Looking for advice
 

Made some wide open runs Saturday on my stock 1997 502 Mag MPI running 7 Lbs. boost pro charger. Brought motor back to idle and it sounded sick. Stalled and I restarted once. Then stalled again. I was in the middle of the shipping channel so I attempted to restart again and broke starter. I figured it blew the head gaskets and Hydro-locked.

Pulled her in the barn today and sure enough 3 cylinders were full of water and the spark plugs were wet on the other 5. Whats my diagnosis? full rebuild? Get lucky and replace head gaskets? I know there is a good chance I bent something in the motor.

At that point I'd prolly wanna do a full tear down and at least inspect everything.

Thanks, Looks like my season is over so I might as well pull the motor over the winter.

A slightly bent rod or hurt bearing. Any of that and your risking block problems. Even if everything else is good at least you know instead of being terrified every time you touch the throttle. Lol. Old saying better to be safe than sorry. Lol

I think the smartest approach is to put plugs in and start her up. Look at pressure and listen for noises/missing. Also, do it with the belt off the charger so you can hear better.
You can run it for a minute/minute and a half without concern of lack of water.
If it sounds ok....then buy a top end gasket set with arp's and swap out the head gaskets. After resurfacing the heads, buying the gaskets, and installing the arp's......you'll be in under a grand and potentially back on the water next weekend.

If anything is amiss.....blow by, rattling, missing....knocking.....time for a rebuild. Either way, use studs on the heads.....

Is this the one with the new Holley EFI system ? how long was the water sitting in the cylinders, is there any water in the pan ?

Pull it apart, unless you don't mind if it get's broken further.

I'm sure you'll find atleast a bent rod, or two, or three....and atleast one head not flat.

Yes it is the one with the Holley. I was doing some wide open runs to make sure the computer would learn the upper rpm ranges before I pulled my O2 sensor to run open loop. I haven't checked the data logs yet but believe this problem was caused by running 7 psi on stock motor. Water has been in cylinders for about 24 hours now. Starter is broken right now. I am purchasing a new starter tomorrow so I can turn the motor over and blow the water out of the cylinders.

Checked the intercooler and it was dry. I am surprised I have water in every cylinder. Boat does have flappers and the exhaust exits well above water line so I am sure it didn't come thru the tips.

Was running 86 mph trimmed out nicely before this happened. Didn't notice a problem till I slowly brought the motor down to idle after the run.

Judging by the dipstick there is no water in the pan.

Still debating my next move !

Headgasket blew (or cyl head lifted) and water went in those cylinders. It's a common plenum intake, therefore other good cylinders (if there are some) pulled water from there.

Same deal when a motor breaks a valve. Sometimes the valve head ends up in another cylinder in the other bank.

I am thinking I will rebuild over the winter. Upgrade motor to where it needs to be to stand up to the 7 lbs. of boost and possibly upgrade the cam. Any suggestions on builders.

What air fuel ratio were you trying to achieve ? what timing are you running ?

7 psi on a stock motor did NOT cause this unless you had rotted gaskets ready to let loose as MANY have ran that much on these mag motors stock. Most these problems lead back to a lean tune, too much timing , insuficcient fuel supply under boost or something like that. Yes, I would pull motor and go thru it but something caused this and you need to figure that out when it goes back in, Smitty

I will pull up my Datalogs tonight and see if i notice anything.

Check to see what your knock sensor was reading, and see what your IAT was. There's a chance the engine was already hurt from running 13:1 under boost with the old MEFI1, and now that it's making some power the head gasket finally let go. Were you running fresh 93 octane, What was your water pressure? Email me over the logs if you want, and I'll take a look.
Hopefully it won't be too bad inside once you get it apart. Give me a call if you need any help.

Thanks, I have a busy day but am hoping to get to the logs tonite.

get a starter om it asap, get the water out, run a compression test, if that happens to ck out ok, fire it up and see what it sounds like, if the engine was in good shape the 7psi should have been fine with proper tuning and fuel system...we've had that conversation...what kind of timing were you at under full boost ? good luck Rob

Motor had 380 hours on it [ATTACH=CONFIG]528415[/ATTACH][ATTACH=CONFIG]528416[/ATTACH][ATTACH=CONFIG]528417[/ATTACH][ATTACH=CONFIG]528418[/ATTACH][ATTACH=CONFIG]528419[/ATTACH]

Had Alex take a look at my Datalogs earlier today. Thought posting them on here might help answer some questions guys were asking me

11.2 at WOT. Datalogs posted above show my timing. Thanks

I don't know anything about the Holley stuff, but it sucks you're having engine problems.

Thanks, Alex told me a possible reason for engine sounding sick when I bring it back to idle is because the O2 sensor got wet which made the computer add a bunch of fuel down low. Other than that data logs looked good.Going to check compression tonight.

Good luck, hope it's a simple fix.

#1 = 152psi #2 = 152psi
#3 = 140psi #4 = 152psi
#5 = 140psi #6 = 60psi
#7 = 100psi #8 = 155psi

Looks like 6&7 got some issue. Good luck.

Commanded is actually 11.8 at 7#'s, and timing is 31 at IAT's below 110 degrees, and then it will start pulling timing gradually if air temp climbs.

Alex Haxby has been a great help even though my problems have nothing to do with the Holley system I purchased.

I'm thinking head gasket on one side, tuliped valve on the other...there was not way water got back up thru exhaust when slowing down was there ?

So if it has 380 hours, does it still have stock head gaskets? I always change them when putting a blower on because the stock gaskets just can't take the added cylinder pressure. I would put the starter on and get the water out then start it, as others have said.

Yes Stock HeadGaskets. According to the people I bought the boat from the motor has never been opened up. I cranked all the water out and oiled it up good yesterday.

99.9% sure no what went in the motor through the exhaust when slowing down.

OK, I am not a pro engine builder, so take my advice with a grain of salt if you like. I think you were on the ragged edge running boost to a stock Merc MPI motor (non-blue motor), especially with almost 400 hours. First of all, I am 99% sure that those engines were not equipped with inconel exhaust valves from the factory. I say this because several years ago, I was trying to answer that very question myself. I called up Mercury Racing and spoke with a tech - he told me that as far as he knew, only the blue motors have the inconel valves, because those were torn down by Mercury Racing, blueprinted and reassembled with better components, including the Manley inconel exhaust valves. He said the black motors just had whatever GM put in them. Maybe GM put inconel valves in their marine engines, but I was never able to establish if that is true.

Secondly, as others have touched on those stock head gaskets were not made to handle the extra cylinder pressure of a blower. A set of Cometic MLS gaskets would be your best bet, but MLS require an absolutely flat sealing surface, with the correct finish. Not sure if you can get that without having the heads and deck resurfaced. Second choice here would be a set of quality head gaskets such as FelPro or similar. Head studs would be advisable for a boosted application as well.

I guess the bridge you have to cross is if you want to continue to take chances with things like they are now, or if you want to back up and use the best parts to make this engine live a while under boost. Of course, nobody wants to hear that they are going to have to spend big bucks on their boat to go fast, including me! ;)

Good luck with it whichever direction you go.

Thanks for your advice. I have decided that my summer boating season is over at this point. Really only had one more event planned this summer and that was Hot Boat at Hardy Dam. I dont want to rush to get the boat back together and hope it runs good for just one more weekend. At this point I am planning on pulling the motor and assessing the damage. Then decide how I want to proceed from there. I really enjoy performing my own work but am not sure if that is the way to go with this project. I would love to learn how to rebuild/assemble a motor, but dont want to use mine as a guinea pig. I may take it to an experienced builder and have them advise and fix it for me.

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Finally tore the motor down. A lot of water in their. I am thinking that i will send it to a pro to have it rebuilt then re-install into boat myself.

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could you see any places head gasket had failed ?

From the first picture it looks like cylinder 6 blew out the fire ring.

yeap..see that now, thats 7 and looks like 3 as well but not as bad...

I was actually talking about the first picture in post #34. That is cylinder 6 and the firing ring is blown out. It does also look like cylinder 7 and cylinder 3is blown out in the third picture of post #33 looking at the head gasket sitting on top of the block.

This thing went full sputnik, that's for sure.

That is everything I would expect to see with stock head gaskets. I have seen that every time a blower was added to a 454-502 without changing the head gaskets. Guys that want my help, I tell them I won't do it unless they change head gaskets. A friend of mine has a whipple on a 525 and has never had a problem, but that probably uses a better head gasket than the 454-502mpi.
It doesn't look that bad, I would have a machine shop check the cylinders and pistons, but they are probably ok. I would just do a complete rebuild since it has 380 hours and start of fresh next year. OH, and lower the boost.

yeap...see #6 as well...killed them both for sure...