Is there a way to post photos here? I pulled the head tonight that had 170 compression. I think it might be a valve guide? Would like to.post a photo so someone could maybe confirm. Never opened a small enginr head before so not exactly sure what it is supposed to look like.
You can add photos by "GO ADVANCED" option on a post, then scroll down and "MANAGE ATTACHMENTS" where you can "ADD FILES" and upload them to the site.
Just curious.....why did you pull the head from the good side (higher compression side)?
One side was 90, and the side I pulled the head on was 170. When I did the pull the pull the plug wires test, unplugging the 90 cylinder caused it to run rougher, whereas unplugging the 170 cylinder caused no change to the way it ran. I thought that indicated that it was running more on the front cylinder the 90 one than the back one the 170? And isn't 170 too high? I thought I read that 90-110 was more normal?Originally Posted by dirtdobber
Thanks Hipowerone
I'm not sure what normal is for these engines, but 170 does seem high. If I'm applying the right logic, pressure and volume are proportional. With atmospheric pressure being 14.7 pounds, and assuming the pressure inside the cylinder on the intake stroke is 14.7, then then it has to compress 11.5 times to reach 170 psi. A good old stock Chevy small block engine would have somewhere around a 8.5:1 ratio, but I'm not sure what these engines should have. But, I can't think of anything that can go wrong and cause increased compression, unless maybe the exhaust valve is not opening and the cylinder is able to draw in a little more air than normal and thus is reading a higher compression (that's just a wild guess, by the way). Especially since the compression on one cyl. is nearly double the compression on the other. You did read your gauge right (psi) and not some other units??And isn't 170 too high? I thought I read that 90-110 was more normal?
Post some pics. Not sure if they will help but pics are always fun to look at.
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I thought the same thing that it was too high and had no clue how it could get that high. I retested both cylinders 5 times always got the same readings 90 in front and just shy of 170 in the rear cylinder. I too am baffled. I know very little about small engines but I think the head looks normal, doesn't look like any of the other ones I had been able to look up with head problems. The gasket is good, and I am able to hand compress both the springs and both valves open?
Stupid question did you have spark in both cylinders at the tester and the plug? a dead plug or burnt diode will cause poor performance and rough running.
Perhaps Nubs knows the rough compression readings.
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Yeah Jim i have spark in both, even put brand new plugs in it.
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