This can't be good...

[CFORBERG]

'77 Johnson 70 hp triple with compression of 110, 110, 60.<br /><br />Anything to check before I tear down the powerhead? Any chance this could be a stuck ring?<br /><br />Thanks in advance, Clint

 

[Dhadley]

Re: This can't be good...

I'd pull the head and take a peek. As long as your sure those results were accurate.

 

[CFORBERG]

Re: This can't be good...

Pretty sure that it's accurate...repeated test 3 times with the same result. Can you replace rings on just one cylinder?

 

[Dhadley]

Re: This can't be good...

Yep. No problem but once you get it apart you might as well plan on rings for all. If not boring. But before you tear into it we might as well pull the head. Lets just see what we got.

 

[steelespike]

Re: This can't be good...

I've seen folks get good compression results with a simple decarb treatment.

 

[CFORBERG]

Re: This can't be good...

The verdict is in...<br /><br />Broken ring on #3 cylinder. The piston crown is "stippled" and so is the head. It seems that the pieces of piston ring bounced around a while before being expelled through the exhaust.<br /><br />Luckily, the cylinder wall looks and feels perfect!<br /><br />I pulled the powerhead this weekend, and am getting ready to order parts. Is there any chance the head and piston can be smoothed out and re-used? Damage seems reasonably shallow.

 

[stan_deezy]

Re: This can't be good...

Good Call Dhadley

 

[Walker]

Re: This can't be good...

Is there any chance the head and piston can be smoothed out and re-used?

Piston - definitely not<br />Head - not a good idea, any little chink, burr, or high spot can be a source of heat build-up hot spot due to the extra surface area and the lack of the huge heat sink that the original casting and milling of the head provided.

 

[CFORBERG]

Re: This can't be good...

Understood. Is there a good source for these parts, or is the dealer my best bet. Are used parts (piston, head) an option?

 

[Goodoleboy]

Re: This can't be good...

A compentent machine shop can resurface your head and shine up your combustion chamber thats bin dinged up.<br /><br />I would not try useing a used piston. New one is not all that pricey.<br /><br />I would also rering the other two pistons as well while you have it tore down.<br /><br />Good luck!