Compression on stored engine

R

rhcotton

Seaman Apprentice
Joined
Jun 13, 2004
Messages
34
I went to check out a 1997 90hp Johnson that was for sale. It has been in storage for two years on a wooden pallet laying on its side. A mechanic told me to check the compression before considering buying the motor. I took out the spark plugs and then turned the engine with some jumper cables. At first check all I could get was approximately 75psi out of each cylinder. I then took a can of WD40 and sprayed down and saturated each cylinder hole. This time the best reading I could get is about 100 on each cylinder. Was this a good test? Is this compression good enough? Any help or suggestions will be appreciated.
 
C

CFronzek

Petty Officer 2nd Class
Joined
Aug 11, 2002
Messages
118
Re: Compression on stored engine

RH<br />I wouldn't touch it. The compression is on a downward slide. It's headed for 60 lbs at which point it won't start. The fact that it increased 25 lbs. when you sealed the rings with oil shows that there is considerable ring and/or piston wear. <br />2-strokes are relatively simple but they need good piston/ring seal. When combustion gases get by the rings it leans out the incoming charge and lowers power.<br />If the price is low enough that you can afford a bore/rings/piston job (and a water pump for good measure) then it's a deal.<br />Charlie
 
G

G DANE

Commander
Joined
Nov 24, 2001
Messages
2,476
Re: Compression on stored engine

Just to add my opinion. I'd give the best price for a motor I tested on a boat for 15 min WOT. I'v measured compression on motors that sat for years and if there were no rust in cylinders they showed normal compression. Try to let it cranck for lets say 3 - 4 5 second periods with plugs in, after you sprayed WD 40, pull plugs and test again. If you get lower readings after the crancking, its leaking be the rings. Good compression is 120 - 140.
 
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