Spinning a bearing??
Spinning a bearing??
05-13-2004, 07:37 PM
#3
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The bearing is in two pieces... One shell on top and one on bottom. They are notched to keep them in place. When oiled properly, the rod slides on a film of oil against the bearings... When the film of oil is suddenly not present or turns into water, the bearing gets stuck to the rod and spins around with the rod... When it does this, it flattens the notches in the rod bearings and scores the bearings... Eventually the bearings disintegrate and you are left with the rod and rod cap slapping against the crank. If it goes further, the rod bolt(s) will break and your crank will smack the piston into your head or knock the rod out the side of the oil pan...
Good times!
05-13-2004, 11:01 PM
#7
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It can happen to any engine, but 944s are very susceptible. It most commonly happens when the oil pickup tube does not pickup oil and the bearing goes dry.
The combination of high cornering forces and poor baffling in the 944 are the major causes. You can not let these cars go low on oil. That is why Porsche put the low oil level indicator light on them in 87.
It can also go dry when cresting over a peak at high speed causing the oil to slosh around the pan.
The combination of high cornering forces and poor baffling in the 944 are the major causes. You can not let these cars go low on oil. That is why Porsche put the low oil level indicator light on them in 87.
It can also go dry when cresting over a peak at high speed causing the oil to slosh around the pan.
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05-14-2004, 02:23 AM
#8
Race Director
"It most commonly happens when the oil pickup tube does not pickup oil and the bearing goes dry."
If this is the cause, why just the #2 bearing? Would a low oil-pressure/supply issue affect ALL of the bearings?
Here's a picture of the insides of the bearings on my car at 175K-miles when I replaced the rod-bearings:
If this is the cause, why just the #2 bearing? Would a low oil-pressure/supply issue affect ALL of the bearings?
Here's a picture of the insides of the bearings on my car at 175K-miles when I replaced the rod-bearings:
05-14-2004, 03:53 AM
#9
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I spun my #2 bearing also... dunno why it's always that one. If i had pics i could show u how bad the damage was. Had a few gouges on the crank, the bearing was basically shredded, and the part of the rod that goes around the crank is so stretched it looks like an egg, i'm surprised it didnt break the rod altogether (forged rods are great)
05-14-2004, 11:45 AM
#10
Rennlist Member
If a car has, say, 114K on it, has never been tracked, and has always been well cared for, when should one consider replacing the rod bearings preventatively? I've been figuring that I'd have it done when/if the oil pan gasket eventually starts to leak, but since it's been bone dry for the past 17 years, who knows when that'll happen.
05-14-2004, 01:36 PM
#11
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It is in the way the oil is delivered to them.
Some cross-drill the crank to
"cure" the problem, but as your comment suggests, it seems that would just take it to the next weakest link because you have just repaired the effect, not the cause.
I have seen cars with under 50k with spun bearings that have never been tracked.
KLR, unless you see a drop in oil pressure you should be OK. As you stated though, they should be replaced when the oil pan is off because you are already there.
The likelihood of spinning a bearing greatly increases when you put slicks on a car.
Some cross-drill the crank to
"cure" the problem, but as your comment suggests, it seems that would just take it to the next weakest link because you have just repaired the effect, not the cause.
I have seen cars with under 50k with spun bearings that have never been tracked.
KLR, unless you see a drop in oil pressure you should be OK. As you stated though, they should be replaced when the oil pan is off because you are already there.
The likelihood of spinning a bearing greatly increases when you put slicks on a car.
05-14-2004, 05:45 PM
#13
Race Director
No simple easy answers or fixes. I had #2 fail on me. Spun then seized and blew out the side of my block. Boom!!!! 
All other cylinders looked good.
Do a search on rod bearings and will find a bunch of threads. None provide a 100% fix. Most will provide number things to merely reduce the risk.
Ain't life Grand?
All other cylinders looked good.
Do a search on rod bearings and will find a bunch of threads. None provide a 100% fix. Most will provide number things to merely reduce the risk.
Ain't life Grand?
05-14-2004, 06:09 PM
#15
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I have never seen a 944 street or track car spin a bearing with an Accusump installed.
It will not help if you have existing damage, it will just ruin the Accusump.
The Accusump forces in oil if the pressure goes down. It also primes the engine so you have oil pressure at startup, no more dry startups, if you hook it up correctly.
If your sump goes dry on a brand new engine it will spin the bearing. It only takes a second for dry metal to metal to heat up.
It will not help if you have existing damage, it will just ruin the Accusump.
The Accusump forces in oil if the pressure goes down. It also primes the engine so you have oil pressure at startup, no more dry startups, if you hook it up correctly.
If your sump goes dry on a brand new engine it will spin the bearing. It only takes a second for dry metal to metal to heat up.