FWIW, the heads are nice. They are really, really nice.

Ryan watch out for the Tubulators being removed. Its a dam for the condensation aka kind of like a drip pan when it gets hot burns off the condensation. Also WHAT others do not know and I can careless what anyone says because we seen this inperson and even messed around with it in OEM training school many years ago for the 496 was the reduced exhaust section of the tubulator is there for a reason to speed up velocity ( no pun intended ) of the exhaust flow to PREVENT water reversion at idle speeds. Keep in mind when ever one scans any marine engine the engine idle does not stay AT ONE rpm only - it moves up and down .

Many people do not know this about why the tubulator was really engineered into the mix. PLUS the big one if I can find the pics to show removing it does not matter period..

Yeah the stock pistons are the drawback. It's worth the extra $$ for peace of mind to upgrade the pistons/rods. Not worth worrying about destroying a new set of heads every time I run WOT.

BUP, appreciate the info. Mine have been removed since 2014. Exhaust has been off numerous times with no signs of reversion. Water mixing with the exhaust at transom vs stock has to be helping here.
Ok, pulled the engine this morning. Very easy setup to unwire/remove. I will be purchasing a beefier engine stand. This fully dressed 496 is a heavy beast! Don't feel comfortable with my current stand. I really like the built in stand of the 496 oil pan. You can just set it down on a flat surface.

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Check your PM! - I just sent you a present! Raylar heads. Need a repair.

FWIW, skip the engine stand. Use you stand to re-assemble the crank and oil pump, put the pan on and stack up 6 cinder blocks with a piece of plywood on top. Then set the engine on it to do the heads, intake and accessories. The 496 oil pan is a flat natural stand.

Update....

Before tearing apart the engine. I leakdown tested the cylinders. All good except #8 Exhaust valve is leaking. 45% leakdown on that cylinder. Rest were 22-24% cold @ 100psi. Heads went to the machine shop for some TLC. They called back and a valve job thru the Serdi machine will do the trick. Valve guides are ok. Intake valves are good. They are telling me the exhaust valves need replaced. Stock valves are Stellite faced and are starting to come apart on the stem tips. Stock scrubber rockers must have taken a toll. I'm going to check them out tomorrow and post some pics. New Stellite valves from GM are $26ea. Enginetech has Inconel for $20ea.

Good news..... With 567hrs the bottom end looks fantastic!!! Journals on crank look new. So much so I am reassembling with same bearings, rings etc... Installed the 203 cam today. Measured main bearing clearance. .002" on 1-4. .0025" on #5. Thrust spec is dead on. Installed crank. Cleaning up the pistons/rods now. Coated skirts on pistons look good. Block cylinder bores look good as well. I can see why many have gone well over 1000 hrs on these bottom ends.

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Pics of exhaust valve tips coming apart. Now the question is do I put money in the stock heads or upgrade?https://cimg5.ibsrv.net/gimg/www.off...1d0b4803b7.jpg

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I would replace the hypereutectic pistons if anything. Heads could be done with the motor still in the boat if necessary.

Yeah dude, the piston kit is like $500. Do it now and you can do heads or a bigger cam and not worry about it later.

$450 from CNC Motorsports. Lol. Then you need $400 of 4340 rods. Then $250 to rebalance the rotating assembly. Then $125 to hone cylinders. To do it right, it's alot more than I want to invest at this time. I'm honestly not worried about the stock pistons at this power level. My fuel system is top notch and I will be monitoring AF/R. If needed Whipple can adjust my tune. I'll be tickled with a 2mph gain from just the 203 cam. Boat runs great now and is turn key. Once I get it dialed in, I don't see that changing from a little larger cam.

I'm keeping the stock heads. Ordered new GM Stellite exhaust valves. Should have the heads back soon. Thought about upgrading to Dart heads, but not worth the $$$ for a low flowing iron head. I did replace the piston rings with new Mahle 41902CP. File fit to .020" top, .022" 2nd. This is per Mahle's spec for marine use. End gaps on stock rings are really tight. Pistons installed and bottom end done. The Gen 7 crank scraper and internal pan windage tray are really nice features for stock.

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Hail Mary, full of grace please let Ryan00TJ see the light of thou art piston failure.... Sign of the cross. Amen.

I am begging you..... :) LOL

This happened after I installed headers, changed my cam, rockers and ported my stock (schitty) heads :

Top picture - after hypereutectic piston failure
Bottom picture - whats left of piston after hypereutectic piston failure

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That's good stuff there!! Lol! I can see why you recommend the piston upgrade. Correct me if I'm wrong, but didn't you drop a valve to take out that piston?

If I loose one, I promise you will get the " I told u so"! I've never worried or had trouble up to this point. My injectors have been cleaned. No more paint in the Gen 3 cool fuel box. Fuel system is maintained correctly. I will be watching air-fuel ratio and not revving above 5200rpms. I just don't see .20" more lift and a couple degrees more duration causing a piston to come apart.

If the pistons are lean burned or over revved then definately! The guys that threw on Raylar 525 kits, set 50psi on the fuel psi gauge and ran the piss out of them were the ones who had trouble. Look at donzimatt's experience.... 50psi had his AF/R in the 14 range. He had to bump to 58psi to get into the 12s.

Yeah, just messin with you. I did drop a valve. My fuel PSI is much lower than everyone else but I have a different delivery system with the Aeromotive pump and regulator and assume that's why. Mine is perfect up top and a little rich down low. I took the cool fuel off and have a different method for that. Could probably use a revision to the ECU tune to make it perfect but its not used that much anymore.

That's my dilemma thru the project. Can't justify the $$ for 25-30 hrs per summer. Mid-high 70s is plenty for me. Family doesn't like it anyway. They want a tritoon with room and comfort.

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My friends 28' Avalon with twin 300 Verados has spoiled them. It's truly a awesome ride though. Runs 60.

You guys make me appreciate my wife. She loves speed although she does get nervous if it is really snotty water. Hell she bought me a new radar detector for Christmas.

Padraig

Engine gurus correct me if I'm wrong but I wrenched on car engines for 20 years and always believed that you can never reinstall pistons with the old rings. A minimum would be new rings and hone cylinders. I also agree with upgrading the pistons at this time.

No problem in doing so. Just make sure everything stays matched together. You also want to orient the ring gaps on the piston according to the manufacturer spec. I installed new rings for the hell of it. Ring tech has come a long way in just the last couple years. These new Mahle plasma moly rings are pre lapped and seat instantly. My cylinders were in great shape. Out of round/taper well within service spec. Crosshatch pattern looked good.

Update. Heads are back and installed. New GM Stellite exh valves. Comp 911 spring kit. Heads milled .006". 1.865" IH 140lbs seat psi. Checked PTV clearance. .180" intake w/203 cam. Exhaust is way over .400". Installed with Felpro marine permatorque gaskets. 4.330, .060" compressed.

Installed Earls 504 oil sandwhich thermostat adapter. Tstat behind to open at 160* and is fully open at 180*. -10 lines. Installed GM 30lb bypass valve. Really cleans up.the oil system.

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correct one gasket fits all the applications for this engine. GM must have Source them from Federal-Mogul as they were what we're stock on my 496ho.

I am going to use Cometic MLS

Definitely a good idea for your power level. For my near stock rebuild the Permatorque's will be fine.

Nice bike!

Thanks man. Pulling double duty changing oil that day. Gotta love the Fatboy! Wish the weather would allow some riding. https://cimg5.ibsrv.net/gimg/www.off...4fc7340673.jpg

Nice work and great thread! Are you a pro wrench, or just a hobbyist that doesn't mind tackling big jobs? (kinda where I fall)

I'm getting ready to pick up a 496HO with almost 500 hours and the first order of business is going through the fuel system, per BUP. Would be nice to clean the cool fuel module without out having to replace, since they are now over $1K new. Hope I don't have to go as far as you did though...

Couple of things:

- How did the cool fuel module look before you stripped the paint off? Was it flaking or visibly degraded?
- I assume the inside of the cool fuel module is aluminum? Any concerns about corrosion going forward? I cant get ethanol free gas where I boat, and wonder if the moisture would eventually start to corrode the inside of the cool fuel module? (assume merc painted it for a reason)...then again at lot of fuel tanks are raw aluminum on the inside, so maybe no worries?
- Doesn't sound like you are raising compression, just adding a little cam? Will you need a reflash or tune? (sounds like you will be watching A/F)
- Would like to see some pics of you air drain delete solution. I live in an area that doesn't freeze, so if/when they start leaking, might be less $$ to remove than replace.
- Problem with your exhaust valve tip coming apart has me a little nervous. Do it appear this would become an issue in the next "couple hundred" hours of use? Or maybe not a catastrophic type of issue?

Engine should run great when it's put back together, bet you'll be chomping at the bit to get her out on the water!

On a J/K note....can I drop off my new to me 496HO for a quick "go through" since you've gotten so good at it? :-) ....i.e fuel system clean, air actuator delete, oil system update, IAC check, etc

Father and I built marine engines for our boats. My first go around with the gen 7 8.1. The internal paint in the cool fuel module is due to merc overspray. The whole internal housing is not painted. I had alot of paint flakes in my injectors when cleaned. I will be monitoring AF/R. Larry @ Raylar said a 4-5psi bump in base fuel pressure will be needed to get fuel ratios on line. I will adjust as necessary. The air drain delete is basically a 1.25" stainless barb adapter in their place. I'll post pics soon when its plumbed up.

The machine shop says they've seen it alot before on GM valves. Bad news if it happens. That top piece will fall into the engine. Many scary scenarios from that alone. Then you lose correct preload on that lifter/valve. Rocker arm no longer pushes on valve. Something will give as the rocker is still moving. Who knows how long they would have lasted? I played it safe and replaced. The new valve tips were not beginning to seperate.

Really looking forward to testing this spring. Bring yours on over!! Be glad to help.

Hey, thanks for the info.

Kinda have me worried about the valve issue. As mentioned I'm looking at picking up a boat with a 496HO with something over 400 hours (waiting to scan when it comes out of winter storage) and was planning on the usual PPI with leakown test, etc.

Now has me wondering if I need to check the valves? Assume you would have to remove a couple of rocker arms to inspect the tips?

If you were buying another 496HO, would you pay to inspect for this problem?

Thx !

honestly I've never heard about it before. When you think how many 496 Motors are out there it's probably not a common problem. I followed my machine shops advise and replace them. they did not make any money on it as I supplied the valves. I would not lose sleep over it but it wouldn't hurt to yank a valve cover and look. You should not have to pull a rocker arm to be able to see the valve from the side.

Coming along nicely. Startup vid here soon.......

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Turned out good for a rattle can job. Little touchup needed once its back home in the boat. Waiting on my adj fuel psi regulator to test fire. Probably next week. Other than that it's ready.

Added a Jegs billet oil catch can. Inside the Raylar intake had a fine oil coating in the plenum and runners. The PCV pulls from the lifter valley into the intake behind the throttle body.

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I posted a couple of pics of a piston we took out of a 496 we are doing with 337 hours,a lot of people say the pistons on the 496s are junk,well they may not be the best thats for sure but I think they are better than people give them credit to be,this engine hydro locked and destroyed the connecting rod as you guys can see,but the piston did not break,also had the crank magnaflux and its fine,just thought I would share this info with you guys,now if you add a whipple or supercharge it then I would think anything could go at any time,but that would go for any engine

Just don't detonate them. Hope to test fire tonight or tomorrow.

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It's Alive!!! Started up yesterday. Ran for 20 sec and shutoff itself. wtf? Attempts to restart resulted in a backfire thru exhaust. Troubleshot. No codes. Fuel, spark all good. No tach signal to Techmate or analog test gauge. Replaced Crank position sensor today and it fired right up. Ohh well, better for it to die now. Everything looks good. Compression test after running 155psi across all cylinders. Time to drop back in the boat this weekend.

Sounds and looks GREAT!

Padraig

just a few things -- the crank position has 3 only pull out and reinstall. After that it needs to be replaced with a brand new --- regardless.

also make sure your fuel pressure dampner internally is super spotless clean and rail lines to it. Paint and or fuel varnish and or rust really can settle in its base and in the dampner itself plus its small rail lines. Just some added info.

The dampner will have U clip for a hold in place and 2 O rings internally and has to SEAL 100 percent. The 2 o rings can also become dried out and or cracked. The 2 O rings alot of times will need to be changed out with new. Sometimes not but alot of times YES they will need to be changed.