Mercruiser 3.0LX - compression tests

[DeanUK65]

Hi from over the pond. Have a Searay Seville with a Merc 3.0 that won't start. I've replaced plugs, points, recon starter, new battery, fresh fuel, still wouldn't start. Decided to do a compression test..... 1 and 4 were fine, 3 was a little down, put oil in pressure came up. 2 well.... hardly anything even with added oil. Am i looking at piston rings or more serious problem? Any help much appreciated.

 

[Don S]

Re: Mercruiser 3.0LX - compression tests

I doubt rings would be the problem, most likely a valve problem, or a hole in the piston.
A leakdown test would tell you for sure what is leaking.

 

[DeanUK65]

Re: Mercruiser 3.0LX - compression tests

Yeah thanks, will try leakdown test when I can get back over to boat. What could possibly cause a holed piston?

 

[enn858]

Re: Mercruiser 3.0LX - compression tests

Check the valve clearance - and do a leakdown test + new compresion test

I just worked on my friends 3.0 (in a 1995 Welcraft) it only ran on 2 cyl - there was full compresion on cyl 1+4 and low/none on 2+3 - checked it with an endoscope - found nothing wrong - adjusted valves and compresione was restored.

I dont know what caused the valves to go way out of adjustment douing winter storage - but something happened

 

[Coors]

Re: Mercruiser 3.0LX - compression tests

or detonation from timing too far advanced.

 

[DeanUK65]

Re: Mercruiser 3.0LX - compression tests

Thanks for all your help and suggestions, will have a further look at the weekend and report back.

Thanks again. Dean