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MG MGA - Derrington Water leak

I was just checking over things to try to find out why my engine is so rough with the Derrington head. I took the rocker cover off and found a little water near a rocker pedestal. I think it's probably coming from the special bolt for the pedestal. Has anyone seen this before? Can it be solved? I have only run the engine for about 20 minutes.

John



John Francis

It isn't so easy to tell from your picture John, it could possibly be condensation, but just to be certain, I would run the engine with the rocker cover off so you can identify where the water is coming up from. (To prevent a lot of mess, lay some old cloths either side of the engine to catch any splashes of oil from the rockers)

If it is coolant coming up by one of the head studs, then unfortunately, you will probably have to take the head off again to investigate where the coolant is getting past the head gasket. (Payen gaskets seem to be the best for a tuned up B-Series)

Sorry you are having such a torrid time with your project John, don't let it get to you, you will get there in the end.

Cheers
Colyn
Colyn Firth

If your coolant is blue then it's coolant. Unless I'm having another brain fart or false memory I think I once had a leak that was cured with running some sealant down without taking the head off.

IIRC Cosworth used to put Barrs in (some of) their new engines as a conditioner, and to seal leaks against leaks(?) (or am I on Fantasy Island again, Cosworth, Jim's End, Northampton).
Nigel Atkins

Hi Colyn

The Derrington has an interesting construction. The small studs for the pedestals screw through into the water jacket in the head. I'm not sure its the head gasket leaking, I think its the stud into the water jacket. However, until I take it all apart I won't know. Im pretty sure its coolant as Nigel says its blue like the coolant with 50% antifreeze.
This project is really testing my patience! I am going to see if I can get the engine running more smoothly before I dismantle it all again though.
John Francis

John,
ask the engine builder or those that know on here (excludes me) but I think on my previous HG replacement it was a small leak rising from a stud and some seal was just run down it, I didn't actually witness the procedure so not sure if it was as straightforward as that but whatever they done lasted 10 years of spirited use (A-series engine).

I'm sure there'd be some 'racing tricks' for such things or there's the likes of K-seal or other such stuff for block/head.

If it's only leaking just there that's probably a good sign the HG is fine so a shame to break everything down again if you don't have to.
Nigel Atkins

Yes, HRG-Derrington heads can leak from the rocker gear stud post holes. See the attached photo from my redundant HRG head (replaced recently with an MSX head) that shows the stud post hole that opens into the water jacket. You will note it has been counterbored. Initially it use large section O rings and thread sealant to seal in this area. Later when I replaced the rocker gear posts I used Wurth Flange sealant to fill the gap and as the thread seal (3/8' UNC). I had no problem with water leaks in this area with either sealing method. (My engine builder/machine shop recommends the Wurth product for sealing all head studs).
Mike





Mike Ellsmore

Yeah, I wouldn't be pulling it all apart -
If you drop some coolant so that it's below that level and then double nut the stud and screw it out , get it nice and clean and dry , and poke some rag down the hole to clean/dry the thread down in there , then apply the sealant to the threads of the stud and wait till it tacks off a bit so that it's a bit stiff and sticky, then screw it back in
It'd pay to do the 4 of them, but if you just do them one at a time and tighten up before doing the next one you shouldn't disturb anything else
That Wurth flange sealant is good stuff ,also CRC and Loctite flange sealant are quite ok as well

Stick at it John, it's a good project you've got going there, think of it as an interesting feature ,not a fault

willy
William Revit

Willy and Mike

Thanks your comments are really helpful. I like your sentiment Willy, it is an interesting feature and project. I just need to sleep on things before tackling the next challenge. No point in rushing when we are in another lockdown here in Wales. For sealant I usually use Wellseal. Developed by Rolls Royce many years ago. Its not a big gap filler though.
John Francis

My mate was against it, he cleaned up and checked my cylinder head when helping with my latest HGF, but I remember being told using stud lock also helps against leaking. I used it on the previous (A-series) heater tap studs as they kept coming loose and I might have also used it on the (A-series) stat housing studs as I was told coolant can creep up the studs making the stat housing even more belligerent about being removed.

He said I shouldn't need to use stud lock but I did with the previous heater tap studs at least.

Even after putting a torch to the heater tap studs he didn't have enough time to put more effort into removing them but I later got them both out just by using the two nuts method (I did break one stud but that was my lack of patience and bravado). I could see evidence of the melted the stud lock on them. The stat housing studs were out so I'm not sure if I stud locked them or not.

To prevent coolant leaks (Forlife which I use will find any leak) I've found with the heater tap and stat housing gaskets rather than using the blue using Hylomar HylotyteŽ Red 100 is much better. - http://hylomar.com/hylomar-product-range/gasket-jointing-compounds/#hylotytered
Nigel Atkins

I have taken the rocker assembly off and found that the one stud was loose which leaked. It's an interesting design with the rocker studs as a one piece with a larger diameter section where it sits in the head.
Not quite sure why its that design. My understanding is that earlier versions had a straight parallel stud.
I took all the studs out and will reseal another day.




John Francis

Thanks for the pic./ update John
Neither of the heads I've had in the past had that style of stud, they were just straight normal studs
Trying to remember back as to if either head had that recess machined into the surface but can't remember and have no pics
I have the invoice from one of them when it was new and there weren't any rocker studs mentioned so I guess it used std. studs or they may have been overlooked--who knows-?

Anyway, that's beside the point
Good find with the loose stud, a good seal up of the thread and underside of the flange and tighten them down and all should be good
William Revit

John,

Do all the rocker studs have that recess in the head?
The adjacent stud seems to the plain type.

Mick
M F Anderson

Hi Mick

Yes they are all the same. The photo is not very clear. I'm going to use Hylo Tyte red for the seal and will also put some Wellseal under the pedestal when I bolt that down. The HyloTyte does gap fill but hardens a bit I think but the Wellseal never hardens and is good on flat surfaces.

John
John Francis

John,
the Wellseal is more liquid but like oil, in storage at least, when cold it's thicker though, I have some in the shed and have just checked.

The Hylomar Hylotyte Red 100 is a "semi hardening gasket and joining compound" so you could just use that if you want as the leak is only from the stud flange and head (unless a washer or other seal is also supposed to be there).

It also has - "Improved gap filling - usable on rough machined and pitted surfaces".

As it's semi hardening I was able to (re)tighten the nuts on my stat housing studs, obviously I didn't tighten them enough previously, as I'd noticed a small weep there (Forlife will find any weaknesses) and it stopped and as I put before I also had to do this with the previous heater tap fixings as the studs were loose until I stud locked them and again the Red 100 solved the problem of the leak and previous leaks.

If it doesn't work blame me - but follow the instructions and I'm sure it will.





Nigel Atkins

Well I have solved the leak which is great. I used HyloTyte red on the studs and some Wellseal under the pedestals over the studs.

However, I am really struggling to get the engine to run smoothly. I have tried to balance the carbs and have adjusted the mixture slightly. I think it might be a bit rich now when I look at the plugs. They have white centres on the electrodes but sooty edges on the bottom of the threads. I made it richer because it seemed to slow down when pulling the Venturi plungers up by 1-2mm before. However, neither richness not timing seem to make much difference to the roughness.
The idle is rough running, varying between 900 and 1200 rpm and its a bit random. It can run smoothly for a second or two then falters.

When I test drive it the engine will stall on idle coming up to a junction and then trying to start it is quite tricky. It shakes considerably and needs choke. Otherwise it seems to go OK but I can sense the roughness.

I have checked the static timing, 5 degrees BTC and the rocker clearances are set at 18thou +/- 1thou. I am going to buy a compression tester to see what the compression is like. I might try a different coil too as mine is the original one. Plugs are NGK BP6ES.

John Francis

Been there, got the t-shirt but it ripped and fell apart! :)

My problem turned out mostly to be trying to set up the carbs with one having an intermittent sticking jet when pulled down by operating the choke passed fast idle, intermittent of course by Sod's Law. I'd get things set well enough for a run and it'd be OK but I had to tinker to get it better which made it worse if the jet stuck on warm up or running but as it was intermittent I didn't twig and I *thought* I'd sorted it off the car previous.

I also found the dizzy cap needed cleaning on the posts, I'm not sure if I knocked the cap whilst bumbling in the engine bay.

I tried a previous coil that had been on the car years ago and given to a mate as a spare who lent it back to me. If anything slightly worse (didn't realise about the sticking jet). Bought a brand new, not so well-made coil and fitted it, obviously no difference.

As my plugs were the same as yours, black at the threads I replaced them even though they weren't that old and I'm glad I did, I could se more with new clean plugs.

I discovered that my air filters needed cleaning too, they must have been helping with the richer running.

Then I discovered the SU and MGOC throttle linkage levers didn't give wide open throttle, but that's another story ...

Moral, check again what you double treble-checked previously.
Nigel Atkins

Nigel That made me smile. Thanks for the encouragement! Its so annoying because everything worked perfectly with the old head. I have actually put in K&N filters recently. One is off at the moment though. I wonder.......?
John Francis

Hi John
have you tried to contact Bill Spohn to ask about the best set-up for your engine? He is based in West Vancouver, Canada and he has an enormous amount of knowledge on the Derrington HRG head.
I think he used to run one on a race TVR with a B-Series and so he must know an awful lot about tuning that motor.
I think you could message him direct on the MG Experience Forum.

You have probably already read all the stuff on his website, here is the link.

https://www.rhodo.citymax.com/HRG.html

Nearer to home, I would think that Peter Burgess would be the man to talk to. I am certain that he will be able to re-jet your SUs and set the timing to get it to run right.

Peter did a dyno set-up on my 1950 cc engine 3 years ago to set up the Weber 45 DCOE and the timing.

The car had a really loud backfiring issue, it would also spit-back through the carbs under light throttle openings and was almost impossible to drive.

I have told the story before of how Peter sorted it out on the dyno, it sounds like Nigel had similar problems on his engine. Peters efforts have completely transformed the car.

So I would book your car in with him as soon as it is run in enough to let it rev a bit.
Also, his dyno now has knock sensor kit which could prove to be an "engine-saver" on a high compression engine like yours.

Cheers
Colyn
Colyn Firth

John,
I cleaned and re-oiled my K&N (external) filters but for a second time it seemed I over done it as they were still restrictive and go the oil cleaned out again.

I just wanted to get my carbs and car set up reasonably well and have it sorted by Peter with a session on his rollers but then as now lockdown got in the way. Twice I had the car running well but just had to tinker more and lost all i had before and couldn't get back there.

Peter put different SU needles in mine this time round - but changing the SU jets is lots more work, done before the rollers.

Amber Valley is in tier two already now, not that it matters after Wednesday.

I changed my coil, rotor, dissy cap and plugs and it did seem to help, which particular part or as a whole combined I don't know, they weren't due for change but it did help to change them, a little.

When the the engine wasn't running well it did seem to loosen a few screws, nuts and bolts on the car, plus our rough roads of course.
Nigel Atkins

John
If your idle speed drops off when you lift the piston 1-2mm then it is lean. At 1-2mm it should slightly increase then drop off with further lifting
Are these the carbs from the car pre Derrington
Is there an air leak around the manifold/gaskets there anywhere or a vac.hose off somewhere
The plugs should be a biscuitey fawn sort of colour centres with a dry charcoal colour around the outside ---White definately says lean unless you've been on a long light throttle run
.018" sounds a bit wide for the valve clearance
(depending on the cam) and i'd lift the timing up to around 10 for a try
Are you doing the timing statically or with a timing light running, if it's running with a light go to 12
William Revit

Willy

My carbs are the ones I had on the old head. I set the timing statically using a light. I tried my old Xenon Hawk timing light yesterday but I found I could not get it to trigger reliably. It flashed a few times but would not do consistently. I haven't used it for about 20 years. I did wonder if the spark wasn't strong enough to trigger it. However, I have played around with the timing using the fine adjuster on the distributor. This doesn't seem to make any discernible difference up to about 8 degrees BTDC which is at the end of the range. I'll have to move the dissy to get more advance range and that means taking the carbs off again.

I found that the vacuum advance pipe wasn't fully tight in the carb body so there may have been a tiny leak of air. However, no sign of any other leak. I enriched the mixture about three flats which made a bit of difference although I am struggling to perceive the engine speed change when lifting the pistons because it's lumpy anyway.

It now will idle at about 800 rpm but its still pretty rough. On start up the engine shakes a lot. The top of the front carb clouts the bonnet stay when the bonnet is shut.
John Francis

Hmm
I can't come up with a reason why the mixture should change from swapping to the new head.
Was there any work done to the carbs while they were off--
Is it the same camshaft as before (pre Derrington)

I have had one horrible little thought, -There can be an issue with the exhaust valves hitting the top of the block if the head has been skimmed or a higher lift cam causing bent valves
You can check if this is an issue with a compression test initially and also check the available travel of the 4 exhaust valves
With the cover off, if you wind it over until each exhaust valve in turn is right down as far in it's travel as it goes then get a large screwdriver or some other lever under the rocker shaft and over the top of the valve spring cap and lever the valve down to make sure you have at least .080" extra available travel remaining
Be carefull not to push down too far on the cap and make the keepers pop out----and be gentle pushing the valve down, don't get heavy with it, they only go down about 1/8" extra at the best of times
If you haven't got clearance,it might have bent one or more valves
I did say it was a horrible thought, I hope it's not the problem but it's something that needs checking anyway and you need to check the four of them, just because one is ok doesn't mean they're all ok
Valves--1-4-5-8 are the usual victims but might pay to check the eight while you're at it
willy
William Revit

Hi John,
If you used the same SUs, it sounds like a re-balance is in order to help with the rough idle. I don't have to take the carbys off to adjust the distributor so you should be able to get away without removing them (with some contortion).

Mark
Mark Wellard

Yippee! Some improvement. I was taking the front carb off to get to the ignition coil and noticed that the float bowl was not full enough and the float was not floating. There was some fuel in it but not a lot. So I cleaned the float valve and hey presto things are a lot better. The float valve looks fine. Its a fairly modern one with a black (Viton?) tip. I have tuned the carbs a bit and it's still a bit lumpy but it's a lot better.
John Francis

That's good news John,
let us know how it drives when you have given it a test run.

Cheers
Colyn
Colyn Firth

John,
I was going to post this before but will now instead. As a total non-expert that went through this recently, I'd suggest you don't worry about getting ultimate tune of mixture and not even bother with the lifting pin tuning (I couldn't get a 0.8-1mm lift or hear any difference).

Having the drop of the jets equal and turned to whatever number of flats you want, get the engine warmed then get the carbs balanced at idle, and help yourself by having the idle higher than usual as you can tell more with it that way. Adjust the jets one flat at a time each until the idle speed increases to fastest and smoothest. Use whichever method you prefer for blowing out and letting the carbs settle between adjustments.

I found the fastest and smoothest idle would be the same for two flats so just go back to, or leave at, the weakest of the two flats, by balancing the two carbs adjust the idle back down to the (faster) idle you started with and this should be at a smooth running idle (if a bit faster than usual) giving a good benchmark for road test runs and further fine tuning.
Nigel Atkins

Took it for a test drive and it went well. However, here's another puzzle. In neutral with foot off the clutch it idles fairly smoothly at 1000 rpm. Put my foot on the clutch still in neutral and the idles drops to 500 rpm and then fluctuates a lot. It goes into gear easily so the clutch disengages fully.

I'm not sure what kind of effect might be happening. Some extra load on the engine or some out of balance. The flywheel and the clutch cover plate are all one item effectively and have been balanced and the clutch driven plate is not connected to the flywheel with the pedal down so I'm wondering what might be happening to the pressure plate or something else?
John Francis

When you depress the clutch in neutral the only extra load on the engine would be the release bearing on the operating fork and the thrust bearings on the crankshaft.
Do you have a carbon clutch bearing or a ball/roller bearing.
Have you checked your crankshaft thrust bearing (end float))?

Mick
M F Anderson

John,
Good to hear you found the culprit to your problem. Trouble with idle stability when you push the clutch is associated with being too rich in my experience.
Regards,
Mark
Mark Wellard

Mick I had a proper crankshaft seal installed on the engine as part of the process of putting the new head on. It had a new thrust bearing fitted from Hi-gear. Interestingly the old one used to squeal when first using the clutch on a journey but went away afterwards. The clutch release bearing is a new carbon one. Mark thanks for the tip. It is possible its still too rich.
John Francis

If you're making adjustments with the air filters off putting them back on will make things a bit richer so you can either allow for this (going for the weakest of the two flats if you get two) or adjust with filters on if you can still get at everything.
Nigel Atkins

Such a large drop in RPM when depressing the clutch pedal could indicate worn crankshaft thrust bearings.

Regards
Colin
Colin Manley

John,
another note on the carb setting is to ensure the cables and linkages have some slack at rest and are not in play when they shouldn't be. I forgot to check both jets fully returned when the choke was fully off.

Also if it's been running rough then check the tightness of fixings, it's amazing how they can vibrate loose.

Nigel Atkins

This thread was discussed between 23/10/2020 and 06/11/2020

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