Buddy of mine has a 350 with a Scat stroker crank. It's a 69 block bored .040 over, and he's using an aftermarket balancer with the original flexplate that came with the engine. Is the original 69 350 internally or externally balanced?? Does the Scat stroker crank require internal or external balancing?? This thing vibrates so bad at 2300 RPM that it would take a week to get rid of Janice's smile if she went out in it.
He had a falling out with the Guy that built the engines, so it's impossible to even find out who balanced it to get specs. It's all new with less than 500 miles.
Your friends 350 should be factory internally balanced. Lots of SBC strokers used the 400 crank and needed to use the balancer AND flexplate from a 400. If the scat crank is externally balanced, he'll need a 400 balancer and flexplate or the aftermarket equivalent.
I'd suggest contacting Scat directly with the part number from the crank (so they know exactly which crank you are talking about).
-- Edited by DB Cooper on Wednesday 21st of May 2014 06:08:27 PM
Question: Is scat 383 crank balanced if so do i still need 400 balancer?
Answer: No they are not balanced and full rotating assy. must be balanced together at machine shop. In fact there is a skull and cross bones warning about this on top of every scat crankshaft box and also a yellow paper thats inside the box that says same thing.
What damper and flexplate/flywheel you need depends on which crank you have.
Scat makes 2 designs of the 383 stroker cranks. 1 is external balance, needing the 400 small block damper and flywheel/flexplate Other is the internal balanced 383 stroker crank. It needs the std sbc damper and flexplate like used on the 350
Me again,
I wonder if the engine shop even balanced anything to begin with. I always thought they required the balancer and flexplate that was going to be used with the engine, to be balanced with the engine when the engine requires an external balance.
-- Edited by DB Cooper on Wednesday 21st of May 2014 06:21:55 PM
Here's some stuff I found on the Scat website. This is for their "rotating assembly" and not just a crank. One kit is internally balanced and one kit is externally balanced. Take a look at the external kit, it states "external balanced rotating assemblies include flexplate and damper". It looks like I was right about needing the balancer and flexplate when balancing an external balance assembly. It definitely looks like your friend needs to find out which crank was used and if it is an external balance crank, he should have been given the balancer AND flexplate to be used with that engine.
Chevy Small Block Series 9000
Cast Stock Replacement 2 - pc Rear Seal
Street Performance Rotating Assemblies
Series 9000 Cast Cranks, I-Beam Connecting Rods with 3/8"
Wav Loc Bolts, HYPER Pistons, Rod Bearings, Main Bearings, Rings
I'm wondering if it's possible that his crank is the internally balanced one (which would explain why the engine shop didn't supply him with a flexplate) and someone else (speed shop?), after hearing he's got a 350 stroker, made an assumption and sold him the wrong balancer (thinking he needed the 400 style). If that's the case, he has the wrong balancer but the correct flexplate. I don't know how much of an imbalance that would create, but it can't be good.
Shouldn't the engine shop have supplied the buyer with paperwork describing exactly what parts have been used in the build?
You could try a 400 small block flywheel and see if that helps also the 400 had half the outer ring missing on the damper check to make sure these are not on there now which they shouldn't be because you said it stock 350 stuff but I'm thinking he will have to balance the assembly I bought a original BB 73 chev pu the guy had just put a 350 in and vibrated very bad he was mad and sold it to me cheap,I took a air chisel and knocked the weight off the flywheel drove it for a couple years run perfect.
Here's some stuff I found on the Scat website. This is for their "rotating assembly" and not just a crank. One kit is internally balanced and one kit is externally balanced. Take a look at the external kit, it states "external balanced rotating assemblies include flexplate and damper". It looks like I was right about needing the balancer and flexplate when balancing an external balance assembly. It definitely looks like your friend needs to find out which crank was used and if it is an external balance crank, he should have been given the balancer AND flexplate to be used with that engine.
Chevy Small Block Series 9000 Cast Stock Replacement 2 - pc Rear Seal Street Performance Rotating Assemblies Series 9000 Cast Cranks, I-Beam Connecting Rods with 3/8" Wav Loc Bolts, HYPER Pistons, Rod Bearings, Main Bearings, Rings
Hey thanks for doing the leg work for me. This engine is a can of worms because the owner has no clue what components were used, and the builder won't tell him. I think his only way out of this mess is to tear it appart like DaveM said. Crappy situation.
This thing vibrates so bad at 2300 RPM that it would take a week to get rid of Janice's smile if she went out in it.
He had a falling out with the Guy that built the engines, so it's impossible to even find out who balanced it to get specs. It's all new with less than 500 miles.
Just tell him to bring it up here then and drop it off at my place.......no use to him
Before I'd tear it apart I think I'd verify that the balancer he's got on it now matches the flexplate (meaning both are for internally balanced engines).
If that doesn't fix it, then (as far as I am concerned) it looks like he has an external balanced set up and not only needs the correct balancer and flexplate, but also needs them balanced with the crank.
If its together I would try the 400 flywheel before ripping it down, if its a 383 it should be a 400 crank unless its scats own crank. is it standard or auto trans? why im asking is I put a standard behind the 400 I had in my buick, I didn't know at the time I had to have a special flywheel, so I found a balance plate on ebay, 40 bucks to let you use a normal flywheel with a 400 or 454 bb.
Don't run it much until you figure out the imbalance issue. You will take out the main bearings.
If you drop the pan, there will be a part number stamped into the crank that you can look up on SCAT's site. IIRC its on the front counterweight. Is it a cast or forged crank? The cast 383 cranks require a 6" rod for internal balance (larger counterweights). The forged cranks from SCAT also require a 6" rod for internal balance if just drilled, or a 5.7 rod and a bunch of mallory metal.
Unless you buy a complete balanced kit, none of the SCAT cranks come balanced. They will tell you what bobweight they generally will balance to out of the box - for a SBC its generally around 1850 grams.
Don,t drive it. Take it apart and find out whats going on. Had a Buick years ago and rebuilt it . replaced 1 piston bought at G M dealership and it was light. Shook pretty bad.
I bought a original BB 73 chev pu the guy had just put a 350 in and vibrated very bad he was mad and sold it to me cheap,I took a air chisel and knocked the weight off the flywheel drove it for a couple years run perfect.
