[grivera]

Pontiac balancers are all neutral balanced, IIRC. The difference with an internally balanced engine would be the flex plate/flywheel would also be neutral balanced vs an own where the flex plate/flywheel have an imbalance.

[Lee]

If you have access to spares, maybe try a different carb and distributor. Those are easier to swap around than flywheels :-)

[Tim Corcoran]

Update:

Removed the trans, clutch, pressure plate and flywheel. Installed two different OEM flex plates and the vibration is still present at 1800 RPM. I did notice that the clutch springs have been making contact with the bolts attaching the flywheel. The flywheel is .135 under the OEM spec of .960. Those issues are unrelated to the vibration but need to be resolved. I am baffled as the what is causing the vibration. It appears the flywheel is an aftermarket SFI unit. (see pic)

[Tim Corcoran]

Originally Posted by Lee

If you have access to spares, maybe try a different carb and distributor. Those are easier to swap around than flywheels :-)

Since the vibration is still present during deceleration with my food off the gas I doubt it is carb or timing.

[Holeshot71]

Maybe try a neutral balanced flywheel/flexplate if you haven’t yet?

[steve25]

Take advantage of doing this experiment if you still have the clutch removed.

Take one of the clutch mounting bolts ( or a long enough different bolt ) and stack two big washers under when you bolt it to the flywheel.

Start the motor and hopefully one of 3 things will then take place .

1) the vibration will be less or gone.

2) there will be no change .

3) the vibration will be worse.
If the vibration is worse the move the bolt washer combo across to the other side of the flywheel as best as possible to be 180 degrees out .

Try this in all six clutch mounting bolts holes or until you hopefully get some kind of result either way.

[Tim Corcoran]

I borrowed a damper from a friend and was going to swap the balancer to see if by chance it was the problem. when trying to remove the balancer I noticed excessive crank movement. I put a dial indicator on it and found that the crank endplay is .018. I'm not sure that's what is causing the vibration but it may be related to some internal issue. I know .018 is way out of spec looks like I will need to pull the engine tear it down and see what's going on.

[HWYSTR455]

Well, that's kind of a bummer, but it does give you the opportunity to answer all the lingering questions.

From here out, you will KNOW what's in there.

I'm still thinking balancer, even after grivera reminded me about the balancers.

Since you're planning on pulling it, would be an easy time to align the bell too. If it's not a blowproof, would suggest getting one, regardless of power level.



.

[HWYSTR455]

Since it looks like you will be purchasing a new flywheel, I suggest have it surface (cleanup) and balance checked.

I am not the only one that's seen new flywheels being out of whack, was comments in another thread about that...


.

[ID67goat]

Originally Posted by Tim Corcoran

I borrowed a damper from a friend and was going to swap the balancer to see if by chance it was the problem. when trying to remove the balancer I noticed excessive crank movement. I put a dial indicator on it and found that the crank endplay is .018. I'm not sure that's what is causing the vibration but it may be related to some internal issue. I know .018 is way out of spec looks like I will need to pull the engine tear it down and see what's going on.

Do you know what year that engine was built and what internals are in it?

I had a similar experience as you with the balanced rotating assembly that was actually out of balance causing vibration issues and then found that the Eagle cast crank ate the thrust surface because the machined surface was too rough.

Tear down is definitely the right choice as I bet you will find that bearing material has probably messed up the crank and bearings anyway…at least that is what happened with me.

[Joe-Touring]

Do you know if Butler did the build or just supplied the stroker kit? I’ve seen on other threads where someone bought a stroker kit that was advertised as balanced, and it was anything but

[PAUL K]

Originally Posted by Joe-Touring

Do you know if Butler did the build or just supplied the stroker kit? I’ve seen on other threads where someone bought a stroker kit that was advertised as balanced, and it was anything but

You are correct. Years ago I was vocal about this and pointed out only one rod is taken out of the package on these "balanced" assemblies. Welp they must've been listening, now most of the time the other seven rods are at least open but never taken out of the package. The seven unwrapped pistons are humourous also.

[Tim Corcoran]

Butler built this engine in December of 2012 and it did come with Ross pistons, Eagle BBC 6.8 rods, and Eagle 3.25 X4.25 cast crank. If the thrust bearing surface was not machined correctly and chewed up the thrust bearing I'm not sure if that would cause a vibration isolated to the 1,800 RPM range.

[Dragncar]

I bought a early cast Eagle crank from Indian Adventures back in the day. Gave it to Whitmore and the note on the crank when his crank guy balanced it was "Thrust VERY Rough". He polished it out but I never ran that crank.
A friend of mine bought one of them in the early 2000s with a "balanced" rotating assembly. Did the billet cap deal on a 400 block. It never made a good pass. It shook so bad he shut it down on the first attempted pass. In the pits he could barely turn it over.
He got out of racing after that.

[ID67goat]

Originally Posted by Tim Corcoran

Butler built this engine in December of 2012 and it did come with Ross pistons, Eagle BBC 6.8 rods, and Eagle 3.25 X4.25 cast crank. If the thrust bearing surface was not machined correctly and chewed up the thrust bearing I'm not sure if that would cause a vibration isolated to the 1,800 RPM range.

Sorry, was talking about 2 separate issues. The balance was off because I don’t think they actually did any balancing as advertised. And the Eagle cast cranks were known for a while to be machined too rough and eat thrust bearings. My parts were from some years earlier than yours…from 2003.

[SRGN]

Sucks that you found the thrust issue, but it's a blessing at the same time since you caught it early. When you have the engine apart, look for mallory metal in the pan. I had one last year that was done by an engine shop, when they balanced it they put the mallory in the counterweight from the side instead of front to rear. Came out at 5k RPM, luckily it shot down and dented the oil pan instead of destroying the whole short block. Had everything rebalanced at a trusted shop and it's been perfect since. I hope you are lucky enough that nothing expensive is hurt.

[Tim Corcoran]

I'm still wondering why it has the vibration. I doubt the excessive thrust clearance is causing the vibration. Tomorrow I will start pulling the engine but not happy about it.

[SRGN]

I don't think that the thrust is causing the vibration either, but at least it gives you a reason to have the rotating assembly rebalanced. It's frustrating, but if you hadn't gone after the vibration you probably would have wiped out the short block from the thrust issue.

[Half-Inch Stud]

Late to the party, but did you try the old power-balance test?

Pull 2 plug wire pairs and see if the power imbalance goes away.
1&6, 8&5, 4&7, 3&2. Load them wire ends into a pair of spare plugs.

May reveal a power imbalance based on ignition(bad plug), fuel-air distro( bad lobe-lifter-pushem rod-rocker-valve-seat deal or head gasket breach).