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compression 140 lbs. - why?
Posted: Wed Apr 13, 2005 11:24 am
by mikehailwood
Spree starts, idles, runs well to about 20 mph at which point it won't accept any more throttle without running roughly. Good steady response up to this point. Head and top of piston have been thoroughly decarbonized. Spark plug is clean and tan. Why is my compression so high? Exhaust system clogged? If so, how can I test and confirm this? Or, what else might cause my high compression reading?
Posted: Wed Apr 13, 2005 2:08 pm
by vette76
a broken comp. tester. i have never seen that kind of compression before.
Posted: Wed Apr 13, 2005 2:19 pm
by noiseguy
1) Are you running a stock head gasket? Should be .020 "
2) Do you have a head gasket?
3) If you have a slide micrometer, measure the distance from the surface of the head gasket face of the head to the top of the head casting. Should be about .020" also.
Smaller numbers on any of these raise compression. Increased compression is not a problem unless carbon is present. Your running problem is elsewhere.
Exhaust clog might cause this, but unlikely. If the head was heavily carboned you should clean the exhaust and exhaust port.
Posted: Wed Apr 13, 2005 5:06 pm
by mikehailwood
Yes, I located my head gasket and it is installed. I assume it to be a stock head gasket. It appears to be aluminum. Is that correct? Don't know the thickness yet. The carbon on the head and piston didn't look too bad to me (1/16" at the thickest spots, mostly less). Gotta go. Thanks
Posted: Wed Apr 13, 2005 7:28 pm
by vette76
that is a lot of carbon in there. i would clean all that out.
Posted: Wed Apr 13, 2005 8:48 pm
by noiseguy
Clean the exhaust port and check the head thickness as described. Gasket sounds right to me.
Posted: Thu Apr 14, 2005 11:12 pm
by mikehailwood
Replaced compression tester guage with spare. Ran a new test on the compression with the same old results - 140 lbs. As suggested, I will check and clean exhaust port when I can. Stay tuned.
Posted: Fri Apr 15, 2005 8:56 pm
by mikehailwood
I cleaned the exhaust port as best I could with the cylinder in place. Quite a bit of tan dry crud in there - kinda like having the dental hygienest clean your teeth. Compression is now down to 128 lbs. Test ride tomorrow.
Posted: Fri Apr 15, 2005 10:12 pm
by vette76
i would pull that head off.u dont want that crap in the cylender when u try to start it.
Posted: Sat Apr 16, 2005 5:21 pm
by mikehailwood
I shot compressed air in through the spark plug hole and blew it all out the exhaust hole (I hope).
Posted: Sat Apr 16, 2005 5:28 pm
by vette76
as long as its out.