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MG MGA - Poor running 1500

I drove my '58 Coupe to work today, which was the first real drive of the season. It ran great this morning (15 miles). About five miles into the drive home, it started sputtering. The exhaust note was off and it wouldn't accelerate. It would idle at a lower RPM. Throttle position made no difference. If I stopped the car and let it idle for a minute or so, like a flipped switch, it would run normally. This sequence repeated twice more until I found a gas station. I checked the fuel filter and is was full both times the poor running occurred. Thinking it was stale fuel, I topped up and finished the drive home by keeping the revs as low as possible. A few times I felt the car misfiring, but I made it home without having to stop. The ambient air temp was about 65F this morning and about 85F on the way home. engine temp was 190F (normal for this car on a hot day). I checked the coolant and there may be a little oil in it (a few brown drops of something floating at the filler) Oil is not milky. Power is as low as usual. Plugs are brown and all match. The car is fitted with a pertronix dizzy and Lucas Sport coil.

Compression (psi):
1=125
2=110
3=115
4=115

2-3 seem a little low. I couldn't find the specs. This is the original engine and it's never been apart. It could use a freshening up, but if I can put it off, I'd like too. The car did the same thing on the last drive before going into storage last Fall. Prior to that it ran flawlessly.

Any suggestions?
Kemper

Sounds to me like your points are a little too close.I would check that first. In 30 plus years of working with these cars I have had only one condensor fail and that was on my own 39 MG-VA tourer. It did it 50 miles from home. No local parts available but NAPA had a universal type that I hung on the outside of the distributer with a piece of fence wire. I cut the internal wire from the condensor
Sandy.
SANDY SANDERS

Pertronix dizzy Sandy, no points.
Lindsay Sampford

It does sound like fuel starvation, blocked filters in the carb. inlets? Quick easy check anyway.
Neil McGurk

My suggestion when this starts to happen is open the float chambers of the carb. and check if there is fuel in them.
If you can't stop the car to open the float right when it happens, it is difficult to know which of the 2 float chambers is starving.

Most probably one of the float valves remains stuck and starves 2 of the cylinders, giving low power.
Used to happen to me all the time when the engine got hot the plastic valve used to stick.
Took it out filed the edges slightly with a nail file, cleaned the float bowl and it was fine after.
Also when you take the float bowls appart check for any debris in the bottom; fuel could be dirty?

This is a quick and cheap thing to do.
Gonzalo Ramos

While I had the plugs out, I looked in the cylinders and #3 APPEARS to have a crack in the top. I tried to clean it off to get a better look, but only managed to smear the light carbon coating around. All the pistons looked uniform and I could make out what looks like MOWOG stamped in the dish. I don't see how I could get 115 psi on that cylinder if it is cracked. At any rate, I'm going to pull the head to see and I'll probably just pull the engine. "While I'm at it" will probably result in a rebuilt engine when it's all said and done. It does act like fuel starvation. I've bought a new fuel filter which was cheaper than the rebuilt will be.
Kemper

Compressions within 10% of each other, which yours are, is OK. Full fuel filter does not mean the fuel is getting to the carbs. Also check the damper oil - if low this will affect acceleration.
Keep us informed of your discouveries. Peter.
P. Tilbury

Kemper, taking off the head and 'pulling' the engine all seems a little drastic before you've done the other investigations. Your pressure test seems good - I'd leave 'well enough' alone until you have more substantial reasons/evidence to embark on such major work.
J H Cole

I figured out the full fuel filter folly and bought a new one. Just the be clear, the suspected crack is in the top of the piston. Because of that and the suspected oil in the coolant, I figured to pull the head. If the piston is cracked that means pulling the engine - classic domino effect.
Kemper

A cracked piston is not going to allow oil into your cooling system. If your car has been resting over winter, the fault is more likely due to stale petrol, crap in the fuel line or dirty points. If it were mine, I'd fill the tank, give it a good run and check the tuning before pulling things apart.
You can change a piston, fit new rings and replace the big-end shells without pulling the engine out!
Lindsay Sampford

Check your carbs. Take the lids off the float bowls and have a glass of gasoline ready. Start the car and insure that the float bowls don't go dry. If you need the gasoline, your pump, tank outlet or filter are giving trouble.
Pistons don't normally crack on the top, although I have heard of it. They usually lose the crown.
Mike Parker

Well, I've pulled the head off. Ignorance is bliss. I still can't tell if the piston is cracked despite cleaning the black crud off. It's either a crack or a casting flaw or some type of other damage. The main trouble is the #4 exhaust valve is burned and is actually a bit flame cut. All the exhaust valve have receded. I assume this happened before I got the car because I tend to be a little generous on valve lash.

Anyway, The head needs rebuilt and I'd feel better replacing the questionable piston. There is a slight ridge at the top of the cylinder. The cheap option is to replace the one valve and put it back together. The options and price increase from there. I'd like some more power so a 1622 would be nice. I'd also like to lose about eight pounds from the flywheel.

If I stay with the standard 1500 bore could I have the head built to 1622 specs (no real increase in cost)?

I'll try to get some pictures.
Kemper

I've uploaded pictures here:
http://smg.photobucket.com/albums/v307/dandomatic2/MGA/

The head is cracked at two water passages. The head gasket looks to have been blown for sometime. A piston is cracked. A valve is damaged. The exhaust valves have receded. That's just at a glance. The odd thing is the head gasket bulge. I can only assume that it is the result of exhaust pushing the gasket up into the water passage of the head. I don't think the engine trouble is related to the fuel starved-like running. Unfortunately, this is my only 3 main engine.

Anyone have a usable head for sale on the cheap?
Kemper

This thread was discussed between 27/05/2010 and 29/05/2010

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