Piston melted on 1977 Johnson 35HP?

[oldfarmall]

Hello-

My neighbor has a 1977 Johnson 35hp with what looks like a melted piston on the top cylinder, full model is 35EL77H. Could someone tell me from the pictures what may have happened? Head gasket looks blown. Did water get in the upper cylinder? What would cause the top cylinder to do this and the bottom cylinder to look fine? I am guessing the piston is shot, the head looks usable if cleaned up. Thanks in advance for any advice.




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[nwcove]

Re: Piston melted on 1977 Johnson 35HP?

i would guess the upper crank seal . but thats just my guess!!

 

[scottmm73]

Re: Piston melted on 1977 Johnson 35HP?

That looks like a routine case of pre-ignition damage. Did the neighbor run his motor lean? Has it overheated before?

 

[oldfarmall]

Re: Piston melted on 1977 Johnson 35HP?

That looks like a routine case of pre-ignition damage. Did the neighbor run his motor lean? Has it overheated before?

I am not sure what you mean by preignition. Also, it uses a single carb for both cylinders. Why would the bottom cylinder not be affected? Thanks!

 

[F_R]

Re: Piston melted on 1977 Johnson 35HP?

Yep, preignition. That is when the fuel violently explodes in the cylinder rather than a controlled burn. In cars you hear it as "pinging" or "spark knocking" Once quite common in cars, not so much now with the computer controlled engines. Caused by several possible things. Low octane gas, high compression, too lean, and/or too much spark advance are most likely culprits. Why just one?? Well, possibly a bit more compression on that one. Or maybe that one was just a tad hotter. Just a guess.

 

[boobie]

Re: Piston melted on 1977 Johnson 35HP?

I've also seen power packs go ape on the timing for one cyl. When you get it fixed, check the timing on both cyls.

 

[oldfarmall]

Re: Piston melted on 1977 Johnson 35HP?

I've also seen power packs go ape on the timing for one cyl. When you get it fixed, check the timing on both cyls.

As far as the timing goes, this motor has the external ignition coils mounted to the cylinder head. Also, I am assuming this is a CDI ignition motor, no more points and condenser under the flywheel? By timing the engine to ignition, are you refering to syncing the magneto to when the carb butterfly opens like you had to do with the older motors? Thanks for all the replys so far.

 

[boobie]

Re: Piston melted on 1977 Johnson 35HP?

What I was talking about is you can have timing set on one cyl correctly and it can go ape on the other. Find the tdc marks for both cyl's and check them.