Pushing the clutch lets idle speed drop until the engine stalls

I know this issue had been brought up before but I couldn't find an answer that could solve my problem, so here again:

My engine (BJ8) idles at 900 rpm. When the engine is warm and I push the clutch pedal the idle speed drops slowly to about 400 rpm and finally the engine stalls if I do not release the pedal before which will bring the idle back to 900 rpm.

I've chanded the timing, changed from lean to rich and back, but only minor changes. When I change idle speed up to 1500 rpm it drops to about 800 rpm when the clutch pedal is pushed.

I guess, there must be a severe kind of load created in the engine that is responsible for this kind of drop or what if there would be a leak in the intake system. When the clutch pedal is pushed and the load rises due to any kind of friction in the clutch system wouldn't a leak reinforce the drop of rpms?

May be someone has any kind of idea what can be done.

Lutz

Lutz Kramer said:

I know this issue had been brought up before but I couldn't find an answer that could solve my problem, so here again:

My engine (BJ8) idles at 900 rpm. When the engine is warm and I push the clutch pedal the idle speed drops slowly to about 400 rpm and finally the engine stalls if I do not release the pedal before which will bring the idle back to 900 rpm.

I've chanded the timing, changed from lean to rich and back, but only minor changes. When I change idle speed up to 1500 rpm it drops to about 800 rpm when the clutch pedal is pushed.

I guess, there must be a severe kind of load created in the engine that is responsible for this kind of drop or what if there would be a leak in the intake system. When the clutch pedal is pushed and the load rises due to any kind of friction in the clutch system wouldn't a leak reinforce the drop of rpms?

May be someone has any kind of idea what can be done.

Lutz

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My idle was just as yours but after I adjusted the carbs which were to rich it now idles better.

You might check the end float of the crank to see if it's within spec. Your thrust washers may need to be replaced.

Patrick67BJ8 said:

My idle was just as yours but after I adjusted the carbs which were to rich it now idles better.

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Patrick, I've checked that already, synchronized the carbs and CO is between 2.5 and 3.0.

Gliderman8 said:

You might check the end float of the crank to see if it's within spec. Your thrust washers may need to be replaced.

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I'll follow your suggestion and try to figure out what the end play is by measuring the crank at the pulley while somebody else ist pushing the clutch pedal. Or is there any other way to check for this with the engine mounted?

If I find to much play, is there any chance to replace the thrust washers with the engine in place by just removing the oil sump?

I don't know your engine so someone more familiar with the Austin Healey should be able to help with that.
My guess is that you may be able to replace thrust washers by removing the sump with the engine in place.

+1 for Elliot's comments and suggestions.

Could be tricky getting that thrust washer in on the 'top' I can't remember as I put mine in on the engine rebuild.

Best of luck with that.



Bob

Hmmmmm. I just had my BJ8's engine rebuilt at about 110K miles since the previous overhaul; I don't recall if I replaced the thrust washers at that time (previous), but likely would have. At any rate, at the recent rebuild the thrust washers showed very little wear (but I did replace them). IIRC, the washers are solid steel; I don't think as they wear they would increase friction much, if at all, at least until they are worn clear through and you're rubbing a crank throw against a bearing (and you'd probably hear that). Before you drop the pan and pull the pump, check the crank end play. I don't know what 'spec' is, but if it's not much more than the specified gap I don't think it's your problem. My cars' idles have always dropped a bit when you push the clutch in; I believe that is normal.

How many miles does your engine have on it? It might just be tired. I'd check the crank end play and compression before I started tearing things down. If compression is low it might be time for overhaul; it's a lot easier to install thrust washers on the bench.

+1 on Bob's comments. First check the end play and other possible causes before replacing the thrust washers. If the end play is way out of spec then it's time to address the problem.

Hi Bob,

the car has about 72K miles on it. The engine was overhauled 12 years ago, but only 6000 miles before. So one wouldn't expect to much problems from there. Of course, you never know.

I checked compression two days ago. All 6 cylinders are close together at 140. The car has a 290° hot cam, which sometimes give problems running it at lower rpms. Three years ago I had this problem once before, but all of a sudden it was gone. Just a drop of 100 rpm was left when I hit the clutch pedal. But know it's back again and even worse and I don't know why, since I haven't done any big changes on the settings of the engine. The only thing I did was to change the pertronix ignitor from version I to II, since the old one was blown. But timing is still set correctly.

Nevertheless I gonna measure the endplay of the crank over the weekend.

Lutz, I would suggest looking into the ignition settings again. An engine fitted with a 290 degree cam needs 18-20 degrees static advance in order to idle reasonable at higher than stock RPM. However, the max advance should not exeed 34-36 degrees!

johnea said:

Lutz, I would suggest looking into the ignition settings again. An engine fitted with a 290 degree cam needs 18-20 degrees static advance in order to idle reasonable at higher than stock RPM. However, the max advance should not exeed 34-36 degrees!

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Johnea, you are quite right with the ignition setting with a 290° cam. I didn't mention my settings, because I feared to start a new discussion again about this isuue which we had in another thread. My setting is even more in advance, it's 24° BTDC and max at 38°. With this setting the car has been running perfectly up to now. So it can't be the timing.

Here are the results of my investigation:

To find out what the end-play of the crank is I tried to mount a gauge between the pulley and the radiator. But no way since the clearance isn't sufficiant to get the gauge in between. So I had a friend sitting in the car and push the clutch pedal, while I was trying to find out with my eyes how much the pulley was moved to the front.

We first started with a cold engine that wasn't running, then the same thing with the engine running and finally with a warm engine but not running. I could hardly see any kind of movemant. It was just a tick to the front that I realized. The specs say 0.0025" to 0.0055", which is a clearance that can only be proved by a gauge. But one thing for sure, there is no excessive play. So I don't think that the drop of rpm has anything to to with the end-float of the crank.

I rather believe it has something to do with the release bearing of the clutch, although there is no kind of noise?!?! I don't trust these carbon bearings. I'ld prefer a roller type.

Is there any way to check the bearing without separating the gear box from the engine?

Before leaving the subject of crank endfloat and the thrust bearings... between each depression of the clutch pedal during your tests did you use a lever to push the crank back the other direction?

Doug, yes of course I did. I used a crowbar.

I have usually found this to be a lean idle mixture problem in C series engines with SUs. Around 3.5 CO may be a better bet.

Danny

Dandare said:

I have usually found this to be a lean idle mixture problem in C series engines with SUs. Around 3.5 CO may be a better bet.

Danny

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Hi Danny,

3.5 CO is a good point. I'll try that, since I keep the car always between 2.5 and 3.0. I'll let you know!

I took the engine up to 3.5 CO and then to 4.0 CO but noch chance to prevent the engine from stalling when pushing the clutch pedal. It's even worse. So now I'm pretty sure it must be either the release bearing or may be the thrust washers of the crank.