Mercruiser 3.0 - Possible Broken Piston Ring

[Wotam]

1994 Mercruiser 3.0/Alpha One Drive

I heard a slight 'tick' in the engine on the last couple trips out... when I first noticed it I thought it was just valve train noise, but by the end of the next fishing trip, it had taken on a 'harder' tone.

Last night I ran the engine on the muffs and pulled the breather plug... oh-oh... there's a ton of blow-by. Good god, this boat probably has less than 150 hours or so and has never been abused, I've owned it since new. There's never been any signs of detonation, lean operation etc. Of course, it's out of warranty.

So where to go from here? I guess a compression test will point at the bad cylinder, then pull the engine and hope against hope that the bore hasn't been damaged. If the bore is ok, honing, new pistion and rings in the offending cylinder (at least). If the bore is crapped... short block time?

I've read some comments elsewhere that late model 3.0's are having ring and pistion issues... is there a fix? Higher-quality aftermarket pistons, different rings? I don't want to do this job and have the engine self-destruct again prematurely.

 

[Bondo]

Re: Mercruiser 3.0 - Possible Broken Piston Ring

Until you diagnose the Issue,........ The Plan for a Repair is a moot point......

Your Plan outlined is a Good Start on finding out What the problem is.......

 

[Wotam]

Re: Mercruiser 3.0 - Possible Broken Piston Ring

With a ticking down in the block and blow-by I'm betting it's going to be 'piston something'. I have the compression tester sitting on the engine cover but have to wait until my son is home for the weekend so I have an engine 'cranker'. (or I maybe could find my old remote starter switch lash-up somewhere).

Basically I was following up on other comments that this is a common problem on late model 3.0L engines. (Maybe by Don S). This will be a wintertime project when the rain is coming down outside. Fingers are crossed that the cylinder bore isn't damaged.

 

[Wotam]

Re: Mercruiser 3.0 - Possible Broken Piston Ring

Did a compression check today... fall is setting in and soon the rains will have me indoors anyway. Time to fix this puppy.

#1 175
#2 175
#3 175
#4 165

A spritz of WD40 down the #4 plug hole brought compression up to 175 for a few minutes. Looks like an incipient ring failure in #4. So let the fun begin. Great hopes that the cylinder wall isn't damaged... at least beyond a quick hone.

Plugs were pretty dark, this engine has been running on the rich side since day 1. Hopefully the #4 problem wasn't due to fuel wash out.

 

[Benny1963]

Re: Mercruiser 3.0 - Possible Broken Piston Ring

THATS NOT THAT BAD you should be able to hone lightly.
silvilite has good low cost pistons but if you rering clean and hve machine shop check also you need to check ring end gap on each cyl
b1963