possible to create enough movement after removing the securing screws so that the front can be pulled forward.

It's the fuel-injected 3.9 and the area is pretty congested.
Roger Walker

Roger, I'm contemplating this very issue myself. If you're lucky, the matrix can leak from one of the hoses going into the matrix, rather than the matrix itself. What happens is that the water gets sprayed from the hose joint through the hole in the front of the casing, thus appearing to come from the matrix. Unfortunately, on mine it's the matrix that leaks.

From I can make out having read loads on the subject is that officially you can't do it without removing the whole assembly. I've read of people undoing the clips and bending the front panel down, or slicing the panel. However, I saw an annotated photograph, from I think Paul H, where he shows that the bottom corner of the matrix sits in a well below the bottom of what you can see from under the bonnet. The matrix of course is at a 45 deg angle in the casing. I think to extract the matrix this way you may have to bend the internal fan shroud as well.

With any luck there'll be somebody along in a minute who's done it!
Peter Allen

Yes it is possible and I have converted all my heaters like this.

It is NOT possible to remove the front panel without removing the whole heater.

To convert you need to remove the heater blower motor and hoses. Then use a dremel or angle grinder to slice across the front panel just above the bottom angle which secures the case to the body.

Once separated you can remove the clips and ease the top part of the panel away.

The heater matrix can then be eased out of the housing.

Take the front panel part you have removed and spot / plug weld or rivet a half inch strip of steel on the inside so it forms a lip to slide behind the remains of the front panel still in the car.

Once the matrix is fixed, replace it with new foam if necessary, slide the new lip in behind the lower front panel and replace the clips, heater blower motor and hoses.

Chris at Octarine Services

That's pretty clear, Chris, and much as I envisaged it, but good to hear how it's been done in practice! Thank you!
Peter Allen

Peter. That is good advice reinforced by a builder of radiators who tells me the matrix is reliable (even though the tanks at each end can spring a leak). I shall certainly look closely at the hose connections. Chris, I may have to follow your advice and I am grateful for it.

The thought that the heater was installed as a complete unit and is sometimes removed during major refurbishment is still tantalizing !

Many thanks for your comments
Roger Walker

As far as the air flap goes it depends on the year. Before about 1970 or 1971 while there were the large adjustable flaps in the footwell the cable is supposed to be accessed through there, i.e. removed and replaced with the heater fitted. After that and the fixed plastic vents the holes in the bulkhead changed and the heater can be removed and replaced with the cable attached.

However with the earlier type once the heater is out the existing hole can be extended to allow the heater to be replaced with the cable.

I think the demister tube arrangement changed at the same time, from the multi-part straight tubes, flex tubes and mounting plate to longer flexies that push into the also new rubber block.

http://www.mgb-stuff.org.uk/heatertext.htm#remove
paulh4

Roger,
another vote for checking hose connections first. The matrix is more likely to be cruded up than itself leaking.
See from 2:20-3:38 here - https://www.youtube.com/watch?v=2gCN3hbtVgQ

I fitted open grommets to the heater box panel (are they standard, can't remember) to keep the matrix outlets more secure in the case but not ridged to allow for vibration.

Next, have you checked the donkey's/Tom's dick isn't blocked?

If you have soundproofing that can hold a hell of a lot of water which can give condensation, the water could be coolant or unknown windscreen or other leak.

If you open the heater box then cleaning the outside and flush cleaning the inside of the matrix, renewing the wrapping foam if required.


Nigel Atkins

The grommets are 7H1993. Not listed in the MGB Parts Catalogue, they are shown on various suppliers websites but not always for the MGB. They provide a neat finish on a repainted unit.

paulh4

They also hold the outlets a bit more, the outlets and matrix can push back into the heater box when fitting the heater hoses leaving less outlet surface for the hose and clip to grip to after the end flare.

So I tend to heat the hoses before fitting them and/or lubricate the hose before forcing it on the the matrix outlet, sometimes they can be a surprising tight fit.

Part of the tight fit might also be a build up layer of crud from the leaking so you want to clean the outlets to a smoother finish for better hose seal.

The more the heater box is sealed or insulted the more heat you can get into the cabin but that's not usually too much of a worry with a V8.

Well done for Paul for turning up the correct part number, NTG show it as "grommet for 18mm hole", I think I just last cut down a couple of electric box grommets that were to hand. Looking at the Toss drawings the grommets appear to replace what would have been foam/insulating rings inside the box, I've got a feeling I made up and added some of those as belt 'n' braces one time.

ETA: that photo shows a bit of a fur coat no knickers job, in that the decorative finish has been attended to but the matrix could possibly benefit from (more) cleaning (or perhaps that was as good as it gets or a trial fit).
Nigel Atkins

Paul that is a most informative link which I may need if I have to change the matrix (not sure yet) - thanks !
Nigel - I have seen him in his funny hat before but this link reminds me that the problem we have with the blower in the MGA is probably because when I followed Barney's advice and converted the car to negative earth, the heater motor may be running backwards. You learn something new every day. - Thanks !

Roger Walker

Roger,
it depends which blower motor you have fitted, I found on my Midget the "fan" was actually more effective when wired backwards but it's a more modern replacement motor I'd guess. Not that I often use the fan, it's not needed above about 25mph.
Nigel Atkins

Paul is correct in the part number for the grommets. I got mine from MGOC - i have also seen them listed under parts for the MGA.
If you do end up taking out the heater box ,which i did some two years ago (with thanks to Paul for his help) i did one further modification. I had trouble getting the box out & had to bend the top "L" shaped mounting bracket away from the bonnet channel.Fearing i would scratch the paint work , never mind the difficulty in easing the box back in, before replacing the heater box,a neighbour removed the welded bracket & mounted a threaded bolt upside down in the heater box top so the bracket could then be fixed to the heater box & the firewall once back in place.
Cheers,Charles
Charles9

"that photo shows a bit of a fur coat no knickers job, in that the decorative finish has been attended to but the matrix could possibly benefit from (more) cleaning "

Polishing the matrix ports is something I'm NOT going to do. If nothing else they are invisible when the hoses are fitted!
paulh4

Perhaps that outlet is clean and it's just the photo but I didn't mean polishing Paul I just meant cleaning. Being invisible doesn't prevent a problem, furred up matrix, furred up arteries, invisible silent problems.

I did also put - "(or perhaps that was as good as it gets or a trial fit)."

"ETA: that photo shows a bit of a fur coat no knickers job, in that the decorative finish has been attended to but the matrix could possibly benefit from (more) cleaning (or perhaps that was as good as it gets or a trial fit)."

Cosmetic - 2. affecting only the appearance of something rather than its substance, fur coat, no knickers.


Nigel Atkins

It must be my poor memory as it's many years since I took the heater box out of my B but I can't remember it being that much of a problem to remove or replace, with new seals including the rubber? block one with circular holes. The only part I never found an answer or solution to was getting the screw back in under the circular fan part of the heater box. Even back then I'm sure I fitted and uprated matrix and blower which were fine until winter use then there was so much cold air getting in from other places you uprating meant very little. The Midget is opposite too easy to overheat the cabin and footwells.

Nigel Atkins

Nigel,

The removal of mine was an absolute pig. It is much easier to pull out & put back when the engine is out (which mine wasn't) as then you can stand in the engine bay vertically directly in front of the heater box. In my case the original rubber block that surrounds the later heater box demister holes had to be cut up by key hole surgery through the vents in the footwells before i could ease or should i say heave the heater box out of its location!

Cheer,Charles
Charles9

Given 30 years reading tales of woe I was surprised how easily the V8 heater came out - just a little prying under the flanges started it moving, and after that it wiggled out. Ditto refitting, with a new rubber block daubed with Swarfega Original as a lubricant. Engine was out though, I could imagine needing scaffolding boards over the engine compartment to stand on to give a good pull otherwise.

I did trim the rubber block as shown though, as looking at it and the recess it has to be squeezed into that part at the top is the fattest and has to be compressed the most. Sealing not compromised.


paulh4

Taking the heater out was one of the first jobs i did on the car. I found Paul's tip trimming the rubber block very useful. I soon realised why the heater wasn't working - see picture. The blocked up Tom's knob caused a lot of corrosion as well. More pictures on my blog at https://mgb.tips/category/projects/heater-box-refurb/
But all the hassle was well worth it as the cabin soon gets pretty warm on cold days - well say after about 2 miles.

steve livesley

Charles,
I can't remember (so may just have forgot) any difficulties getting the heater box out or back in again, engine was in, and can't even remember using lubricants, all seals were renewed. The box was in reasonable condition unlike Steve's. Perhaps it was just brute force (unlikely) and ignorance (definitely) and extremely rare for me good luck on a car job.

The one thing I couldn't achieve, which nobody here seems to have a problem with, was getting the screw back in under the fan part, I bought a flexi-drive and right angle screwdrivers but in the end I had to just leave the screw out.
Nigel Atkins

I love the way someone put that foam strip! Looking as old as that it must have been done when the car wasn't very old. Surely it can't be original? My 75 V8 wasn't that much worse.

The case has the hole under the fan space, but no screw as I recall, so I didn't bother putting one back in.

paulh4

Nigel,
For me it was probably one of the hardest,frustrating & uncomfortable jobs i had to do. I seem to recall taking out the screw beneath the heater fan with a pair of molegrips,but left it out when replacing. Spray on hammerite gives a great finish! (I srayed the fan motor with engine paint).
Cheers , Charles

Charles9

Paul,
I presume the foam strip was originally put in like that as it is was the same in my heater box (see attached) when i took it apart albeit in better condition than the one in your picture. I removed my heater box because the foam circle between the heater box & the firewall had disintegrated into dust + i wanted to repaint the engine compartment.
Cheers,Charles

Charles9

Charles,
I'm glad you confirmed there was a screw under the fan as I was sure I took one out and couldn't work out how to replace it, I remember asking how the factory done it but never found out.

I must have just had dumb luck with mine, IIRC the foam around the matrix was twisted at the sides (to stop the foam slipping?) but I'd no idea if it was original but it wasn't as fulsome as the one Paul shows and like you the foam circle was more dust than foam.

Of course I could set the heater valve to fully open or full shut, but not both, I tried either but can't remember which I settled on.
Nigel Atkins

I'd planned just to cut the cover as detailed by Chris above. Anyway, I subsequently found that the flap underneath the heater seemed to have seized, even though the control would fully turn in both directions. The heater box would therefore have to come out. I've had this car 36 years, but never noticed that two of the Philips screws around the heater box were missing, probably because it was all hidden under a layer of oily gunge. Two came out easily, and one had to be drilled out. Ominously, the whole box was moving too easily. I'd already released the knob from the dashboard and the box came out sufficiently that I could access the cable connection on the flap. Tried to undo and the mounting came off flap! This isn't going well, methinks. Anyway, now box could be removed completely. What a mess! All bottom of box where flap is situated was mangled. Obviously somebody had been there before me, despite car only being twelve years old when I'd bought it. There was masses of an adhesive that looked like that filler foam that builders now use. No insulating foam or rubber. The heater box is kaput. The matrix likewise. The heater's never been much good and I wonder how long it's been like this.

Exasperated, I've temporarily?!? made plates to go over the holes in the bulkhead, while I think what to do next, and imagined I'm an original owner in Southern California who chose not to have a heater fitted. Hey, it's almost the summer, and besides we're not supposed to be driving anywhere, anyway.......
Peter Allen

Peter,
I think many owners view the marque with rose-tinted glasses, these were not Japanese built cars by 12 years old many would have been rust buckets so you've done well with yours.

Wouldn't the heater have been like it for 36 years?

Whilst in fresh-air mode you want to check security of fitting and emptiness and clearness of the dick drainage.

IIRC the screws should be pozi, if they are it's best to use a pozi screwdriver of the correct size to get the better torque to remove them and not to loose the socket on the head.

I'm a big believer in the use of a good penetrating/releasing fluid like PlusGas (not ordinary WD40) and plenty of patience to release seized fixings, let the chemical do all the hard work.

As I remember it, fitting the uprated matrix might have been effective if you need to replace anyway but the uprated fan was a waste as the standard are good enough, the secret to the fan efficiency is more that the seals are in good order.
Nigel Atkins

Peter
A guy called Richard Woolley does a lot of refurbished powder coated dash boards and heater boxes for Midgets and ISTR he does some 'B' bits as well, he's in Derby I think.
I have used him quite a few times in the past and he was very reliable. He has some bits currently in the Classified section - maybe worth a call.

R.
richard b

Charles - your foam strip is correct - round the sides of the matrix, Steve's was round the top and bottom so blocking air-flow through the matrix.

I bought a new seal for the air inlet but as the one on the heater was rubber, or dense foam, and the new one was flimsy foam I kept the original as it was in good condition. I think Ashley Hinton do the denser seal.
paulh4

Peter,
If the upper part of the heater box is ok you can always just replace the bottom part that contains the flap mechanism as the prices the main box either new from Moss etc. or used & in poor shape as advertised on ebay are not clever!
Admittedly mine wasn't in bad shape but see the attached "before & after " photos. The "after" photo shows my attempt at following Paul's trimming of the rubber block.
Cheers,Charles




Charles9

On Nigel's screw beneath the fan housing bulge, I used hex-headed screws in each spot (for uniform appearance) so could drive that one home with a spanner - socket for the rest.

My 69 (assembled from late 68 body/mechanicals) had no sign of a block seal ever being there. Trial fitting that seal sans box it was clear it would not fully cover the apertures between front/rear compartments. The demister tubes are of a length to securely hold in the box openings, so I left the block out on refit.

Tom's knob was fine but the drain tube to which it fits was corroded away from the bottom but leaving the top section (I/2 to 3/4) there and sound. I de-rusted that and the plenum floor/lower sides, carefully cleaned and coated with Killrust and coated that with a bitumen body sealer product. That was applied using appropriately sized cheap brushes with the handles cut down to allow handling through the aperture beneath the dash.

I refer to that part as my "17 bandaid job". That was the number I was wearing on fingers, hand and lower right arm for cuts from the various spurs on metal edges unavoidable in the prone position needed and reaching in and around the plenum chamber.

I reconnected the control cable through the RHS heater flap aperture in the foot well. I had tried reinstalling the heater complete with the cable fitted but could not manage that without a significant kink in the cable about a half inch from where fitted. I was concerned that might affect control over full range of the flap so went with the method mentioned.

I had the engine out at the time which made the extraction/installation easier than it otherwise would have been.

That was about 15 years ago. Not a job I would like to tackle again.

Regards
Roger

R Taylor

Roger,

I believe the earlier MGBs utilised two long sleeves to link the demister tubes & the heater box rather than the rubber block.
On the later MGBs like mine, the heater controls are in the lower console & i attached my flap control to the heater box first(the work shop manual for the later cars i recall said do that) before putting the box back in the car - it took some fiddling & cursing , but using a small piece of plastic hose i was able to thread the control cable back through a path through all the wiring etc. behind the lower console area.

Cheers,Charles
Charles9

How to make it easier. :)

Early tubes I think.

(photo via Paul's site via the MGB cut-away, British Motor Museum, Gaydon)


Nigel Atkins

As posted a few days ago. The later bulkhead has a recess for the block which the longer flexi tubes push into (first pic). The earlier stiff tubes pushed into the holes in the heater, and had a mounting plate and elbows for the flexi tubes.

Prior to about 1970 that recess didn't exist so I don't see how you would ever get the heater in with a block. Second pic is from Chicagoland MG Club and also shows the modification to the egg-shaped hole to allow the heater to be refitted with the air direction cable already attached.





paulh4

Paul,
When i was in the process of putting my heater box back in i toyed with the idea of gluing the rubber block to the recess first and then easing the box into the hole ,which might have got round the tighter gap at the top.(If i had had an assistant inside the car at the time watching & being able to stop the block from moving then i would have tried that approach, but was concerned i would end up with everything being jammed up & out of alignment). I did wonder if that was how they were assembled in the factory. I suspect the original rubber block was more supple than what is now available.
Cheers,Charles
Charles9

Thanks for helpful comments.

Nigel - I wasn't under any illusions when I got this car. My first MGB built pre-BL had rusted out sills at ten years old. The two Midgets I had before that were even worse. This one I bought minus engine, to smoke around in for a summer.....I guess the equivalent now would be buying a £1000 MX5. The saving grace with an MGB is the over-engineered running gear, but if you try to run one as a daily driver in the UK (which I generally do) then IMHO you've got to be adept with a mig and have access to plenty of old washing machine carcasses.

Richard B - thanks for the tip on Richard Woolley. Might be worth a follow up.

Charles9 - components like the heater cases s/h do seem to fetch a premium. Yes, one good one out of other remains could be the answer.

The heater always was mediocre, probably for the reasons stated before, but it wasn't until it started to leak that I did anything about it. All I ever used it for was to try and demist the windscreen, which it singularly failed at, so maybe the back of a Dents glove would do the same job.

If I re-install it'll have a modified case, so matrix can be changed with case in situ, and socket headed screws (if they're available). Therefore, I have read this thread with interest!


Peter Allen

Charles, I like the hose guide idea-well done.

Peter, the screws I used were a standard hardware pack item. From memory metric thread and 1/2 inch, but they spun in and held perfectly. Matched to the diameter of the screws withdrawn. There is not a lot of force bearing on them - they only need to hold the box down

The Gaydon photo reflects my tube set-up. However, the floor of my plenum chamber is gently curved up to the walls on three sides - only the rhs against the drain hole is square, I imagine to flow water toward that outlet.

Is this another variation in early cars or perhaps my body build was on the cusp of a change to the later heater set up? No recess for the rubber block in mine though. CKD cars a bit of a mystery in some respects because of the lag between component production and assembly dates.

Securing the cable to the flap box I packed the lower area as best I could with cloth smoothed off to a dish in the event the screw parted from the driver. Used Bluetak to hold the screw/driver connection. Did drop it once (magnet retrieval) and added plenty of Bluetak to prevent a repeat. Relied on driver torque to expel bulk of the Bluetak between screw head and mounting face. Withdrew the cloth and refitted the heater outlet flap.

Chris's front cover modification makes a heap of sense re future matrix servicing - I would certainly do that if ever I need to pull the heater again.

I agree this has been a most interesting thread and is saved in my service files for reference in future.

Regards to all from Oz

Roger
R Taylor

Peter,
I've been running various classics as daily drivers for about 30 years now hence I'm poor but have contributed to the general running and coffers of the industry and country. Previously I'd get shot of a car before it needed metal work and have bought a couple of Heritage re-shells but due to circumstances of life I've had my present Heritage shell Midget so long now that it's starting to show very minor rust.

I'm not one for any particular marque and think all British classics have many faults, just that some are more enjoyable to own and run than others.

Considering how bad your heater was I think you'd find the normal mediocre B heater to be excellent.

In the meantime I can thoroughly recommend Pingi - https://pingi.com/shop/car-dehumidifier/car-dehumidifier/
Nigel Atkins

Started to look at my heater to see how much can be retrieved. Not much to it and I think I can replicate the damaged bits. The worst bit is the box at the bottom with the flap (the gondola to the main heater section airship). There seems to be some felt floating around in this section. Does anybody know where this bit goes?

Everybody talks of the nightmare rubber moulding (which I haven't got). Does this go on the vertical bit at the back where the two demister outlets come out? This is where I had loads of the glue/filler put by a PO or his hired hand.
Peter Allen

Peter,
If you look at my "before" & "after" photos in my post of 2nd April you will see where the rubber block goes & how it is easier to get everything back in to the recess if it is cut down from that supplied. (See my & Paul's examples).
The felt goes in the gondola as you call it on each of the long edges (and moving flap) which helps to seal the flow in which ever direction the flap is set.
Cheers,Charles
Charles9

Peter,
Here is a picture of the bottom of the gondola before i refurbished mine . i had to replace a couple of felt strips.
Cheers,Charles

Charles9

Brilliant, Charles, thank you very much. I'd heard the horror tales, but can now start to put it in context!

I was trying to get my head around whether a more user friendly arrangement could be rigged for working the flap eg a lever poking out of the vent in the transmission tunnel. Also, if one didn't have the rubber seal where would the the lost heat go (if that what it's sealing against) - into the cabin?
Peter Allen

Peter,
I don't know what year your car is, but if yiu use my hose approach, far easier to connect the heater flap cable before puting the heater box back in the car. I suspect the rubber block was partly to stop rain getting in,minimise heat loss & fumes from the engine compartment.
Cheers Charles
Charles9

Judging by the V8 heater the felt strips are on the fixed sides of the air channel as well as on the moving flap - one side at least.

With the hobby-shop felt I got putting it just on the sides of the channel, was good enough, I felt ...

The rubber block is more about preventing air from the engine compartment getting into the cabin, rather than air from the heater going where it shouldn't




paulh4

Useful pictures, thank you both.

In terms of fumes etc getting into the car from the engine bay, I wonder if that in part is down to the joint between the casing and the bulkhead ie the bit held down by the five (No 10?) Posidriv screws, and the clipped on lid of the casing. If these were well sealed, would not that issue be addressed? Any leaks further on would then just mean more hot air getting into the cabin, rather than the demisters, or have I missed something?
Peter Allen

Peter,
I think it would be difficult to get an air tight seal on the fire wall side as there is no horizontal surface to screw the heater box down on. The box sits out from the fiewall when in place by approx 5-10 mm.
Cheers, Charles

Charles9

No I'm with Peter, whether it's to seal the heater box or seal out engine bay fumes or both as there's a 4 piece gasket set it is to seal. I don't think we should ever think that precision enter these matters too much. The rubber block (and other seals) would also add their parts to sealing.

Toss only show four screws (SE910201, 3/16" unf x 5//8") you say five, and I remembered it as six!

BTW Charles the flexihose on your boiler looks a bit tight.
Nigel Atkins

Nigel,

I agree that the fitment is not precision engineering!
The way my heater box was originally fitted did not inspire confidence as to it's air tight fitting at the rear.
However some years before i removed it i did experience fumes in the interior when the hood was up. I eventually traced this to the grommet that surrounds the choke cable that had come out where the cable passes through the inner firewall metal.
I guess that also proved that the original rubber block was still doing it's duty at the time!

What boiler flexi-hose are you referring to ?


Cheers,Charles
Charles9

Nigel-
Those screws can't be 3/16" UNF because the Unified system classifies anything that is smaller than 1/4" as a BA thread.
Stephen Strange

Like these Nigel---(---, they're unf though)

https://www.ebay.com.au/i/111995972264?chn=ps&norover=1&mkevt=1&mkrid=705-139619-5960-0&mkcid=2&itemid=111995972264&targetid=1087152002312&device=c&mktype=pla&googleloc=1000479&poi=&campaignid=9767734220&mkgroupid=99377634146&rlsatarget=aud-692203741102:pla-1087152002312&abcId=1145981&merchantid=109947039&gclid=CjwKCAjwg6b0BRBMEiwANd1_SCdRlZEYVPEDwnsMqU_yY6YJ_BBU1EB6UMIEmbjzBBCO-YX-buu-vRoCw_EQAvD_BwE


and for you Steve-

https://www.austain.com.au/useruploads/files/austain_technical_information_sheet_imperial_tpi_table.pdf
William Revit

William- Evidently the Imperial system is different from the Unified National system. Yet it identifies 3/16" as both UNC and UNF. That's confusing, to say the least.
Stephen Strange

When i refurbished my heater box & other items under the bonnet i replaced a significant number of the screws & bolts with stainless steel. Other than the original air filter long bolts which are UNC the rest were UNF.The 4 screws fitting the heater box to the bulkhead are 1/4 x 5/8 UNF. I matched them with A2 screw bolt HexHd WF10789 from Westfield Fasteners.
Cheers, Charles
Charles9

I was trying to find what threads these were and found myself on the Brown & Gammons site that said they were a No 10 (whatever that means!), that aligns with Sussex MGs sizing on small cross head screws for the MGB. Doing a bit more research on engineering fastening sites this led me to a 10-32 size. I don't think they're a BA size, as I use 2BA on my earlier Riley and this seems a different threadform, more akin to BSF which of course pre-dated UNF in the UK.

Anyway, my general philosophy is to banish cross head screws wherever I can (anybody with experience of old British motorcycle chaincases may well empathise).

Roger T above reports of metric threaded screws spinning in easily. I've a pile of metric fastenings, some with socket (Allen) heads, so had a go. These must therefore have the same tpi as the MG captive nuts, as they generally went in OK, some easier than others. I'm hazarding these are M4.
Peter Allen

Yes, No10 UNF, as far as I know.

Here's a table from britishfasteners.com - in the US

https://britishfasteners.com/threads/unf.html
Dave O'Neill 2

Peter,
there's nothing wrong with cross head screws as long as you and those before you use the correct type and size of screwdriver. All the one I've noticed on my MGs have been Pozidriv (not that I know if they were original).
As I remember it No. 10 was an old (and still used) way of sizing screws, probably British as it was unnecessarily confonfusing, and then you had to work out a different number drill bit size to use - anything to avoid using a sensible metric system, we still have an Empire you know, what, what.
If you're mixing threads then it's no surprise you sometimes encounter difficulties later.

Willy,
those can't be the correct screws as they're clean and shiny, where on earth would such things go on a car? And I like that check sheet pity I can't print it off, or to scale.

Charles,
your, I guess, c/h boiler flexi-hose. A neighbour had a flexi-hose split on a basin tap connection and going round the suppliers we could only find piss-poorly made ones, the only alternative was a better set of two for £3 retail including VAT, everything is just a rush to the bottom. And it'd normally cost £70+, then add VAT, to fit this rubbish.
Nigel Atkins

Peter,
I meant to put, never trust a database be it from Toss or B&G they all have errors and omissions.

I'd look in the relevant original factory Parts Catalogue (not that that can't have errors too) but I don't have a copy for the MGB.

Perhaps if someone looking on has a copy of the relevant original factory Parts Catalogue they could post what it lists as the screws used (and the quantity).
Nigel Atkins

The problem with the Parts Catalogue is that it rarely indicates where fasteners go, just lists them, not always in conjunction with whatever they are fastening. You can take a stab going by quantity, and there are two screw types with a quantity of 4 for the heater. One is a 1/4" self tapper so obviously not right (they are for the air duct on the bottom of the main heater casing), the other is PMZ310 which is a Pozi pan-head No. 10-32 (3/16" UNF) 5/8" long as already said, and screws the heater unit to the shelf. Well, three of them anyway.

Generally speaking rusty fasteners aren't available from the usual suppliers, you have to create that finish yourself.

And yes, the Parts Catalogue contains errors as do parts suppliers listings, and Clausager.
paulh4

Thanks for looking it up. Where the micro-fishe plates any better for listing fixings?

No the parts that won't fit from suppliers always are shiny, if it's shiny it doesn't matter about its quality.

Only 4 screws, and one you can't get in anyway, seemed more at the time, I sometimes wonder if my memory is always accurate!
Nigel Atkins

Nigel said:-

"As I remember it No. 10 was an old (and still used) way of sizing screws, probably British as it was unnecessarily confonfusing, and then you had to work out a different number drill bit size to use - anything to avoid using a sensible metric system, we still have an Empire you know, what, what."

No, actually it comes from Unified and American Screw Threads! 10 is just a random number and 32 is the tpi.

Don't blame the Empire!
Chris at Octarine Services

This chart shows how close the 2BA, 3/16 BSF and 10-32 are.

Chris at Octarine Services

Nigel,

There are only 4 screw holes in the bulkhead to fix the heater box down. (See my photo on 5 April).

Moss catalogue shows 4 X SE910201 screw heater to bulkhead &
1 X SE604051 screw heater to bulkhead (L bracket fixing)

(Apologies but the Stainless steel ref i gave earlier was for the single screw above , albeit slightly longer than the original as that was all i could get.I blame the glasses)!

Well spotted with my C/H top up flexi-hose!

It used to just hang loose , but i got fed up of knocking it!

Cheers,Charles
Charles9

As far as I'm aware the original microfiche were produced from photographs of the printed pages.

'#10' or No.10 doesn't seem to be a random number as such, but the penultimate number in a series from 0 to 12 covering major diameters smaller than 1/4".

https://en.wikipedia.org/wiki/Unified_Thread_Standard:

"Major diameter = Screw # × 0.013 in + 0.060 in. For example, a number 10 calculates as: #10 × 0.013 in + 0.060 in = 0.190 in major diameter. "
paulh4

Charles, re your 4 screw holes in the photo: I've got those four, plus another one opposite the single one on the short side of the rectangle ie a total of five. In your 5 April photo I can't see the screw hole for the difficult to get at one underneath the fan. Has yours been filled in? Of course, if inc the fatter one above it makes a total of six.

From what I can make out 10/32 is as near as dammit a coarse pitch M5 (I mistakenly said I thought M4 before).

Thread sizes are an involved subject. Our MGBs are generally UNF or UNC, but amongst other threads the odd BSP; my old Riley is mostly BSF, but with BSP an Enots and the odd BSW; my Triumph motorbike BSF, UNF and BSCyc; my wife's Volvo metric (but luckily as a lease car, I don't have to work on it), as is my John Deere Briggs and Stratton engined lawnmower. Of course you can get a mixture of coarse and fine metric threads. The most readily available high tensile nuts and bolts in the UK seem to be metric coarse.
Peter Allen

Chris,
I do apologise, I thought America was part of the Empire, next you'll be saying we've lost the Malvinas Islands, I can remember that nice Mr Patten handing Hong Kong.

I was wrong, it often happens. :)
Nigel Atkins

Having started this hare running, I really ought to report that Peter (second post) was spot on - there was a small leak from the lower supply hose - dribbling past the perished OE grommets causing the mist. Very easily sorted. Now it's only the refurbished radiator and the pool of hydraulic fluid under the back left.
The winter service is perforce extended - not a problem in the lockdown.

Stay safe everyone

Roger
Roger Walker

Good news Roger thanks for reporting back, so nice as an owner to have an easy find and fix - also proving it worth asking first.
Nigel Atkins

Charles,
my BGT was a '74 and if Peter's is around that period it seems earlier models and your later model had differences, and number of screw holes for some.

I'm a totally ham-fisted, and now ultra-reluctant, mechanic but as I put before the only difficulty I can remember was not being able to get the screw in under fan (I never thought of hex-head or socket though).
Nigel Atkins

Peter / Nigel,

I have reviewed all the photos i took when refurbishing under the bonnet of the heater box area & they all indicate there was no hole at the short side under the fan bulge. I certainly didn't fill in any hole prior to repainting. The photo attached suggests there was "just a slight dimple" where a hole might previously have been pre-drilled.

I had no difficulty in sourcing UNF threaded bolts & screws, washers & nuts in A2 stainless steel for everything i removed out of the engine compartment, leaving only the engine block, brake & clutch gear.(Fuse box excepted & one or two self tappers which i achieved through trial & error). The original air filter long bolts are however UNC which again i located in stainless steel.

Cheers,Charles


Charles9

Also shows that there were four (as shown in the Parts Catalogue) without one under the fan bulge.
paulh4

They must have changed the spec over the years. Mine's a '72. If your car is later (Inca yellow - a later colour?) , Charles, they may well have deleted that hole as it's virtually inaccessible, doesn't add much value, and couldn't have been much easier to access on production line. Just a thought: was the extra sealing below added when they deleted that screw?
Peter Allen

Peter,

In Moss's catalogue it says the rubber seal was from 1970 on.(Previously connector tubes were used). So the hole at the fan bulge end must have been deleted sometime later.
For the record my car's colour is Snapdragon being the last variation of yellow.

Cheers,Charles
Charles9

Peter,
the black bumpers, and now colour, will give you a clue to Charles's later B model year.

Charles,
looks like at least two Bs between '72 and '74 had an extra fitting under the fan bulge. I can't think I done anything to the heater box of my '78 B to see any difference as it had a V8 engine heating was never a worry and by this time I paid others to cock the work up (and some did).

No doubt some think-they-know-it-all concours judge will be able to tell us the exact minute Fred on production stopped drilling out the extra hole, they probably will be wrong about it and we'll all be in tears as those docked points take us into a negative total score.


Nigel Atkins

I’ve just checked mine. It has the tapped hole and the hole in the heater box, but I didn’t put a screw in there when I refitted the heater.

I don’t remember taking a screw out of there when I removed the heater, but I’m sure I’d have remembered if I’d struggled.

It may well be that Fred on the production line fitted a screw, but Bob didn’t.
Dave O'Neill 2

In one of those workers cooperatives they had in those days, they all decided that heater screw was too difficult and consigned it to history along with the proposals by management for enhancements such as a twin cam head, independent rear suspension, balljoint front suspension and so on. Think I'm having a Bobby Ewing moment.
Peter Allen

Bob moved on to Ford management for exactly this type of intuitive money-saving thinking.

I don't know why but I can't remember a struggle getting that screw out, perhaps there wasn't one fitted there anyway for the same reason I couldn't fit one.
Nigel Atkins

Nigel / Peter,
At the risk of stating the obvious i believe the heater box was used in various cars where the hole in the flat surround under the fan bulge was more accessible & presumably then utilised - now back to the gardening as i am fortunate to have a garden to enjoy in the current COVID-19 situation!
Cheers,Charles
Charles9

When time was money, and as dewy eyed about MGs as we can get, they were mass produced cars. So how in all that's remotely sensible you'd have an inaccessible crosshead screw directly under the fan housing beggars belief. We know by anecdote, some of these screws were fitted, so Bob fitting the heater must have held up the whole line for hours until he got beaten up by co-workers missing out on their bonus.
Peter Allen

My 1973 roadster has no hole in the heater box flange under the blower but my 1977 GT does ...
Chris at Octarine Services

Obvious Chris you've fitted the heaterboxes to the wrong cars!

I'm not sure the MGB heater box, exactly as it is, would also have been fitted to other cars and which box the one with four or five holes.

I'm often dewy-eyed about British made cars but not out of nostalgia or sentiment more anger and frustration.

There never seems to be an end to discovering the thousands of variations to even one model over the (too) many years of production.
Nigel Atkins

My 73 roadster and 75 V8 have holes in the heater flange but not in the shelf.
paulh4

Obviously signs of serious crash repairs on both cars then!
Nigel Atkins

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