Yanmar GM10 compression

[canpaofgosport]

Hi,

I have just bought a boat with a 1991 GM10 installed. The boat is ashore, engine winterized for 1.5 years. When I viewed the boat and when the survey was conducted the compression was normal.

Now - last weekend I went down and with the decompression leaver down the engine turns freely- there is no compression. I am told this is normally the exhaust valve stuck.

What is the best thing to do - take off the rocker gear cover and give the value a light tap?

Many thanks,
Tom

 

[Tranona]

It must be stuck for a reason, probably water getting back through the exhaust. Suggest you take off the exhaust manifold first (3 bolts) and check that the inner part is not corroded. You will then be able to feel through to the valve. You can also take the rocker cover off and see if the valve stays down as you turn over. Probably not a good idea to try and tap it free without finding out why it is stuck in the first place.

 

[steve28]

The exhaust valve can stick if the exhaust has been left open over the winter, slight rust builds up on the stem thts normaly racing up and down.
If it wont free up by spinning the engine over decompressed then it will need a tap from above, use some diesel to soak it before and after freeing it.

steve