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Old 05-26-2011, 01:19 PM
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Biodiesel300TD Biodiesel300TD is offline
Join Date: Dec 2004
Location: Albany, OR
Posts: 4,845
Originally Posted by mach0415 View Post
My understanding is that blowby indicates ring wear or a hole in a piston - some kind of lower end issue. Valve adjustment would not allow compression to leak into the sump. It would only leak through the exhaust or intake. This is the purpose of doing a cylinder leak-down test as the result of low compression numbers - to find where compression is being lost.
Yes you are right but I also think that if the valves aren't closing all the way due to tight clearances then oil will have a chance to slip past the valve stem seals up into the head, assuming the stem seals are worn. While this may not be the largest portion of oil in the blowby it's not helping at all, and it's something easy to fix and is preventative maintenance.
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