Compression on 2004 9.9 Outboard

[hz293]

I'm about to buy a 2004 Mercury 9.9 EXLH for my 1976 Catalina 27. I'm told compression is 190 and 160. Anything to worry about?

I'm also told that Tohatsu makes the 4 stroke Mercury. Is that true?

Harris

 

[Cool Beans]

I'd look up a mercury dealer or authorized repair shop and just call and ask them. 12% difference on a 2 cylinder. . .I dunno, but I wouldn't purchase it until I had ask an expert. They might even be able to tell you what could be causing it as well

 

[Winkfish]

When I bought my boat, used, I was really worried about my 1985 6 cyl Merc. I asked a couple of mechanics locally, and I called Mercury. All said the same thing - the actual compression "figure" doesn't matter so much as that all cylinders should be within a 10% range from the highest to the lowest.

For your 2 cylinder motor, there could be something wrong there. I'd ask to get it checked out by an outboard mechaninc.

 

[Joe]

Tohatsu makes Nissan and Mercury.

 

[sailaway78]

Too much differential

IMHO that is too much variation between cylinders. On most small engines, a variation of more than 10% is considered excessive. Squirt a little oil in the spark plug hole and test again. If the low one comes up, the rings are very questionable.

 

[kloudie1]

I'd want to know how the readings were taken.. if the engine was stored for a while before the readings were taken, more residual oil could have been in one cylinder .. Would have been best to start it and run it 'till mildly warm.. THEN pull the plugs and read compression.. AS Nice&Easy points out a little oil can make a big difference in the readings. If those readings were correctly taken, then I agree that there is too much difference in the readings.. Could be a bad valve or rings or a scored cylinder.. or a valve set badly.. or a bunch of other things.. Caution

 

[hz293]

Thanks for the info. To be safe I decided to pass. I may just get a new Tohatsu.

Harris