Thirim

Recently fired my my 383 lt1 (yay!!) .. Recently figured out is shakes like crazy! (boo!!)

.. made some changes along the way, just trying to confirm I didn't bugger something up.

Motor was balanced per normal 1pc SBC .
Decided midway to convert to Vette accessories (motor is in a '89TA)
Would the stock vette balancer be any different than a 4th gen? My research says no.
Would a vette balancer, 4th gen spec'd crank (if there is such a thing) .. and a 4th gen flywheel work? (again, my research says yes)

All I know at present about the shake is that the coils and plug wires are delivering spark in the right order (I went 24x.. but system working fine on old motor)

We got the car running late after getting a drivable but not nearly perfect tune... went for a drive, discovered the wicked vibration.. parked car, caught the flu and have been going crazy for the past 3 days lol.
Tonight I proved the coils and wires.

Thanks

Chimera96

typically 383 "stroker" rotating assembly are "neutral" aka "zero" balanced. You would need to then run a neutral balance flywheel or the motor will shake like a dog shiating razor blades. This balanced is refered to as "internal balanced" motor

stock LT1 is rear balanced using a weighted flexplate or flywheel and a neutral balance front damper. This is refereed to as "external balanced" motor

so if your motor was not balanced using the stock FW than you need to get the FW neutral balanced. A machine shop can do that.

Thirim

Thanks.. I'm told they balanced it with a 1pc sbc flexplate and I did have to buy some heavy metal for them to balance it. The flywheel is used, maybe someone was hacking at it before I got it. I'll work my way backwards I guess until I find it.

Chimera96

IDK if the rear balance weight is the same for Gen 1 SBC and the Gen 2 LT1

if you could get the actual flexplate they used and take that and your FW to a machine shop to have the FW matched to it

Problem with including a FW in balancing externally a 383 is the FW is a wear item whereas a flexplate is not. You will need to have the FW matched to whatever balance they had from the flexplate they used and also have your clutch then "neutral" balanced

stock LT1 FW has the weight cast on the back side. It is about 1/2' wide x 2" long. There are also various partial holes drilled into the backside of the FW and or pins (better) put in the outer holes of the FW (edge)

You can get a stock FW neutral balanced by grinding off the cast on weight and drilling or adding pins where needed. Or buy a aftermarket zero balance FW. Always confirm the balance of a "zero" FW.....mine was 26 grms off because it is the same as the weighted one just has a screw on weight....and the 4 taped holes in the FW where the weight went = 26 grms....so always have a shop confirm the balance and also then spin the clutch PP on it to zero that out if you do go internal balance on a motor

Injuneer

Interesting reference on SBC cranks.....

1955-1996 Chevy Small-Block Performance Guide: Crankshafts Manual (Part 2)

Thirim

Thanks guys
Hopefully get back to the car on the weekend. Looking like a few quick things to check but then going after the FW.. Should have had it checked before I got too far into it.
As I recall though, my engine guy used a "off the shelf" gen1 1pc flexplate.
I'm not entirely sure on the balancing myself but Injuneer's link didn't specifially mention a difference and I have personally run my stock 1989 WC T5 behind the LT1 for a short time years ago without any issues.
I owe it to myself to check the obvious things first but I'm likely going after the FW.