Advice taken...slowly the mystery build will be unveiled.

Screw that, if you paid for a comp. test and got results as if they did it I'd force them to buy the boat from me for the price I paid for it. Someone would be taking that POS back from me especially if I had a written bill of sale documenting all of the parts that were supposed to be included that the seller removed. Lawyer up!

I'm going forward with an autopsy and rebuild...leaning more toward reliability vs. performance if necessary. Not knowing IF the crate motor has the correct oil filter by-pass, I will order the correct one(s). I've read some varying answers even on this site. So including the part# for the correct 30# bypass valve...to encourage more (not all) oil through the filter...can someone show me the parts shopping list for a Gen VI 502 block? I want to hand them to the engine builder and rule out that possible repeat mistake. Is it one or two valves? I'm assuming I won't need to force all oil through the filter. Finally, I most recently used the Napa Gold 1060 filter...was that ok? Thank you.

Nothing wrong with that filter. Wix makes it.

So is gm part #******** (edit/25161284) (30#) all I need to swap in??? Do I need one 30# bypass valve for the oil cooler line, also?

as i was waiting for this answer...and preparing the boat for the motor yank, I see that my oil circuit currently goes from block through the OIL FILTER 1st.... THEN into the OIL COOLER 2nd... then back into the block (center of adapter)...IS THIS OK & should I repeat that route next spring when it all goes back together??? I swear I saw a schematic showing feed the cooler 1st THEN the filter...but now I can't find it.

and once again which bypass valves go in & at which location? I assume none of these bypass valves are at the remote filter location? IS this correct: at the block location: remove the center return bypass completely & install the 30# bypass @ the side (outlet) location (which currently feeds my filter 1st). I know I'm starting to talk like Trump ;).

Pretty much everything that you need to know is right here.

http://www.offshoreonly.com/forums/g...-hardware.html

Cooling the oil before or after the filter is debatable but not an engine killer.

Can't be mad about that. Those 500s were the best blue motors.

I found this a handy reference.

http://i1166.photobucket.com/albums/...pslkrodntd.jpg

Sooo if that's the "bible", doesn't it show the 30# bypass part # incorrectly? Here it is:"If your running a gen 5 or 6 block and it started life as a crate engine,it has 11lb bypass relief valves. If your motor has unknown origin,who knows what it could have. Buy a new 30lb bypass relief valve for the outside(the one near edge of block casting for filter adapter) or plug it off,they are available at your local chevy dealer part #25013759,they are under 5$."...
I have seen that valve part #25013759 described as the oem 11lb. valve AND part #25161284 as the correct 30lb bypass...No wonder so many builds get jacked?!

Summit's catalog.

https://www.summitracing.com/parts/nal-25161284

I wouldn't say that it's the Bible, but just a lot of info about the shortcomings of the stock system. The part# that you're looking for is #25161284. I got mine from Amazon and put it directly in the hands of my mechanic. Even though he was referred to me as the best wrench in the area he knew nothing about that valve.

BajaRooster: I make sure the center valve is removed (because I won't use the side tap ports next to the boss) and put the known 30# valve in the offset port, yes? Not sure I understand how
a plug in the center position, enables oil to return to the block����

Replacing the oil cooler.
 

I'm settling on the 30# bypass for the outgoing port to the filter & removing the bypass altogether in the center return from the filter. Since this is the 3rd rebuild in what I can see the last 70 hours I will replace the oil/PS cooler which is 2" X 17" & looks to be a Merc 806423T (or aftermarket copy). Is there a pretty simple swap/upgrade that gives me a bit more capacity/insurance???

I would worry about upgrading the oil cooler until you know your oil Temps. Buy the original size cooler and install it as well as an oil temp gauge. This way if you are getting to high of oil Temps you can look into it at that point.

I pulled the valve out from behind the center nipple as it's unnecessary and just another restriction, but it isn't a big deal to leave it in there. The new valve replaces the one in the offset port.

You can upsize your oil cooler but get one that's thermostatically controlled and you'll be fine. I went a little big on mine and have to get a thermostat as I get a lot of condensation in my oil at the moment.

Link to be sure my builder is on the same page as you guys...
 

I'll be picking up my 502 long block to bring it to a reputable circle track race engine builder...I just want to go over the important requirements of the marine engine environment, etc. would love to have a discussion punch list for him...trust but verify.

4100# 24' cobalt with Bravo One 1.50 drive & 19p Mirage Plus prop (for the moment)...it was dyno'd @527/570 in '11. Thunderbolt IV ignition.

I will at a minimum replace the stock oil/ps cooler with a new clean one from MrCool...then monitor oil temps...

Remember this will be the 3rd rebuild of the Gen VI GM Crate Motor model 12568778 from '06...the heads are GM marine
heads #12562934 (not sure which rebuild)...Only 70 hours in 10 years.

The last rebuild (2011) upgraded the crank, cam, lifters. Has forged pistons. It has EMI Thunder exhaust which routes through the drive (corsair through stern has been abandoned/disconnected). Has Edelbrock 7562 Performer RPM Air-Gap intake... Has Edelbrock 1410 Performer 750cfm marine carb...
I already bought the 30# oil filter by-pass . I will upgrade the rockers and springs (recommendations?). I'll reassess after the tear down and discussion with the builder.

So regarding piston to cylinder wall clearances, marine head gaskets, etc. what should I bring up or remind him. Seeking words of wisdom from this awesome site.

Find a reputable Marine Engine builder. You should not have to be giving "tips" to the proper shop.
A 500+ HP engine should not be running through prop exhaust.
You need to do more research before letting anyone work on the engine or your next thread will be about the 4th rebuild in 80 hours.
The oil system changes you are talking about are only two of many important engine requirements.

Nor a 750 Edelbrock.

If there is a better source to do my "research" let me know, please. I thought this site would be considered research, in a way...The shop I have entrusted to make this motor right is capable (Google: Earl Wham Jeff Bird) as the best builder in Northwest if not the country...Pretty sure if I give him some specs, he can make it happen.

The last "builder" of the motor was supposed to be "the sh*t" near Seattle but is now out of business...Maybe they got so big the right people weren't doing the work? Who knows. All I'm asking from you guys is some bullet talking points to go over with him (he may already know)...He mentioned even toning down the horsepower if needed by replacing the cam and get back to a more reliable build...If I need to re-plumb the Corsa Exhaust that's what I'll do. The parts are in a box & need some parts & new harness, I'm told. If I need to get a different carb, I'll do that, too. We'll know more when he tears it down. He mentioned signs of water around the exhaust port of #3 (the problem cylinder) from the starboard head...He just has 4-5 builds to wrap up before mine. Also the bellows had water in it when the drive was pulled.

I appreciate the help, I'd just like to have some knowledge going into it. Thanks.

If I were you I would contact Alex Haxby now.

I am not saying anything about your engine guys' credentials but Alex has built many a 502 for boaters including guys on OSO.
Call or email him to get some straight poop. I would not hesitate to drive the 7 hrs to his shop from your house.

http://www.haxbyspeed.com/

Thanks...I'll keep him in mind, but across the border would be a slight disadvantage for me...Although, been up there twice for Mustang car club events.

I've learned a few important things already about this boat's issues...The latest being the recent re-direction of the exhaust back through the Bravo I...I hadn't thought of it as being a higher horsepower necessity. Wondering if there was a direct correlation between the restrictive exhaust, water in the bellows, & #3 cylinder's exhaust & intake valve's issues from an apparent steam event. When we see the condition of the internals I'll be in a better position to decide either to dial back the power or fix the weak links. Thanks for all the input.

Reading up a bit on reversion this weekend and wondering which came 1st...the water or the valvetrain damage...with the unknown specs of an aftermarket cam, EMI THUNDER low riser, I'll want to address that before hitting the water next spring. Anxious to get a part number off the mystery cam but it's looking more like going back to a near stock cam is in my future, makes my carb work better, my prop work better, and the exhaust work better (including the fact that the thru transom exhaust was disconnected).
http://i690.photobucket.com/albums/v...s/IMG_2122.jpg

The acute angle on those riser connectors for the y-pipe is one reversion issue on your combo.

Just before I picked up the boat, the consigning dealer changed the exhaust configuration to make it quieter. As I look at the box of parts I see the mechanical diverter had been "fixed" into a position to feed exhaust thru both the prop and the exhaust tips. Is that even a workable alternative? Could that (the elimination of the "Y" plumbing) have actually caused or contributed to this mess?

Post some pictures of your transom from inside the engine compartment.

The motor is out & the boat is all buttoned up for winter...Disregard the cover it's not a 5.7 Alpha (anyone have a 502 cover or stickers?)...Here are some pics just prior (with the engine hatch off & curbing removed):
http://i690.photobucket.com/albums/v...7/DSCF0152.jpg
http://i690.photobucket.com/albums/v...7/DSCF0153.jpg
http://i690.photobucket.com/albums/v...7/DSCF0154.jpg

Thanks for the input!

Any input/advice is appreciated? How about proper advice to the correct questions?

As of now the only thing we know is that you suffered valve train failure. Was it from over revving your engine running a 19P prop and relying
on the RPM reading from a tachometer from 1992? Probably.
Did you suffer reversion? How the hell can we know? We are not clairvoyant. Your engine builder will be able to address all these questions.
If he can't then you need a different builder.

Worrying about which oil filter to use or where you should place a 30 lb. bypass valve is a bit premature. Find out what parts are in the engine,
what needs to be replaced because of damage, and what kind of performance you want to have will dictate most of your decisions.

Rebuilding a 527 HP engine to a stock 502 configuration so that you can utilize a 750 cfm carburetor already in hand is just plain stupid. This
may be the reason the gear heads of OSO are ignoring this thread.

Your boat's former owner's claim of running 70 MPH with the 527 HP engine is not out of the realm of possibility.

For comparisons sake my Cobalt 233 runs over 72 MPH with a stock 502 Mag MPI.
--- I removed the stamped rockers for Crane Golds.
--- I removed both bypass valves and tapped/plugged the outer hole.
--- I run a digital tachometer from Aetna Engineering. http://www.aetnaengineering.com/
--- I run 25P props Rev4, Mirage, Mirage Plus

Get your engine apart and then evaluate the parts, broken or otherwise, then start making decisions.

Good luck.

Here is your engine cover:
http://www.ebay.com/itm/Mercruiser-E...lV9yh6&vxp=mtr

Correcting the exhaust...
 

I'll try to not ask TOO MANY more stupid questions. While waiting to get the longblock torn down I'm realizing the exhaust set up as purchased (remember the consigning dealer's mechanic had set it up to go back through the Bravo 1 only because of noise) may be the culprit as they used 4.3L V6 elbows (#14478) to make it work...there ARE signs of water backing into the head @ the F'd Up #5 exhaust & intake...there ARE signs of water @ the correlating exhaust manifold port...there is also a dimple that is showing water leak in the manifold directly above #5 (see picture/ not sure if this is just a coincidence as the leak would be towards the engine compartment).
So while I wait to see the internals damage report, I'd like to start planning on fixing this STUPID exhaust situation.

Side view: http://i690.photobucket.com/albums/v...7/IMG_2155.jpg

The external dimple leak: http://i690.photobucket.com/albums/v...7/IMG_2154.jpg

The V6 Elbow: http://i690.photobucket.com/albums/v...7/IMG_2153.jpg

Thanks for any constructive advice you can give...I'll do a manifold leak check if that dimple doesn't automatically create buying new...Also I'll get the old plumbing back installed even if loud.. the diverter's are fixed/bolted to direct to both exhaust routes...http://i690.photobucket.com/albums/v...7/IMG_2158.jpghttp://i690.photobucket.com/albums/v...7/IMG_2157.jpg

What is the water level while sitting in the water with people on the back compared to the riser level? I have seen a lot of bad things happen when you back your boat in a steep ramp and it doesn't slide off and get level quick. fills those risers and manifolds right up. Its just something to check

I don't think it's an issue. Never launched with peeps in it. The moment of failure was several hours post launch...Those risers may be addressed anyway once we check/know the cam specs...IF the cam even survives.

Finally had my guy get a look at my motor...looks like cam, lifter, rockers, pushrods are the worst...pistons and cylinder walls looks good. Will look at bottom end closer tomorrow. Knowing I want to dial back the cam to stay within the means of my EMI Thunder short aluminum riser exhaust and Corsa Captain's Call, does this cam and lifter kit from comp look good to you guys?

http://www.cpperformance.com/p-11596...ifter-kit.aspx

Block still has BOTH filter by-pass valves in place...not sure if they were the original crate motor by-passes but will get that corrected.

Do yourself a favor and ditch both of the bypass valves. The one under the nipple can just be removed. The one in the filter pad must be plugged. You can either tap the hole with a 1/2" NPT tap or knock in a 13/16" plug. If you have a 30# differential that opens the valve, it's probably from a plugged up oil filter. At that point, who gives a chit. THe engine is trashed and that bypass plug isn't going to help.
Eddie

Great...expecting the bottom end bad news today. Surprising that the cylinder walls and pistons look ok from the top? Wow, 2 previous rebuilds (2 previous owners) of the same Crate engine and no one discovered the original "sin".

I'm hoping the last rebuild left the center by-pass in (not great/not catastrophic) and knew to replace the outer by-pass with the 30# one. This is like finally getting the cancer diagnosis BUT at least you know why you were sick ��...Time to fix it either way.

OK, it looks like I got lucky. Pan off all looks good on the surface. Found the residue of the rocker ball shrapnel in the pan. He said many others appeared to be headed for the same fate. The mystery cam appears to be a bad regrind that has a 224-232-12 hand engraved on it, but it is trashed. So I need a new cam, lifters, springs, rockers, and redo the heads. He has a barely run takeout cam and lifters from what appears to be the 450/ 502. Here is a picture of the numbers on it.
http://i690.photobucket.com/albums/v...7/IMG_2225.jpg. It would still have an exhaust duration of 230, exceeding the exhaust recommended <225...
Does the Comp kit I linked above PLUS the Scorpion 4014 endurance rockers, although about $1500, look like a wise kit investment to you guys?

So this is where I'm at...On the road to recovery/reliability.

Some facts:
1) The wrong 11# by-pass valves, in fact were still in place...corrected...center removed altogether &offset one replace with the 30#.
2) The mystery cam had a lift of .600 and when coupled with ****ty springs and rockers (Scorpion 4014's and BeeHives going back in) + too many RPM's contributed (likely) by the small 19p Mirage+ prop. I'll be trying out a Bravo I 22p prop when I get back on the lake (picking it up this weekend @ the Boat Show)...propping to a more conservative rpm with a full load.
3) The old design EMI Thunder (wet joint) has been converted to dry joint (welded) and should (hopefully) work fine with the mellowed stockish cam (.211/.230/112/.540 Lift)...
4) I've had Corsa rebuild my diverters with new solenoids, flappers, and wiring harness to get the Captain's call back to operational to allow better WOT breathing (had been 100% forced through the prop while using V6 exhaust elbows).
5) I'm replacing the 25 year old oil lines with Russell ProClassic II hose along with their full flow swivel capable fittings. I found a new Merc oil cooler which should work fine with the stock 502HO motor. I suspect here could have been at least 4 rebuilds in their service life.
6) The new oil plumbing will have a new 215 degree oil cooler stat which will help get up to temp in the often cold lake environment up here. I'll work an oil temp gauge in somewhere.
7) I'm willing to give the existing Edelbrock 1410/750cfm carb another shot, along with a new K&N flame arrestor setup.
8) Replaced the seized up oil pump...the bottom end was fine.

Fingers Crossed...Thanks for the help OSO.

That sounds great! It looks like you've sorted out the devils very well.

Been a loooong winter. http://i690.photobucket.com/albums/v...7/IMG_2448.jpg can't wait to run it.

Finally 1sr run on the lake, typing this while anchored in the 70 degree sunshine. My initial concern
Is 65+ psi Oil Pressure until the oil temp reached the 210 degrees to open the oil thermostat circuit and through the cooler. At that point oil pressure fluctuates normally between 20
& 45. Going to chill a while limiting the run time today until I'm sure of the situation. Don't know what normal is yet.

Engine looks great.

Did the engine get run on a dyno or stand before being installed in the boat?

Oil issues should be investigated immediately.

Post up all info you have concerning the rebuild and the parts that lowered the horsepower from the original crate motor.
Deliberately loosing horsepower in your 502 may get your man card revoked here but I get the reliability thing.

Are you saying that you have run the engine a few times and the oil pressure goes from 65+psi cold then down to 20 psi hot
and then back up to 45 psi after it cools a bit?