I'm putting a 305 in my 50 Sedan. It is a 86 with a 1 piece main seal. I noticed I need to run a weighted (externally balanced) flywheel on it. Can some one explain this to me? I know the rotating m*** is balanced by the crankshaft. So what is the externally balance flywheel for? And why 305's and 400's and not all SBC? Thanks in advance. Todd
I don't think that is correct. I've never heard of an externally balanced 305. The only externally balanced small block is the 400. And the only other external balanced Chevy is the 454. Except for maybe some of the newer BIG big blocks. Roger
I'm not sure about the 305 but right around sometime in '86, things changed for SBCs. The one piece seal 350s are indeed external balanced in the rear. I would think that the 305s followed suit.
ALL small block Chevrolets with a one piece rear seal are externally balanced. Look at the crankshaft flange on any pre-'86 sbc. Notice the shape of the flange on an early 327? It looks like a circle with two notches cut out of it. A 305 or 350 has an offset m*** on one side. That's part of its balance. All '86 and newer one piece seal engines have a perfectly round crank flange---they have to, or the seal wouldn't go over it---so the remainder of the balance has to be handled by a weight on the flywheel.
One piece seal small block Chevies don't have the small counterweight on the flywheel flange. The flange is round for the seal to ride on it. So the flywheel must be counterweighted to make up the weight of the small counterweight that is not there. Sometimes instead of a weight being added to a flywheel there will be holes in the flywheel opposite from where weight is needed. It's kind of like the reason that 400 and 454 Chevies were counter weighted they just didn't have the room inside to be internal balanced. Have fun,Smokey
Just to clarify, they are still internally or neutrally balanced in the front though. Only the 400 was externally balanced both front and rear. With the correct aftermarket crank selection, any later small block can however be neutrally balanced. I built my '95 LT1 stroker that way. All that's required beyond the correct crank is a neutral balance flexplate or flywheel to match up, readily available in the aftermarket for the one piece seal engines.
Heathen and Notorious, Thanks for reminding me how slow I type. RClark, Yep, the small block ain't as simple as it was at one time. Have fun,Smokey
having never built anything that new (86) when i got to the fly wheel it was oh **** wrong one, but did some checking and found out about the rear flange. guess i might ought to work on something newer than 60'ish. what he said above is right.
I bought a "Mr Goodwrench" 350 out of an old truck, and it too has the counterweight on the flywheel, the one piece rear seal, and yet not the newer style intake bolt angles.
The goodwrench motors are a basic crate engine for replacements of early SBC applications. They did not continue to make the early block and crank, but did keep the early heads with a few revisions. The one pc seal motors are far less likely to leak oil and run a little smoother with the balance arrangement.
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