Any 944 Rod bearing failures WITH drilled crank?
10-29-2003, 11:32 AM
#1
Race Director
Thread Starter
Any 944 Rod bearing failures WITH drilled crank?
Ok any one have rod bearing fail when using drilled crank on a 944, 968, or 951. Could be cross drilled or perp drilled or anything.
Just looking for some data
Just looking for some data
10-30-2003, 01:51 AM
#2
Burning Brakes
I've heard people have had success with making the bearings live by doing a good job of venting the crankcase. No solid data to back it up, just something I've heard.
10-30-2003, 09:41 AM
#3
Race Car
Locally, we've had SEVERAL failures on the 944 rod bearings...even after having the crank cross-drilled. 
This is, of course, on track-driven 944s, a few of them full race prepared.
It seems that it may help, but cross-drilling, coupled with installing an Accu-Sump seems to be decent protection.
This is, of course, on track-driven 944s, a few of them full race prepared.
It seems that it may help, but cross-drilling, coupled with installing an Accu-Sump seems to be decent protection.
10-30-2003, 10:20 AM
#4
Rennlist Member
According to John Milledge the only real way to fix the problem is a dry sump. He says that you can drill the crank, add baffling to the oil pan and pick-up, and add an additional air-oil seperator. This however will only be a bandaid for the problem, but it will certainly help. This the route I took.
PS I also have a crank case vent .. but John did not mention this as part of the cure.
944turbo
PS I also have a crank case vent .. but John did not mention this as part of the cure.
944turbo
10-30-2003, 10:38 AM
#5
Race Director
Thread Starter
Here is my theroy of how these bearings fail.
The way a hydrodynamic bearing fails is when the two surfaces contact. If there is an insufficent volume of fluid in the bearing then contact can occur.
In order for the bearing to function properly it MUST be supplied with enough oil. The volume of oil being supplied is less than what is needed to support the load bad things happen.
Why might there not be enough oil flow? Well oil flow requirements are driven by viscosity of the oil among other things. As speeds increase the there is more heat generated in the oil film layer. Thus the viscosity of that oil drops. Therefore more oil volume is needed to support the loading. If oil is supplied at volumes greater than required it will flow throigh the system and will act to extract more heat from the bearing this makeing the oil film layer cooler.
Now if a rod bearing fails during engine operations it most likely failed due to metal contact (well duh).
What could cause that? A reduction of oil film layer thickness.
What could cause this thickness reduction?
1) lower oil viscosity
2) lower than required oil volume being supplied (more oil lost out the side than supplied)
Note that load is assumed contant and higher RPM actually require a thinner oil film to prevent contact! (This is in physics of hydrodynamic bearings as not my assertion)
What speed does do is to lower the oil viscosty through local heating.
So to prevent rod failuere you need to maintain oil viscosity and supply sufficent oil volume.
1) If your oil pick-up tube becomes uncovered you can create problems with respect to oil supply. Thus a failure.
2) If you have air pockets in the oil you can a momentary oil supply issues.
3) Crappy oil can mean lower viscosity at the bearing thus a failure
4) Low flow through the bearing can cause localized heating of the oil this reducing viscosity
5) dirt or other particals can block or limit oil flow through existing passages.
Enough theory...
The way a hydrodynamic bearing fails is when the two surfaces contact. If there is an insufficent volume of fluid in the bearing then contact can occur.
In order for the bearing to function properly it MUST be supplied with enough oil. The volume of oil being supplied is less than what is needed to support the load bad things happen.
Why might there not be enough oil flow? Well oil flow requirements are driven by viscosity of the oil among other things. As speeds increase the there is more heat generated in the oil film layer. Thus the viscosity of that oil drops. Therefore more oil volume is needed to support the loading. If oil is supplied at volumes greater than required it will flow throigh the system and will act to extract more heat from the bearing this makeing the oil film layer cooler.
Now if a rod bearing fails during engine operations it most likely failed due to metal contact (well duh).
What could cause that? A reduction of oil film layer thickness.
What could cause this thickness reduction?
1) lower oil viscosity
2) lower than required oil volume being supplied (more oil lost out the side than supplied)
Note that load is assumed contant and higher RPM actually require a thinner oil film to prevent contact! (This is in physics of hydrodynamic bearings as not my assertion)
What speed does do is to lower the oil viscosty through local heating.
So to prevent rod failuere you need to maintain oil viscosity and supply sufficent oil volume.
1) If your oil pick-up tube becomes uncovered you can create problems with respect to oil supply. Thus a failure.
2) If you have air pockets in the oil you can a momentary oil supply issues.
3) Crappy oil can mean lower viscosity at the bearing thus a failure
4) Low flow through the bearing can cause localized heating of the oil this reducing viscosity
5) dirt or other particals can block or limit oil flow through existing passages.
Enough theory...
10-30-2003, 10:42 AM
#6
Three Wheelin'
Dry sump? That may work for people that run in PCA GT classes, or SCCA Gt2. But for those of us that run PCA stock classes or ITS, or even E Prod., that is not a solution, we are not allowed to run Dry Sumps.
My engine is mostly stock, and I have never had the problem. I have seen three of the problems on competitors cars, and every one of them had a warning. Two of them were burning at least one quart of oil per session. On about the 3rd session---Ballowie. The other one happened after the car had overheated in a session. He solved the overheating problem, qualified on the pole in the next session, and burned the number two while he was doing it. I have been racing my car since 1990, and have never let the motor go too far before I did a rebuild. I have never had a bearing go bad, but I guess I may not be pushing hard enough, who knows. Also, my motor is pretty well stock.
Bill Seifert
1987 944 Race Car
My engine is mostly stock, and I have never had the problem. I have seen three of the problems on competitors cars, and every one of them had a warning. Two of them were burning at least one quart of oil per session. On about the 3rd session---Ballowie. The other one happened after the car had overheated in a session. He solved the overheating problem, qualified on the pole in the next session, and burned the number two while he was doing it. I have been racing my car since 1990, and have never let the motor go too far before I did a rebuild. I have never had a bearing go bad, but I guess I may not be pushing hard enough, who knows. Also, my motor is pretty well stock.
Bill Seifert
1987 944 Race Car
10-30-2003, 10:46 AM
#7
Race Director
Thread Starter
Originally posted by 944turbo
According to John Milledge the only real way to fix the problem is a dry sump.
According to John Milledge the only real way to fix the problem is a dry sump.
No oil frothing?
I would think that if you can supply sufficient volume of clean oil you would be fine.
A dry sump should prevent....
1) no uncoverd oil pickups
2) no oil frothing resulting in air bubbles displacing oil.
anythign else a dry sump would do?
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10-30-2003, 12:00 PM
#8
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Originally posted by pig4bill
I've heard people have had success with making the bearings live by doing a good job of venting the crankcase. No solid data to back it up, just something I've heard.
I've heard people have had success with making the bearings live by doing a good job of venting the crankcase. No solid data to back it up, just something I've heard.
running an Accusump, Canton Mecca oil filter and a Kokeln air/oil separator so presumably, I did everything I could to insure reliability (with a completely stock engine).
There were no heat issues or warning signs. Kept blowing the dipstick up, though we weren't sure if it was a result of vibration (I doubt it was, since we also blew a little bit of the oil pan gasket out as well). We even put a one-way valve into the oil fill cap to help out. I have seen other 944s with make-shift crankcase breathers.
On the previous aborted rebuild, we had huge crankcase pressure issues which turned out to be bad ring lans on the pistons (we have to run all stock parts, which means "used" in a rebuild situation). Is it a bitch to get the rings to seat on these alusil blocks even if they have been properly honed and lapped? How might this contribute to rod bearing failure?
10-30-2003, 12:26 PM
#10
Race Director
Thread Starter
Al,
I know what you mean. I there is also a thread in 928 forum I am following about oil and RPM's
I posted this hear to capture racer input. There may be 911 guys with 944 friend not on the list that could provide input.
I know what you mean. I there is also a thread in 928 forum I am following about oil and RPM's
I posted this hear to capture racer input. There may be 911 guys with 944 friend not on the list that could provide input.
10-30-2003, 01:52 PM
#12
Race Car
I have had thoughts journeying towards the possibility of CAVITATION. Like on a boat, when you involve any impeller (i.e. water pump), blade (screw for you ex-Navy guys) or gear mesh at high speeds, there is an incredible HP/LP (high-press./low press.) differential at rapidly changing RPMs or sustained high RPM, when involving any liquid/fluid.
This would certainly contribute to oil frothing, and possibly lean towards M758's "lack of oil supply" theory, which is obviously apparent in bearing failures. But frothing or cavitation wouldn't be a SUPPLY issue, it would be a, well, how 'bout QUALITY of the supply issue??
I believe that repeated metal to metal contact is the culprit fer sure, but our local shop has seen evidence of contaminated oil, like a foreign object in there (evident by scratches on the bearing journal, etc.) - but then that could just be particles from the crank/bearing as they contact each other.
Like shavings!?
From theory, I would think an Accusump would provide the most protection, it is supposed to be used as a capacitor, in a sense, keeping constant oil pressure, which is normally synonymous with supply (volume).
BUT, I've seen failures just as catastrophic with an Accusump when compared to a setup without.
I agree with the others who basically advocate the practice of compounding the "band-aide" solutions in the hopes to gain "insurance".
I think a good solution would be to design a VERY efficient oil pump, that runs at lower speeds and creates higher oil volume? If you are the guy to come up with said contraption, you could fund your own race car off the profits!
This would certainly contribute to oil frothing, and possibly lean towards M758's "lack of oil supply" theory, which is obviously apparent in bearing failures. But frothing or cavitation wouldn't be a SUPPLY issue, it would be a, well, how 'bout QUALITY of the supply issue??
I believe that repeated metal to metal contact is the culprit fer sure, but our local shop has seen evidence of contaminated oil, like a foreign object in there (evident by scratches on the bearing journal, etc.) - but then that could just be particles from the crank/bearing as they contact each other.
Like shavings!?
From theory, I would think an Accusump would provide the most protection, it is supposed to be used as a capacitor, in a sense, keeping constant oil pressure, which is normally synonymous with supply (volume).
BUT, I've seen failures just as catastrophic with an Accusump when compared to a setup without.
I agree with the others who basically advocate the practice of compounding the "band-aide" solutions in the hopes to gain "insurance".
I think a good solution would be to design a VERY efficient oil pump, that runs at lower speeds and creates higher oil volume? If you are the guy to come up with said contraption, you could fund your own race car off the profits!
10-30-2003, 03:19 PM
#13
Race Director
Thread Starter
Jeff,
Certainly oil pump cavitation will generate air in the oil this would mean less oil flow volume. Thus an additioanal oil passage would help.
Assume that 50% air/oil mix in the passages at high RPM. That means only 50% of the intended oil flow goes to the bearings. Thus the band-aid is another passages that can fill with the same 50/50 mix so in total you still have originally designed oil flow.
In that case you have not solved the problem, but provided a band-aid that may help.
Normally cavitation will cause pump damage. Anyone see this on 944 oil pumps?
Certainly oil pump cavitation will generate air in the oil this would mean less oil flow volume. Thus an additioanal oil passage would help.
Assume that 50% air/oil mix in the passages at high RPM. That means only 50% of the intended oil flow goes to the bearings. Thus the band-aid is another passages that can fill with the same 50/50 mix so in total you still have originally designed oil flow.
In that case you have not solved the problem, but provided a band-aid that may help.
Normally cavitation will cause pump damage. Anyone see this on 944 oil pumps?
10-30-2003, 03:24 PM
#14
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other than some very minor scratches (presumeably from all the metal circulating after the bearing disintegrated) no other damage was noted.
Same oil pump is currently being used on the rebuilt motor.
Same oil pump is currently being used on the rebuilt motor.
10-30-2003, 04:20 PM
#15
Rennlist Member
any failures not using Mobil 1????????????????????????????
ive seen (first hand) , lower oil pressure on race days with hot temps.
personally, with Amzoil or Redline 20-50, never seen the dips in oil pressure, even on high gTurns. plus, no engine falures on a 928 engine, that is known for #2-6 bearing failure. (however, also known for a community that uses Mobil1 )
MK
ive seen (first hand) , lower oil pressure on race days with hot temps.
personally, with Amzoil or Redline 20-50, never seen the dips in oil pressure, even on high gTurns. plus, no engine falures on a 928 engine, that is known for #2-6 bearing failure. (however, also known for a community that uses Mobil1 )
MK