Question on compression

[Gill.nason]

Hoping someone can help Or offer some guidance. I recently picked up a 2001 rx injected with the 947 engine. previous owner told me he had recently done a top end and there was low compression in one cylinder after what he thought was a oil issue. I ran a compression test and found no compression on both cylinders. I removed the head and checked the piston and rings. They piston fine from the top and the walls were not scored, and the rings were all intact through the rave holes. what’s your opinion? Gasket, rave valves or something completely different. It turns over fine and when i cranked it with the plugs remove you could see fuel being pushed through the hole. I have worked on two strokes for many years, but never rebuilt one. But i am going to try If that’s what it needs.

 

[glsmohio]

Check your compression gauge

 

[mikidymac]

With everything looking good there’s no way to have zero compression.

951’s typically don’t survive a new topend on a used crankshaft.

Second did he actually have the cylinders bored and new oversized pistons fitted? You can’t just install new pistons on worn cylinders.

If you have a DI 951 you have to use DI pistons.

 

[Gill.nason]

Check your compression gauge

A new one is on its way. I thought about that but hooked it up to air hose and it registered, but lets hope.

 

[Gill.nason]

With everything looking good there’s no way to have zero compression.

951’s typically don’t survive a new topend on a used crankshaft.

Second did he actually have the cylinders bored and new oversized pistons fitted? You can’t just install new pistons on worn cylinders.

If you have a DI 951 you have to use DI pistons.

I wish i knew, and i agree with you about zero compression. But its what i had. Do you think it could be a gasket or rave valve problem?

 

[mikidymac]

Don’t get too worried until you get the new gauge.

For zero compression you would basically have to have no rings or a hole in something.

 

[SabrToothSqrl]

I had several cylinders in my boat's twin V8s with zero shown... replacing the engines fixed it Odd to see both at zero, but at this point I think you're looking at a new engine...

 

[mikidymac]

I had several cylinders in my boat's twin V8s with zero shown... replacing the engines fixed it Odd to see both at zero, but at this point I think you're looking at a new engine...

Glad to see you here again Sqrl, it's been too long.

 

[SabrToothSqrl]

Thanks. I miss my skis that's for sure. Had I known I'd be working from home all last summer with no-where to go, I would not have sold them years ago!