scat stroker crank balance

[hbstang]

so it goes bad to ugly on this crank balance.i bought a new set of molnar h-beams that are almost 70 grams lighter,and a set of pins that are 20 grams lighter,so bob weight went down to 2225 ,sounds good right? well now it moved the front weight completely off the counterweight into space,to the right ,and the rear is to close to edge to put a weight in it.my guess is this is a junk crank from scat!counterweights must be mislocated.i will have to source another crank,as i wont changed pistons/rods etc.so i will contact scat on monday.
any of the engine builders on here can tell me if you had a scat forging that was defective ?counter weights clocked wrong or bad machining?would removing weight from other end of counterweight bring it in?
any one please help.
maybe scat will help.

[My427stang]

This seems a little too hard, any chance his machine is off?

I suppose a counterweight could be off, but it sounds unlikely

[pbf777]

. . . . . . so bob weight went down to 2225 ,sounds good right? well now it moved the front weight completely off the counterweight into space, . . . . . .

     Yep, that's how it works!   And before you ran out and spent that money (I think I might have previously commented on this) the "balance guy" 'should' have been able to tell you that! 

My guess is this is a junk crank from scat! Counterweights must be mislocated.  I will have to source another crank, . . . . . . .

     No arguments from me on your assessment of the crankshaft execution;  but just as in your endeavor sourcing a different set of rods and pistons, I'm afraid the same outcome will be had with another crankshaft!     Because as I also previously stated:

Seriously, this issue isn't that uncommon, . . . . . . it just kinda goes with the territory!          

     And even tough previously I might have stated that:  "there's nothing wrong with the owner being involved", but here it sorta seems like the "balancing guy" is making it your job to solve the issue of transforming an "unappreciated job" into "easy pickings" for him? 

Scott.

[hbstang]

This seems a little too hard, any chance his machine is off?

I suppose a counterweight could be off, but it sounds unlikely

brian has balanced hundreds of cranks and built more engines and is very good at what he does.i am sure he double checked everything.
what i dont understand is how thee location can move to the right with a lower bob weight? but i dont balance/build engines ever!but i like to understand whats happening

[My427stang]

What was your initial bobweight?  sorry if I missed it

FWIW, last 4 forged SCATs I did, 2130, 2101, 2230, another 2101 and a 2050, all came in easy.

If he is willing to play a little, SCAT said the target is the high 1900s, maybe hang some bobs around and see if the crank does what it's supposed to with a lower weight.

I never heard of a SCAT being incompatible with a cammer, but I haven't built one either

[hbstang]

the new bob weight is 2225.old one was 2368.do you have pics of the one you did at 2230?where and how much weight were the slugs?was it a scat forged 4.250 fe crank?
did scat change there 4.250 crank forgings at any time?

[pbf777]

What I don't understand is how the location can move to the right with a lower bob weight?  But I'd like to understand whats happening.

     Again, because that's how it works!  i.e., You add or subtract a "little" weight, the imbalance as registered rotors one way or the other, progressively based on the sum and resultant influence on the assembly that that adjustment might produce; add or subtract enough and it'll just flip to, or opposite to, the point of change.   

     And it is this phenomenon that the "guy" must harness, but it often makes for significantly more time invested, in order to achieve a balanced result.   

     Scott.

     

[pbf777]

SCAT said the target is the high 1900's

    But then, how often does one end-up with a bobweight in 1900's (with a margin for balancing) with an FE?   

    Or is it that, rather than SCAT having actually "targeted" this, it's just the sum that was left for, in as the counterweights had been executed, sufficient in sum or placement or not?   

    Oh, and that's really not a question!   

    Scott.

[My427stang]

SCAT said the target is the high 1900's

    But then, how often does one end-up with a bobweight in 1900's (with a margin for balancing) with an FE?   

    Or is it that, rather than SCAT having actually "targeted" this, it's just the sum that was left for, in as the counterweights had been executed, sufficient in sum or placement or not?   

    Oh, and that's really not a question!   


    Scott.

I agree with your not question....

[hbstang]

What was your initial bobweight?  sorry if I missed it

FWIW, last 4 forged SCATs I did, 2130, 2101, 2230, another 2101 and a 2050, all came in easy.

If he is willing to play a little, SCAT said the target is the high 1900s, maybe hang some bobs around and see if the crank does what it's supposed to with a lower weight.

I never heard of a SCAT being incompatible with a cammer, but I haven't built one either

when you did the scat forged crank with 2230,can you tell me where and how much weight you had to put in it?any pictures by chance?

[My427stang]

I have two, o don’t know weights but can show pics of the cranks

Unfortunately can’t be until Friday

[pbf777]

       Though pictures of someone else's stuff might be interesting, but it isn't conclusively valuable in providing any sort of solution to your predicament as each assembly sum is unique.

       Surely, your "balance guy" isn't still waiting on 'you' to solve this!     If so, perhaps allow me to make a suggestion, this to aid in the endeavor:  "throw something at it"!    He should understand what that means. 

       Or if, we're going to adopt the position that the crankshaft 'is' "unbalanceable" (it happens), send it back to SCAT and pay to have them balance it!  Just have your guy match-weight the pistons & rods "properly", supplying the bob-weight value and then re-spin the crankshaft when you get it back from them for "refinement" . . . . . . . maybe.   

       Scott.

[hbstang]

update on this scat stroker crank balance.scat has agreed to exhange the crank for another thru where i bought it.took it to engine shop in torrance ca and said the same as my engine builder,it would take a lot of time ,and he said it may flip the counterweights,and may not ever get balanced.if he added weights to the front or rear,and end needing more out in space.basically he will not do it,as it is a risk of not working on either,also wth weight on flywheel he said it was iffy at best and didnt want to try it!
scat has agreed to exchange it for another crank.oh boy! what could go wrong with that one.a lot of shops will not work on scat cranks any more!
scat was sold to prvate equity in 2022 that also owns afr heads.
hope to get the the other crank next week and try again.

[pbf777]

      After all this, . . . . . .PAY THE EXTRA MONEY AND HAVE 'THEM' (Scat) BALANCE IT!   

      They're relatively cheap, as they (generally) don't make "match-weight" corrections on the rods & pistons, dampers & flywheels/flex-plates and the crank balance work is only what I'd call "O.K." at best;  but doing such will insure that you'll get something workable, which your balance guy, along with correcting the rods & pistons might only need to "refine" anything remaining in the crankshaft after Scat's effort!   

      Scott.

[hbstang]

they told me they wont balnce the crank,they only sell balanced assemblys.crank is defective.