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.

What year is the boat? I would be surprised if you had a forged crank

i burnt a piston like 15 years ago in a 496 mag.
I really could not tell why... some say you can run them up to 2000 hours no problem, some say they are proned to burn pistons...

so we changed the only one damaged piston, and never melted another one...
scary in my thoughts, but it worked... must have gotten lean somehow for a couple seconds...

BoatNT,

Boat is a 2002. Engine was built in 2001, in that grey area when the HO may or may not have been built with the forged crank. I ran the serial numbers through Merc tech. According to their build sheet, it has the forged crank.

Thanks. Brad.

Jeff32,

I spoke with Larry at Raylar and he suggested 90-95% chance we cracked a piston. If we recall, back in late 2022, I had an injector issue that resulted in the #4 cylinder running at about 40% fuel. If I had to bet, I'd say it's that cylinder with the cracked piston. I'd much rather it be something simple like a blown head gasket, but the likelihood of that is dwindling with every conversation I have with the various gurus there are out there. :(

Thanks. Brad.

Guys,

I'm assuming potential worst-case scenario: We need to replace rods and pistons at the very least. I'm kinda over the "what-ifs" at this point, until we get a look inside the engine. So, I'm juggling options....

I've spoken to Larry at Raylar. Cool guy, BTW.... $1820 for a complete rod/piston set, including pins, clips and rings. Rods are SCAT I-beam rods to Raylar specs, whatever that means. I'm assuming they will be Merc OEM 6.693" rod length. Pistons are forged 4032 aluminum; no skirt coating, no specs on rings. These are on the shelf at Raylar, which has a fair bit of value in and of itself.

I am also looking at Wiseco pistons, which will also include pins, clips and rings, and Molnar PWR ADR H-beam rods. Pistons will be skirt coated, but still no specs on rings. Rod length will be 6.700" (I can't imagine the engine will even notice the .007" difference that can be made up for with head gaskets). I really like what I read about Molnar rods. From a toolmaker's perspective, the finishing process and the custom spec'd cap bolts are worth the extra money, IMHO. Total package is $1540 The pistons are cheaper, the rods are more, but the total is less.

So far, all the calls I've placed have verified stock on the shelf, either with the OEM or through retailers; Raylar, Wiseco (Summit), Molnar, SCAT (Summit) are all ready to ship.

We are also going to address the valve train with stronger springs and potentially Raylar's BP111S cam, as per advice from 87Mirage.

What does OSO have to say on any of this? Any suggestions on other MFRs out there? I'm all ears.

Thanks. Brad.

Brad,
If you’re replacing rods and pistons might as well address that cast crank.

SecondWind,

Engine was built with a forged crank. If we get into it, and it does have cast, we will definitely address it while it's apart.

Thanks. Brad.

Hey Brad, what is your current peak HP and rpm?

What is your new power goal?

These would also
https://cimg6.ibsrv.net/gimg/www.off...cf6c6c1816.png
go well with the stroker kit. It sure is fun spending someone else’s money😃

Tartilla,

ProCharger advertised their 496HO/M1 package at 615HP. I have no idea what we actually had. As far as I know, it was a factory PQ build; it's never been out of the boat since, let alone dyno'd. I do know we are turning 2" more pitch and running 10-15MPH faster than the same boat/engine combo, NA. I sent the ECM to Whipple for their stage 2 flash and asked them to set the rev limiter to 5350.

Goals: This is not an "upbuild", per se. I'm all good with improving performance while we're at it, but we are really just repairing the damage done and correcting some limiting factors and weak links in the process. With the forged pistons, we will be able to take it to Eddie Young for a live ECM tune (We have already discussed; he was unwilling to touch it with the cast pistons), which will likely render some HP, and we can elevate the rev limiter. If we end up replacing the cam with Raylar's BP111S cam, that will also render some HP. My guess is better valve train components and rods will safely allow for more RPM. At the end of the day, we still have the stock Bravo1 outdrive, so I have to keep THAT in mind, although we were already considering the XZ conversion, so we may address that while the drive is off. Scope creep.... :rolleyes:

At the moment, I'm really just seeking advice on MFRs of the various parts I've mentioned, past experience, etc. I'm keeping my hopes and intentions on a short leash until we have a look in the cylinders.

Thanks. Brad.

SecondWind,

Oh, but to dream....

If somebody's got a decent used set that will fit the 496 heads, cheap, I MIGHT be able to consider it. Otherwise, and additional $8K+ is NEVER going to make it past the finance dept. As of right now, she's still hoping this was just an overheat, and everything is going to be fiiiiiine....

Thanks. Brad.

Guys,

Pretty sure we found the problem….
https://cimg0.ibsrv.net/gimg/www.off...665701ebb.jpeg
https://cimg1.ibsrv.net/gimg/www.off...6e8edacdb.jpeg
https://cimg2.ibsrv.net/gimg/www.off...a49372c99.jpeg
https://cimg5.ibsrv.net/gimg/www.off...801cb184a.jpeg

A thumb-sized hole in the top of the piston in cylinder #1.

Th bright side is we are gonna have a virtually brand new engine, with solid parts inside, come springtime. Probably a few more CI, too.

Thanks. Brad.

Brad, I was recently faced with some of the same decisions on parts. Since i was building two complete new engines I went larger. As far as pistons i went with J&E, Molnar PAD rods, and Manely forged crank. Whatever you think you will spend figure at least 1.5 times that amount. Also since you are already there make sure to go through your heads as well. i cannot believe the amount of worn valve springs I've heard and seen lately. good luck, i think you will like the Molnar stuff.

1Zoom,

Block and heads are getting the full machine shop treatment. Valve springs are already on the docket, per advice from 87Mirage. 130-140lb, as opposed to the stock 90lb. The builder is going to be doing a full valve job.

I haven’t settled on the pistons yet. Wiseco is a bit less expensive than JE, and I’m not sure I need to go premium on an engine that’s just a bit warmer than stock. Wiseco seems more than adequate, although there’s only about $300 difference between the two.

Pretty well settled on Molnar for the rods. I really like the proprietary specs on the bolts. As a toolmaker, the asymmetrical threads and larger controlled root radius are good selling points. I called them the other day and the guy (not Tom) recommended the PWR ADR rods, simply on the marine application aspect alone, let alone the mild boost.

I think we’re gonna keep the crank, unless we get in there are discover a need to replace it. It will likely be a Molnar if we get to that point.

Lots more talk about….

Thanks. Brad.

What are your plans to keep this from happening again? That piston was severely lean burned. I see you are running Whipple's Stage 2 tune. Were you running 93 oct? Data logging I saw max timing advance of 34* with my Stage 2 tune. Stock HO tune was 24*. IMO too much timing with crap iron heads under boost.

Ryan,

Gotta figure out where the lean condition originated. Check the fuel pump, lines, filters, etc. The injectors are going to Smitty for an eval. May replace them. I’m thinking we will replace the 2-stage fuel pressure regulator with a proportional regulator, get a good AFR table with O2 sensors and have a proper tune done by Boos or Whipple.

I’ve been running a 50-50 mix of 93 & 89, keeping it an average of 91 or better, as per the Whipple tune requirement. May have to stick with straight 93.

Thanks. Brad.

https://cimg4.ibsrv.net/gimg/www.off...2ccb4a693.jpeg
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https://cimg6.ibsrv.net/gimg/www.off...30e47f4a8.jpeg
https://cimg7.ibsrv.net/gimg/www.off...0d6af0242.jpeg
https://cimg8.ibsrv.net/gimg/www.off...49d4620a1.jpeg
https://cimg9.ibsrv.net/gimg/www.off...71f52abc8.jpeg
https://cimg0.ibsrv.net/gimg/www.off...b3fdd2043.jpeg
https://cimg1.ibsrv.net/gimg/www.off...446f00f28.jpeg
Brand new plugs prior to the weekend this occurred.

Obviously #1 is oily. That was expected. 2 & 7 appear to be way cleaner than the rest. It could be we are still getting some debris in the injectors. The rust that was found when Smitty did the injectors in late ‘22 came from somewhere. I’m wondering about the fuel rail, being the OEM steel version. It may be that, once that rusting got started, it has continued. May have to replace with a stainless unit.

Thanks. Brad.

Eddie Young will tell you never ever run a projected plug in a boosted engine.
That electrode hangs out in the middle of the chamber like a glow plug.

^^^true.

And i’ll tell you don’t run huge gaps gm determined okay for epa guidelines car/truck engines in cars/trucks.

Stay with normal .035”-.040” gaps. No matter composition of plug and even if coil near plug systems.

Dan, SB,

I have noticed a fair bit of carboned-up threads when I change plugs, suggesting they extended into the combustion chamber.

Those are ACDelco 41-983 plugs, the spec’d plug for the Merc/GM 496, gapped to .045”, as per an OSO respected opinion’s advice. I’ll check to see if they have changed during running. Do they do that?

Suggestions for an alternative?

Thanks. Brad.

Guys,

Dwelling on the fuel rail and its potential role in this incident….

Are there any aftermarket fuel rail kits readily available for the 496 intake manifold?

I could easily make a set of rails and fit them up with AN lines. I have resources that will allow me to determine the spacing and angle of the injectors, and making stuff like this is right in my wheelhouse.

Thanks. Brad.

nope

BoatNT,

Looks like time to solve that problem.

Thanks. Brad.

The heat range is 14!? Gap at .45?
They dont foul at idle and it idles well in gear?

How much boost you running ?

I run .32-.35 max gap.
8 heat range
non projected plug

R5671A-8

https://www.rockauto.com/en/moreinfo...&pt=7212&jsn=1

Dan,

3lbs @ WOT, zero @~4300RPM. It’s a baby supercharger. And not a real one, at that. No. I have not noticed any significant fouling, other than what you see in these pics. It idles fine; 650-700 RPM.

I’ve just been going with OEM recommendations. There are many a thread here on OSO, and comments by those I’ve come to respect, that suggest this was the way to go. That said….

I’m all ears. The right plug, gapped correctly, will go in on reassembly.

Thanks. Brad.

The PSI suggestion is a good one. They already have good parts in them and offer bigger bore and longer stroke. Steel crank, Scat I-beam rods and Mahle pistons.
The propane version has forged flat tops and the gas version has Hypereutectic dish pistons. Skirt oilers are also a nice feature in the PSI blocks.

I didnt have the cranial bandwidth to learn Holley EFI tuning so I put an 8.1 top end on my PSI 8.8 shortblock. The cam is probably a little too big for my wet exhaust but I do still have a new 496HO cam sitting on the shelf to use if needed.
You could easily just grab a PSI core off ebay and toss your top end on it for way cheaper than trying to fix the 496.

I used a Dart intake and Quick Fuel marine 850 on this one.

Brad,

if you come up with anything let me know,

thanks

DragracerArt,

We already have a care plan in place, at least preliminarily. 87MirageIntruder turned me on to a guy local-to-me that has done a ton of high-performance marine work. We will be stripping it to the block, full machine shop treatment (decks, line bored for new bearings, etc...), new Wiseco pistons, Molnar PWRADR rods and Cometic head gaskets for starters. We are going to replace almost the entire fuel system, proportional pressure regulator, new lines top to bottom. I will be fabbing up a new stainless fuel rail for the OEM intake manifold, and the manifold will be carved into and modified for better airflow. We are adding a 600SCI oil cooler, repurposing the OEM oil cooler as the PS cooler and scrapping the old PS oil cooler. I have chewed on the prospects of going for considerably more power, with a new cam, headers and scrapping the SilentChoice, but the outdrive will suffer, and scope creep and the CFO (who likes the SilentChoice at times) is keeping me from going down that road. I'd LOVE to ditch the PCM555 and go with a Holley HP system, but it's just not in the budget ATM.

I'm hoping to be a fairly hands-on "helper" as much as he will let me. I will be documenting what I can of this process in pics and posting here periodically as I can. It will be a couple weeks before we get started. Hopefully, I will be getting a shelved intake manifold from him in the next week or so, so I can get started reverse engineering the fuel rail, which is likely going to bloom into a business opportunity for me. Welding aside, this is right in my wheelhouse. Raylar is already interested in sourcing them, and I'm sure a few others, like Mosetti, will be, too. Black clouds and silver linings and all...

Thanks. Brad.

BoatNT,

As stated above, I am going to develop a stainless drop-in replacement. It won't look exactly identical, and it will not have the FP regulator, but it will drop in and bolt down just like OEM.

Thanks. Brad.

well if you need a good core.

https://www.ebay.com/itm/17510910010....c101506.m1851