Compression release?

[Lyle29464]

Helping a friend with his 2009 Mercury/Tohatsu 4 stroke. Will not run.I looked at the carb It is clean and clear. Great spark. 55 # of compression. I ran a bunch of tests and found out it must have some sort of compression release that is not working right. This is doing a lot of guessing. I put a leak down test on it. It shows almost no loss at top dead center. I took the valve cover off and you can see that the exhaust valve is still open around 50% of the compression stroke. I ran this test a dozen times. I used a dowel to check where the piston is at the time the exhaust fully closes on the intake stroke. I even used the leak down to see when it would start building compression. ( Maybe after 1 inch of a 1.77 stroke. My questions are.
1. am i out to lunch?
If this is a compression release should it limit compression to 55#

Do I have a problem deep in the engine.

His teen kids will pull on it for and hour and get it started but it will only run a minute then die and not restart.
Any advice is greatly appreciated.

Lyle

 

[TOHATSU GURU]

Re: Compression release?

What model engine do you have? Secondly, the engine should be in warranty so why are you working on it?

 

[Lyle29464]

Re: Compression release?

Thanks for the reply. The model number is ME5M 4 st SN 0R014770
The motor was dropped overboard a year ago. The dealer charged him $490.00 to fix it.
He just does not want to go back there. I have found one thing that really needs to be fixed first.
The choke is broken and needs to be replaced. It is plastic and the arm broke off flush with the carburetor housing. He has been working it by hand. I would like to replace this. How can I order it? Then I will do some more trouble shooting.

Thanks Lyle

 

[TOHATSU GURU]

Re: Compression release?

No compression release on a single cylinder engine. Any Nissan, Tohatsu, Mercury or Evinrude dealer can order it for you.

 

[Lyle29464]

Re: Compression release?

No compression release on a single cylinder engine. Any Nissan, Tohatsu, Mercury or Evinrude dealer can order it for you.

Thanks again. The valve action really has me stumped. I have checked it many times. When the piston is near the bottom end of the intake stroke the the exhaust valve is open and stays open through the first half of the compression stroke. I have checked this several ways. I put air into the cylinder and it rushes out till almost 1/2 of the compression stroke is over. Then it will build around 55 lbs. At TDC The loss is very small. does not even show on the gauges.

I am quite familiar with the overlap, valve timing, ect. Just finished a 350 for my 17 and I'm putting together the 3 rd set of 454's for my 28. ( bought it in 1979). Any thoughts on what is going on?


Thanks again Lyle

 

[pvanv]

Re: Compression release?

The 4/5/6 4-stroke has geared timing, so the only way it would actually be off would be if the motor sheared a woodruff key. The exhaust timing is a bit late on those, to assist scavenging. Of course... If the motor submerged when tunning, all bets are off.

But.. since it does eventually run, the valve timing is probably OK. I would check the fuel and ignition systems, paying special attention to the fuel system. As Elvin mentioned, you can use the warranty to have a dealer look at it.

 

[TOHATSU GURU]

Re: Compression release?

Chances are the rebuild was spotty on it. May be a leaking seal on the block.

 

[sutor623]

Re: Compression release?

Man I have a hard time understanding how a 3 year old motor has already taken a swim. I am very careful with my little $300 motors. Couldnt imagine negligently creating an anchor out of a $1000-$2000 fourstroke. Yikes.

 

[Lyle29464]

Re: Compression release?

Man I have a hard time understanding how a 3 year old motor has already taken a swim. I am very careful with my little $300 motors. Couldnt imagine negligently creating an anchor out of a $1000-$2000 fourstroke. Yikes.

He has two teen aged boys.

 

[sutor623]

Re: Compression release?

He has two teen aged boys.

I'd be giving those fellas the '70's model evinrude.