Okay, so I am a Chevy guy so I need some help from you GMC guys...
On Chevy 216/235/261 engines, the harmonic balancer hub to pulley are attached with 6 rivets, whereas on the 228/248/270/302 GMC's it looks like bolts are used in lieu of the rivets. Can anyone give the bolt diameters for those six bolts used on the GMC HB?
One data point...............my 1950 GMC 228 has riveted balancer. I don't know the whole past history of the truck or the engine other than it was pretty much stock when I got it.
There are a couple of them on Ebay, and they're both riveted. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
I got a new balancer with 2 belt grooves for a 292 that also fits a 302, a while back, made in Oz. Might still have box. Had to modify slightly for the GMC.
Ed
'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires. '47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle. '54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed. '55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.
I had my original Chevy HB come apart on me. Fortunately I caught it before it exploded, so no real damage was incurred. The rubber portion sandwiched between the hub and pulley is long gone. What would be the result of just bolting the hub/pulley together?
Maybe Hotrod Lincoln or one of the other really knowledgeable guys will chime in, but I'm guessing it won't do its job of dampening and you'll end with with engine damage, that rubber material served a purpose. I wouldn't chance it. I think you can get a replacement from www.damperdudes.net without having to break the bank. There are some places that "rebuild" them but I couldn't find the thread......
Ron - - Dusty53 1954 Chevy 3604 In the Gallery Forum "You can't dance with the Devil and then wonder why you're still in Hell." "They will forget what you've said, and they will forget what you have done but they will never forget the way you made them feel."
Maybe Hotrod Lincoln or one of the other really knowledgeable guys will chime in, but I'm guessing it won't do its job of dampening and you'll end with with engine damage, that rubber material served a purpose. I wouldn't chance it. I think you can get a replacement from www.damperdudes.net without having to break the bank. There are some places that "rebuild" them but I couldn't find the thread......
Thanks for the reply Ronnie. Yes I completely agree that the rubber portion does have a purpose otherwise it would not have been used in production. Engineers and designers certainly don't add components for no reason. My question is more towards what would happen if the pulley were bolted to the hub without the rubber? Would there be terrible vibrations? Would the assembly create such shock as to harm the crankshaft bearings? This truck is lucky to get 2000 miles on it per year.
I have another good original HB back on my truck, but was contemplating rebuilding the one that deconstructed. The only problem is that testing is not very convenient as there is considerable sheet metal disassembly required to remove/replace a HB once in service. The only reason I am worrying about all of this is that the pulley is 7/8 wide on my application and not super easy to find.
Bolting a balancer solid without the rubber damper ring probably wouldn't be a good idea. The reason the ring is there is to absorb, and then oppose torsional twisting of the crankshaft every time a cylinder fires. Inline sixes are pretty forgiving so far as balancing goes, because each connecting rod journal is 60 degrees of crankshaft rotation away from the next one. When spinning an I-6 crankshaft up on a balancing machine, it's not even necessary to use "bob weights" to simulate the weight of the pistons and connecting rods. Try that with a V8 crank and it will jump right out of the machine.
Now, before some self-appointed engine guru chimes in, dampening torsional vibration is different than balancing a crankshaft. That's where the damper comers in. If an engine is going to be used for pulling heavy loads at or near full throttle and high RPM, having exactly the right damper in very good condition is much more critical than on an engine that's driven at moderate speeds and loads. So far, I haven't heard of any catastrophic failures of the 2-groove dampers I've been putting together from new V-8 parts, and they're being used on several 235's. Something similar can probably be fabricated for a GMC, since the hub diameter, inside and outside, is the same as Chevy sixes, and the balancers will interchange, I believe.
Now I'll retreat to my foxhole, put on my steel helmet, and duck and cover from the incoming ridicule in 3-- - - -2- - - - -1- - - - -! Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
I will take some images of the original HB and post them here. I believe I will create a new topic as the HB I am dealing with is for a 1941 Chevy, not a GMC as my initial tread was trying to determine something different. From dissecting the assembly, I am not sure how the rubber portion of this unit served much of a purpose. I trust it did, but cant really see how it is supposed to suppress shock. My goal here is to determine how stovebolt HB's function, and to determine the suitability in rebuilding the HB that came apart.
Not trying to start a cyber war with anyone one the site, just a desire to learn. Jerry, I appreciate your willingness to help me here and look forward to hearing your input. Oh and before the semantics of terminology get off the rails here, I have included an image of my original parts manual depicting the name of the part.
