Well our 3.5 engine is apart after 900 kms....Mr. Pistons meet Mr. Cylinder heads !!!
07-02-2008, 12:48 PM
#1
Three Wheelin'
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Well our 3.5 engine is apart after 900 kms....Mr. Pistons meet Mr. Cylinder heads !!!
We took it apart after a knock developed. 
The 3.2 Carrera case was machined for the Mahle 3.5 P+C set....and the piston to head clearance was plastiguaged 2-3 different times to ensure clearance.
What's up with that eh ?
We don't want to do double gaskets and lose compression, so we were thinking we'd machine the pistons for clearance as there does not appear to be enough meat on the heads before you cut into the valve seats.....and there is no consequential damage to either component.
Any ideas from the engine builders here who've done this before ?
Also I found out the tech plastiguaged the calico coated Jerry Woods bearings.....a definite no no
....but doubt that would have caused our problem.
TIA for any answers........and I am going to cross post this in the Performance forum.
The 3.2 Carrera case was machined for the Mahle 3.5 P+C set....and the piston to head clearance was plastiguaged 2-3 different times to ensure clearance.
What's up with that eh ?
We don't want to do double gaskets and lose compression, so we were thinking we'd machine the pistons for clearance as there does not appear to be enough meat on the heads before you cut into the valve seats.....and there is no consequential damage to either component.
Any ideas from the engine builders here who've done this before ?
Also I found out the tech plastiguaged the calico coated Jerry Woods bearings.....a definite no no
....but doubt that would have caused our problem. TIA for any answers........and I am going to cross post this in the Performance forum.
07-02-2008, 02:10 PM
#2
RL Technical Advisor
Precisely, where were the pistons contacting the heads? Have pics???
Generally speaking, one uses base gaskets to adjust deck height and machines the heads or pistons for head-to-piston clearance.
FYI, the heads must be machined when using 100mm P/C's.
Generally speaking, one uses base gaskets to adjust deck height and machines the heads or pistons for head-to-piston clearance.
FYI, the heads must be machined when using 100mm P/C's.
07-02-2008, 02:22 PM
#3
Three Wheelin'
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At the very edge of the outside diameter of the piston. There is a very slight discoloration and a .5 MM mark around the edge piston and on the head........
We are going to send the pistons out for machining....the heads were done at assembly which is why we are scratching our heads. Pun intended.
We don't want to lose compression, so we are tentatively going to machine the piston edge which is outside of the chamber.
Will have pics in 2 minutes.
We are going to send the pistons out for machining....the heads were done at assembly which is why we are scratching our heads. Pun intended.
We don't want to lose compression, so we are tentatively going to machine the piston edge which is outside of the chamber.
Will have pics in 2 minutes.
07-02-2008, 02:30 PM
#4
RL Technical Advisor
While I can well appreciate the need to maintain compression, the very last thing you don't want is excess deck height since that promotes detonation: twin-ignition, race gas or not.
I cannot tell you what to do but its always a juggling match to keep the CR AND .038-.040 of deck height.
I cannot tell you what to do but its always a juggling match to keep the CR AND .038-.040 of deck height.
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07-03-2008, 01:11 PM
#8
RL Technical Advisor
Q's:
1) Assuming you used Glyco rod bearings, were they dealer sourced or from a warehouse?
2) Was the crankshaft's plugs removed and cleaned before assembly?
3) Was the car's oiling system completely dissembled and cleaned?
4) What did the rest of the rod bearing look like? pics?
5) Was the engine detonating?
1) Assuming you used Glyco rod bearings, were they dealer sourced or from a warehouse?
2) Was the crankshaft's plugs removed and cleaned before assembly?
3) Was the car's oiling system completely dissembled and cleaned?
4) What did the rest of the rod bearing look like? pics?
5) Was the engine detonating?
07-03-2008, 01:45 PM
#9
Three Wheelin'
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JWE rod bearings......the calico coated ones from Smart Racing, unfortunately the tech crushed them a couple of times..........yes the crank was done.......yes the oiling system was done as you say, new oil lines were used and coolers cleaned out...etc...etc...........the other rod bearings looked much better....no detonation at all......I'll post pics later today.
07-03-2008, 04:44 PM
#10
Quit Smokin'
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I'm a little confused. When I saw the pictures and read the respective post, I assumed that the rod bearing failure was caused by incorrect piston deck clearance, and repeated impacts right from the first start up. The internal forces here (on the rod journal) being similar to detonation at all times, which is know to destroy rod bearings.
Steve, are you assuming that the rod bearing failed from other causes first?
Do you guys think they were hitting at all times, or only at higher RPM when the strain on the internal compnents would have been greater? Could this by why it passed a plasti-gauge test?
Sorry if this seems to be from left field.
Steve, are you assuming that the rod bearing failed from other causes first?
Do you guys think they were hitting at all times, or only at higher RPM when the strain on the internal compnents would have been greater? Could this by why it passed a plasti-gauge test?
Sorry if this seems to be from left field.
07-03-2008, 05:37 PM
#11
RL Technical Advisor
I'm a little confused. When I saw the pictures and read the respective post, I assumed that the rod bearing failure was caused by incorrect piston deck clearance, and repeated impacts right from the first start up. The internal forces here (on the rod journal) being similar to detonation at all times, which is know to destroy rod bearings.
Steve, are you assuming that the rod bearing failed from other causes first?
Sorry if this seems to be from left field.
Steve, are you assuming that the rod bearing failed from other causes first?
Sorry if this seems to be from left field.
Good questions, all...
I would not dare to assume anything without seeing the engine for myself as thats the only way to perform accurate forensics. There are MANY things that destroy rod bearings and one would need to inspect the whole assembly to find the root cause,...
All I can do from here is ask the easy questions and offer general suggestions.
07-03-2008, 05:50 PM
#12
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Originally Posted by smokintr6
or only at higher RPM when the strain on the internal compnents would have been greater? Could this by why it passed a plasti-gauge test?
Still working on pics Steve.
07-04-2008, 07:21 PM
#15
RL Technical Advisor
Damn. I hope the technician gets told that such things are not acceptable otherwise the root cause will never be assured.
Don't forget to remove and clean each & every part of the oiling system as bearing material hides in the tiniest of cracks and crevices.
Don't forget to remove and clean each & every part of the oiling system as bearing material hides in the tiniest of cracks and crevices.
