Difference between 1 piece and 2 piece heads

[Banana Boat]

What are the differences between 1 piece and 2 piece heads on a v6 merc? Are they interchangeable? Any compression differences or anything? To me the 1 piece heads look better and have one less gasket to worry about. Would somebody ever prefer 2 piece heads?

[Jay Smith]

The obivious is the differences in the water chamber the two piece being exposed by removing the top gasket plate and the 1 piece a closed water system. Also most 2 piece heads are more like a hemi head and a 1 piece resemble an umbrella , Each can be cut to yield any compression wanted. The 2 piece heads is whats usually refered to as the BAD HEAD BOLT PATTERN motor. The pattern on most 2 piece are from very early V-6 and the bolts are very narrow and are next to the bore itself unlike the newer style 1 piece that are a wider bolt pattern will seal and hold greater compression , the two heads can't be interchanged...

Good luck,
Jay

[Banana Boat]

Thanks for the info Jay

[T-REX]

83 up 2.4,s and 2.0s had 2piece heds with the later bolt pattern...Up untill 88...altho tha 2piece heds from 83/88 will bolt on tha later motas, the still don't have the cooling capasity that tha one piece haz, and haz one more gasket to spring a leek....I use the 2 piece all the time without problems, kuz if the cooling system works well, U don't have a problem...But if U cut the 2piece heds for big compression, then U start building chamber heet ya kan't git rid ov...For a river mota, U won't know tha differnce between tha 2 piece and tha lost foam hed....Even tha combustion chamber shape(Hemi/top hat) don't make enuff(if any) differnce to matter...

[M.CHAPMAN]

Another thing I have noticed as I'm sure you have Rex, is when you cut the 2 pc. heads you start seeing porosity in the casting due the the process they used to cast the older heads, sometimes you wind up with a big enough pore to cause a "hot spot" that could lead to possible detonation. Dad cut some heads down that you could hardly get a dill pickle slice in the chamber and it look like moon craters in the "squish" area.
-Michael

[T-REX]

Hell, datz what bubble gum iz fer, after tha taste iz gone!!!

[jallen355]

Frickin' Red-nek! Aieee!