'77 Johnson 35hp: Problems after overheat

[Tallahatchie]

Hi Folks,
I thought I was old enough to know better, but I guess not, after running into shallow water my motor sucked mud in the water intake and ran hot. I shut it down and rowed back to the dock hoping no damage was done. Got it home and today I started to check for damage. Seems to turnover fine nothing is seized up. I hooked it up to the water hose and water flows through fine and out the pee hole. I tried to start it with the hose attached and it was very hard to turnover with the starter, so I pull the plugs and it ain't good, water is flowing into the cylinders! After I got the water hose off I turned over by hand to get most of the water out of the cylinders and after spraying lubricant in the cylinders hit the starter a few times to try and blow all moisture out. I have repeated this a few times. After that I checked the compression and both cylinders are at 120. It turns over smoothly and freely. Does this sound like a problem with the gaskets (head or exhaust) or possibly something much worse i.e. cracked cylinder block?

 

[whatsagm]

Re: '77 Johnson 35hp: Problems after overheat

Sounds like a head gasket. But without pulling it apart and checking for other damage its only a guess

 

[Tallahatchie]

Re: '77 Johnson 35hp: Problems after overheat

If the block is cracked should I be able to see it when I pull the head? Would compression still be good if block is cracked?

 

[Tallahatchie]

Re: '77 Johnson 35hp: Problems after overheat

So what is the next step, go ahead and pull the head? What should I be looking for when I get the head off?

 

[tashasdaddy]

Re: '77 Johnson 35hp: Problems after overheat

time to pull the head.

 

[Tallahatchie]

Re: '77 Johnson 35hp: Problems after overheat

Ok, I just pulled the head off and all looks good with the cylinder walls and pistons, smooth as a baby's butt, no scratches at all, not even small ones. Pistons look good, no holes and very little carbon buildup. I did not see any cracks in the cylinder walls or anywhere on the block. Does that indicate that it is either the head gasket or exhaust cover gaskets. Are there any other places deeper in the block that would cause a leak into the cylinder? Sorry for all the questions, just trying to determine if this is an easy fix or if it is hopeless.
Anybody ever had this problem?

Thanks

 

[Tallahatchie]

Re: '77 Johnson 35hp: Problems after overheat

Hi all, I just wanted to update this thread to let everyone know that I installed new head gasket and new exhaust cover gaskets and all is well! The motor cranked right up and runs better than ever. Compression is up to 130 on both cylinders. This was a fairly easy fix for a novice like myself, if anyone has a similar problem, just make sure your head isn't warped (mine wasn't), clean the old gasket off, make sure you clean out the water jacket area (mine had chunks of rubber clogging around the t-stat) and install a new gasket and torque to specs. The exhaust cover gaskets are the same process. While I had all the tools out I also replaced the clutch dog in the LU and installed a new water pump kit. If you're a novice like me don't be afraid to tackle any of these tasks, it's fairly simple with a good shop manual to guide you. Thanks for the help guys, now I'm going fishing!!!!!!!!

Tallahatchie

 

[tashasdaddy]

Re: '77 Johnson 35hp: Problems after overheat

congrats, should run another 30 years, just watch the coils. they are about due.

note on the clutch dog, quick deliberate shifts will save a clutch dog, slow shifts eat the edges.