Outdoor Power Equipment and Small Engines - compression

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Blink182
03-28-03, 10:07 AM
hi everyone

im doing a small engine repair for my auto class i cant seem to find why i have low compression. i replaced all gaskets lapped the valves and i still ony get 35psi. apparently its supposed to be higher to start and then it lowers while its running. any ideas would be greatly appreciated.

thnx

paul

Blink182
03-28-03, 10:09 AM
oh by the way its a brigs and straton lawnmower engine
Joe_F
03-28-03, 10:35 AM
How's the rings and piston?

Blink182
03-28-03, 10:41 AM
the piston is in good condition i think the rings are good but i was thinking it might be the crankshaft because unless my partner im workin withs measured got messed up the measurements of TDC and BDC are way different.
DennisG
03-28-03, 09:57 PM
HUH?? ok...you are going to need to explain yourself better...first of all what engine are you working on....model/type?? you said you lapped the valves...did you set clearances...did you check ring gap? Give us some detail...
Bald Eagle
03-29-03, 05:14 AM
You mentioned that you can only get 35psi. Would this be using an automotive "in the spark plug hole" type of pressure gage? If your small engine has compression release, which most have, you will have to use an air compressor along with a compression tester designed for this application. Hope this helps.
cheese
03-30-03, 08:13 PM
Agreed...most newer engines have compression release. An automotive tester is not made for this type of application. Check the valve tappet clearances...If you lapped the valves, you might have valve clearances that are too tight.