middle 2 mains lost
- Thread starter BMFB
- Start date
BMFB
Not to scale
Re: middle 2 mains lost
No, it drove fine. the only vibration I ever got was under a heavier load at around 1600 rpm, 4rth gear going from about 38-48. i always attributed that to the poly mounts. Other than that it ran smooth. I told my builder about the externaly balanced flex plate too, so he knew what I had at least when he built it.
No, it drove fine. the only vibration I ever got was under a heavier load at around 1600 rpm, 4rth gear going from about 38-48. i always attributed that to the poly mounts. Other than that it ran smooth. I told my builder about the externaly balanced flex plate too, so he knew what I had at least when he built it.
RealFastV6
@jb_and_his_coffee
Re: middle 2 mains lost
It's a theory - but did he not have the flexplate when he balanced the motor?
It'd be a pretty rookie move (for an engine builder) to balance the rotating assembly without a flexplate and then bolt up a flexplate that's obviously got weights on it.
It's a theory - but did he not have the flexplate when he balanced the motor?
It'd be a pretty rookie move (for an engine builder) to balance the rotating assembly without a flexplate and then bolt up a flexplate that's obviously got weights on it.
BMFB
Not to scale
Re: middle 2 mains lost
You know I don't remember? I *think* he did the first time when I rebuilt the whole thing myself and I had him balance it. The second time when the Converter blew and took out my thrust bearing and he said he would do the whole thing for free....I don't think he did...I wish I could remember that more clearly...But I don't think he did...
You know I don't remember? I *think* he did the first time when I rebuilt the whole thing myself and I had him balance it. The second time when the Converter blew and took out my thrust bearing and he said he would do the whole thing for free....I don't think he did...I wish I could remember that more clearly...But I don't think he did...
Re: middle 2 mains lost
All crankshafts with a one piece rear seal are internally balanced and must use neutrally balanced flex plate that is equipped with a weight. The weighted flex plate is to compensate for the lack of a counter weighted flange on the crankshaft with a one piece seal. The weighted flex plate becomes neutral balanced after it is attached to the crankshaft. A weighted flex plate will only fit a internally balanced crank that has a one piece rear seal for that reason. Do not remove the weight from the flex plate or attempt to neutral balance a weighted flex plate.
All crankshafts with a one piece rear seal are internally balanced and must use neutrally balanced flex plate that is equipped with a weight. The weighted flex plate is to compensate for the lack of a counter weighted flange on the crankshaft with a one piece seal. The weighted flex plate becomes neutral balanced after it is attached to the crankshaft. A weighted flex plate will only fit a internally balanced crank that has a one piece rear seal for that reason. Do not remove the weight from the flex plate or attempt to neutral balance a weighted flex plate.
Don W.
Stab it and steer it
Re: middle 2 mains lost
With respect,
I'm sorry but this doesn't make sense. Internally balanced means no weights on the flex plate or damper. A flex plate, by itself, can't have a weight and be "neutrally balanced." Can it?
Did our engines ever have a two piece seal with a counter weight flange on the crank?
Regardless, doesn't the entire assembly (crank, rods, pistons, flex plate, and damper) become neutrally balanced when balanced "as an assembly?"
Just wondering...
With respect,
I'm sorry but this doesn't make sense. Internally balanced means no weights on the flex plate or damper. A flex plate, by itself, can't have a weight and be "neutrally balanced." Can it?
Did our engines ever have a two piece seal with a counter weight flange on the crank?
Regardless, doesn't the entire assembly (crank, rods, pistons, flex plate, and damper) become neutrally balanced when balanced "as an assembly?"
Just wondering...
Throws
Active member
Re: middle 2 mains lost
Damn dude... That's some bullshit. Hope he's making things good?
-P
Damn dude... That's some bullshit. Hope he's making things good?
-P
Don W.
Stab it and steer it
Re: middle 2 mains lost
To some extent it will depend on what was changed. For example if you toast a piston and new piston of the same mfg is made to equal the weight of the old (and other pistons) then a re-balance would not be necessary. But yes, the ENTIRE assembly has to be balanced. That means everything. pistons (to the lightest), rods (each end), weight of rings is added in and weight of rod bearings is added in, plus damper and flywheel or flexplate regardless if they have a weights on them or not.
My example? I fried a crank also. My shop had all the weights from the original balance so all I had to take him was the new crank, flexplate and damper.
HTH
To some extent it will depend on what was changed. For example if you toast a piston and new piston of the same mfg is made to equal the weight of the old (and other pistons) then a re-balance would not be necessary. But yes, the ENTIRE assembly has to be balanced. That means everything. pistons (to the lightest), rods (each end), weight of rings is added in and weight of rod bearings is added in, plus damper and flywheel or flexplate regardless if they have a weights on them or not.
My example? I fried a crank also. My shop had all the weights from the original balance so all I had to take him was the new crank, flexplate and damper.
HTH
Re: middle 2 mains lost
The 1986 and later 4.7L V8 and 4.3L V6 engines have a one piece rear seal and are internally balanced in front with a neutral balanced damper and externally balanced in rear with a counter weighted flex plate. However, the counter weighted flex plate becomes neutral balanced after it is bolted to the crankshaft that has a one piece rear seal. After the crankshaft has been balanced according to the equalized weights of the rods and pistons, and the neutral balanced damper and counter-weighted flex plate is attached to the crankshaft, the entire rotating and reciprocating assembly is completely internally balanced.
Be advised, some engine shops do not have the correct bob weights that fit a 4.3L V6 crankshaft with 30 degree offset rod journals. That is because the 4.3L V6 engine is considered a "utility" engine and is not normally used in high performance vehicles.
Shops often try to balance a 1986-and later 4.3L V6 engine as if it was a 1978-1985 4.3L V6 engine which does not have a one piece rear seal. In order to do that, they must use a 1986 and later flex plate and remove the counterweight and then zero balance the flex plate. A zero balanced flex plate will throw off the balance of a 1986 and later crankshaft. A 1978-1985 flex plate has a different bolt circle and will not fit a 1986 and later crankshaft.
When the shop removes the counterweight from the 1986 and later flex plate and zero balances that flex plate, it becomes impossible to internally balance the 1986- and later 4.3L v6 engine.
The 1986 and later 4.7L V8 and 4.3L V6 engines have a one piece rear seal and are internally balanced in front with a neutral balanced damper and externally balanced in rear with a counter weighted flex plate. However, the counter weighted flex plate becomes neutral balanced after it is bolted to the crankshaft that has a one piece rear seal. After the crankshaft has been balanced according to the equalized weights of the rods and pistons, and the neutral balanced damper and counter-weighted flex plate is attached to the crankshaft, the entire rotating and reciprocating assembly is completely internally balanced.
Be advised, some engine shops do not have the correct bob weights that fit a 4.3L V6 crankshaft with 30 degree offset rod journals. That is because the 4.3L V6 engine is considered a "utility" engine and is not normally used in high performance vehicles.
Shops often try to balance a 1986-and later 4.3L V6 engine as if it was a 1978-1985 4.3L V6 engine which does not have a one piece rear seal. In order to do that, they must use a 1986 and later flex plate and remove the counterweight and then zero balance the flex plate. A zero balanced flex plate will throw off the balance of a 1986 and later crankshaft. A 1978-1985 flex plate has a different bolt circle and will not fit a 1986 and later crankshaft.
When the shop removes the counterweight from the 1986 and later flex plate and zero balances that flex plate, it becomes impossible to internally balance the 1986- and later 4.3L v6 engine.
Re: middle 2 mains lost
The Chevrolet 90 degree V6 engine family was introduced in 1978. They were 200, 229 and 262 cu. in. and had the same stroke, deck height, have the same firing order, used the same casting dies, and were based on the 350 cu.in V8 . The only differences in the 1978 - 1994 V6 engine w/o balance shaft is the bore size.
The bob weight balance factor of the '78 -'94 V6 engine without balance shaft is 50% reciprocating weight and 100% rotating weight. I wrote before, some shops do not have bob weights for the Chevrolet V6 engine with 30 degree offset rod journals..
The Chevrolet 90 degree V6 engine family was introduced in 1978. They were 200, 229 and 262 cu. in. and had the same stroke, deck height, have the same firing order, used the same casting dies, and were based on the 350 cu.in V8 . The only differences in the 1978 - 1994 V6 engine w/o balance shaft is the bore size.
The bob weight balance factor of the '78 -'94 V6 engine without balance shaft is 50% reciprocating weight and 100% rotating weight. I wrote before, some shops do not have bob weights for the Chevrolet V6 engine with 30 degree offset rod journals..
RealFastV6
@jb_and_his_coffee
Re: middle 2 mains lost
Interesting. Sounds like we've got some theories.
Let us know how it ends.
Also learned that the end of the crank is different between a counterweighted flexplate and non-counterweighted flexplate - did not know that.
Interesting. Sounds like we've got some theories.
Let us know how it ends.
Also learned that the end of the crank is different between a counterweighted flexplate and non-counterweighted flexplate - did not know that.
dgoodhue
BuSTeD 4.3
Re: middle 2 mains lost
The 200-229 have odd fire cranks. I would guess the blocks are not interchangeable either. You definitely can't bore out a 305 (which the 229 is based) into a 350.
The 200-229 have odd fire cranks. I would guess the blocks are not interchangeable either. You definitely can't bore out a 305 (which the 229 is based) into a 350.
Don W.
Stab it and steer it
Re: middle 2 mains lost
This, (50/100%) as I understand, is common. I did not know about the bob weight issue. Is that a journal width issue or?
This, (50/100%) as I understand, is common. I did not know about the bob weight issue. Is that a journal width issue or?
ed hess
race or get outta the way
Re: middle 2 mains lost
having made that mistake myself I can say the vibration you felt is because of using the internally balanced crank with externally weighted flexplate.
I had that also. took the weight off, carefully smoothed the flywheel and after that there was no vibration.
End of story, weather or not that took out the 2 inner mains... who knows.
But even so internally balanced has to match to unweighted flexplate and externally balanced to weighted flexplate.
having made that mistake myself I can say the vibration you felt is because of using the internally balanced crank with externally weighted flexplate.
I had that also. took the weight off, carefully smoothed the flywheel and after that there was no vibration.
End of story, weather or not that took out the 2 inner mains... who knows.
But even so internally balanced has to match to unweighted flexplate and externally balanced to weighted flexplate.
Throws
Active member
Re: middle 2 mains lost
Opinion on the billet main caps? They seem to be fairly popular with the GN crowd.
-P
Opinion on the billet main caps? They seem to be fairly popular with the GN crowd.
-P