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Low compression top piston

C

CCH

Contributing Member
Hello all I have a 1991 20hp motor I am getting 90 psi on the top and 120 on the bottom. Here is what I have done so far.
Both cylinder walls look great no gouges or major scratches.
New pistons and rings and bearings all new and ring gaps are in spec.
Still get low comp on top I am at a loss.
Bad Head Gasket?
Warped head?
Leaking bottom end ( would assume would effect both)
Any help would be great.
Thanks
 
Wanted to add when assemblied motor start fine but when in the water it boggs at about 1/2 throttle big time. But till then runs great. Big spread on the compression 90 to 120
 
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