2005 DF50TL 4 stroke, no compression on one cylinder

[MDG1982]

The other two cylinders have 130psi and holding. The bottom cylinder though doesn't build any compression at all. Any suggestions?

[artdf175]

a few questions
how many hours on the engine?
what may have been issues that caused you to look at compression now?
last time the valves were checked for clearance?

art

[MDG1982]

The motor has a little over 300 hours. And I was selling the boat and a buddy of mine came to check the motor for me. We did a compression test and found the bottom cylinder has no compression.

[MDG1982]

The valves have never been checked since I've had the boat. The top of the piston looks good from what I can see through the sparkplug hole.

[redlowrey]

pull the cam cover off and have a look inside.

[MDG1982]

What would I be looking for when I pull the cam cover off?

[catacom225]

no commpression

Put a few squirts of engine oil in No 4 and test again, The oil will put a little seal around the rings, If it increases it would suggest blow by, If it still remains the same then i would check the valves or possibly the cam

[MDG1982]

Ok thanks. I will try that this weekend and post results

[redlowrey]

Some thing is not making sense, you only have three cyls and if one was out the engine would have been running like a dog, if it was running alright you better do your test again.

[mike.floutier]

Out of interest, was it a leak-down test or a dynamic test, ie. running the engine with a meter in the plug hole. I seem to remember, from my car mechanic days, there can be a big difference.

[mike.floutier]

See Compression and Leak-Down Testing | DSMtuners for a good article explaining the difference and how to use the results in diagnosing issues.

[MDG1982]

To start with, I didn't run the motor at all in 2015. Decided to sell the boat earlier this year.. try to get the motor to crank and it wouldn't. It would turn over but never start. Sparks lok fine, getting fire etc.. thought it was the old gas that's over a year old.. got new gas (100% gas) still wouldn't start. So my buddy came over to help me look at the motor, and he did a compression check (with the screw in gauge in the spark plug hole). That's when we found the bottom cylinder doesn't register any compression at all. But the the top two was good and held the compression. The test was done while bumping the key