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Cylinder compression
Posted: September 19th, 2011, 6:27 pm
by Rolling Stone
We have one race left in Oct in Ontario,I need an engine rebuild over the winter,I did a compression test at the track this w/end and # 1-2 cylinders were at 120lb but #3-4 were 90lb,what should I check for that?as a quick fix for the last race......piston rings?intake valves?..yes Im a novice!!
thanx for any advice.
Re: Cylinder compression
Posted: September 19th, 2011, 7:52 pm
by BLS
If you do a leakdown test you can usually detrmine the problem by where the air is exiting. "Hissing" in the intake is an intake valve, exhaust indicates an exhaust valve, and the crankcase indicates rings.
Re: Cylinder compression
Posted: September 20th, 2011, 11:14 am
by hojo
compression test wont tell you much frank. you need to do a leak down to calculate loss. and the engine also needs to be warm too.
if you dont get the timing mark in the right spot for each cylinder 1 or 2 degs either way will give you crazy numbers.
Re: Cylinder compression
Posted: September 21st, 2011, 3:54 pm
by FV80
The FIRST thing you should check is for broken head stud. - since both cylinders are down, I'd guess it would be one of the middle ones. Fairly common problem.
Take an old head stud and braze a PUNCH to it (or just sharpen the end.
Take another one and braze an appropriate drill bit to it (can't remember the size you might need).
Take another one and braze an appropriate sized EZ-0ut to it.
With these three homemade tools, you can (usually) get the old broken stud out and replace with a new one without having to remove the head.
Good luck,
Steve, FV80