We hurt the 496....
 

Guys,

It looks like we may be doing a "refresh" on our 496HO a bit earlier than we'd planned. All signs suggest we've dropped a cylinder. Don't really know what exactly is going on but I' thinking we took the top out of one of the pistons. Working on diagnosis; taking it to "Skinny" in Somerset as soon as he gets back from vacay. In the meantime, I'm examining options.

We have the stock Merc forged crank, confirmed through Merc tech build sheet, so we're good with that at the power level we're at. Don't plan on ramping that up at the moment.

Obviously, we'd replace with forged pistons. I'm thinking JE, but don't have any real details yet. I don't know if we will have to bore yet but would plan on at least cleaning up with honing. Bore may increase a bit.

Considering replacing Rods, as well, as they are the NEXT weakest link, being powdered metal. Don't know for sure. Thinking Molnar.

Might also address valve train improvements while it's apart. Definitely new springs at the very least.

This is a bit (at least) outside of my wheelhouse, though, so I'm seeking advice. I also understand Merc used something other than the typical rod length and compression height stack-up, so I really don't even know what to look for. Should I mimic Merc's specs, or are there better?

Suggestions? If I'm thinking way bigger on the budget than I need, tell me. I've got the cash to make it happen, but really didn't want to drop it on the boat at the moment.

Thanks. Brad.

PSI time?

Raylar would be my first call for parts once it is apart and inspected

Vortec 8100 8.1L Chevy GM Performance Parts - GEN 7 Big Block - 496MAG HO Marine Performance Parts - Raylar Engineering

Tom,

As much as that idea intrigues me, I've gotta keep in mind we're putting it all through a (AFAIK) stock Bravo1 drive.

Damn it.... :(

Thanks. Brad.

SnapMorgan,

That's what I'm getting from 87Mirage. I'll be calling them today to explore options.

Thanks. Brad.

Dead hole. Pull plugs? Head gasket? Would go along with your temperature issue.

Rookie,

Don't know anything just yet. I didn't do anything other than scan it with the TechMate and take this video. TechMate shows no fault codes, but 16sec of guardian mode, which was probably the "sagging" we had before realizing anything was wrong.

Boat is in our driveway in Burnside, KY. We left it when we came home (Dayton, OH, 180mi away) as I was hoping our guy "Skinny" would tell me to bring it on over, and I would have driven back down and dropped it off. As it turns out, He's on Vacay, and won't be back in til next week.

I'm honestly hoping the head gasket hunch is right. I'm not optimistic, though. The excessive oil out of the dipstick tube is usually telling of a failed piston. I just wanted to get ahead of the parts hunt ahead of time, in the event we needed to pull triggers.

Thanks. Brad.

You can get cheap bore scopes on e-bay now and have a look through the spark plug holes when u get back to it.

Wildman,

Yup. Thought about that. And I may do just that. But the reality is that, by the time I get to the boat, within 12-16hrs, I'm gonna be talking to Skinny, face to face, and that's likely the first thing he's gonna do.

Thanks. Brad.