Holman Moody Manifolds?

[superhatz]

I've been reading that the H&M exhaust manifolds can crack. Would a fresh water boat be less likely to develop cracks? Are they repairable?

I'd like to keep the boat original...:)

A side note...the Glenwood Marine manifolds look similar but they don't seem to list one for a 351W?

[MOP]

Salt or fresh they will crack in freezing temps if not drained, can they be fixed sometimes. Small block Fords all use the same port & bolt pattern 302 & 351 are interchangeable.

Phil

[BigGrizzly]

Let me save you the trouble. they crack without freezing if it is a salt water boat they cannot be fixed. Salt impregnates the aluminum and the weld fails quickly and motor is trash by the time you find out. If the fresh water boatr has a high calcium content the same thing happens too. So if you want to keep then in good shape put on a set of look alike and park the H&M after you oil them up complexity inside and out, including the water passages..

[mattyboy]

if winterized properly they last along time in fresh water, on your boat you might find that the crossover water passages are blocked or clogged from lack of use I know of atleast 4 4o year old boats still running the original exhaust there are probably alot more out there. the biggest thing to remember is when draining them after pulling the plug is to take a wire hanger and poke it around and make sure there is not sand,mud or muck holding water in them

[superhatz]

Thanks guys....how will I know if they're cracked?.....water in the oil?

Thanks,
Aaron

[MOP]

Most crack the outer jackets, if the inner cracks water gets into the cylinders. A minor crack will show up as rust on the plugs, usually the back cylinders. Randy is mostly right on the welding, most shops just don't know how to do it right, my guy grinds the crack quite wide out to bright clean metal stop drills the cracks end then Migs back it in. He finishes them off where the weld is not visible when done, he is an X Navy welder they are the very best in my book. He has also done a ton of freeze cracked gear cases and skeg repairs, best of my knowledge none kicked back.