Quote:
Originally Posted by Jamesp
You've got the point. I made this video a year ago
https://www.youtube.com/watch?v=qzHwWUgU37k
There are 7 short ( 2 minutes or so) videos detailing precisely what you are saying, and showing how I approached this problem. I'm at just about 3000 miles since I made this simple modification to the IMS and all is well. I redline just about every day because it is fun. Click on my name under the video if your interested in seeing what I did. There's been an implication that Porsche blew the bearing design by overloading it. I have a hard time buying that unless the mistake was assuming grease in the bearing instead of oil when doing the load calcs. That is part of the reason I went back with a sealed high temp (high temp grease and Viton seals) greased deep groove steel ball bearing with a vented IMS. The other reason is that the fully sealed bearing feature coupled with venting keeps any trash in the oil out of my IMSB. |
Hi jamesp,
some thoughts first:
Fluids do expand much more than air. So if you have oils in a sealed IMS tube the overpressure expands much more than you'll just have air in a sealed tube.
I would estimate that the inner volume of the IMS tube is around 0.5 litre (500 ml) and you said that there was a cup of oil in the tube - so around 100 ml? Would you agree with that? (because i want to calculate the overpressure at different temps).
If the car is on leveled ground the chains of the IMS tube run in engine oil, whereas the bearing is a little above the normal oil level. But if the car moves (accelerates, etc.), the oil level can be above the bearing. Also if the car stands or drives with the nose up a hill.
Watched your videos on Youtube:
01
http://youtu.be/qzHwWUgU37k
02
http://youtu.be/JXPMWDVn4Ec
03
http://youtu.be/PTk_xehieFc
04
http://youtu.be/Y5cgLrPsAdg
05
http://youtu.be/pKImRZ2reNY
06
http://youtu.be/SxhFdPCoYYs
07
http://youtu.be/1vrX6rmV_nI
Understand now what you mean with vented.
Where i struggle is if we really have a sealed IMS tube filled with around 50-100 ml of old engine oil, why isn't the oil pressed out of the tube / sealing, if we have overpressure (compared to the rest of the engine) in the IMS tube when the engine is hot?
If there is a way in, in general there also has to be a way out. The only way i could imagine is that materials expand when they get hot and so there is no way out, while materials shrink when they get cold and than there is a leak so that the oil can get in over a long time.
Also i'm not 100% shure that the system is 100% completely sealed system. The "weak" part might be the bolt that holds the inner part of the bearing. Also it could matter what engine oil you use. Too "thin" oil might get in faster than "thicker" oil.
You've drilled 2 holes in the IMS shaft - now i understand why you called it vented. I think it is good idea. Oil can get in and will get out when you start the engine, because of centrifugal forces, even if the oil level is a bit above the IMS shaft. Only thing to mention is that the bearing seal can be harmed over time by temperature changes and agressive oil. So it is still important to change engine oil and filters regularly.
Regards from germany
Markus
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