Is it true the crank pulley and hub are completely neutral balanced. I have found chevy to be iffy about this in the past. It's for my Lt1 motor which is still shaking the pulley even after I re-torqued everything.

 

It's my understanding that the 350 SBC is internally balanced and that the damper behind the pulley is for harmonic damping.

The L98 is pretty straight forward but not sure how the LT1 is setup with that OPTI and all.

 

No no no. The LT1 is externally balanced.

There are many threads on this topic.

If your engine is still shaking, then your harmonic dampener might be bad. How many miles on the engine? The harmonic dampener has a rubber ring between the hub and the outer, weighted ring. If this rubber starts to deteriorate, it may allow the outer ring to rotate with respect to the hub. This would change the balance of the dampener, effectively rendering your engine out of balance. Pull the dampener and look for signs of this rubber piece going bad. If it is bulging out in places, or if you can move the outer ring by hand, replace the dampener. Also look to make sure there are weight/weights in at least one of the holes. If someone replaced the dampener and didn't put weights in the new dampener in the exact places they were located on the old dampener, the engine will be unbalanced.

If the dampener is ok, then you may have a miss. Check your plugs and wires.

L98s may be different. Don't know, I don't have an L98.
:cheers:


[Modified by HammerDown, 2:25 PM 2/9/2004]

 

Yes, the LT1 is external balance, however I believe it is all done in the flywheel. That means the balancer/pully/hub assy should be neutral balance. That is what I was told, but I haven't personally verified it.

 

Nope, the harmonic dampener has little holes all around the perimeter. In one or more of these holes, you will find a little, pellet-shaped weight. The location of the weights (which holes they are in, and how many) will be different from engine to engine.

Look in your service manual. It warns that when you replace the dampener, you should match the amount of weight and location of the weight to the old dampener.

The dampener, like the flywheel, is neutrally balanced (no weights). You have to balance them with the weights to your particular engine.

 

Well, the balancer looks like it is fine. I'm going to look for a miss. I found a couple of codes(15 and 43). Apparently I busted the coolant sensor while trying to re-torque the hub, so that is the code 15. Code 43, I'm not to sure on this one. Is says knock sensors or ESC fault. I put 2 brand new knock sensors in when I built the motor and I had not had a problem with the system before. However, there are a couple of issues I'm going to look into. I did the cut-back spark plug thing, maybe it was a mistake. Also, I have open headers which are not helping anything, that will all get fixed this weekend, then we will see if the problem persists.

A question, what else besides the knock sensors are in the ESC system?

 

OBD-I or OBD-II?

 

I

 

I think it basically just uses timing data from the Optispark, and info from the knock sensors to determine spark control.
I may be overlooking something, though.

 

Yep, you are right on the balancer. I checked mine out. I hope my underdrive pulley is neutral balance. I internally balanced my 383 and I never checked the new pulley. But I didn't add any weight to it either.

I don't agree with you though on the flywheel. I had to have it neutral balanced, and it is nowhere near neutral with all the small pins around the perimeter removed. There is a cast in counterweight bulge on the engine side that basically all has to be removed also.

 

I think the flywheels can be made neutrally balanced but I know on mine they had to pull a giant weight that was attached to the back of it off to get it balanced.

As to the pulleys, I was doing some reading and I read that the pellets within the pulley are to balance the pulley out, not the whole rotating assembly. So that would mean that it is neutrally balanced. This was on some online instructions for installing a fluid-dampner on an LT1. So, you should be alright as long as the weight of the pulleys is the same which I am sure they are designed to be the correct weight.

 

Is this the stock flywheel? I would think that they were all neutrally balanced from the factory (without weights), or close to it, because in the FSM it again states that you should use the exact same amount and location of weights when replacing the old flywheel. Then again, all the factory flywheels may have been equally "unbalanced" (that cast in bulge you were talking about), so adding weights to match the old flywheel would have still made sense.

I will still stand by my assertion that the LT1, at least in 92-96 Corvettes, is an externally balanced engine.

 

If the weights were used to balance the pulley (to itself, and not the engine), then that would mean that each pulley had a different amount and "location" of unbalance. Therefore, it wouldn't make sense for the FSM to tell the mechanic to install the weights in the exact same location, in the same amount as the old dampener. Sooooo, the dampener must be balanced to a specific engine.
Here's the way it worked at the factory. The engine was completely assembled. The flywheel and the harmonic dampener (both neutrally balanced, or close to it) are installed on the crank. The engine is run and the amount of vibration measured (similar to a tire balancing machine). Weights are added to the dampener and flywheel as necessary to balance the entire rotating assembly.

Do you have the Fluid-dampener instructions?

 

Yeah, this was an oem dual mass I was working with for an LT1. I think I came to the same conclusion that you have said. All of the flywheels out of the box have the same amount of unbalance. My guess is that after doing enough of them, they figured out that as long as all the cranks, rods, etc met specs, there would be a certain amount of unbalance in rotating assy. So they cast in a large counterweight on the flywheel to account for this for the most part. But, because there are small tolerance differences from engine to engine (although in spec) that is what the holes around the perimeter are for. The small pellets that go in the flywheel basically fine-tune that particular unit to the rotating assembly. Again, this is my best guess. All I do know is that I watched the machinist balance it and a lot of material had to be removed around the cast bulge to get it neutral. And we checked balance with the dual masses locked in several different positions. Some say to lock it with the internal dampener loaded. Others said to lock it in the neutral position. I ended up locking it neutral and found that it was about 2 grams out of balance at either end of the dual mass movement.

I can't verify the pulley balance though. I was told the factory had a machine that would spin balance the assembled engine. Don't know if that is true or not. I can't understand though why they would add weight to both the flywheel and balancer to get balanced. I would think one or the other would be fine since they are all bolted together.

 

Here is what I found.

(all stock LT1's are neutral on the front damper, but externally balanced against the flywheel)

Now that was just something on someone's website, but this link shows the install instructions for the fuild dampner with LT1 part number underneath the internally balanced engines. http://www.fluidampr.com/install_ins...ons_fluid.html

Now here is a question, are these fluid dampers worth it. For instance, if I have to replace my damper, I am looking at getting one of these or an underdrive pulley. Since I can only go with one, which one do I choose? I spin my 383 to 6400rpms, or I will once it is broken in. So, hmmm. The underderive pulley is definitely cheaper, by a long shot.

 

I'm using an underdrive. But I have to say my main reason for using it is because it was given to me in the mass of parts that I got. I have an oem balancer too, but I wanted to try the underdrive.

 

Are the power gains actually noticeable or is it just junk? I am shying away from it a little because I run a disc-changer, an aftermarket iginition, and I plan on getting an electric water-pump. I could still do it with the alternator overdrive pulley but that would negate some of the effect of the pulley, what to do...

 

Well, I guess I should of said the underdrive is what I will be using. I haven't used it yet, and I don't have any before experience on this car to tell the difference.

I think you have the alt pulley backward though. Going to a larger alt pulley will have the same effect as a smaller crank pulley - it will turn slower relative to the crank. My pulley set is a 2 piece - a smaller crank pulley and a larger alt pulley. Using both will make the alt turn the slowest. What I plan to do is use only the crank underdrive and that will put the alt somewhere between the oem setup and the complete underdrive setup. Make sense?