compression issue question

[boater121]

i have a 74 6hp evinrude 6402c and i did comp test and got 80 psi on both cylinders is that low? what is factory?..will a seafoam and a head gasket get comp back up?

 

[Daviet]

Re: compression issue question

80 psi is fine for your engine. If it had electric start the numbers might be a little higher, but from a manual pull start you are ok, the important thing is that they are within 10% of each other. There are no listed factory specs for compression.
Seafoam will help decarb the pistons but will not have an effect on compression, I wouldn't worry about the head gasket unless there is visual signs of leakage.

 

[boater121]

Re: compression issue question

paint missing around head area like it got hot one time..should i replace head gasket?..ive done everything else to this motor , ignition, wp, fp carb rebuild...

 

[Rick.]

Re: compression issue question

A little history. Sounds as though the motor might be new to you? Was it in use or sitting for a number of years? Let us know. Best of luck. Rick.

 

[boater121]

Re: compression issue question

sitting for 11 yrs got it from dad did all ignition, rebuild carb, water pump, fuel pump, all new rubber lines,
i ve ben using quite often..runss good just seems to lack alittle power..i know its only a 6 but its gota have a little more ..i was going to do head gasket anyways as part of doing everything else i already did..kinda of a refurbish..just from how long it sat i would do one just because

 

[Rick.]

Re: compression issue question

sitting for 11 yrs got it from dad did all ignition, rebuild carb, water pump, fuel pump, all new rubber lines,
i ve ben using quite often..runss good just seems to lack alittle power..i know its only a 6 but its gota have a little more ..i was going to do head gasket anyways as part of doing everything else i already did..kinda of a refurbish..just from how long it sat i would do one just because

Do what you like but changing a head gasket is by no means considered good maintenance practice. There should, IMO, be a reason to pull the head. I appreciate, in fact, commend you for the work you've done on it so far but the head gasket is over the top. A decarb would/might be beneficial if your rings are a little frozen in place but at 80#'s I rather doubt they are. Enjoy your engine. Rick.

 

[nwcove]

Re: compression issue question

i agree with rick, if the motor works good and there are no obvious signs/symptoms of a blown head gasket, leave it alone. as far as getting "a little more" from your almost 40 year old motor.......just be pleased with your work getting it up and running well......and enjoy the fact that it will get you "there and back"!

 

[mstahl1171]

Re: compression issue question

if it is not broke...leave it alone.....lol

 

[lindy46]

Re: compression issue question

That engine would probably run fine with 60lbs. of compression.

 

[kenmyfam]

Re: compression issue question

Compression is good for a rope start motor.
Did you change out the lower unit oil ???