2 cylinders low compression

[cooney]

88 xr4 150 merc had pecking come in engine. checked compression & top left cylinder has 55 lbs. & top right cylinder has 70 lbs. the other 4 have 110 each. if sleeves are alright would you rebuild just top 2 or give it a complete overhaul? this engine never made any noise before. think carbeurator caused it may have been to lean . dont know please anyone that knows let me know as i do not have a lot of money & only want to do 2 cylinders if there are no bad consequences thanks

 

[Hooty]

Re: 2 cylinders low compression

First thing I'd do cooney, is a de-carb. It's relatively cheap a could solve your low compression problem if ya got coked-up rings. If it is pistons, cylinder walls, rings, whatever, just repair top two.<br /><br />c/6<br /><br />Hooty

 

[cooney]

Re: 2 cylinders low compression

hooty this engine never made any noise before . it done this after gunning it to come out of hole. it blew out [the prop that is & then this pecking noise started. you cant hear the pecking at idle but after about one-third throttle you can & its pretty loud

 

[dmessy]

Re: 2 cylinders low compression

You KNOW what you did right? Over-reved then the noise...doesn't sound good.<br />Don't believe anything in a can will help but the decarb will make it cleaner to tear apart to fix your broken ring( I suspect). Pull the head on the worse one and inspect cylinder. Only fix whats broke but check all pistons/rings/cylinders etc. against factory specs.

 

[Hooty]

Re: 2 cylinders low compression

Well, ya could pull a head and look at the cylinder and see if it's a busted ring or loose wristpin, or, I'm not sure about that engine, you might be able to remove a by-pass cover and have a look at the piston and cylinder, but I'd still do the de-carb first. Mercury makes a de-carb, it's called Power something-or-other and it's good caca. Get some and follow the instructions. Doesn't cost much and may save ya some time and bucks.<br /><br />g'luck & c/6<br /><br />Hooty

 

[ob]

Re: 2 cylinders low compression

Cooney, if this motor was not showing signs of poor performance before mishap I fear Dmessy is probably right on decarb not having much effect.Hope I"m wrong.However it won't hurt a bit following Hooty's suggestion and decarb to see if it has any positive results.