Mercruiser 350 one cyl no comp....
 

Hi !
Just pulled the Head on a Mercruiser350 magnum efi , the aft left cyl had no compression , the exhaust valve was cracked and burned severe... the seat needed a lot of grinding to come clean but there are many hair line cracks on the exhaust seat, will it work to put in a new valve or do I have to put in a insert or something like that?

The inlet valve on the same cyl also look bad and the seat is leaking , the cyl has more wear than the others but no scratches but traces all over from rust or something , seems like the head are wrapped in the end and maybe that cyl has used water.

2 new valves a valve seat job and resurface the head and bolt it up?
What do you guys think?
The boat needs to be on the water and running, fast...
Thanks Espen

I'm thinking that the cylinder got burned because it ran lean. You can just slap it together, but if there are cracks, the head is junk. The valves are also junk. Also, have you check your fuel injection system? I'm guessing that you have a bad injector.

thanks for the advice Cord.
I will check the injectors...
All other cyl look rich, checked with a mercruiser scan tool and the air temp sensor showed -17deg c ! when I checked with the dealer he could not find any air temp sensor at all on that engine....
I wonder if hairline cracks on the exhaust valve seat are ok? how long will it work?
thanks espen

I know you wanty to get back on the water, but do it right unless you don't mind getting towed in in the near future.

Since one head is already off, pull the other one and take them to a reputable speed shop for magnaflux and warpage. You're gonna need at least one new seat. Was the intake valve tuliped?

The inlet valve had sunk into the seat deep. the valve looked very corroded and the seat deep into the valve,
it looked like it was burned to.
Thanks for the advice 220BR. All the other cyl had 15kg on the compression gauge .
Thanks

You need to trust your machinest...
 

The problem you are describing is common in the industry. If all of the other cylinders look good and the valve springs are good I would suggest that the problem came from one exhaust seat/exhaust valve not having as good of a valve job from the factory as the rest. It just took some time before it failed (could take hundreds of hours). Mass produced engines are not perfect. Probably wouldn't ever show up on a low rpm truck engine but a high rpm marine engine needs a little better valve job.
Sincerely
Dennis Moore