7.5 hp Evinrude Compression

[Rudy AZ]

I've read this site for a while and asked questions before so I knowthere's some pretty informed people who contribute to it. Can anyonetell me the compression spec for a 7.5 hp Evinrude (83)? My manualdoesn't have it listed and I don't know if 90 psi is OK or low. Yep, Iknow you're thinking why doesn't he go to Evinrude site to get thisinfo. Well I did and many more as well. The company that boughtOMC has Bombed the site. Thanks Rudy

 

[John renfro]

pressure

hello Rudy, in a two cycle, cylinder pressure is not a big deal, the crankcase pressure is what runs the engine and unless the case has a leaking gasket or hole in it, it should not be reduced much from new, and if 90 is not fouling plugs, then use it. in abos third edition outboard motor service manual copyright 1965, mcculloch lists 75 psi for the 3.6 hp, Clinton lists 60 psi for the 5hp. mercury lists " not more than 15 psi between cylinders " for 6hp to 100 hp.john

 

[Rudy AZ]

to John renfro

Thanks John you are a Prince. Your information is a Godsend and of course I always look for parameters and this not exception. The plugs are clean and dry. Do you know any books that might tell me how bad, bad is, as in what are the high and lows that are acceptable. Maybe I just spent too much time in Government Defense work. Thanks for your help, Rudy

 

[Jim Maroldo]

compression seems to be...

...too much of a variable on these small 2-stroke engines, Rudy. I'm no expert on the subject, but I have worked on many 2-stroke engines; from small model glow types to the marine outboards. I don't recall ever seeing compression specs. Just as John said, if the crankcase is sealed, rings are good, fuel & spark are available, she'll run! I had a problem last year with our 5hp o/b where the rings got stuck in the piston grooves over the winter (forgot to add oil before storage!). Blasted thing wouldn't even pop with ether! The problem was obvious since it was TOO easy to pull! After digging the rings out of the grooves and replacing them with new (didn't NEED new ones until I broke the old ones!), she started up on the 2nd pull! To repeat again what John has said, don't get too excited about these things. If it starts and runs well, just go sailing!Jim Maroldos/v: Lil' Wass Ett