OK guys so here's the situation... I picked up a complete used GM goodwrench crate motor, and will be mating it up to a Muncie 4 speed. I did a thread search, but couldn't find a definitive answer to my question. GM changed the bolt hole pattern and size of the crank flange center hub in 86. When I do research, all of the flywheels for 86 and later say "external balance". Wouldn't a crate motor be neutral balance, requiring the flywheel to be neutral balance as well? I also want to run a 153 tooth. Any help would be appreciated!
Depends what you mean by "crate motor". My son bought a GM "crate motor" as a direct replacement for the 350 in his 87 Suburban, and of course it had the small diameter flange with the one piece seal, which works with the weighted flexplate that came on the thing new. If you buy a "crate motor" that is the 1985 and earlier design, it will be the larger old crank flange, for use with the earlier neutral balance flywheel. So...it sounds like you got the later engine, and you need the correct flywheel to fit it. They are external balance, and mostly the same flywheel fits the 86-up 4.3, 305, and 350. But make sure you get the right one for the original application of that engine. Might be that the small diameter flywheel was used in cars like the Camaro or Vette, while trucks usually used the 168 tooth. Do some research on rockauto.com, etc
I installed the crate engine with the old style valve covers. 350/290 H.P. I also installed a harmonic balancer. All the old engine had was a hub for the crank pulley to mount to. I bolted up my power glide flex plate and fired it up. Been driving it for years. I replaced a 283 in which I believe was internally balanced.
I saw your photos of the engine on another thread, and it's what used to be called a Target Master; now it's called something else (I forget), but is the same engine. Should say Hecho En Mexico on the bellhousing flange area. They are a re-placement engine for pre 86, have perimeter type valve covers, non-roller cam, and a 2 piece main seal. Or, am I wrong on your engine; does it have a one piece main seal? IF it's what I think it is, then you don't have to worry as long as your flywheel/flexplate is neutral balanced. It's those odd ball, one piece main seal, centerbolt valve covers, roller motors that had a neautral balanced dampener, and an externally balanced flywheel/flexplate (?????). I think yours is the 260 or 290 HP 350; I don't really keep up with the newer stuff......................yet. I am Butch/56sedandelivery.
86 engines had the old style heads (perimeter bolt valve covers), and the one piece rear seal and external balance crank. The 87 engines got the new center bolt valve covers. Rollers came along somewhere in there, but some cars got them before others. 87-95 truck motors are flat tappet.
I looked up the block # and its a 71-85 2 piece rear main seal. 10066036 is the casting number for gm replacement motors
If you just look at the crank flange, you can tell right away which one it is....the old design has a flange sticking out around the crank, the newer design does not have a flange, and you can see the rear seal right there around the end of the crankshaft. If there's a flange on the crank, it's an internal balance (unless it's a 400 crank). If there's no flange, it's external balance.
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