well, Im getting a new rotating assembly this week. getting it balanced ofcourse. I dont know much about how they do this. saw the other post about the scat 9000 crank bal. issues. I dont understand what is the best way to bal. this crank? if I get it internally balanced, what is the benefit of grinding off the weight from the flexplate, just to add it to the crank? should you leave the weight on the flexplate, and have the crank lightened to match the rotating assembly in the front? Im hoping my machinist knows about this. I just want to be educated w/what is supposed to be done so I'll know it if he doesnt know what he's doin. explain please.
thanks chris

 

The BEST way is to take it to a good machine shop that does all work in house and is used to doing this type of work(builds race engines) There is no need to internally balance a street engine.An LT-1 is 1/2 and 1/2 the front half is internal balance and the back half is external balanced (reason for weight on flywheel). Expect to pay $200.00-250.00 for a balance with no heavy metal.If they use heavy metal it goes up as to how many pieces are used.
Trust me,ALL balance jobs DO NOT look like the latest one posted.
A good local machine shop will know what to do and get you fixed up.
Don't take it to someone that you feel you have to quiz about how to do the job.A GOOD shop will KNOW and don't need to be educated on how it is done.They have done "one"or"two".

 

Actually, most people don't realize this but that weight on the flywheel/flexplate is there not for external balance but to make up for the part of the crank that disappeared when gm went to a one piece rear main seal. If you compare to the two flywheel/flexplate of the 2 piece rear main crank and the 1 piece you'll see why the 1 piece needs that weight. But you can have that weight moved internally if that's what makes you feel all warm and fuzzy inside. And the same thing is true for the big blocks well just the truck engines based on the 366/427.

 

That's correct, the external weight was added with the switch to a 1-piece rear seal. But I don't understand what you mean when you say "that weight on the flywheel/flexplate is there not for external balance". That's exactly why it's there, to balance the weight removed by switching to a 1-piece rear seal.

As far as what 1racerdude, I generally agree. But the cost shouldn't be all that much more for internal balancing unless you are using a heavy piston assembly. Internal balance does make me fell warm and fuzzy, but I do agree that it won't make much difference on a street or street/strip motor.

Rich Krause

 

Technically the weight is external, but the old crank was considered an internal balance even with that little couterbalnce of a rear flange. They redesigned the rear crank flange and well they cheated and stuck that weight on the flywheel/flexplate rather than try to get it back inside. If you compare a 1 pc to 2pc all the couterweights are still the same.

 

why is everything on strokermotor.com listed as external balance? so basically an internal balance is only for race eng.s or real high rpm eng.s? and it will cost more due to the use of mallory heavy metal slugs? so a normal bal. job wouldnt require the slugs? Im plannin on using srp pistons or maybe probe, but Ive heard the srp's are better. would those be considered "light" or "heavy" pistons? they will be for a 6.0" rod if that makes a diff. like I think it does.
thanks for the reply's so far
chris

 

the 3.75" stroke crank was orginally from a 400 small block, which was externally balanced. Most of the cranks built spefically for the lt-1 where the harmonic balancer was never offered with a counterweight are created so that it is internal balanced except for the mystery weight on the flywheel. I just had a scat crank balanced for my 6" rod motor and my machineist had no problems getting it to balance. he did have to drill out some on every counterweight but no heavy metal was needed.

The new 3.75" one piece rear main cranks have the 400's external balance problem corrected for use as a stroker crank in 350 blocks. They also have the mains turned down to the smaller 350's main bearing size.

Any piston for a 6" rod will be lighter than a piston for the 5.7 rod. SRP's are by far the better choice, and full blown JE's would be a step up from there. The JE makes the SRP's, and the JE's tend to be even lighter than the SRP's.

 

There is nothing wrong with internal balance,Just not necessary on a combo motor.After all is said and done the weight on the flywheel is to balance the back half of the crank EXTERNAL.
If the same crank had a 2 piece seal and the early flange it would still have a weight on the flywheel,for EXTERNAL balance..It may not be as large but it is still there.The front half of the crank is INTERNAL balanced,no weight on balancer.ALL SBC 265-283-327-350-400 were external balance from the factory-ie.weight on the balancer and flywheel.There my have been some performance series that were internal but it was on a select basis.


Internal balance,in certain set ups,(light rods and pistons) will require a ton of metal to be removed from a standard or stroker aftermarket crank and if it is not necessary,why pay the extra money to have the balance changed


IrocSS85,
There is nothing wrong with Probe pistons,I use a lot of them and never had a quality issue.They are comparably to ANY piston on the market,and they can make anything you want.

 

The advantage of a Internal Balance vs. and External with the weight on the flywheel is that the inertia of the motor is less since you have the weight/mass concentrated closer to the centerline of the mains. Same reason that ultralight cranks have mallory metal in them because the counterweights are cut down so much and the weight/mass is closer to the center of the crank.

Callies has some nice cranks that concentrate on this.

Bret