jaybird82

iTrader: (1)

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?

MichiMike

Any bbc head works on gen6 block

Jonesyfxr

iTrader: (1)

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.

dereknkathy

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.

jaybird82

iTrader: (1)

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.

jaybird82

iTrader: (1)

Could send me that pic and info?

dereknkathy

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.

jaybird82

iTrader: (1)

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

dereknkathy

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?

dereknkathy

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.