This is what someone told me.

I was given a scat internally balanced 350 crank for our school project car. When I spoke to a local machinist he told me not to trust it, that it would cause problems, since these "balanced" cranks are not actually balanced at all. he felt that it could possibly survie if I were to have him rebalance it with the rotating assy.

I mentioned that the engine it came out of had been grenaded, breaking three pistond and bending two rods and the block. he replied that it was probably the fault of the scat crank. I felt it could have been the H.U pistons sticking due to heat and improper ring gap.

Is this guy trying to sell me on a balance job or is he right about scat cranks?

This engine will be .040 over, SP 9.75:1 pistons and L82 cam (224/224/450/460/114), 186 heads.

 

Maybe yes and maybe no. About the balancing? If you can, do it. It's always better to have them balance everything right before it's installed. Not everyone can do it, or afford it, but if you can...do it.

 

The crank caused the piston and rod damage?...IMO,find another machine shop. I have not heard anything bad about scat cranks. I balance every engine I build. No exceptions, unless it's a direct/exact piston swap.

 

Well, lets consider it from this aspect.....the camel's head in the tent....

when you redo a short/short block, meaning lower end without cam/chain but including cam bearings...and of course everything from pistons down.....you NEED TO BALANCE with stock harmonica balancer, and flex/fly in rear.... you don't, and you taking a HUGE chance...spend the bux....today 200?? last engine I had done was 80 bux....been a while...

spend a lot, and scrimp on balancing?? I don't think so....course you have to trust the shop enuff, chances are if the have the gear they will use it right...but you gotta know what you looking at....

 

i had a local machine shop check the balance on the last rotating assembly i installed, happened to be scat crank and rods, SRP pistons. assembly was supposed to be within 2 gms. local machine shop said one end of crank was out of spec - didn't say how much, but i got the impression that a good machinist would have been embarrassed to have to stand by the 2 gm claim.

can't believe that it would fly apart though, or that they are "junk". have to have a little more evidence than one unknown (so far) person's testimony . . . i'll let you know if mine flies apart

 

i know many engine builders and all of them like scat parts...... but these are people that balance the parts either way so they said that they hold up well and normally hold true to the tolerances. i have seen all makers of products out of spec i know some people that say that eagle parts are junk so i guess it is all what the builder likes.

 

My new motor is going to have a 4340 forged 4" Scat crank at the recommendation of the speedshop. He thought that they are a little better quality than Eagle (for what it is worth). He is going to check the tolerances and rebalance it with the pistons, rods dampner though.

If someone assembled the motor without checking things out, wouldn't take much to blow it up at high rpm. As everyone knows, lots of things could have gone wrong, I suppose. Bore, mains not true, pistons not clearanced properly, assembly error by someone like me, etc..

 

Scat's good so's Eagle, check them and mic them good before assembly

 

I've spent good money on 4340NT cranks for my automotive engines such as $2500+ Crower, etc but when I was building a pair of 700hp Dart 540's for my 38' Cig, I used a pair of forged 4340 Scat cranks. I mainly used them because the expense of building 2 custom engines at the same time meant that I couldn't use the level of parts I'd normally have used. I still used decent stuff like new Dart Big M blocks, AFR CNC heads, JE pistons, Crower rods, etc but had to make some compromises. It was the first time I've ever used them, and I was very impressed with the forging and machining. In all honesty, it looked just as nice as some cranks I've bought that cost 2-3x as much. I always have my crank balanced for the rods/pistons, and they balanced pretty easily with only a couple of slugs of tungsten.

If you're not familiar with what an offshore powerboat engine endures, it's alot of extended running at relatively high rpm, 5000+ for an hour is not uncommon, or it's part throttle-full throttle-part throttle-full throttle repeatedly for extended periods of time depending on the the water condition (waves). Marine engines endure a much harder duty cycle than almost any automotive application and I enver had any problems with the Scat cranks, or anything else really.

I don't know if I'll use them in my current twin turbo project (~1500hp)but I'd certainly use them for for a more budget contrained project.

 

I have to agree with Big_G. How could the crank cause piston and rod damage, and still be in useable condition.

Sounds like this guy is feeding you a load of crap.

 

Scat cranks are not junk ... they have their place ... even scat cast OK for OA's proposed combo [.040 over, SP 9.75:1 pistons and L82 cam (224/224/450/460/114), 186 heads].

All cranks/assemblies should be balanced locally.

Any crank that's had a rod/piston failure should be magnafluxed first ... then checked for bend-twist.

I ran a cheap scat CAST 3.48" for 3 seasons in a CT motor making 360+hp ... LOTSA hard on-off throttle ... no problem w/ crank. Assembly was balanced ... & rebalanced each time I changed weight of anything in the rotating assembly.

 

Jackson, etal,
I was not really even talking to this machinist about cranks or even machine work, but about heads. I have been warned by locals not to use him, since he does lousy work and "finds extra things" wrong with every piece he works on, padding the bill. He is a good sprint car driver, but he is also known as a a dishonest business man.

 

BTW, Jackson,

What will be the static compression ratio on this combo, with a normal head gasket? I'm guessing about 9.8 or 9.9:1 with the .040 over. Does that seem about right?

 

I cannot tell you scr without more info ... need:
Part Number of S-P piston?
Deck height of block? ... stock or has it been cut? ... how much?
Have heads been cut/milled? How much?

-edit- here's a handy, accurate SCR calculator from Federal Mogul aka S-P ... but you have to know the correct data to put in.
http://www.21cgt.com/FMWebCatalog/frmConversion4.aspx

If the build is a legit school (non-profit) project ... suggest a decent local machine shop might do some machinework for free ... to engender good will & help develop future business from graduates ... don't hurt to ask.

 

Stock virgin 010 block not shaved-
l2256-40 pistons
stock #186 2.02 heads, not shaved

Summit says that on a stock block this combo will make 9.72:1 @ .030 overbore. I wonder what the extra .010 will do to the comp ratio.

 

with a "normal?" gasket (9cc) I get 9.69 @ +30 ... 9.73:1 @ +40. That piston has 1.563" CD (0.022" deck clearance in uncut block) & minus 6.1cc DV ... take those specs & use w/ the calculator I linked above ... get comfortable w/ it.

 

i would have it balanced.....I bought mine (ext balanced lightweight cast crank) and also bought an ext harmonic balancer along with ext flexplate and the guy at the machine shop told me he's never seen one out of balance that bad, said his machine was shaking.....it is an ext balance crank, but should've been balanced to a 400 HB and flexplate and apparenlty it wasn't.....


technically it should be balanced and everything for the 350 balancer/flexplate......i would have it balanced, better be safe than sorry....this way, you know it's right and no guessing!

just my opinion



ryan