Oh dear this doesn't look good. Is the long block stock, meaning factory pistons etc?

87Mirage,

Yup. Bone stock, ProCharger and ECM flash aside. Forged crank and rods, but still has those damned cast pistons.

Compression test time….?

Thanks. Brad.

So the engine was rebuilt using a forged crank and rods, but with cast pistons? OMG.

87Mirage,

No. At one time, as I understand it, Merc Built the HO with forged crank and rods, then later on they started using the cast crank and rods, but they always used the cast pistons. There was a transition period, that my engine came from, where it may or may not have been built with forged. I have no idea what the criteria was for deciding whether to use the forged parts or not. I’ve called Merc and confirmed through serial numbers that I have the forged parts. As far as I know the engine has not been out or apart since the initial build. Purely an assumption, but is my guess that PQ was planning the build and specifically requested the forged parts in anticipation of the ProCharger. The ProCharger kit was specifically designed for the Merc 496, and only puts out 3lbs at WOT.

I was told the ProCharger was an original PQ build. I know the fuel pressure and boost gauge wiring is part of the main wire bundle running under the gunwale, indicating it was part of an original build. I can all but 100% guarantee that either the engine came out to do the ProCharger install, or it was done before initial install. I cannot imagine doing the install with the engine in the boat. There just ain’t no way. It is WAY too tight a fit. Just changing the belt is a nightmare.

Thanks. Brad.

That's a neat package, a procharger installed at the PQ factory!

When the 496 came out in the 2001 model year, the first 1000 HOs built had a forged crankshaft that was sourced from Kellogg Crankshafts. These 1000 cranks took them through the 2001 model year, and partially into the 2002 model year HOs. Non HO engines didn't get the forged cranks. As you stated, all 496s from all years got the weak hyperutectic pistons that are prone to breaking. They did change piston pin retaining styles over the years but still cast pistons. All engines over the years used powdered metal rods, stronger than a traditional cast rod, but weaker than forged. This is why we saw some rod failures. They were a weird length too as compared to earlier BBC engines.

I hope your engine is OK!

87Mirage,

Me, too.

While that's definitely more info than I got from the Merc tech, it pretty well lines up with what I was told. Although, he specifically stated "forged crank and rods". Don't know for sure myself. My engine was built in '01.

So, what are we thinking? potential cracked piston? Ring land? I've got a compression gauge, and I'll get readings before the end of the week. Anything to look for on the plugs? I intend to secure use of a borescope and have a look while the plugs are out.

Could it just be that the fill tube vent tube is not connected to a vacuum? I'm assuming that vent tube connected to the throttle body in stock configuration. Or is it just an open vent in stock configuration?

I'm not all that worried, but my antennae are up now. The oil has been present from day one since taking possession of the boat, and it is still running strong since getting the injectors back in proper working order. We ran 75 or so at ~5200 RPM last Thursday, with no change in behavior at any time. Whatever is there has been there a while and isn't changing at the moment.

Thanks. Brad.

Is there any sort of PCV valve on the valve cover breathers?

As a comparison on the Whipple supercharger 496 system they run both a PCV valve, and another 1/2 hose going to a mini K&N type filter for more ventilation.