Too Lean?
 

I have a set of newly reman'd 468's with about 2-3 hours of break in time. Now I don't have compression in #3 on the starboard side. It started with a little smoke in the cockpit, then I shut it down. A leak down test shows it leaking into the crank case so I have had either a ring or piston problem.

My problem is I have a feeling the builder and the installer are going to start pointing fingers at each other. What do I need to be looking for to be able to tell what is up. I have a feeling that they were set up too lean and it burned up a piston, but the installer said the plugs were black so what other tell tale signs are there of what could have happened here?

Re: Too Lean?
 

From your other thread it sounds like detonation. I don't think either one of your mechanics is going to warranty that. If you have knock sensors check them. Mine was bad and I burnt two pistons.

Re: Too Lean?
 

When a engine change has been made or even just a carburetor change for that matter- either high performance, stock rebuild, or reman the carb calibration has to be checked IMMEDIATELY on water and/or dyno .

Not doing this is the #1 demise of all engine installs.

A boat creates a ton of load. If the A/F ratio (or timing) is off then it's not a question of 'if' rather a question of 'when.'

Good luck - keep us posted with what's happening.

Re: Too Lean?
 

Check the plugs yourself to determine how the engine has been running. If the combustion has been normal you know that someone screwed up when assembling the bottom end of the engine. Just a question, even if it turns out that it has been running lean, wasn´t the builder responsible for the whole engine incl fuel system?

Re: Too Lean?
 

get the boat to a third party, talk to a different builder to look at the motor, he SHOULD be able to tell you what is going on. At this point you do not want the investigation committee having potential liability.

Re: Too Lean?
 

Well it was a blown head gasket on the inside of the cylinder wall where it is the thinnest between the oil passages. It blew out about an inch of the gasket material. I was standing there when he removed the head.

The cylinders had black residue from them running a little rich. There was no other signs of damage. I am going to have the deck and head checked for straightness, but they were both machined because you can see the honing marks on the surfaces. All the bolts seemed to have the proper torque. The builder is talking now about pre-ignition causing this and I am very sceptical. This definately seems like a manufacturing issue or a faulty gasket issue at the very least.

Any ideas?

Re: Too Lean?
 

Pre ignition does not sound right. Still dont understand why the builder would point n the wrong direction?

Re: Too Lean?
 

You could be rich at idle / low speed but lean under load or higher rpm.

Lean or too much timing are #1 causes for detonation and lifting cyl heads off block allowing head gaskets to fail. Detonation will also try to pound the bearings out. Look down into spark plug with magnifying glass to look for small spec's of aluminum.