compression?

[pikefisherman]

Can some one tell me what good compression is on a 4.5 johnson motor?
I can make it run but need to turn it over with a drill. Will not idel or pull start.

 

[Monte1961]

Re: compression?

90psi

 

[raczekp1]

Re: compression?

i had this motor, so
it stoped firing by pull start when compresion went to 4 bar(60 psi)
over 60 psi(65 or so)sart only with choke out, run 5 sec and die( i think could not manage to suck fuel from the carb when choke pushed in)
i think 90 or more is good compresion

 

[pikefisherman]

Re: compression?

Thanks: It ran good last year I did not bring in over winter I'll check later for compression. Did you repair your motor? It is a nice trolling motor.

 

[raczekp1]

Re: compression?

i got this motor after overheating accident.
rings stack in piston groves(lower one).i put new rings(rebuilt water pump, gearcase seals), but after assemble he run 3 hours, and compresion went down to 60 psi.cylinders went out of roundnes(bearings play).so i should order oversize pistons ,rings and rebore.but the needle bearings its not easy to get and are expensive.
so i'm planing to post some parts on ebay

 

[lindy46]

Re: compression?

It should run fine with 65psi or better, but the most important thing is that both cylinders are close to the same (within 10%).