Cylinder compression

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Rolling Stone
Posts: 90
Joined: January 13th, 2011, 7:54 pm

Cylinder compression

Post 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!! :roll: thanx for any advice.
Posts: 412
Joined: May 11th, 2011, 7:52 pm

Re: Cylinder compression

Post 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.
Old Zink FV,
'87 Citation
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Joined: December 20th, 2007, 3:56 pm

Re: Cylinder compression

Post 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.
Andrew McMurray
EX - Ontario F1200
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Re: Cylinder compression

Post 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
The Racer's Wedge and now a Vortech, FV80
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