47-55.1 Google search challenge for 178 tooth SBC external balanced flexplate

[Kevin Mac]

I have been on the search for couple days and can't find one, the one I took off my 383 stroker is bent and I can find 168 tooth all day but the 178 tooth is a tough one. I have been told a 168 could work with shimming the starter to match, does anyone know that to be true? BTW it's 14" dia.
Thanks Mac

[jwhotrod]

I've never heard of a 178 tooth flexplate. either 168 or 153 are normal. The 168 tooth is used with the staggered bolt starter, the 153 is used with a straight bolt starter. most automatics use the 168 tooth wheel. my zz4 and the 700r4 in my streetrod use the 168 tooth wheel. so I don't know where the thought came from that it should be 178 I don't think that is correct.

[Kevin Mac]

That’s what I took off was a 178 tooth, it can’t be the only one lol. I think I will have to order a 168. Mac
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[Kevin Mac]

I did find a internally balanced 178 tooth on eBay. Must be an odd duck.
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[Kevin Mac]

I bought a 168 tooth tonight, still not sure what the 178 was all about.

[mongocanfly]

I couldnt find a 178...
Heres this..https://www.chevrolet.com/performanc...els-flexplates

[1project2many]

That’s what I took off was a 178 tooth,

Hmmm....
Early SBC with 2 pc rear main was internally balanced except 400 SBC which had counterweight welded to flywheel.
Late SBC with 1 piece rear main had counterweight welded to flexplate and is sometimes called "externally balanced." Counterweight is to make up for loss of weighted flange on back of crankshaft.
GM 383 with 1 piece rear main uses 14088765 flexplate, 153 tooth, 12 3/4" diameter, counterweight added, stock part for 305 and 350 engines.
GM trucks with later SBC using 1 piece rear main require 14088761 flexplate, 168 tooth, 14" flywheel, counterweight added.

Is your engine 1 piece or 2 piece rear main?
Is your flexplate 12.75" diameter, 14" diameter, or a different size?

[Kevin Mac]

It's external balanced 14". I assume it's a 400 crank because PO said it's a 383. I don't know a lot about stroker motors, I thought a 383 was a 350 block with 400 crank. I bought a flexplate tonight (168) and installed it. I will Google how to shim the starter and check that as well.
Next up learning how to adjust shift linkage.
Thanks Mac

[mr48chev]

In the 48 years that I have actively been dealing with all sorts of Chevrolets I have never heard of a 178 tooth ring gear but did find just the ring gear advertised used on
ebay.

I don't know what the original application was but if it were me I'd get a quality external balanced 168 tooth flex plate and swap nose cones on the starter. You are using a GM starter an not one with the Mickey Mouse picture on it?

Endframe/ nose cone for the starter usually costs about 15 bucks new at the starter alternator shop.

The only thing I can think of is that possibly there was an odd ball application like a motor home chassis that ran a 400 Chevy back in the time frame that they were common in motor homes.

[1project2many]

Originally Posted by Kevin Mac

It's external balanced 14". I assume it's a 400 crank because PO said it's a 383. I don't know a lot about stroker motors, I thought a 383 was a 350 block with 400 crank. I bought a flexplate tonight (168) and installed it. I will Google how to shim the starter and check that as well.
Next up learning how to adjust shift linkage.
Thanks Mac

Once upon a time the only way to build a 383 was to drop a 400 crank into a 350 block with 400 rods and 350 pistons. In addition to the 400 rods you would use a 400 flexplate or flywheel and balancer. If you were a really sharp guy you would have the assembly balanced because the 350 piston weight is different than the 400 piston weight which causes the rotating assembly to be out of balance. It made sense because the machinist turning down the 400 mains to fit the 350 block was probably a little frustrated at the amount of time he had to spend on the crank compared to what he was charging. An experienced builder could assemble a torquey little mouse while most "budget friendly" attempts had a bit of a vibration and would sometimes tear an engine mount, snap a bolt here or there, or crack a flexplate due to vibration.

These days you can go to Summit, Jegs, Speedway, your local GM dealer, or any number of companies and buy pre-made 3.75" stroke cranks for relatively short money. The cranks are manufactured to fit 350 mains. There are usually options for piston weight and rod length which are really just a way to better match counterweight mass to piston and rod mass. 3.75" stroke cranks are available to fit "old" two piece rear mains and "new" one piece rear mains. Additionally, with the use of adapters it's not too expensive to put a two piece rear main crank into a one piece rear main block. You can buy your crank with internal balancing or external balance needed. You can buy a crank with a combination of balance methods. In short, when it comes to building a 383 there are a pile of tools available to skin that cat.

There is no such thing as a "178 tooth" flywheel despite the fat-fingered ebay ad saying otherwise. 14" ring gear indicates 168 tooth. 12.75" ring gear = 153 tooth. Since you've found a flywheel that bolts on you've figured out whether it's one or two piece rear main style. If its a two piece rear main style please do yourself a favor and ensure you have a flexplate that actually matches what was removed. With two piece rear main crankshafts you can get an "externally balanced" 400 flexplate, a 454 flexplate, or a "400/454" aftermarket part. You can also get a small weight that slips over the crank hub to allow the use of a non-balanced flexplate. When the engine is built, if it's balanced at the machine shop the parts choice is less important than when you're in the shop looking for a replacement. Folks who have never been down this road will try to tell you it doesn't matter what you use but I promise the weights are different. A slight vibration on a big stroke crank can do all sorts of damage over time.

400 flexplate:


Notice the thicker weight and the cut-out for the converter bolt on the 454 flexplate: