A few main bearing questions
05-02-2011, 01:26 PM
#16
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Oil pressure when the pan temp is 230F is showing about 4 bar at 5k RPM. (Mobile One 20/50) I'd like to see it a bit higher but am also wondering if the lower pressure be due to pressure drop from my inline secondary oil cooler. An unnamed person of significant authority suggested that a setup like mine would lead to a pressure drop of about .5 bar.
05-05-2011, 01:33 AM
#17
Three Wheelin'
On my '86 (which is not only the same color as yours, but seems to live a similar life, mine is my DD and only car but also sees 2 all-weekend track events a month 137K miles, engine has never been apart, but I did the rod bearings a few K miles ago), I installed a second factory oil cooler last year and I have noticed no drop in pressure, street or track, hot or cold, low RPMs or high. I can see the theory behind why installing the second cooler inline could decrease system pressure with everything else remaining equal, but I think in my case the second cooler helped drop the oil temps enough that my off-track hot idle oil pressure is actually .5 bar HIGHER than before installing the second cooler. I also switched from Mobil 1 15W-50 to Total Racing 10W-50, and I have gone from using 3/4 of a quart of oil in one track day (~1.5 hrs track time) to using less than 1/4 quart in a whole weekend. Plus used oil analysis results look better.
As far as the main bearings go, used oil analysis is one way to go to monitor bearing wear (they check for trace amounts of wear metals). But, that has to be done long term. The only way I can think of to check the thrust bearings is to pull the bellhousing. I have seen several 944s at my shop with some pretty significant thrust bearing wear, and that is a major case for not sitting on the clutch pedal at traffic lights like Chris White mentioned.
I also would make the case for making sure that the driveshaft inside the torque tube is set at the correct depth relative to the rear bellhousing per the factory manual before tightening the clamping sleeve in the transmission bellhousing. On a couple of the cars that I've seen with wasted thrust bearings, the driveshaft was pounded into the clutch disc as far as it would go; not only does this wear out the clutch prematurely, it would also likely contribute to thrust bearing wear.
Anyway, if you decide to pull the trigger on the bearings, pull the engine. One of my fellow techs did the main bearings in the car on his 944, but he is a very experienced Porsche tech who has worked on 944s since they were new and has done a lot of 944 engines. He would never do it that way on a customer car, but since he picked the car up for 1000 bucks and had one afternoon to do it, he did it in car. But, you need to make sure that all the bearings are in place correctly, make sure the sealant between the girdle and the block is distributed evenly, etc.
Good luck.
As far as the main bearings go, used oil analysis is one way to go to monitor bearing wear (they check for trace amounts of wear metals). But, that has to be done long term. The only way I can think of to check the thrust bearings is to pull the bellhousing. I have seen several 944s at my shop with some pretty significant thrust bearing wear, and that is a major case for not sitting on the clutch pedal at traffic lights like Chris White mentioned.
I also would make the case for making sure that the driveshaft inside the torque tube is set at the correct depth relative to the rear bellhousing per the factory manual before tightening the clamping sleeve in the transmission bellhousing. On a couple of the cars that I've seen with wasted thrust bearings, the driveshaft was pounded into the clutch disc as far as it would go; not only does this wear out the clutch prematurely, it would also likely contribute to thrust bearing wear.
Anyway, if you decide to pull the trigger on the bearings, pull the engine. One of my fellow techs did the main bearings in the car on his 944, but he is a very experienced Porsche tech who has worked on 944s since they were new and has done a lot of 944 engines. He would never do it that way on a customer car, but since he picked the car up for 1000 bucks and had one afternoon to do it, he did it in car. But, you need to make sure that all the bearings are in place correctly, make sure the sealant between the girdle and the block is distributed evenly, etc.
Good luck.
05-05-2011, 05:05 PM
#18
Burning Brakes
Thread Starter
Chris - thanks for the input. What sort of oil pressure are you seeing at 5k RPM and at what pan temps? Also, did you note any oil pressure changes when you swapped oil?
My information on my oil pressure drop is anecdotal. Unfortunately, I didn't do a real survey before made the changes. It seems like I had a bit more pressure before the oil cooler but then I also swapped my OPRV from the early 86 version to an updated (but used) model at the same time. That could be the culprit as well.
I did a quick search on the Total Racing oil - seems to all be out of the UK or AUS. Where are you getting yours? I've been considering going to either straight 50w or a multi grade oil with a 60w rating but this may be a better option.
Yes, if I do the mains, the motor will come out. I have no desire to try to install a crank and gridle while laying on my back.
My information on my oil pressure drop is anecdotal. Unfortunately, I didn't do a real survey before made the changes. It seems like I had a bit more pressure before the oil cooler but then I also swapped my OPRV from the early 86 version to an updated (but used) model at the same time. That could be the culprit as well.
I did a quick search on the Total Racing oil - seems to all be out of the UK or AUS. Where are you getting yours? I've been considering going to either straight 50w or a multi grade oil with a 60w rating but this may be a better option.
Yes, if I do the mains, the motor will come out. I have no desire to try to install a crank and gridle while laying on my back.
