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MG Midget and Sprite Technical - Hot Starting Problem

At my wits end after 14 month Sprite re-build. Would welcome any ideas.

We have completed a full nut & bolt re-build. Engine has been bored out to +40 thou. New pistons, rings etc. MG Metro Turbo Head. Fast road cam. HS4 su's.

Starts, runs and drives fine. Oil pressure & temp fine. Then the problems start. Once at normal temperature if your turn the engine off & then try to restart the starter will just about turn it over - like a slow cough - not fat enough to blow the skin off a rice pudding.

Couple of goes and the starter just clicks. Starter is re-con. Have taken it off and had it checked. All is fine. Tried different batteries which are known to be good & fully charged. Once it's gone stone cold again it turns over & starts fine & runs till you turn it off.

Stumped.

Any ideas anyone?

Rob
R J Harris

Rob,
just new engine syndrome. Not uncommon on a new build! I have a 1500 doing exactly the same. Take it for a good long run (down to Monti Carlo should do it lol) and it should loosen off.
If that's not an option, don't stop or stall when its hot or invest in a jump start pack from machine mart or similar. The extra power seems to get over the problem, at least on the one I'm working on it does.

If it's still tight after it's bedding in period I would start looking at the clearances on the pistons and/or crank. Did you check them during the build?

MGmike
M McAndrew

Rob,

I have a similar problem with my rebuilt engine. If left for a time it will start fine but if I try to start it 10mins after a run the starter struggles to turn the engine over.

I have done 250 miles on mine and still the same.

I have read on this site that a poor earth can cause these problems. I've started to check these but can't find the problem. It is possible that I have painted over a metal to metal bearing during the rebuild that need to transfer the neg earth.

Halfords do a good range of thick battery cables so I,m going to try a direct route starter to neg battery terminal.

Tim
tm wainwright

The spins well on starter when cold, but not when hot is the oddity. Two scenarios that fit this.

Either the starter isn't doing its job properly = poor starter or poor electrical supply or earth or lazy battery. But less obvious why this should only occur when hot?

Or the engine is too tight when hot = close clearances that get very tight as components heat up, or high compression which goes even higher when the bores are well oiled after a short run giving better ring seal.

One thing that you could try is to slightly retard the ignition. This won't make it spin more freely, but the later spark and flame spread after tdc does help with that first bang. Many old cars used to have a manual lever on the steering column to retard the ignition for starting. Saved a few thumbs for those who held the starting handle wrongly, apart from anything else!
Guy

Yes I too would suggest setting the timing at 30 degrees all in vac disconnected for a little while until things settle down. Also be 100% sure that the earth from engine to body is first class.

Why have you used a Metro turbo head?
Robert (Bob) Midget Turbo

Check your starter. Try another.
J.W. Vlaanderen

Hi Guys

Thanks for all the suggestions.
I have had not time to work on her till tomorrow so will keep you posted.
To answer Bob we used a metro turbo head mainly so it would run on unleaded. My engine builder was of the opinion that it would also give a few more bananas.
I live near to Peter May's in Ombersley. I haven't taken it down for him to look at but just on the description he thinks it's likely to be an earth problem.

Thanks again.
Rob
R J Harris

If it does turn out to be an earth problem - or the starter motor, then it will be interesting to know why it is worse when the engine is hot and ok when cold.
Guy

Well the end of a long day.
Checked all the earths & to be fair there was some paint left over from the re-spray. Buzzed it all back with dremill. Multi meter now fixed so that makes things easier. Battery showing 12.5v so all good.
She turned over faster than Usain Bolt - loads better then before - so I thought problem solved.
Went on a run of about 30 miles. Stopped. Started again fine. Return journey 30 miles. Stopped. Dreaded cough and click. Checked battery which was showing 12 v. Every time you try to start battery drains quickly suggesting a short. I have borrowed a jump pack (thanks MG Mike)put this on & it started fine. Tried again without the pack & nothing. It seems that if the battery is just a little down then goodnight. I have retarded the timing slightly to no avail.
Left her an hour & even with the battery reading 11 v started fine.
I think it's a dodgy starter even though it's re-conditioned. Are these high torque starters worth investing in?
Side issue. Spent the rest of the day trying to fit those buggering weather strips to the door with those well designed, easy to fit little clips with the special tool.

Failed & came indoors for beer. As Homer says... "the cause of & solution to all of life's problems."
Rob
R J Harris

Rob,
Does your car have a dynamo, and regulator box on the bulkhead? I am wondering if the regulator is sticking?

The puzzle seems to be why the failure to start is only when it is hot? But maybe it isn't so much as hot, as after it has simply been running and the regulator contacts are randomly remaining stuck on. But electrics isn't my strong point so I may be talking rubbish here!
Guy

This thread was discussed between 22/06/2011 and 25/06/2011

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