M96 Engine failure teardown this weekend
01-18-2009, 02:32 PM
#47
Burning Brakes
Interesting that it was cylinder 4.
It's more common to find one of the center cylinders cracking.
That's why I was asking if the head had cracked as well, as this is more common on the outer cylinders.
Did you have any signs of intermix or coolant loss before the engine eventually let go at the track?
It's more common to find one of the center cylinders cracking.
That's why I was asking if the head had cracked as well, as this is more common on the outer cylinders.
Did you have any signs of intermix or coolant loss before the engine eventually let go at the track?
We have seen all cylinders fail from all models and years.
01-18-2009, 06:32 PM
#49
Burning Brakes
Mainly due to the difference in oiling from the opposite G forces the engine oil encounters during cornering, accelerating and decelerating..
In a Boxster the engine is inverted when compared to a 996.
In a Boxster the engine is inverted when compared to a 996.
01-18-2009, 09:33 PM
#50
Burning Brakes
+1. This is a good thread, informative as well. Stop trying to manifest a confrontation where there isn't one. And for what it's worth, I've never seen or heard anyone in these forums or otherwise say "all M96 engine's are bad".
01-18-2009, 09:50 PM
#51
Drifting
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Do you see the lack of lubrication under load as the main issue?
or is the cooling of the block inconsistent for similar reasons, leading to differential expansion and eventual stress fracturing?
01-19-2009, 10:59 AM
#52
Ironman 140.6
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01-20-2009, 10:15 AM
#53
Parts Specialist
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my question is:
from looking at the cams and the way the contact the valves, what is used to set the gap? I have "heard" these had hydrolic lifters but from the pictures I dont see anythng there.
Doens't have anything to do with the failure, just the motor in general
from looking at the cams and the way the contact the valves, what is used to set the gap? I have "heard" these had hydrolic lifters but from the pictures I dont see anythng there.
Doens't have anything to do with the failure, just the motor in general
01-20-2009, 10:35 AM
#54
Nordschleife Master
Not the engine police but the validity police. Something which you have no desire to learn and something you instead proliferate with hysteria and inaccuracy. And you wonder why so many people get bitch-slapped for asking questions like "Interested in a 996 but I have read here that these cars are prone to failure, what do I look for". People like you create the hysteria instead of trying to support the argument (either side) with facts. All I have done (and others) is try to get you to support your argument with fact instead of anecdote.
Not going to get into the same argument with you anymore. You know my stance, and I know yours. Enjoy.
Unsubscribe time
Not going to get into the same argument with you anymore. You know my stance, and I know yours. Enjoy.
Unsubscribe time
Ray, you need to just start to ignore this troll. See post #9 and #12 and that's all you need to know (they are quoted above in this post of mine. Not at any time did you, I, or anybody else come to this thread "attacking" cdod, but instead he chose to post not once, but twice with his usual diarrhea of mouth and instigation to try and pull us in so that he can have some forum to release his irrational unsubstantiated crap. I've decided to quit engaging such bottom feeders. See my last post to him (quoted above as well). Yet I still don't think he will get it. In predictable fashion though he won't be able to keep from posting some sort of irrational rebuttal to you and/or myself.
01-20-2009, 12:23 PM
#55
Race Director
When I first read of the cylinder cracking failure it was stated...
Understood that the 986 has the block rotated 180 degrees horizontally, I have one of each - so the absolute physical position determines the most likely cylinder to fail in your scenarios?
Do you see the lack of lubrication under load as the main issue?
or is the cooling of the block inconsistent for similar reasons, leading to differential expansion and eventual stress fracturing?
Do you see the lack of lubrication under load as the main issue?
or is the cooling of the block inconsistent for similar reasons, leading to differential expansion and eventual stress fracturing?
Mr. Raby reports the failure is not limited to any cylinder but appears in all of them with no apparent pattern.
Thus this would appear that twisting of the block not to blame.
Several things come to mind: One is that the failing cylinder experiences improper combustion -- detonation or something close to it -- and the extreme pressure spikes cause a crack. I note the crack is always at the top of the cylinder. The open deck design doesn't help.
Another possibility is the cooling of the area that cracks is uneven. Perhaps low coolant or maybe coolant that has lost some of its ability to resist boiling causes an air pocket to periodically form. This allows this area to heat up and then when the pocket collapses the relatively cooler coolant heat shocks this area. If this happens, over and over again, at some point the wall fails.
The Boxster engine can suffer from oil starvation under some circumstances. One is under extreme braking in (IIRC) a left hand and high speed corner.
This forces oil under the right cylinder bank camshaft cover away from the scavenge pump located at rear of head under camshaft cover. A huge volume of oil is constantly fed to the cams and valve gear. It doesn't take much time for a considerable volume of oil (just several guarts is all it takes, maybe less if oil level a bit lower than optimum) to accumulate under the camshaft cover.
This can result in the oil level in sump going down to the point the oil pump may ingest oil with more air in it. If the oil "old" its anti-foaming additives may have been depleted too.
If the main bearings, or rod bearing don't suffer the hydraulic lifters might. With air in the oil these lifters will collapse though how this can result in engine failure I'm not sure. That is causes a drop off in power at higher rpms is a given as the valves no longer follow the desired valve action and lower lift, less duration, etc. work to reduce engine output.
If this air laden oil makes it ito any of the camshaft chain tensioners a tensioner could fail to maintain proper cam chain tension. This can be very serious cause the chain with more slack -- and at high speeds -- jump/skip a tooth and valve contact with piston can result with disasterous results.
Or the chain slams against tensioner that has lost its ability to maintain tension and breaks the tensioner/guide. Same bad result for engine.
Sincerely,
Macster.
01-20-2009, 12:32 PM
#57
Drifting
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it was always a center cylinder. My thinking was the block was undergoing some stress/twisting and the crack happened at the weakest point.
Mr. Raby reports the failure is not limited to any cylinder but appears in all of them with no apparent pattern.
Thus this would appear that twisting of the block not to blame.
Several things come to mind: One is that the failing cylinder experiences improper combustion -- detonation or something close to it -- and the extreme pressure spikes cause a crack. I note the crack is always at the top of the cylinder. The open deck design doesn't help.
Another possibility is the cooling of the area that cracks is uneven. Perhaps low coolant or maybe coolant that has lost some of its ability to resist boiling causes an air pocket to periodically form. This allows this area to heat up and then when the pocket collapses the relatively cooler coolant heat shocks this area. If this happens, over and over again, at some point the wall fails.
The Boxster engine can suffer from oil starvation under some circumstances. One is under extreme braking in (IIRC) a left hand and high speed corner.
This forces oil under the right cylinder bank camshaft cover away from the scavenge pump located at rear of head under camshaft cover. A huge volume of oil is constantly fed to the cams and valve gear. It doesn't take much time for a considerable volume of oil (just several guarts is all it takes, maybe less if oil level a bit lower than optimum) to accumulate under the camshaft cover.
This can result in the oil level in sump going down to the point the oil pump may ingest oil with more air in it. If the oil "old" its anti-foaming additives may have been depleted too.
If the main bearings, or rod bearing don't suffer the hydraulic lifters might. With air in the oil these lifters will collapse though how this can result in engine failure I'm not sure. That is causes a drop off in power at higher rpms is a given as the valves no longer follow the desired valve action and lower lift, less duration, etc. work to reduce engine output.
If this air laden oil makes it ito any of the camshaft chain tensioners a tensioner could fail to maintain proper cam chain tension. This can be very serious cause the chain with more slack -- and at high speeds -- jump/skip a tooth and valve contact with piston can result with disasterous results.
Or the chain slams against tensioner that has lost its ability to maintain tension and breaks the tensioner/guide. Same bad result for engine.
Sincerely,
Macster.
Mr. Raby reports the failure is not limited to any cylinder but appears in all of them with no apparent pattern.
Thus this would appear that twisting of the block not to blame.
Several things come to mind: One is that the failing cylinder experiences improper combustion -- detonation or something close to it -- and the extreme pressure spikes cause a crack. I note the crack is always at the top of the cylinder. The open deck design doesn't help.
Another possibility is the cooling of the area that cracks is uneven. Perhaps low coolant or maybe coolant that has lost some of its ability to resist boiling causes an air pocket to periodically form. This allows this area to heat up and then when the pocket collapses the relatively cooler coolant heat shocks this area. If this happens, over and over again, at some point the wall fails.
The Boxster engine can suffer from oil starvation under some circumstances. One is under extreme braking in (IIRC) a left hand and high speed corner.
This forces oil under the right cylinder bank camshaft cover away from the scavenge pump located at rear of head under camshaft cover. A huge volume of oil is constantly fed to the cams and valve gear. It doesn't take much time for a considerable volume of oil (just several guarts is all it takes, maybe less if oil level a bit lower than optimum) to accumulate under the camshaft cover.
This can result in the oil level in sump going down to the point the oil pump may ingest oil with more air in it. If the oil "old" its anti-foaming additives may have been depleted too.
If the main bearings, or rod bearing don't suffer the hydraulic lifters might. With air in the oil these lifters will collapse though how this can result in engine failure I'm not sure. That is causes a drop off in power at higher rpms is a given as the valves no longer follow the desired valve action and lower lift, less duration, etc. work to reduce engine output.
If this air laden oil makes it ito any of the camshaft chain tensioners a tensioner could fail to maintain proper cam chain tension. This can be very serious cause the chain with more slack -- and at high speeds -- jump/skip a tooth and valve contact with piston can result with disasterous results.
Or the chain slams against tensioner that has lost its ability to maintain tension and breaks the tensioner/guide. Same bad result for engine.
Sincerely,
Macster.
Is it even possible to tell after tear-down?
01-20-2009, 12:42 PM
#58
Burning Brakes
I started reading this thread to learn whatever I can about the project, but I have to read yet another diatribe from cdodkin. Get a life and another car! I and a bunch of other people are here to learn about the engine project - not hear your endless jabs at other members who have a different opinion from yours. You took a great thread and pissed on in.
Bob
Bob
01-20-2009, 12:58 PM
#59
Nordschleife Master
Don't worry about his usual and predictable diatribes Bob. He continues to give strength to the kettle-pot theory. I take great pleasure now in watching him continue to talk to a wall as I will not address him anymore.
01-20-2009, 01:07 PM
#60
Ironman 140.6
Rennlist Member
Rennlist Member
Ray, you need to just start to ignore this troll. See post #9 and #12 and that's all you need to know (they are quoted above in this post of mine. Not at any time did you, I, or anybody else come to this thread "attacking" cdod, but instead he chose to post not once, but twice with his usual diarrhea of mouth and instigation to try and pull us in so that he can have some forum to release his irrational unsubstantiated crap.
I started reading this thread to learn whatever I can about the project, but I have to read yet another diatribe from cdodkin. Get a life and another car! I and a bunch of other people are here to learn about the engine project - not hear your endless jabs at other members who have a different opinion from yours. You took a great thread and pissed on in.
Bob
Bob