I know the L98 is externally balanced, but i can't seem to find a torsional damper part number anywhere! Does anyone have any specs for this damper, or a part number? I am building this engine from scratch and I have no original parts. I've looked in the service manual and various other books and I've searched summit's site and they only seem to show me internal balance dampers. I've got a two bolt main, if that spec is needed. Any help would be greatly appreciated

~Steve

 

That's because the L98 IS internally balanced...... You will not find a stock 350 that is externally balanced.

 

Bet you don't. . .

 

 

Let's not start a war over this again, but the facts are that late model 87-up 305s and 350s with the one piece rear main seal design do us a small weight on the flywheel/flexplate that is part of the engine's balancing. Externally balanced? Yes, a little bit.

The dampener on the front of the engine is just like earlier engines, though- it's a neutral-balanced unit. You can find one anywhere.

 

Exactly. The batwing weight on the flexplate takes the place of the counterweight that was cast into the 2-piece rear main seal cranks on the outside of the RMS.

So, technically, both are "externally balanced" when you look at it that way.

But, since the 3.75" stroke 400's had extra weight on the flexplate/flywheel and damper (it's not a "balancer", it's a damper), the "external" thing came into vogue.

FWIW, in the BBC world, 396 and 427 are "internal" balance, while 454 are external and need the same weights SBC 400's need.

 

"What many Chevy fans may not know is that ALL '86-and-later Chevy small-blocks are also externally balanced engines requiring specific flywheel/ flexplates and torsional damper" -"John Ligenfelter on Modifying Small-Block Chevy Engines", by, of course, John Ligenfelter (p.32)

"All of the one-piece rear main seal Gen. 1 engines made from 1986 to the present are externally balanced and use different flywheels or flexplates with smaller 3" bolt circle patterns on the crank rear flange" -"Chevrolet Small Block Parts Interchange Manual", by Ed Staffel (p. 41)

So please tell me again that I don't know this. Or tell the two quoted above that they are wrong. And in either case, the rotating assembly that I have for my L98 is externally balanced and I'm just looking for a proper diameter torsional damper that is compatible/ appropriate for my set up. I don't mean to be a dic*, but please make sure you are actually steering me in the right direction. Honestly, the first couple of responses would have confused the hell out of me if I didn't have these books to set me straight.

So it seems I will find many stock SBC's that are externally balanced (L98, LT1, LS1, etc...)

Thanks for the help guys,
Steve

 

I'd love to be able to tell John Lingenfelter that his book is wrong, but sadly he's passed on. The Staffel book you'll notice says that a different flywheel/flexplate is needed, but doesn't say that a different balancer is required.

If your L98 is balanced to stock spec, you need a neutrally balanced dampener. That doesn't change, regardless of whether you have a 2 piece RMS, or a 1 piece RMS. They all use the same balancer, regardless of whether you call the engine internally or externally balanced.

 

So, whether the engine is internally or externally balanced, it is balanced to accept a neutrally balanced damper? And you're saying there's no inherent difference between external and internal balance in this case?

 

Right... the whole term "externally balanced" has become polluted to the point of being nearly meaningless. 2 piece RMS engines used an irregular shape on the crank hub where the flywheel bolted up. When the 1 piece RMS was designed, it needed a round hub, so the hub on the 1 piece RMS was "trimmed down", and that irregular bit of material was put on the flywheel instead. Some people say this makes the engine "externally balanced", but some people say that it's still "internally balanced".

Either way, overall the engine is still balanced exactly the same, and both the 1 piece RMS and 2 piece RMS engines use a neutrally balanced dampener.

The exception is the 400. It's the one engine that's unambiguously called "externally balanced. The longer stroke brings the pistons close to the counterweights at the bottom of the stroke, so there wasn't enough clearance to put all the mass that was needed to balance the assembly on the crank counterweights, so some of the mass was moved to the dampener and the flywheel. Because the 383 originally grew out of a non-standard configuration of factory 400 parts, most 383s have been externally balanced as well, although internally balanced versions seem to becoming more common.

 

Ok, thank you. I didn't think this would be a hot topic. Now that that is out of the way, would a 6.75" or an 8" damper be in order? Are there any advantages to having over or the other? I should be producing 350-375hp at the flywheel, if that matters.

~Steve

 

If you have your stock timing cover, only the OE size (6¾") will fit, because a larger one will try to crush the timing tab.

If you have an aftermarket timing cover and timing pointer, then a stock balancer's inscribed mark is in the wrong place for it, and your timing indication will be DRASTICALLY (like, about 35° or so) wrong.

I'd suggest getting a good quality stock replacement one, such as a Pioneer. NOT one of those cheeeep chinesium ones, some of which are even chrome-plated, that you see on eBay.

 

Isn't that backwards? The one piece is the round one.

 

Yup, my fingers don't listen to my brain sometimes.