Engine dies when clutch operated.

Thanks Simon fully agree, my biggest fear is brains, knowledge, and ability far greater than mine will not be able to identify what caused it, so it could all happen again further down the line.



Hi Allen,

Thanks for the advice, Transaxle is a Porsche G50 with standard Porsche clutch / pressure plate set up
A preload on the clutch from the master cylinder can cause the clutch to be pushed in a bit and in turn keep the crankcase pushed forward constantly, wearing the thrust bearings.
Also, if the clutch pedal is going too far past the point where the clutch is disengaged it will also cause the crank to be pushed forward and wear the bearings.

The standard Porsche clutch shouldn't be an issue.
 

Neil

Supporter
Is your thrust bearing getting sufficient lubrication? Maybe checking oil passages for blockage might be a good idea.
 

Ian Clark

Supporter
Hi Nick,

We had a very similar thing happen here.

A new GT40 owner who had recently purchased his car from the owner/builder, drove it a while and then brought it here to solve some cooling issues.

Initially I thought air cooling system, incorrect piping to the rad or header tank or a malfunctioning header tank / overflow tank.

There were corrections required in all those areas, some of it quite extensive. All said and done the car now was drivable without overheating.

On my short test drive the car (RCR GT40 with a Ford 347 stroker, G50 transaxle) it pulled really strong through the gears, however could barely pull itself up a drive way ramp. Made no sense at all but the cooling system worked fine.

About a hundred miles later the party was over, oil pressure dropped, the driver shut off the engine and called for a tow. The engine was not happy to restart.

To make a long story short: a) Engine and Transaxle out b) Engine sent to reputable engine builder for diagnosis and repair c) Problems: Crankshaft and rod bearings wiped out, crank thrust bearing wiped out, several rod and crank bearings spun d) Probable causes: 1) improper bearings for forged stoker crank 2) Excessive thrust on end of crankshaft. e) Solution: Complete rebuild required. There was less than 350 miles on the engine by the way.

Before reassembling the new engine to the transaxle checks were made to the condition of the clutch, flywheel, pressure plate, throwout bearing and slave cylinder and verified to be usable.

Also, I checked, rechecked and triple checked the distance between the pilot bearing in the new crankshaft against the input shaft on the transaxle.

The pilot bearing (or bushing) holds the input shaft concentric with the crank however it should never be end loaded, as would happen if the input shaft was too long, the bellhousing adaptor thickness was not accounted for correctly, the pilot bearing carrier or bushing was not fully seated in the crankshaft or otherwise too long.

The input shaft of the transaxle was about .035 longer than the space available to avoid end loading the pilot bearing (and therefore the crankshaft thrust bearing). A new, shorter aluminum pilot bearing carrier was spun up, installed, test assembled and measured to confirm there was no end loading of the crankshaft.

I suspect that was your problem. Hope this helps with the diagnosis regardless.

Cheers
Ian

Unless you're in the habit of leaving the car in gear while stopped at intersections or in the pits, meaning you are holding the clutch pedal down for long periods of time, I doubt there's enough pressure in the clutch pressure plate(s) to hurt the crankshaft bearings.
 
Hi Guys,

Thanks for all the advice much appreciated, the really confusing part is the thrust washer and the crank surface nearest the water pump end are badly scored. If it was pressure on the crank from the clutch end that had caused it the wear would have been on the side nearest the clutch. All clearences seem fine but I am planning to get some expert engineers in the Northern section of the club to check it once it is all back together.
 

Sean Starkey

Supporter
Hi Guys,

Thanks for all the advice much appreciated, the really confusing part is the thrust washer and the crank surface nearest the water pump end are badly scored. If it was pressure on the crank from the clutch end that had caused it the wear would have been on the side nearest the clutch. All clearences seem fine but I am planning to get some expert engineers in the Northern section of the club to check it once it is all back together.
The crank is definitely getting pushed towards the transmission if you see the wear on the front of the thrust bearing (water pump side).

Just curious, how did the timing set look? Also curious, did the front of the crank get checked to make sure the timing set could slide all the way on? The timing set should slide on easily by hand and not bind anywhere. I cant see anything else putting pressure on the front of the crank to push it to the rear of the block.
 

Randy V

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Standard Porsche G50 clutch configuration works inverse from the rest of the world in that the release bearing PULLS on the clutch diaphragm rather than PUSHes... This will pull the crankshaft towards the rear of the car putting stress on the forward facing surface of the thrust bearing.
I respectfully submit that either the thrust bearing was damaged on installation or the crankshaft thrust surface was improperly machined - which may have never been a problem in a standard clutch configuration....
 

Dwight

RCR GT 40 Gulf Livery 347 Eight Stack injection
Supporter
I'm dealing with the same problem. G50 with a Ford small block 347. The aluminum adapter for the pilot bearing was not driven in enough. The pressure on the crank wore 8 thousands off the rear thrust area on the crank. New forged Eagle cranks are not available till late Dec. Maybe? I found a shop in Memphis Tenn that rebuilds cranks. It cost $300. New crank was $675. Next for me is to get the block line honed and back together. This projects is slower than a large two legged turtle
IMG_7732.jpg
 

Randy V

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I'm dealing with the same problem. G50 with a Ford small block 347. The aluminum adapter for the pilot bearing was not driven in enough. The pressure on the crank wore 8 thousands off the rear thrust area on the crank. New forged Eagle cranks are not available till late Dec. Maybe? I found a shop in Memphis Tenn that rebuilds cranks. It cost $300. New crank was $675. Next for me is to get the block line honed and back together. This projects is slower than a large two legged turtle
View attachment 118656
Aw crud Dwight! You just can’t catch many breaks with this car....
What a pisser.....
 
I'm dealing with the same problem. G50 with a Ford small block 347. The aluminum adapter for the pilot bearing was not driven in enough. The pressure on the crank wore 8 thousands off the rear thrust area on the crank. New forged Eagle cranks are not available till late Dec. Maybe? I found a shop in Memphis Tenn that rebuilds cranks. It cost $300. New crank was $675. Next for me is to get the block line honed and back together. This projects is slower than a large two legged turtle
Thanks Dwight,

Interesting, although I would have thought if the pilot bearing was not driven in enough the gearbox input shaft would butt up against it causing the crank to be pushed forward, resulting in damage on the front nearest the gearbox surface of the thrust washer not the rear nearest the water pump as in our case. I purchased my engine in 2006 which was the start of the project so my turtle may only have one leg if that!!!. Apparently it's all about the journey ;)

I have passed all the suggestions onto my ever patience and extremely knowledgable consultant engineers, aka members of the UK North West area GT40 enthusiasts club for some more lively debate. It is keeping a lot of people awake at night thinking about it :)
 

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Randy V

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Thanks Dwight,

Interesting, although I would have thought if the pilot bearing was not driven in enough the gearbox input shaft would butt up against it causing the crank to be pushed forward, resulting in damage on the front nearest the gearbox surface of the thrust washer not the rear nearest the water pump as in our case. I purchased my engine in 2006 which was the start of the project so my turtle may only have one leg if that!!!. Apparently it's all about the journey ;)

I have passed all the suggestions onto my ever patience and extremely knowledgable consultant engineers, aka members of the UK North West area GT40 enthusiasts club for some more lively debate. It is keeping a lot of people awake at night thinking about it :)
Did you read post #27? The Porsche pressure plate pulls the crank towards the rear of the block when being activated.
 

Dwight

RCR GT 40 Gulf Livery 347 Eight Stack injection
Supporter
My machinist picked up block and crank today. He is going to line hone it this week. He need to take an extra thousands off the #3 main cap. The shop that rebuilt it turn that main down one thousand to much. Maybe I can start putting it together next week.
 

Neil

Supporter
My machinist picked up block and crank today. He is going to line hone it this week. He need to take an extra thousands off the #3 main cap. The shop that rebuilt it turn that main down one thousand to much. Maybe I can start putting it together next week.
That should not have caused what was shown in the photo. Something else is wrong (too).
 
Update as I believe the root of the problem has been found. Drove up to EDA yesterday to drop off some bits, Ben looked at my sump pan and asked if it had been powder coated, he knew of a £40000 boat engine that had been ruined by blast cleaning residual left over by a pre powder coating process. I had my sump Cam Coated he suggested contacting them to see how they had prepared it prior to the coating.

Rang them up and they blasted aluminium media at it prior to coating, spoke to Ben again to let him know and he said after I had gone he rubbed of some of the oil left coating the inside of the sump and it had plainly been blasted with something. So confirms Pete and Mike in my section of the GT40 club first thoughts it was contamination of the oil that caused the bearing issue. Bad news is he advised not using my expensive GT40 replica oil pan (which I love) again. :(
 

Randy V

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I don't know Nick. The thrust bearing, like all bearings, gets only filtered oil. I would think that the filter would have been plugged up to the point of bypass in order to put trash in the oil galleys. If that were the case, all of your bearings would have been trashed - not just the one side of the thrust bearing.
Don't go tossing that sump into the bin.
 

Howard Jones

Supporter
If you have a G50 you can check piolet shaft alinement and longitude clearance into the piolet bearing by assembling the gearbox onto the engine with all the clutch/throwout bearing components removed.

Offer up the gearbox (sinch down the mount bolts to spec) with the flywheel on the engine. Leave out the clutch pressure plate, friction disk, throwout bearing, and cross shaft. Now, look into the bell housing through the holes in the bell housing. You can clearly see the pilot shaft being inserted into the pilot bearing. Turn the gearbox in gear and the input shaft should (MUST) turn freely without radial interference.

Now mark the input shaft where it is inserted in the piolet shaft with a sharpie all the way around for one revolution. You are going for a depth witness mark indicating input shaft plunge into the piolet bearing. Pull off the gearbox a see what you have.

The plunge depth of the input shaft MUST be less than the total depth of the piolet bearing hole. A 1/8th inch would be plenty and less than a 1/16 and I would start some deep thinking on that along with a series of careful measurements to be sure that the input shaft is NOT bottoming out in the piolet bearing bore. As long as the input shaft is fully inserted into the roller bearing and not bottoming out against the end of the bearing adapter and does not bind when turned you have a pretty good place to start from.

If all the above looks good install the clutch friction disk without the pressure plate and be sure it slides back and forth on the input shaft spline freely. Ok now take the friction disk out and install the pressure plate onto the flywheel. Is the input shaft still easy to slide into the clutch pressure plate when correctly aligned? Put the clutch together (pressure plate and friction disk) with the throw-out bearing and cross shaft and check again.

Everything MUST still slide freely with a bit more fiction because of the combined components but still free when you slide the gearbox onto the motor. If the clutch is aligned correctly ( you must use the correct clutch alignment tool) it all should slide right on.

I bet you have found the problem at this point.

I believe that something is tight and you are going to need to find it before you repair the engine. If it was me I would bring the engine home and do this stuff first. Maybe with only the crank installed in the block to keep things lighter.

If the input shaft has any binding it will not work and will result in trust-bearing failure. Be aware this only takes a few min at idle when you start it up to ruin them if they are loaded. They are not meant to remain under load for anything other than clutch engagement cycles as you change gears as well as stop light stuff.


Last point: install the gearbox mounting bolts onto the adapter plate and use them for guide pins. If the bolts are meant to screw into the adapter then buy some long bolts and cut off the heads to serve as extra-long alinement pins. Once the GRBX is tight up against the adapter plate the long headless bolts can be replaced with the ones that hold on the gearbox one at a time. This is the way I do my R21 in my GT40. I do not recommend the other way around where you attempt to place the gearbox onto the adapter plate by using only the short little alinement dowels that are installed in the adapter (or engine for that matter in other applications.

I am not surprised to hear that the engine builder inspecting the engine did not find a cause. I assume that he is experienced and not an amateur. The input shaft is being loaded in an in/out direction when the gearbox is installed. It more than likely wasn't the engine itself.

Anything you can do to help with gearbox installation such as a strong bench or chain hoist will make all this MUCH easier. I do not recommend installing the engine into the car first and then fighting the gearbox onto the engine. I have been removing the entire power train as a unit for near twenty years after fighting this gearbox install thing at first,

Here are twenty years of experience worth of trying to make things easier on myself. I can now install the gearbox onto the engine and the power train into the car with one hand (well almost but surely alone and without any hammers). All this stuff can be made from wood with a little ingenuity and at little cost.
 

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Howard Jones

Supporter
I went back and edited the above. Sorry about that. Lots of wine flowing around here yesterday..................... As far as your oil pan goes. Have it hot tanked just like the block. If the hot tank process will clean a block it will clean an oil pan. You are going to completely disassemble the engine and reclean it anyway.............right?

The pan is steel or aluminum? Steel will most certainly clean up because the aluminum blast material only "clings" to it. Aluminum is a slightly different problem because the medial is impregnated into the surface somewhat depending on the air pressure used and thus the velocity of the media. It may take some lengthy hand cleaning. You might even try having it blasted again with walnuts to blast off the aluminum medium. Then the lengthy hand cleaning. That's what we did with parts that cost two or three times the cost of an engine. After that have it finally cleaned with the hot tank.

By the way. I used to work in a repair shop that handled very critical electronic controlled braking valves similar to aircraft-related parts. There was a bead blast unit on the other side of the shop that repaired larger dirty parts that came off the train (commuter mass transit). So some of the lazy people would use the bead blaster to clean everything. A LOT OF STUFF got ruined because aluminum grit (media) gets sort of embedded (really just fattened onto it due to the high impact speed) in harder steel or iron parts. They went to walnuts to avoid this and in the end, just took out the bead blaster and bought a dedicated parts washer.

When thrust bearings have failed you will have all sorts of heavy metal (bearing and journal material) debris mixed into the oil. This slurry gets into everything and will ruin the rest of the bearings very quickly. It's just a matter of minutes, really just seconds. Find the thrust load source and then rebuild the motor. Supper clean the pan and I think you will be OK. Sorry for the bad news on Christmas. And a very merry one to you and yours anyway.
 
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Bill Kearley

Supporter
Nick, The only thing that makes sense is an input shaft endplay problem. Put a little plasticine in the pilot hole and around the bushing entrance. It should show if there is any interference.
 
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