Derrickw87
New member
I have a 1974 85 hp Evinrude and all 4 cylinders have 82 psi compression. I am wondering if it could just be bad head gaskets or do I need to do a ring job also? Thanks.
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I have a 1974 85 hp Evinrude and all 4 cylinders have 82 psi compression. I am wondering if it could just be bad head gaskets or do I need to do a ring job also? Thanks.
Excellent information, however, I am so sorry about your motor. Maybe you had better pull the heads and have a closer look. At this compression you will have about 1/3rd less horsepower. It may likely only get worse.
I had just replaced head gaskets today and got same results.....am I in need of piston rings?
Thanks for the answer so low cranking speed problem could that just mean my starter is getting weak? And the psi readings are with another guageThe first thing to do is to get another gauge somehow, somewhere and compare..... it may simply be your gauge that is failing.
Also... keep in mind that the psi reading will vary with the speed that the engine is cranking over... think about that! If cranking the engine over with a rope, pulling it slowly thru... you might have 10 psi if you're lucky. Cranking speed of roughly 300 rpm is desired.
The fact that you have the identical reading on all four cylinders indicates (my opinion) a cranking speed problem. Normally, with the engine cranking at a normal rpm (all spark plugs removed)... if there's a compression problem, it's going to pertain to one or two cylinders... IT IS NOT going to show up as identical low psi readings on all cylinders.
Now.... Pertaining to compression. Throttle butterflies open or shut, leaf/reed plates broken, welded shut, whatever... it doesn't matter. You could remove the entire intake manifold assembly, everything... it wouldn't matter. There's plenty of air for compression available via the exhaust ports... and compression does not begin until the exhaust ports are closed.
Low cranking speed can be contributed to a good but discharged battery, a good fully charged battery with either loose connections...OR... tight but dirty connections, or yes, a failing starter.
The place to start (all spark plugs removed), although you're absolutely sure that the connections are okay... is to remove all cables from the battery, clean those cable terminal ends and the battery posts so that they look better than new... then do the same with all the cables/wires at the engine such as the cables connected to the starter solenoid, the electric starter, and also (Important) the black battery cable where it grounds out to the powerhead.
When you have accomplished the above... and the battery is known to be good and fully charged... see if there is an improvement in the cranking speed of the engine. And if not...........
The second task (if it were me) would be.... with a good known fully charged battery and known good jumper cables... to run those jumper cables directly to the electric starter... and if the cranking speed is still slow, dismantle that starter motor for inspection.
The absolute clean and tight cable routine is however a must!
If any of the heavy duty cables related to the electric starter system becomes very hot (battery, solenoid,starter, ground) that normally indicates that either the cable has a bad connection at the shortest distance from that hot spot... OR... the internal wires of the cable at that hot spot has become corroded and not capable of carrying the current, in which case, replace it.
Like 6 gauge pure copper, not copper clad.
Alright and I know the job is pretty easy but other them headgaskets is there any other gaskets I would need or just the pistons and rings?