yakmastermax

Dropped my 383 rotating assembly off today at the machine shop. Neutral balance front damper, SCAT 9000 3.75" crank, rods, rod bearings, pistons, rings

I also left them my OE GM ZF6 dual mass flywheel and clutch kit.

They said they couldn't balance the dual mass flywheel and pressure plate.

Is that true?

Gale Banks 80'

Yes. Are you setting up your 383 internally balanced or externally ballanced. ? It must be a 1 piece rear main seal crank.

yakmastermax

"Neutral" zero balance front harmonic damper (not a 400 front damper) and external rear balance, one piece rear main seal setup, brand new SCAT 9000 383 stroker crank.

If it were a solid single mass ZF6 flywheel you would balance the rotating assembly with the flywheel and clutch kit right? But because I am using the GM dual mass the machine shop at best they will throw a factory GM spec external rear balance flexplate on my rotating assembly and balance it with that.

Does that sound right?

It isn't that I don't trust the shop, it is just that the ZF6 setup isn't the most common...

WVZR-1

They should be able to check/confirm balance of the pressure plate. Why not a solid mass flywheel?

yakmastermax

I already have a nice low mileage ZF6 dual mass flywheel that is in good rotation spec, and this build is going to be definitely both a street car and track car, but still needs to be streetable.

I want to play it safe sorta and just keep the DMF

GREGGPENN

The DMF flywheel has an "imbalance" molded in. It's to offset/balance the 1pc RMS in our cranks. The SCAT9000 is different. It requires 1pc mallory to balance. I never found out WHY that is but, essentially, that crankshaft is cast "out-of-neutral-balance" DIFFERENTLY that your stock crank.. IOW, that cast in weight won't balance or "offset" the 1pc Mallory required..

There are a couple of ways a SCAT9000 can be used with a ZF6 DMF; (But not with a neutral balancer)

1. Use a 400 balancer and drill the crank until everything balances. My shop did that so I could buy any other 400 balancer and be golden.. (Eh...OK. Had I KNOWN he was going to do that, I would have yelled "Everyone out of the pool!"
2. Use a 400 balancer and progressively remove the BALANCER offset weight until it matches up to the DMF offset -- bringing both into balance. (Probably as tough as my 4th option below)
3. Use a 400 balancer and get someone who can correctly determine the (large?) amount of heavy metal required to offset the DMF and SCAT9000's heavy metal needs.
4. Have a REALLY REALLY good shop grind off the EXACT cast-in offset weight on a DMF until IT'S neutral -- and can mate with a neutral balancer. EVEN AFTER DOING THAT, that should would need to weld on that 1pc "heavy" mallory THEN drill the crank to finish. (Maybe that's why my shop did #1?)

You have another option:

• Return the SCAT crank and buy an EAGLE (or other neutral crank) and a 400 balancer. THAT would require less crank drilling to bring into balance -- though it won't be a neutral balanced engine.

In fact, nothing balanced with that offset built into the DMFs can be neutral. Not unless you can find someone who thinks they can grind it off where drilling (or adding weight) to your crank -- will end up balanced.. I can tell you people have tried this. . Most didn't turn out that great. One or two (over the last 20yrs) said it worked for them? I wasn't there so I can't vouch.. PLUS, I think they probably accomplished this using an Eagle crank?

If you need a pic of the cast-in weight, I can post it. Otherwise, take this info to your balancer/builder and see what THEY recommend. Maybe they already suggested what they can do? The bottom line is you're working with two pieces (DMF and crank) that aren't neutral). Putting them with a neutral balancer is their challenge.

ANYWAY....I bought and installed the SAME option on my 383 I can show you how much they drilled the chit out of my crank to achieve balance WITH that 400 balancer I'm not even totally positive it would be good for a 6k rpm (or higher) application. It's one of the reasons I stuck with a lower rpm TPI. (Because I do have an HSR I've never installed)

BTW....if there are "pegs" in the outer holes on your DMF, remove them before balancing. Between you and me, I wonder if those pegs could be leveraged to offset the cast-in weight. IDK the answer to that. Probably not because I'm thinking the pegs aren't THAT heavy?

yakmastermax

Sorry man I am really not following. I thought the ZF6 DMF had the same weight on it balancing it as any flexplate that might be bolted behind the same motors that ZF6s came behind?

Also the 400 front harmonic damper that is NOT neutral balanced, I am confused what that has to do with this kind if build? All one piece rear main seal C4 Corvettes I thought came with 350 style neutral balance front harmonic dampers?

Sorry man I am just super confused...

If a SCAT 9000 3.75 aftermarket stroker one piece rear main seal crank can be balanced with a standard 350 neutral balance front damper, and a standard GM spec one piece rear main seal rear external balance flex plate, then it should be doable by proxy with a ZF6 DMF since the ZF6 DMF has the same balance weight as the flex plates that came behind auto C4 350s, other than I think the 1984 and 1985 cars?

C4industries

This sounds like an interesting build. Are you using the stock block and stock rods or aftermarket?

On a build like this for street and track performance, I would recommend converting to a quality single mass FW setup. I converted my 1990 Vette with a 383 to a Centerforce setup.

Centerforce part #s
Flywheel: 700175
Clutch & PP: DF039000

I've been running this setup for 2 years on the street and occasional HPDE track events. It's awesome. Relatively light pedal with smooth engagement and tons of grip. The car currently runs a 12.5 @111mph 1/4 and I could (and will) throw a lot more power at this clutch setup with no problem at all.

IMO, the factory DMFW was a complicated and compromising method to quiet the ZF tranny gear noise. It was for the general masses that didn't want transmission noise to interfere with their favorite Steve Miller song. If you're serious, and by the specs in your engine build it seems like you are, switch to a quality single mass flywheel.

FWIW, I believe Carolina Clutch sells a countershaft shim kit for our ZF6 trannys that reduces gear rollover noise.

Also, to address this:
I believe you are correct and technically the DMF can be balanced in the same manor as a standard 1pc RMS FW. But the balancing shop probably doesn't want to, or isn't setup to, balance the DMF. The springs and movement between the 2 components in the DMF throw in more variables and the balancing shop doesn't want to be on the hook for vibration caused by the DMF. They see the DMF and run away. If that's the case, I don't blame them. But see if you can get them to admit to that.
​​​
Dave

GREGGPENN

A Scat9000 crank requires 1pc Mallory to be welded to the crank. Some shops won't do that. Mine wouldn't -- CLAIMING they'd had them fall off in 7k rpm dirt track engines. Ask if that's what the shop can't/won't do.


See if this thread helps....

AZSP33D

1 Piece RMS OEM cranks are balanced with ~23.4 oz/in in the rear and zero in the front.

When building a new engine with a new crank, there's a certain bobweight that will be close for zero balance, depending on which crank you have... and often it's difficult to achieve zero balance without adding heavy metal to the counterweight, depending on your bob weight. That's when you look at the option of using the standard GM 23.4 oz/in balance. The crank manufacturer should provide that info... I have a zero balanced 383 crank, and there was mallory added to both ends.

The DMF may be difficult to balance with, I've heard of people adding a few spotwelds between the masses, and grinding off when finished, but I've always changed to a SMF.

Of course the 400 harmonic balancer will not fit a 350 spec snout.

GREGGPENN

Pretty sure I used a Pro Race Pro Sport 64266 balancer. It has a bolt in weight....and will fit the SCAT9000 Yak likely has.



FYI: I'm not saying the 64266 is THE damper Yak should use...It's an option -- for a shop that doesn't do the Mallory.
J

C4industries

Good discussion.

So the spot welds just convert the original DMF to a SMF. Correct?

I believe the snouts are the same and the balancers will physically interchange.

The Scat 9000 3.75 stroke 1pc RMS crank can be setup to internally balance (front and rear) without Mallory with the right combination of components. I believe this requires a 6" rod. I'm currently building an engine with these specs. It's documented here:
https://www.corvetteforum.com/forums...638-block.html

yakmastermax

My rods are 5.7 Eagle SIR
Pistons are Icon forged 3314-030

I believe my shop can add Mallory heavy metal to cranks and does so if necessary

Looking at the product description for the SCAT 1 piece RMS 3.75" crank I bought it says it is an "internal/external" balance crank that can be balanced with a neutral zero (350 not 400) balance front harmonic damper, a weighted (external rear balance 1 piece RMs style spec) flywheel or flexplate, and the necessary metal on the crank itself. Pictures attached.

The question is can this route of balancing be done for a DMF ZF6 flywheel by using a flexplate or other non dual mass rear external balance component that hopefully is the same spec as the ZF6 DMF, so a balance by proxy component?
Not a true optimized balance, but hopefully close enough?

I like the idea of welding the DMF lol. Can I pitch that to the shop?

C4industries

Yes. What you just described should work.

Gale Banks 80'

I built a similar engine to what your doing. It might make sense to think about the difference between a 2 piece rear main seal Crank and a 1 piece. The 2 piece has an odd shape casting where the Flywheel bolts to. This is for balancing. A 1 piece has to have this machined off otherwise there wouldn't be any way to slip on the Seal.
I also used the Scat 9000 Crank. I made the move to a Ram C4 Clutch conversion at the same time. My balance shop charged me another $80 to use Mallory to get it to balance out. So everything is now neutral and any component can be replaced as long as its neutral.
I put the Duel Mass Flywheel behind me and I have never looked back.