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MG MGB Technical - 1972 MGB distributor

Everyone,

We are trying to get our car running but to no avail. The car is a 1972 MGB given to Shaun as a gift after sitting for about 3 yrs.
1st - The distributor in the car is a model 41427 which in my searching seems to be a 45D4 the car was originally sent with a 25D4. Local supplier gave me the Lucas parts for the 25D. How do I get the right parts (points, condenser etc.)? Would any one know of a year I can use to referance?
2nd - Tried to remove the unit to work on it but could not budge it. 1st tried to loosen collar screw nut and it would not move. Do not want to force unit out.
3rd - Corrosion seems dominate in the unit.
Does anyone have any suggestions for my son and myself?
Will try to add photos of unit
Thanks,
Bruce and Shaun

B Barbour

Additional photo of distributor

B Barbour

Hi Bruce & Shaun,

It does look pretty sad.

What I would be doing is the manually check for spark. Stick a plug lead into the top of the coil, with a plug at the other end, touching the engine somewhere for a return path and manually open and close the points with a screw driver.

If there is not spark then you need to check whether the fault is in the coil or the dizzy. To check the coil leave the plug etc connected and disconnect the lead to the dizzy. with another piece of wire connected to the earthy end of the coil (where the dizzy connected) brush
the free end against a screw head the is bolted to the body. This should give some sparks, indicating that the coil is probably OK.

In the dizzy things to check are, as you pointed out, the points and capacitor. Also I have found that the earthing wire for the points plate can be open circuit. Its the brown cloth braided wire seen next to the capacitor in photo one.

I don't know anything about 45D dizzys, mine came with an Hillman Imp 25D, which I've replaced with a 123 electronic dizzy. To me it looks as if the fixing plate is part of the dizzy and there is a screw still holding it in place. They do come out and maybe a bit more twisting effort will be needed to free it.

One tip: keep an eye on the small braided oil hose, seen in the top left corner of photo two.

Good luck.

Herb
Herb Adler

41427 45D4 was supplied by Lucas and Moss etc as the replacement for the correct distributor(s). All replacement bits available from the usual bandits. Of course, as with any "universal" part, will work but isn't quite right.
The clamp plate is upside down which isn't helping you. The clamp bolt should be uppermost and the raised center of the plate away from the block. Two screws into the block hold it in, and the clamp bolt holds the distributor in position. The dist can be removed with the plate still clamped to it, but it is hard to reach the screws. Penetrating oil is your only friend, use lots and be patient. Spray around the base of the dist as well as the bolts; the dist sticks in the block and can take some persuasion if it hasn't been moved recently.

FRM
Fletcher R Millmore

Herb,
1st-We checked the coil (removed dizzy lead attached clamp to post on coil , removed coil lead to dizzy
held it to motor took jumper from coil post and touched to block got spark from coil ).
2nd-We thank you for the other information you also gave us.
3rd- Novices that we are what is with the hose does it rupture easily?
******************************************************
Fletcher,
Thank you also! Your added information helps we are using PB Blaster so I / we will get the economy size as we have found out how great it is for loosening things.
Will try to move the plate once we can move the screws.
Thanks,
Bruce and Shaun
B Barbour

Hi Bruce, Shaun,

That hose connects the engine to the oil pressure gauge.
When I first got my car it was the second major oil leak I had, a hole underneath. Mine was in far better looking condition to yours, too.
Local supplier has them for $A15.

Herb
Herb Adler

Hi Bruce, Shaun,

The clamp screw has one end trapped so you can loosen it with one wrench; if you are trying to turn the trapped end it will not turn. Normally but not always the trapped end is a square headed screw, and you turn the nut, but people manage to put them together in odd ways with weird bits. Since it's where you can't see it, this might not be obvious.

If you don't know anything, be a little careful here. When you loosen the dist, you lose the timing, so be sure you know how to reset it. A good precise mark on the dist body and the block will get you close enough to start & run, but not exact when you reinstall. Always assuming it had run as it is!

Most likely there is nothing wrong with the points & cond, as the dist was likely pretty new when the car was parked. Learn to use a test lamp; be sure there is power at the point where the wire connects to the points with the key ON and the points OPEN, then that there is power near the actual contact points. This system simply has a spring tensioned connection between the power feed, cond, and points spring. They tend to get corrosion/bad contact after sitting a long time.

It is quite likely that the actual points contact surfaces are oxidised, giving no spark. Clean with point file, fine silicon carbide paper, or a fingernail emery board. I use 400 wet or dry and Brakekleen or contact cleaner. Then, with power ON and points closed, take the coil wire out of the dist cap and hold the end 1/4" from the block and manually open the points - should have spark.

Clean the dist cam off and use a bit of Lubriplate or even regular grease on the cam; the two pronged thing coming up from the points plate was to hold a felt wiper to hold lubricant against the cam, but it is not required - millions of dist did not have them.

Clean the rust off the shaft where the rotor goes as it will cause trouble fitting or removing rotor - you DO have the rotor?! Put 3 or 4 drops of oil down the shaft center hole and wriggle it back and forth to be sure the advance unit is free.

FRM
Fletcher R Millmore

If it cranks but won't start there is a fault with what you have, probably any 45D4 or 25D4 distributor ever made will fit your engine and allow it to run, albeit at various levels of effectiveness.

As Herb has said you need to diagnose, and logically. A 72 being chrome bumper is quite straightforward. With the ignition check you have 12v on the coil +ve. With the distributor cap off open the points, check the coil -ve, and you should still see 12v. Close the points, and now the -ve should drop to zero volts but the +ve should stay at 12v.

If the 12v is missing from the +ve, or drops more than a couple of tenths of a volt with the points closed, then there is an open-circuit or bad connection back towards the fusebox and ignition switch on the white.

If there is no voltage on the coil -ve with the points open then the coil is faulty, however if there is an *earth* on the coil -ve regardless of whether the points are open or closed, then the points are short-circuit somehow i.e. chafed wire, missing insulator on the points, etc.

If there is 12v on the coil -ve regardless of whether the points are open or closed there is an open-circuit through the points *and the points plate earth wire* to the body of the distributor.

Flicking the points open and closed should also show some sparking at the points if that part of the circuit is working.

After that you need to check the HT circuit isn't breaking down anywhere, and that is even if the problem is ignition and you have fuel getting to the cylinders!
PaulH Solihull

Herb,
Thanks will look into it once we get running.
************************
Fletcher
Thanks for more input it all helps us.
1st-Tried to loosen the collar but no movement of the dizzy. Should we turn it around so it is proper?
2nd-Car did run when PO parked it outside.
3rd-Had spark at points as mentioned in forum months ago when spread with screw driver.
4th- Have the original rotor and replacement that doesn't match original .
5th- will follow your instructions for cleaning and lubing.
*************************
Paul,
Thank you for replying. You have given me/us help before.
Will check items you have listed as instructed.
*************************
We have rebuilt/cleaned the carbs which were filthy.
ADDITIONAL QUESTION:
What is the set-up with the condenser wire being connected to the lead to the coil? Have never seen this before.
Thanks,
Bruce and Shaun
B Barbour

Hi Bruce & Shaun,

Assuming the condenser is external to the dizzy and connects to the hot, ie not the dizzy, side of the coil, it is a radio interference suppressor, meant to stop ignition noise in the radio.

Herb
Herb Adler

The condenser being part of the coil wire is part of the later quick-fit points for the 45D4, you don't have to fiddle about with a nut and insulating washers (which catches out a lot of people who get things in the wrong order and kill the ignition), just slip the tag into the hooked part of the points spring, but the spring must be resting on an insulator which is attached to a sticking-up part of the points base, see attached, otherwise again it will kill the ignition.

A suppression capacitor would have a wire on the 12v terminal of the coil, the body at earth potential under one of the coil mounting bolts.

PaulH Solihull

Paul,
Thanks for clearing up the set-up with the wire off the coil.
Your photo also shows me the missing "felt" from our points.
Can you tell me if the reversed bracket needs to be corrected for the "dizzy" mount?
Thanks,
Bruce
B Barbour

Having the clamp bolt on the bottom makes it v difficult to adjust timing. Having the raised center toward the block greatly increases the danger of breaking the distributor, a common problem. So yes, change it.
That requires that you get the dist out, which won't be a problem once you get it free, and it must be free to adjust the timing.

FRM
Fletcher R Millmore

Fletcher,
Thank you for the information once we get the distributor loose we will turn the bracket.
Guess I better get the drum of PB Blaster now.
Thanks,
Bruce
B Barbour

Hi Bruce,

Recently in this forum there was a discussion about freeing frozen nuts etc. The best method is to use a 50 - 50 mixture of acetone and auto transmission fluid.
Might be easier than your PB blaster.

Herb
Herb Adler

Hadn't picked upon the reversed clamp bracket but yes the raised part must definitely be towards the distributor to give the greatest surface to clamp on to and the least chance of damaging the distributor shoulder which causes it to keep jumping out of the clamp plate (once it is free to move, that is!). At that point the distributor is generally said to be scrap, but about the one decent bit of spannering to come out of The Garage - a fly on the wall documentary about a garage in Spain run by a Scotsman who could really only cope with cars designed before the 80s - was when he had an MGA where this was happening and he chamfered the inner face of the clamp plate to form a sharp edge that gripped the upper part of the distributor shoulder.
PaulH Solihull

Yes I saw that too Paul the whole thing was hysterical as he couldn't fit the points. If I remember rightly he had to get his 13 year old daughter to do that. What an admission and me a Scotsman too.
Iain MacKintosh

Did you see the one where they were boost charging the battery in the boot of a BMW? Took the charger clamp off the battery terminal, without turning off the charger first, and the battery promptly exploded! The mechanic was very lucky he only got battery acid up his arm. I bet they charged the customer for a new battery claiming it was faulty!
PaulH Solihull

This thread was discussed between 31/07/2010 and 04/08/2010

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