Scat 4.250" cast crank and adding Mallory?

[Mike_R_SCJ]

I have a Scat cast 4.250" crank at the machine shop now to get it balanced. They are telling me that the front needs a lot of weight added. He thought maybe we needed a counter balance spacer to add to the front. I told him it's supposed to be internally balanced. He seems to think it may take a lot of Mallory. Is this normal on these cranks? The components are all light weight.

I know on the Scat 460 based cast cranks, it's pretty normal to add a lot of Mallory. I just wasn't sure what's normal on an FE.

[blykins]

n/m

[Jb427]

Mine took a bit as well all lighter parts callies ultra rods diamond piston ati balancer billet spacer and flywheel coated bearings maybe a builder that sees more quanty can chime in but I hear it's not un commen.

[Barry_R]

Between one and three slugs total (front and rear) is very common.
Depends on the set of the combination and the size of the chosen slugs (we use a lot of 1"x1.200")

[mbrunson427]

I went back and looked at pictures in my phone from when I did mine. Looks like I used one big slug in the front. Not sure what he qualifies as "a lot", but I'm with Barry, if it needs more than 2 or 3 I'd be questioning what he's doing.

[Mbowling]

Mine needed some

[pbf777]

The components are all light weight.

    So, for curiosity, what is the bob-weight value?  And approximately how much is "a lot of weight" to be added?      At the point your crankshaft assy. is at, mounted on the balancer and "spun", I generally can tell the customer approximately what size and how many "slugs" it's going to take, along with the increased costs incurred for such, before proceeding to actually install any heavy metal.

    And let me say, that particularly with the chinese cranks one never knows what going to be required until it's spun!  So hopefully the shop is capable, and if so, second guessing their work isn't helping matters!         And if not, and reputation will generally answer this (though with the unknowledgeable whiners these days on the no-recourse irresponsible internet it can be difficult) , why are you there?     

    Scott.

[Mike_R_SCJ]

Thanks guys!

I want to first make it clear that I'm not questioning the shop. If that's the way it sounded, that was not intended. This is a shop I have used a lot and I like them. I was just asking generally if is expected to add Mallory to the cast 4.250 cranks and if it's a lot. It doesn't surprise me at all that it would be the case.

One thing I found after I have started weighing the components is that the rods and pistons were heavier than I expected. The rods (I-beam) are 840 grams and the pistons are 620 grams with the pin. So maybe that is a problem. I do have a set of Eagle h-beam rods that are 810 grams. So that may help.

At this stage, he seems to be concerned that it's "way out of wack" and he's unsure if Mallory will fix it. His balancing guy was out today, so I may hear more tomorrow or another day. We'll see what happens. I'm pretty much just telling him, if it needs Mallory, it needs Mallory and I am fine with that. I could potentially use the H-beam rods and maybe get a lighter set of piston pins to help reduce the bob weight.

[bill_396]

I recall my machine shop also questioning me when they tried to balance my 4 1/4" Scat. If I'm remembering correctly it also took a fair amount in the front which the shop thought was rather unusual. It did balance up fine though.

[pbf777]

 I was just asking generally if is expected to add Mallory to the cast 4.250 cranks and if it's a lot.

     I would say I wouldn't be surprised if the crank require 'some' metal, maybe one or two pieces in each end, but more than that, I would begin to realize that what I was working with was a less than ideal piece of engineering.  It would seem that your 'bobweight is perhaps in the 2200 gram range which I would consider "typical" to expect, but with the longer 4.25" stroke which moves the mass outward from center and the fact that the crankshaft cores often started out engineered as and with the counter weight mass for something less in stroke, not to mention sometimes the counter weights get trimmed for clearance of the longer stroke, then issues leading to the requirement of heavy metal in the balancing effort prove unavoidable.     

One thing I found after I have started weighing the components is that the rods and pistons were heavier than I expected. The rods (I-beam) are 840 grams and the pistons are 620 grams with the pin. So maybe that is a problem. I do have a set of Eagle h-beam rods that are 810 grams. So that may help.

     Obviously, less bobweight leads to less required counter weight, hence less heavy metal.     

At this stage, he seems to be concerned that it's "way out of wack" and he's unsure if Mallory will fix it.  I'm pretty much just telling him, if it needs Mallory, it needs Mallory and I am fine with that.

    Well, heavy metal, enough of it, 'will' fix it, but if it's truly "way out of wack", and if particularly a cast crankshaft, I would question the advice of the effort or expense?     

    My personal record for the sum of metal installed in a singular crankshaft, even after my advice to the customer was to just throw the P.O.S. on the ground and walk away, was 23 pieces!        So it can be done, it's just sometimes a question of why!   

    Scott. 


     

[pbf777]

............ it also took a fair amount in the front which the shop thought was rather unusual.

     Not 'terribly' unusual (chinese shyt ya-know), but, an indicator of poor engineering effort by the manufacturer.      

     Should make one wonder what else 'sucks' with the product that just wasn't so evident!   

     Scott.

[Mike_R_SCJ]

Well, heavy metal, enough of it, 'will' fix it, but if it's truly "way out of wack", and if particularly a cast crankshaft, I would question the advice of the effort or expense?     
 

Great feedback on all of this! Yep, my thoughts exactly. I guess we will see what he comes back with as far as how much heavy metal it will require and go from there.

The sad part is, this was supposed to be somewhat of a budget build for my brother's 63 unibody truck, which is to be maybe 450 hp. Nothing too radical. In hindsight, I probably could have or should have just gone with a 3.98 stroke or 4.125 to help reduce the offset. It's been very tough to get any parts during Covid, so we have really scrambled even to get the parts that we have. So I'm really hoping one way or another it works out. I'm not afraid to add Mallory up to a point. But, as an example, if it goes past say $600 in mallory, then it would have made more sense to just get a forged crank. But we are kind of stuck with it at the moment.

[gt350hr]

  Last year when I talked to Alex @ Scat , he said the 4.250 cast FE crank would always take "some" heavy metal in front and rear to go "internal". Forged didn't unless the rods were super heavy.
   Randy

[Dumpling]

Never thought about it, but what's bad about the factory idea of external balancing? Especially in such a plebian application...

[GerryP]

Never thought about it, but what's bad about the factory idea of external balancing? Especially in such a plebian application...

There's nothing extraordinarily bad about external balance, but it's not the favored balance because of where the mass is located.  Sort of like would you use forged or cast pistons in a mild build?  The Chevy LS6 454/450 is an external balance engine and they're not very pokey.  They'd be welding weight to the flywheel and that would make that flywheel forever married to that crank.