1977 85hp low compression

[fordsohc46]

my motor runs but idles rough, hard starting, smokes badly the compression is 70, 75, 75, 75. i am suspecting is needs rebuilt. the marine mechanic said it needs rings and pistons. i was wandering if i could hone the cylinders and do a ring job. i am new to outboard mechanicing and didn't know if you had to replace the pistons or if you can just put new rings. also is is possible to remove the carbs, reed valve plate, and head to replace the rings or if i have to teardown the whole engine.

 

[JB]

Re: 1977 85hp low compression

Heck, it's only 30 years old. Can't be worn out yet.

First, sohc, do a thorough decarb on it. See the Engine FAQs for how to do that.

Then redo the compression, with a freshly charged battery, screw-in compression guage, spark plugs out, after a warm-up and with the throttle at WOT.

Do at least 5 revs on each cylinder.

My guess is that compression will still be near equal, but it will be up closer to 100psi.

Then crank her up and go fishing.

 

[ezeke]

Re: 1977 85hp low compression

It is unusual to have that compression level and to all be within 5 PSI. You might want to try that again with a different tester. Make sure that all of the plugs are out, that the tester is of the screw-in type and that the warm up lever is up.

A rebuild is a rebuild - to do the rings, you need to disassemble the whole engine. You need the rings plus a complete gasket kit, plus whatever you run into inside.

Edit: You type too fast JB :|

 

[fordsohc46]

Re: 1977 85hp low compression

decarb motor this morning retest with throttle open results: 115, 120, 120, 120. thanks to everyone for all the help.

 

[tashasdaddy]

Re: 1977 85hp low compression

i was gonna say decarb it before you tear it down. seafoam is great, it's like an enema. let us know how it is on the water. carbs may still need attention.

 

[kenmyfam]

Re: 1977 85hp low compression

Amazing what a good decarb will do. I used to decarb my old 50cc 2 stroke moped about every 2 weeks !!! but manually. Went through a lot of head gaskets !!!