67 evinrude sportfour 90-90-70-60-psi

[a70eliminator]

Results of my comp. test not to good, I've used this motor alot and think I've almost worn it out. I've always kept it tuned and clean, have gotton 28 years of service. I'm thinking the cylinders are in pretty decent shape, would it be reasonable to fit a new set of rings without any major dissasembly? Could it be as easy as pulling each head fitting the rings and reassemble?
While running the motor on muffs I pulled each plug wire one at a time just to hear the effect of each cylinder, and #4 the one with only 60psi is hardly contributing anything, the others note a definate miss, but that #4 doesn't make as much of a difference, which to me just reinforces something going on with rings, also by adding a squirt of oil the comp. goes right up to 120. I didn't even try it the others as i'm sure the same will happen.

Is there anything else that should be addressed during a re-ring job that I'm not thinking about? It looks like a fairly simple task for your above average backyard mechanic.

 

[tashasdaddy]

Re: 67 evinrude sportfour 90-90-70-60-psi

your first step.
Decarb, take a can of seafoam put 3/4 of it in the gas tank, with only 1 gallon of premixed gas. put the rest in a spray bottle. start the engine, and let it come up to temperature. then remove plugs, and them some real good shot of seafoam into the cylinders, replace plugs, let sit 15 minutes. restart, and spray the rest of the seafoam into the carbs, so the the motor almost stalls, wait and repeat until the seafoam is gone.then take for a wide open spin. then put in new plugs, ad premixed gas to the tank, and take it for a wide open throttle spin. it is going to smoke like a house on fire, during this process.

afterwards compression.recheck

hate to tell you, rings are not that simple. you have to crack the case and remove the crank etc. may as well do a rebuild, and make it new.

 

[F_R]

Re: 67 evinrude sportfour 90-90-70-60-psi

This is the motor that you ran with insufficient oil, right? The decarb won't hurt to try, but the next step if that doesn't work is to pull the cylinder head and exhaust covers. Could be a simple thing like a blown head gasket. With the exhaust covers off, you can see the side of the pistons and see if there is galling from lack of lubrication.

 

[alangf]

Re: 67 evinrude sportfour 90-90-70-60-psi

Unfortunately, piston rings is not a quick or particularly easy fix. The powerhead has to be split in order to disconnect the connecting rod bolts. The pistons then need to be removed (heads have to come off too) in order to get to the rings. Rings rarely go bad suddenly. It is possible for rings to break but why would they do it in two cylinders at the same time after 40+ years? More info is required to properly interpret the compression test readings. Are both low cylinders on the same side? If so, head gasket problems are more likely and far easier to fix. When the head is removed inspect the block surface carefully to insure the aluminum surrounding the steel cylinder sleeve has not separated from the sleeve itself. If it has the block is a basket case.

 

[a70eliminator]

Re: 67 evinrude sportfour 90-90-70-60-psi

Very good thanks thanks guys, I was just thinking like a motorcyle jug, thought the pistions comes up out of the block where you could at the rings. A blown head gasket Hmmm I'll see what a good decarb does first, the low cylinders are on the same side. If I bring the piston to TDC and block the flywheel I'm able to compress 80lb with no leakage in each cylinder, could this rule out the head gasket?