The Stovebolt Site Forums The Shop Area Engine Shop GMC 270 Damper - Update

Is the damper bolt right hand thread? The engine is clockwise rotation from the front and it seems like the bolt would have reverse threads to help keep it from loosening. Or am I overthinking this?

Thanks

Hy jmoore, as far as I'm aware there are no left hand thread bolts in a GMC 270 engine, hope that helps.

It does, thanks.
Now, what's the best way to keep the engine from turning while loosening the bolt? I have it in gear, but the crank is still turning. Prybar on the flywheel? Brakes applied?

You may need to hold the flywheel although on my Chevy being in 1st gear usually works. But, yes, it might just be easier to have someone press the brake so the truck won't roll.

OK, got the damper pulley off.
Once I got the bolt out, I was able to wiggle it off by hand. That doesn't seem right.
I found it to have some wobble on the shaft, that's the reason for pulling it. Also found that whoever had put it on put the retaining washer against the bolt head and then put the lockwasher against the shaft. Wouldn't that make it not pull in all the way?
I looked and have found repair sleeves, but no damper. What purpose do the sleeves serve?
Anybody know of an available replacement damper? Will a 235 damper work? I found through search that a GMC 302 should work, know where to get one?
Original part number is 2341682
Sorry for all the questions.
Thanks for any help and advice.

Jeff

The repair sleeve is for a groove on the balancer where the seal makes contact.

Place a want ad in the Swap Meet for a used balancer.

Thanks Tim.

Placed the ad. Is there nothing new that would replace it? I need some kind of cross reference.

Slight looseness on the crankshaft snout isn't a terribly bad situation, as long as the damper can't rotate back and forth due to a worn Woodruff key and/or the keyways in the crankshaft and the balancer. Red Loctite can take up the looseness, and a properly torqued center bolt will hold the damper tight against the timing gear on the crankshaft. Be sure to use a THICK flat washer, at least 1/4", and thicker is better. You don't necessarily need a lockwasher. Threadlocker and torque does just fine at keeping the bolt tight.

If there is rotary slack in the balancer, it's possible to file the keyway in the balancer wider, and custom make a stepped-down Woodruff key to eliminate the looseness. A keyway in the crankshaft that's worn into a V shape is a problem- - - -that needs to be welded up and a new keyway machined with a milling machine- - - -time for a complete engine teardown to get that done!
Jerry

Can you use, or do they make a fluid damper that would fit a 270 or 302 crank, say if your dampner needed replaced? Jim

What are the dimensions of your crankshaft snout? Chevy 6 cylinder engines and small block V8's have a 1 1/4" diameter crank nose. The OD of the balancer snout is 1 3/4", which will be the same size as the lip of the front seal. I'm not sure if those dimensions will be the same on the GMC engine. If they are, it might be possible to modify a Chevy balancer to fit.
Jerry

Thanks. I will get the measurements and report back.

I used a '59 235 balancer on my 248 in the Suburban.

Looks to be 1 1/4" diameter crank nose and 1 3/4" balancer snout. What modifications would be needed on a smallblock V8 balancer?

I built up a 2-sheave damper for a 235, using a new 6" diameter balancer for an early small block V8 (265/283/327, etc.) By inverting a 2-sheave pulley for a big block engine over the 6" damper, the fit is very close. It is necessary to shorten the balancer hub about 1/4" and machine the OD of the hub back a similar distance to prevent oil seal damage. It's not an easy fix, but the engine ends up with a brand new balancer, not a recycled or repaired 50-something year old one.
Jerry

Well, I think the damper and crankshaft are ok, it seems I have a worn woodruff key. This key has the standard woodruff that goes in the shaft, with an extension that sits in the groove on the damper about 3/4 inch. Is this for added strength? If I use a replacement woodruff key without the extension, would it be strong enough? I am considering taking the old key to a machine shop and having them make a new one.

Thanks again everyone.

A standard Woodruff key should be OK, but I've never seen a worn key that didn't get that way because of a loose-fitting balancer. The balancer should be a TIGHT press fit on the crankshaft snout- - - -either installed with a BFH, a jackscrew pusher, or by heating the balancer hub until a drop of water sizzles on it, then tapped on with a block of wood and a hammer.
Jerry