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MG Midget and Sprite Technical - Starter is rough when hot

Hi,

After a long hiatus, I hope to get my '67 A/H Sprite on the road. It needs a couple of things like carpet and seat covers but that's only cosmetic.

My one tough mechanical problem is that the starter on this car has always had a tough time when the engine is at operating temperature. When the engine is cold the starter will crank all day long. But, if I take it out for drive and the engine is hot, I can try to start the engine and the starter is always very sluggish. Scary sluggish! Like...is the car going to be able to start? Luckily, this car has always fired right up with very few cranks so it doesn't need much help but the starter is not very comforting nonetheless.

This is the second starter that I have put into the car (third if you count the original) so I doubt its the starter. It acts like there is almost too MUCH compression for the starter to handle.

Has anyone seen this before?
It is a:
1967 1275cc
I believe its positive ground and I have always treated it that way.

Thanks,
Marty
MP Peck

I would check all of the ground wires and battery terminals. You may have a connection that is fine when cold but through heat expansion it gets weak. Do you have a good engine to chassis ground wire?

I found that the ground wire from the chassis to the clutch slave cylinder mounting bolt gets oily over the years so I replaced mine with a cable from one of the pedal box mounting bolts to one of the engine to transmission bolts. Not standard but it hasn't needed attention in years.

Martin Washington

Definatly X2 martian, inside track all the way.

That would be the 1st place id look is the ground strap ... also physically remove your battry cables from there post and look inside there inner windings for the greenish white powder... many times you wont see it by just a fast look at the clamp connected

If all your groundings are good... id check your timing that its not to overly advanced.... should be around 10 deg.

Prop
Prop and the Blackhole Midget

A simple trick to test if your grounding properly ...

drive for 1/2 hour then feel up your choke cable inside the engine bay... if its really hot... then you have a grounding issue

Prop
Prop and the Blackhole Midget

Okay one last thought....and probably not likely, but ill put it out there

Make sure the solenoid is making a good clean contact to the engine bay, no paint, or rust between the noid and the body panal or its mounting hardware and that its secured tightly

Prop
Prop and the Blackhole Midget

I'm going to go with the overly advanced timing on this one.
Trevor Jessie

Martin's description of the earth ('scuse me - ground) being okay cold and not so good hot is very plausible. Exactly the same happened with my last LandRover. I added another earth strap which sorted it.

If you're grounding is poor or intermittent it will affect other things besides starting but they won't be so obvious while the car is running. Effective earthing is absolutely key to efficient electrics and is the normal cause of things like dim lights and sluggish turn signals.

Good tip from Prop re: the choke cable. If it's earthing thru that it won't be a particularly good earth - the high resistance will cause the wire to get hot, but I'd suggest the best time to check would be immediately after (or even during) a hot engine start with the starter struggling as you described because the starter is easily the biggest electrical load in the car's system so that's when the choke cable would heat the most if it is carrying the earthing loads. Be careful tho - it can easily get red-hot very quickly with that sort of current.

You could also check easily if the starter is hot after a run. If the bendix doesn't disengage and the engine is driving the starter it will get good and hot PDQ. That's not so likely as you've changed the starter, but it's possible. In fact it's not that uncommon.

I'm not so sure on the timing theory - can't see why that would affect the cranking speed.

Easy to verify if the car is positive earth. Look for the + pole on the battery and follow the cable to see where it goes.
RS Hughes

With a hot engine the flame front reaches the piston earlier than in a cold engine. If his timing is too advanced it may start ok when cold, but fire too early when hot thus forcing the piston down in the compression stroke.
Trevor Jessie

Fair enough, Trevor - but as Marty says the engine fires readily when it does turn over. Also if it's as far advanced as that I'd expect other symptoms like high running temp and pinking (pinging) which Marty didn't mention.

That said I'd think a quick timing check would be prudent anyway. I'm just not convinced that timing is the problem in this case. It's so typical of an earthing issue to my mind and exactly to the letter the same behaviour I saw from the LR (where ign timing was not an issue as it was a diesel).
RS Hughes

There's another simple test. You could connect a HD jumper calbe between the starter where it mounts to the engine and whichever is your ground pole on the your battery. Then try a hot start.
If it cranks and starts "normally" you've verified a poor ground. You'd probably need an assistant for that one tho.
RS Hughes

To quickly check if it is over advanced timing, just pull the hot wire off the coil and see if it cranks at normal speed.
Trevor Jessie

To come at it from the opposite direction you can disable the ignition by disconnecting the primary feed wire, or the HT cable, from the coil and trying the hot start. That'll tell you if the timing has any influence on the cranking speed. If it still cranks super-sluggish you're back to grounding. (It doesn't prove the timing is correct tho).

Edit: Whoops - beat me to it Trevor!
RS Hughes

Thats a great tip on disconnecting the coil wire as a test to see if its over advanced

Thanks for that trevor and rod...pays to learn something new every day

Prop
Prop and the Blackhole Midget

Marty,

Two weeks ago I had similar problems eventually found the end plate of the starter was loose tightened it up all now OK. there are two small screws on the brush end of the starter which came loose

Mike
M J Pearson

That's a good idea Mike. I didn't think of that. I think the general drift here is that it's not likely to be anything too hard to find :-)

Good luck Marty - let us know please what you find.
RS Hughes

This thread was discussed on 05/05/2015

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