Ok, I pulled the balancer and hub off and put on a UD pulley. Little did I realize GM decided for some unknown reason to skip the keyway in the hub unlike all the other engines they make. I know the hub has a mark as does the timing cover at 12 o'clock but how is someone going to be confident that it's put on exactly without a key in the hub? I'm guessing GM made the LT1's so that it doesn't have to be exact for some reason???? Anyway, I've got it back on and it seems to idle fine and doesn't seem to shake when revved. It's also fine up to... well .... beyond the speed limit with no vibration. I'm just paranoid that it could be off a few degrees either way and I can't really tell for sure. What have you guys done in the past?

Thanks for any help on this.

 

it's not used to time the motor so no need for any keyway.. Although the blown car's could use one...

 

LT1 is internally balanced, what direction you put the hub back on doesn't matter one bit.

It does suck that they are not keyed from the factory though, but it makes no difference in your application.

 

Thanks for the info guys. I'm feeling a whole lot better right about now!

 

LT1's are externally balanced, via the flywheel. The front vibration dampner/pulley wasn't used for balancing so can be placed on in any position. Just don't use the arrow to reference for lash adjustment later.

 

I believe the crank pulley can only go on one way (out of the three possible directions the arrow could point) in relation to the hub.

 

Not entirely correct. I reference a document from Doug Anderson. And I quote,
HUB AND BALANCER
The balancer is a two-piece assembly with a pulley that bolts onto the hub. Separating the two made it easier to install the Optispark distributor on the assembly line and out in the field. The holes in the hub are offset, so the balancer only fits on it one way, but there’s no keyway in the hub to index the hub on the crank. This shouldn’t be a problem unless the damper was drilled at the factory to "trim" the final engine assembly.

If it was drilled a lot to compensate for an engine that was out of balance, you could end up with a shaker, depending on how everything stacked up with the remanufactured engine compared to the original engine. If you encounter a balance problem on a remanufactured LT1, try rotating the balancer assembly on the crank 90° at a time to see if it eliminates the problem.

I have yet to see one that wasn't "trimmed" by the factory with several holes drilled in it for final balancing.

If it does have a mark in it for TDC, the best place to put that mark is at either 1 or 6 TDC to start. Then work from there.

I guess I don't need to say that when you remove things in the future, mark them for reference.

 

Are the trim holes there to perform the final neutral balance of the pulley itself, or to perform fine tune balancing of the rotating assembly?

 

The pic on Shoebox's site (taken from the service manual) shows a counter weight installed in the balancer:



The service manual also states to mark the position of the balancer on the timing cover before removing it. It states to not crank the motor, or move the crank while it is off so it can be lined back up when reinstalling. It warns, installing the balancer in the wrong orientation can cause the motor to be out of balance.

Thomas.

 

Ok, that makes sense but if they keyed it then there wouldn't be any question.... It's just too easy to align it slightly off without the key. I'm thinking I have it close since I could see the light crank key mark in the hub so I used that to eyeball it back up. GM...... and I used to only complain about Fords!

 

Like we already said, the balancer only goes back on the hub one way, so it doesn't matter if you move the crank. But as speedy said, if the hub is supposed to be drilled for balance then installing it off *might* give you some bad vibes.

What speedy's post is saying is that if you look at the hub there are holes actually drilled into it to help balance it out.

 

There are no holes drilled in the hub. Speedy is correct in stating the dampner has holes drilled in it.

I mistyped in my previous post ....... let me correct it here:.

What I meant to say is, the balancer should be marked against the timing cover before removing the hub. It's the hub that can go on in the wrong orientation, because the hub is not keyed to the crank.

So even if the balancer can only bolt to the hub in one orientation, the hub itself can be installed in any orientation on the crank; and if the balancer (dampner) has a counter weight to balance the rotating assy, then it should be reinstalled in the same orientation as from the factory (or as speedy pointed out, it could vibrate).

If you look closely at the service manual picture, you'll see the holes are drilled in the dampner (not the hub) and may be filled with a weight. I have my balancer off right now, and I remember seeing one or more of these holes filled with a weight. I neglected to mark the balancer against the timing cover when I removed the hub, so I did like '95 TA' and noticed a small mark on the inside of the hub where it sat against the keyway. I will align it as best I can from this.

Thomas.

 

haha You're right I misinterpreted his post. There are 3 divots drilled into my hub, though.

 

As the illustration from the service manual shows the hub and pulley are two separate parts. The hub will have an arrow casting on it. Per the General Motors service manual if the crank has been rotoated or if the original position was not marked. Bring the number one piston up to the top of the compression stroke then install the the hub with the arrow in the 12:00 position. The pulley will only install in one position as the holes are offset.
I have found that mine will run just fine in any position.

 

Basically a LT1 engine is internally balanced in the front and externally balanced in the rear via flywheel.
I must be lucky. Every LT1 as well as my own I've installed the hub on has never had a vibration issue...