1972 johnson new piston

[coop1954]

put a piston im my 65 hp johnson last year. it ran good. took compression test,2 cylinders have between 115 and 110 lbs. the one i changed hass 100. is it gonna last?

 

[jbjennings]

Re: 1972 johnson new piston

Just curious,
What was the problem that caused the need for a piston replacement in the first place? If you never found out and solved the problem, it won't last. If you did, your new piston/rings might need a little break in time and may actually improve on the compression with a little time. If you did it right and solved the original problem, I'll bet it will last a while. WHat was the compression on the new piston shortly after you changed it? If compression on that piston has dropped since you replaced it, that's not a good sign.
JMO,
JBJ​

 

[Joe Reeves]

Re: 1972 johnson new piston

Did you deglaze the cylinders so that the new piston rings would seat properly? If not, that would account for the slight difference in compression. Whether it will last or not is anyones guess...... if the compression last year on that new piston's cylinder was 100, and it's still 100 now, I wouldn't be concerned.

However, it the compression last year was say 110 or 115, and it has NOW dropped to 100, a problem exists.