View Full Version : Flexplate or flywheel?


Skunk Works
09-10-2006, 08:29 PM
I'm nearly embarrassed to ask this, but I joined the HAMB to glean some knowledge from veterans, so here goes...

Could someone please explain the difference between a flexplate and a flywheel? I have a new SBC crate motor, a 2000 stall torque convertor, and a 700R4 transmission that I'm ready to bolt together, but not sure what goes in between...

s.r.i.
09-10-2006, 08:32 PM
In the common world, flywhhel uses a clutch,,,, flexplate is for a tourque converter.I'm nearly embarrassed to ask this, but I joined the HAMB to glean some knowledge from veterans, so here goes...

Could someone please explain the difference between a flexplate and a flywheel? I have a new SBC crate motor, a 2000 stall torque convertor, and a 700R4 transmission that I'm ready to bolt together, but not sure what goes in between...

Bob K
09-10-2006, 08:35 PM
Flexplate is for an automatic transmission.

Flywheel is for a manual transmisson.

Flexplate is lightweight and very thin with holes througout.

Flywheel is heavy and solid so as to take the abuse that the pressure plate exerts on it to engage the clutch.

Thats the way I learned it but would be glad to have someone add to or correct as necessary;

B:DB

Skunk Works
09-10-2006, 08:52 PM
Thanks Bob K. and s.r.i.! I appreciate the explanation for why a manual transmission needs a heavier surface - that makes sense!

How about whether to get internally or externally balanced? And what about 153 or 168 tooth?

97
09-10-2006, 08:59 PM
Thanks Bob K. and s.r.i.! I appreciate the explanation for why a manual transmission needs a heavier surface - that makes sense!

How about whether to get internally or externally balanced? And what about 153 or 168 tooth?
The balance thing is decided by the motor , or more to the point the crankshaft, most small blocks are internally balanced. the only factory externally balanced one is the 400 . It depends exactly what crate motor you have....best to consult the supplier.
As far as size goes that depends on the size ( diameter) of the torque convertor more than anything , once again consult the supplier, the starter motor you need will also depend on which flexplate you use.... I would have thought they would sell you a flexplate and starter to match the engine/trans combination when you bought the package.

squirrel
09-10-2006, 09:06 PM
also depends on what year the motor is, the 87ish and newer motors have a small crank flange, one piece rear main seal, and take a weighted flywheel/flexplate (same one for 4.3, 305, and 350)

Skunk Works
09-10-2006, 09:20 PM
I've been buying pieces as money allows, so unfortunately, it couldn't be a package deal.

The engine is an older style block with flange bolt valve covers (instead of the newer center bolt ones) but I specifically requested it with the newer one piece rear main seal (seems like it would have less of a chance of leaking). The engine also came with a harmonic balancer installed, so I thought that meant the crank was externally balanced? I'll check with the supplier for a recommendation on the flexplate.

How do I determine if I have a small crank flange?

squirrel
09-10-2006, 10:26 PM
How do I determine if I have a small crank flange?


the seal is visible, and there is an aluminum piece around the end of the crank, like this

Skunk Works
09-10-2006, 11:01 PM
Thanks, squirrel. I'll have to look at the crank flange after I get home from work...hehe. Awesome that you were able to post a picture.

Attached is the only picture I have of the engine right now, but it shows the harmonic balancer pretty well. I'm digging through a Jeg's catalog and they sell balancers for internally OR externally balanced cranks, so I suppose the harmonic balancer has nothing to do with it.

The engine supplier should be able to recommend the type of flexplate I need for the odd combination of older style block with newer style rear main seal.

Is there any advantage to either a 153 or 168 tooth ring gear?

squirrel
09-11-2006, 08:49 AM
The big th400 converter won't fit a small flexplate. The starter sits closer to the engine with a small flexplate. For years, Chevy put the small flexplates on 6 cyl and 307 V8s, and the big one on the bigger engines.

You might price starters before you buy the flexplate, too.

Skunk Works
09-12-2006, 06:18 AM
Thanks for all your input, squirrel. Here's what I found:

I talked to the supplier and they told me I had a 86-87 block with a 1 piece rear main seal. They suggested using a 97 or later flexplate. They also claimed the crank for this engine is EXTERNALLY balanced, which goes against almost everything I've heard about all SBC's being internally balanced. I also attached a picture of my crank flange - I'm pretty sure it's the small one that was mentioned because it looks exactly the same.

Next, I wrote down the casting numbers and did some research on the internet. The Mortec website says I have a 95-00 block with a 1 piece rear main. Now I'm confused.

The casting date # is A087, which I think means the block was cast on January 08 of either 1987 or 1997, based on what I've read about casting numbers.

I ordered a TCI externally balanced, 168 tooth flexplate from Jeg's. I hope it all goes together - I'd like to drive this thing next Spring!

squirrel
09-12-2006, 09:28 AM
Sounds like you have it mostly all figured out. I mentioned earlier that the 87ish and newer 4.3, 305 and 350 engines all use a weighted flexplate, when people say that these engines are all internal balanced, they're talking about the older versions of the engines with the two piece rear seal, not the "late models" (which are 20 years old now!)

btw, be sure to buy the correct bolts to hold on the flywheel, I think you can get them from speed shops, or the dealer. They are quite a bit smaller than the ones used on the earlier design cranks. And manual flywheel bolts are different from automatic flexplate bolts. Also get the correct converter bolts to work with your transmission.

Skunk Works
09-12-2006, 01:30 PM
Thanks again, squirrel. When I ordered from Jeg's, I also got ARP flywheel and convertor bolts. :) When I read your last post, it made me feel like I was doing something right!