56 Johnson 15hp / Compression

[seawolf]

The other day I removed the cylinder head to remove carbon deposit as per other members instrutions.

I am wondering , when looking at the piston head there seems to be a slight clearance between top edge of the head of the piston and the cylinder wall.

I know when the motor is warmed up the rings should seal, but when cold should I see this small amount of clearance? ( I am strictly talking about the top edge (head) of the piston against the bore.

I have recently aquired this motor and have not run it yet. Any thoughts would be greatly appreciated.

 

[jbjennings]

Re: 56 Johnson 15hp / Compression

You removed the cylinder head to remove carbon deposits, eh?
Interesting......
I don't think you should worry one bit about that piston head stuff unless you see scoring (scratches where the piston has rubbed against the cylinder bore) on the cylinder walls or chips or something else odd about the pistons. Put your head back on your new head gasket and check compression. If it has good compression and you don't feel any binding or anything when you turn the flywheel by hand, I think you're in good shape to get it running. The piston head is not supposed to touch the cylinder wall. If it does, then you've got problems! Do you mean that there's one area around the piston that's wider than the clearance around the other sides of the piston? If so, then you may have a bad wrist pin that's allowing the piston to slop around. But if you did, I would think you'd see some scoring.
JBJ

 

[seawolf]

Re: 56 Johnson 15hp / Compression

I guess I should have clarified. I removed the head because I am tuning the motor and am going to replace the gasket anyways. I wanted to check the condition of the cylinders and noticed that there was carbon build up. I removed most of the carbon by gently (very gently) scraping away with small soft brass brush. Worked well I think. I was just wondering if I should be able to see a tiny biy of play when looking at the head of the piston in relation to the bore.

Thanks for the quick repy. Perhaps I'm worring too much but I've yet to run the motor.

 

[tashasdaddy]

Re: 56 Johnson 15hp / Compression

don't over think things, until necessary. put the head on and check compression. actually should have been done before pulling the head.