Heads
 

I've got a mkIV 454 in my boat that has been rebuilt mutiple times by 2 different builders and every time the same result, it spins bearings. One head is a 781 and the other is an 049 which I ve been told doesn't matter but made me Feel the motor is just a bunch of random parts thrown together that "should run" but it doesn't. So I picked up a gen6 454 mag mpi "complete drop in" which checked out but after being put in and ran the oil is milky,so I did a leak down and found 4 cylinders leaking 40% past the valves. Naturally the seller is no where to be found. So I was wondering if anyone knows weather it truly doesn't matter if those heads are different casting numbers and will they bolt on a gen6 block?

Any bbc head works on gen6 block

Sorry to hear about your situation. There are tons of threads about mixing different generations of heads and what works on what blocks. It really comes down to using the proper head gaskets.

Honestly, if you have milky oil, it's not the valves...something else is going on. I'd say check the exhaust manifolds and risers. Hopefully it's nothing internal.

The diff between 781 and 049 is 732. The differences between the castings is less than the random differences between 2 heads of the same casting numbers. But you now have gen 6 rectangle heads. Why would you want to run the ovals, unless you suspect rot thru on exhaust guides on the gen 6 heads. Which, BTW being 20 years younger than the ovals are that much less likely to be a leak issue. Get a crossover and build yourself a leak test rig. Bolt heads on with good head gaskets. Fab block off plates to cover the 4 water outlets where intake bolts to heads. I actually block off 1 side of crossiver, put it on hanging off 1 side, and leak test each side seperately. Pica and description on request. Crossovers can usually be had used for 100 or so. You can't trust water pumps cuz the seal could leak.

Thanks. I know it's not because of the valves, once I saw the the oil I went to a leak down as the next step to see the general health of the engine. I'm hoping an intake/head gasket issue is causing the milky oil but I now know the heads are junk. Didn't want to pull it apart without knowing if the heads from the other engine would work cause I'm at the point of just cutting it into pieces and selling parts or trying to make something work.

Could send me that pic and info?

How do you know the heads are junk? Although any great amount of head work will push a set of old castings into the price of a new set of aftermarket iron that don't need guides, seats, etc. I have a set of 215 closed chamber ovals that had some extensive port work. Guides are loose. Called a shop, they said about 800 bucks.

I guess technically I don't. I just know it needs a valve job and by what your telling me it sounds like a stupid idea to put those other heads on it so I need find out how the water is getting in and if it's worth rebuilding

049 and 781 are pretty good heads. You can get 450-500 with very little port work. Did the mk-4 run well before eating bearings? Oh yeah, where are you?

049 and 781 are pretty good heads. You can get 450-500 with very little port work. Did the mk-4 run well before eating bearings? Oh yeah, where are you? Milkshake, first culprit is intake manifold gaskets and the water passage running across front of intake. Especially with raw water boat motor and more so with salt water. Although the factory mag motor has a brass or bronze piece cast into the alum manifold.

Spins bearings.....are you using the right bearings?

i disagree,leaking exhaust valves can cause the cylinder to revert enough water to milk the oil.

After you mention that, he did say he's leaking at about 40%. That could be highly probable then.

its probably more likely you have a cracked water jacket.

Im in west Chester pa. The mk4 ran its ass off just kept eating bearings. But if they aren't the right heads I won't bother switching them over

Are you trying to get thru this season, or looking into what you need for this winter's build? Was mk4 dished or flat pistons? Is this a mag motor? Or a gen 6 that has mag heads on it? And is it still in the boat? Also, what is the boat and how is it run? A lot of people push it to WOT for a few seconds each trip out and spend the day at 3500 to 4k. If that is the case, the ovals are just fine for you. And the alum rectangle mag intake will fit and run just fine on the oval heads.

the boat is a 24 checkmate enforcer. I probably run between 4K-WOT which maybe that's why I keep spinning bearings. The mk4 is in the boat but sounds like it's starting to knock and at this point I figured I would start over with an entirely different engine which is how I came across this mag motor. It's definitely a mag and I ran it on the ground and it runs rough and oil got milky so I did leak down. I was hoping to use heads from mk4 and make one good engine out of the 2 but I didn't realize they were oval heads and at that point the mk4 is a flat tappet cam so I assume to put the heads on the mag I would have to change the valve springs be cause it's a roller. Sounds like too much work and I should just address the mag motor and see what all it needs. Not sure what pistons are in the mk4

No.

No, you could run the ovals on the mag just fine. Chambers essentially identical. No piston to head clearance issues. Valves, springs will run on the oe roller lifters. You would have to run the newer pushrods so if pushrod dia are different you will need 3/8 guideplates to fit the 7/16 rocker studs. I have at least one set here. Gen 6 no fuel pump mount. Did the mag come with the water pump-fuel pump combo? Otherwise an electronic fuel pump is necessary. The one pain is if using all the mk 4 brackets, the gen 6 are 7/16 instead of 3/8 and drilling that little bit bigger is no fun. But most attach to the heads, not the block so less holes to adapt. You could have that gen 6-oval beastie together in a couple evenings. You will want to drop the pan and check the rods and mains. I bought 2 different supposedly good engines and found bad bearings after installing the engines.

The mag motor came fully dressed. All accessories fuel pump fuel injection computer everything. If the intake manifold looks ok do you think I should stick with the fuel injection with these other heads or swap the intake carb and everything from the mk4?

what do you have for intake and carb on the mk 4? the efi is a nice setup, but rarely trouble and bug free. I would consider the efi conversion for over the winter. where do you run this boat? I was assuming mag carb engine.

I run in the upper Chesapeake around Elton Maryland. It has a dual plane edelbrock air gap manifold and a 750 edelbrock carb

Good carb and manifold. Does the trick. If you tried that efi with all its foibles, you would be chasing bugs all fall. Like the VST setup. Cantankerous. The injectors themselves need cleaned and flowed, or better yet replaced. You spun bearings in the mk4. Your bottom end work? Or having motor built?

I might pull the bottom end of the mk4 just to look myself but it's been built about 5 times by 2 different builders and every time after running at 5k rpms for 5 minutes it blows the dipstick and wipes the bearings

When I take the mag motor apart I'll check the bearings as you suggested

That mk4 block is ready for its next career as a mooring anchor in Georgetown yacht basin...

hahaha. That it is

Mota
 

My friend has a 454 marine short block for sale 631 902 4665