LT 383 Balance Issues - vibration
Thread Starter
Racer
Joined: Oct 2001
Posts: 444
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Re: LT 383 Balance Issues - vibration (Denny McLain)
When you internally balance any motor it should have the crank, rods, pistons, flywheel, balancer hub, all in sink with the balance. Anything else and you asking for trouble.
Thread Starter
Racer
Joined: Oct 2001
Posts: 444
Likes: 0
Re: LT 383 Balance Issues - vibration (Denny McLain)
Denny, the 400 balancer will not work on your LT motor, It's to big (clearance wize) and you also have pully issues. I just had my 383 LT4 balanced about a month ago, I too was told that the crankshaft was set up internally balance. And it could'nt have been more wrong.. I think you've already found your answer by trying the diffrent flywheels and such.. The motor needs to be rebalanced..
[Modified by JB'S LT4, 7:04 PM 6/15/2002]
[Modified by JB'S LT4, 7:04 PM 6/15/2002]
Safety Car
Joined: May 2002
Posts: 4,659
Likes: 82
From: Toronto ontario
Re: LT 383 Balance Issues - vibration (JB'S LT4)
Before you get into costly things try the ATI dampener. I am going with that for my 388 LT1. it reduced accessory speed by 10 % as well.. an added bonus. It will dampen the vibrations BUT, it will not stop them. If your motor was designed using external balance and you cant use the proper dampener ur ina fuss. Only option if you want to do it properly is pull it apart and rebalance it. Think about it, with that kind a of a motor wouldnt you want it perfect instead of using bandaid fixes??
Racer
Joined: Nov 1999
Posts: 434
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From: Plaistow NH
Re: LT 383 Balance Issues - vibration (Denny McLain)
I think there is a standard for balancing stroker motors. Which is, each one gets balanced before it goes together and in the car.
I *think* all these 383's running around with stock flexplates and flywheels (like mine) are Internally balanced. And the externaly balanced motors have weights added to the flexplate/flywheel (which you already know)
If he is saying it was balanced for external weights, then he should have that info! Ask him where the flywheel is! (the one he used to balance your motor)
If he does not have that info, then it's lookin like the motor might have to come back out. If I remember right, the motors get balanced all together, the crank, the rods, the pistons and the flywheel and balancer. Trying to balance it any other way is asking for trouble, you've already spent all this money, dont you want to do it right???
It should have been right the first time I know!!
Bill
I *think* all these 383's running around with stock flexplates and flywheels (like mine) are Internally balanced. And the externaly balanced motors have weights added to the flexplate/flywheel (which you already know)
If he is saying it was balanced for external weights, then he should have that info! Ask him where the flywheel is! (the one he used to balance your motor)
If he does not have that info, then it's lookin like the motor might have to come back out. If I remember right, the motors get balanced all together, the crank, the rods, the pistons and the flywheel and balancer. Trying to balance it any other way is asking for trouble, you've already spent all this money, dont you want to do it right???
It should have been right the first time I know!!
Bill
Team Owner
Joined: Apr 2001
Posts: 22,267
Likes: 3
From: Dallas TX
Re: LT 383 Balance Issues - vibration (BillRed85)
I *think* all these 383's running around with stock flexplates and flywheels (like mine) are Internally balanced. And the externaly balanced motors have weights added to the flexplate/flywheel (which you already know)
Burning Brakes
Joined: Nov 2001
Posts: 1,241
Likes: 9
From: Houston TX
Re: LT 383 Balance Issues - vibration (Denny McLain)
denny, ya, but what if they balanced your rotating assembly like a sbc, instead of an LT series. then you can't put the proper balancer on the front of your engine, so you'll never meet the spec.
Safety Car
Joined: Mar 2000
Posts: 3,620
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From: Hillsboro OR
Re: LT 383 Balance Issues - vibration (Denny McLain)
The 350 LT1 and LT4 motors come stock with neutral balance balancer (no external weight on balancer) and external balance weight on the flywheel.
Your balancing vibration problem maybe from several possible sources:
The stock LT1 and LT4 balancers have places on the balancer for an external weight that GM used in some cases to fine tune the balance of the engine. Yours may have an external weight on the balancer that the shop would may not have taken into consideration when they did the motor balance.
Also,
The clutch and pressure plate assy are supposed to be lined up on the stock dual mass flywheel also using a mark on the flywheel and a mark on the pressure plate. GM does not always mark the flywheel so its possible to get that miss aligned too.
My 383 had some vibration problems too but they were not severe enough to worry about. I had to take my motor apart recently because of oil pressure problems and I am going to get the balance problem fixed while I get the rest of the stuff fixed.
Your balancing vibration problem maybe from several possible sources:
The stock LT1 and LT4 balancers have places on the balancer for an external weight that GM used in some cases to fine tune the balance of the engine. Yours may have an external weight on the balancer that the shop would may not have taken into consideration when they did the motor balance.
Also,
The clutch and pressure plate assy are supposed to be lined up on the stock dual mass flywheel also using a mark on the flywheel and a mark on the pressure plate. GM does not always mark the flywheel so its possible to get that miss aligned too.
My 383 had some vibration problems too but they were not severe enough to worry about. I had to take my motor apart recently because of oil pressure problems and I am going to get the balance problem fixed while I get the rest of the stuff fixed.
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Le Mans Master
Joined: Jul 2001
Posts: 8,183
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From: Santa Maria, CA
Re: LT 383 Balance Issues - vibration (AquaMetallic94LT1)
The clutch and pressure plate assy are supposed to be lined up on the stock dual mass flywheel also using a mark on the flywheel and a mark on the pressure plate. GM does not always mark the flywheel so its possible to get that miss aligned too.
Burning Brakes
Joined: Nov 2001
Posts: 1,241
Likes: 9
From: Houston TX
Re: LT 383 Balance Issues - vibration (Denny McLain)
denny, i think you missed my point. pre LT sbc engines have counterweighting on the balancer. but LT balancers are basically neutral. so if the shop balanced your engine to regular sbc standards, then it will never be balanced in your car. (nothing but an LT series balancer will easily fit your car.)
in other words, even if you could figure out how much weight to add to a flywheel to account for the loss of front external counterweighting, then you're getting into an ugly situation where all of the weight is on one end. the stock LT series cranks have a heavier front counterweight, so there isn't as much of this weight bias to one end. (like putting all of the balance weights for wheels on the inside, it will never be balanced as well as if you put weights on the outside, inside, and middle.)
lastly, you said there's heavy metal on the crank. not completely unusual for even externally balanced 383s, but it does raise some doubt. what brand of crank is it? what pistons/rods? with most of the parts used nowadays, i think externally balanced strokers rarely need heavy metal to balance.
edit: scan the balance sheet, and let us have a look!
[Modified by MSR, 7:47 AM 6/17/2002]
in other words, even if you could figure out how much weight to add to a flywheel to account for the loss of front external counterweighting, then you're getting into an ugly situation where all of the weight is on one end. the stock LT series cranks have a heavier front counterweight, so there isn't as much of this weight bias to one end. (like putting all of the balance weights for wheels on the inside, it will never be balanced as well as if you put weights on the outside, inside, and middle.)
lastly, you said there's heavy metal on the crank. not completely unusual for even externally balanced 383s, but it does raise some doubt. what brand of crank is it? what pistons/rods? with most of the parts used nowadays, i think externally balanced strokers rarely need heavy metal to balance.
edit: scan the balance sheet, and let us have a look!
[Modified by MSR, 7:47 AM 6/17/2002]
Le Mans Master
Joined: Jul 2000
Posts: 5,012
Likes: 5
From: OKC OK
Re: LT 383 Balance Issues - vibration (Denny McLain)
What a crappy story :sad:
Please let us know how the shop resolves your problem. If they keep jacking you around, please disclose their name. I think the guys on this board are smart enough to draw their own conclusions. Keep in mind that if people don't warn others, we might still not know about a certain viper/vette tuner in Texas.
Please let us know how the shop resolves your problem. If they keep jacking you around, please disclose their name. I think the guys on this board are smart enough to draw their own conclusions. Keep in mind that if people don't warn others, we might still not know about a certain viper/vette tuner in Texas.
Burning Brakes
Joined: Nov 2001
Posts: 1,241
Likes: 9
From: Houston TX
Re: LT 383 Balance Issues - vibration (Denny McLain)
denny, no need to scan and/or post the balance sheet, it's pretty rudimentary. it doesn't tell you what the counterbalance spec of the flexplate/flywheel was, just that one was used.
it says the engine was balanced with a "stock," counterbalanced flexplate, and with no counterweighting for the balancer. one slug of heavy metal in the front counterweight, to offset not having a counterweighted balancer.
it appears to be proper for an LT series engine, then. so now you're left with trying to decide if the sheet is bogus, or if there's something wrong with some additional parts you have (clutch?).
since you verified that the crank does have a heavy metal slug (is the sheet right, just one slug in the frontmost counterweight?), then the engine is balanced to something. but, if you've tried a neutral, counterweighted, and even stock flywheel, and you're reasonably certain there aren't clutch (or other) issues, it might be time to cut your losses and have a local shop rebalance everything.
ymmv, dunno what else to say. sorry, dude. good luck!
it says the engine was balanced with a "stock," counterbalanced flexplate, and with no counterweighting for the balancer. one slug of heavy metal in the front counterweight, to offset not having a counterweighted balancer.
it appears to be proper for an LT series engine, then. so now you're left with trying to decide if the sheet is bogus, or if there's something wrong with some additional parts you have (clutch?).
since you verified that the crank does have a heavy metal slug (is the sheet right, just one slug in the frontmost counterweight?), then the engine is balanced to something. but, if you've tried a neutral, counterweighted, and even stock flywheel, and you're reasonably certain there aren't clutch (or other) issues, it might be time to cut your losses and have a local shop rebalance everything.
ymmv, dunno what else to say. sorry, dude. good luck!
