Compression Variation

[jsfpilot2b]

I have a 1988 mercury 8ohp that has a 15-20 lb. variation between it cylinders. Should I expect it to die any day or are there steps that I can take to prolong the life of it? <br /> thanks.

 

[roscoe]

Re: Compression Variation

It would help to know what the actual compression readings are. 90 and 70? or 145 and 130?<br /><br />You can decarbonize your engine, which may free up a stuck ring, giving you higher compression. It definitely won't hurt anything, and may help tons.

 

[jsfpilot2b]

Re: Compression Variation

The readings are : #1 cylinder 130<br /> #2 cylinder 115<br /> #3 cylinder 135<br /> <br /> I have just ran a bottle of decarb- thru the motor. I don't know if it has had an effect on it yet.

 

[rickdb1boat]

Re: Compression Variation

jsfpilot2b <br /><br />A little low on # 2, but not finished yet. See what happens after you run it again allowing the cylinders to clear out from the decarb. Then check it again. There's really nothing you can do to improve the compression, outside of rebuilding or decarbing, which you did. Just be sure to use quality oil, gas and the proper mix. Did you do the compression check hot or cold? Throttle wide open? Try putting a teaspoon or 2 of TCW-3 in the # 2 cylinder and see if that brings it up.

 

[Capt Ken]

Re: Compression Variation

If all else fails, run it till it dies. Lots of engines out there are running with one or more cylinders lower than what you found. As long as it runs decent enough for you, let it ride. You never know, it could have been that way for years now and you're just now finding it out.

 

[jsfpilot2b]

Re: Compression Variation

Thanks for the replies guys. Like I said, the boat has been setting up for a long time. I think that over a period of time the readings may come up a little. I will be babying it this summer. It's in for a tune-up know.<br /> jsf

 

[sony2001]

Re: Compression Variation

You could concentrate on #2. Thru the sparkplug hole spray decarb on the warm piston then start it up. Repeat, and let the decarb sit overnight. Then take another reading after a short run at WOT.