The Stovebolt Site Forums The Shop Area Engine Shop Drilling the harmonic balancer

Quite some time ago there was a post about putting the harmonic balancer back on a 235. The recommendation was to not hammer it back on, but rather to drill and tap the end of the crankshaft to use a bolt and press the balancer on. My thought was that this might mess up some balance in things. I'd be interested in hearing from anyone who has done this and if there were any special procedures used. Depth of drilling, size of bolt recommended, etc. Also from anyone else who thinks this might be a bad idea and what other recommendations there might be. I know what the shop manual says, but the earlier post said this was not a good idea. Thanks!

Drilling is recommended, you can even buy a bolt and washer kit that includes a 7/16NF bolt with the correct size and thickness washer. I made my own from a piece of alloy bar. It's easiest done with the crank out of the engine, and a good machine shop should recommend that it be done when the crank is ground. If you're doing it yourself, buy the kit, drill the hole about 3/8" deeper than the bolt (minus the washer thickness) and tap. Torque is in the 90-100 ft-lb range, iirc. After everything is together (engine is ready to run) take the bolt out, clean the bolt and hole and re-torque with red loctite. Don't worry about the balance, just drill as close to the shaft center as you can get. Unless you paid extra, your crank and rods are out of balance far more than the weight of the bolt head and washer.

Having experienced a damper pulley launched into the radiator at 60 MPH, I highly recommend this modification, it sounded like a grenade went off under the hood...Fred's method is undoubtedly the right way to do this, but I did it in my driveway on a 228 GMC with an electric drill and a hand tap. I used a grade 8, 1/4 X 28 bolt and a big washer. Torque ...?? a lot ...Also used JB weld on the threads. Not the most elegant of repairs but it was a daily driver and had to be ready the next day. It lasted for another 25K miles or so, at which time the engine was retired. No vibration problems or other ill effects.

If you had the foresight to do this before you pulled the balancer off you could use the running engine to find the rotational center of the crank. Watch out for spinning fans and pulleys, obviously.

Just a different point of view.The crank on my two 261's and one 235 were drilled when the crank was at the machinist.Can't use a retainer bolt as the shortened water pump leaves the fan passing a scant 1/4 inch from the damper.So the threaded hole would accept a tool to draw the pulley on.Well, not me the hack, all three dampers were installed with a 5 pound mash hammer and large drift , 4 blows and you're good to go.Some say the hammering ruins the thrust bearing. Those cranks weigh in the neighborhood of 80 pounds, a lot of metal to absorb the impact.My 261 powered 37 is run pretty hard, pulling a travel trailer long distances at 3000 rpm .The damper hasn't flown off yet,.Many of those old dampers are a sloppy fit on the crank , everytime it gets pulled off, a little metal comes with it.So a bolt is good insurance if you have any doubts. Sixpack drives like a maniac,dampers fly off and he runs them Jimmys till they explode.

Okay, this is different than what I expected. I thought the only purpose of drilling and tapping the end of the crankshaft was to give you something to thread into in order to use a tool to draw the balancer onto the shaft rather than to beat it on with a hammer. Fred T if you then use the bolt and washer to hold the balancer in place and provide extra security to make sure it doesn't fly off, that washer must have to be about 1-14" to 1-1/2" in diameter. And then I'd be in the same boat as what Tony mentioned here since I had to go with a short shaft water pump and the flat back fan off of a 216 in order to clear the radiator on my '53 3/4-ton. So I sure won't have any room for a bolt to stick out beyond the balancer. Still, though, it sounds like the safest way to do it is to drill and tap to use a tool to draw the balancer on and then leave the hole open when I'm done -- unless I'm missing something which could easily be the case.

Yer gonna be missing something alright!! Yer truck!! If you don't quit talking about it and fix it right soon. You don't live all that far from me ya know!!-LOL On a serius note- I've whacked a lot of balancers on in my time and it didn't seem to hurt anything, but that didn't mean I liked the idea. I like the idea of at least cinching it up with a bolt, even if I remove the bolt afterwards. I don't believe that you can hurt the thrust bearing by the whacking but there is always the first time for everything, so why take the chance?

My washer is roughly 1/4" thick and 2-1/8" diameter. I have a late 54 235, high water pump, and what I think is the fan from the car it came out of. Of course, I used an aluminum timing gear to make it a truck engine.

Fred, its a good thing you put on that aluminum gear,a car engine will instantly blow up in a truck, spitting main bearing shims everywhere ; Standard model 283 and 327 engines have press on dampers.Used to rev them up pretty good , never saw too many dampers lying in the road. You have to consider the 40-50 year old damper on your inline engine engine.Is the rubber damping discs all hard and useless? Who knows? All those torsional vibes scurring up and down the long poorly supported crank , loosing up the maybe marginal pressfit on the damper. The retainer bolt ain't a bad idea.I have a genuine NOS damper on one of my trucks, and it is sure a tight fit on the crank snout.The other two dampers were rebuilt by the Damper Dudes or Damper Doc. But who knows if the rubber they use is tuned exactly as the original GM part.The Owner of the Damper Doc told me on the phone that good Stovebolt dampers are hard to find, most of them are broached oversize as a result of being removed several times.

Sounds like a lot 'o work to me...

Let the balancer sit in some hot oil for a while, while icing down the end of the crankshaft. This will expand the balancer enough to allow an easy fit. Don't use a torch, there's rubber and stuff inside the balancer.

Tap the balancer on gently, using a length of pipe with a larger diameter than the crank, to get it on straight. Should go on very smoothly.

-Boyo

I agree with Tony (although he may exaggerate just a wee bit for effect sometimes), the damper pulley on the 228 had been loose for a while and I thought the noise was from a bad water pump. Well I changed the water pump. The noise seemed to go away (probably from tightening the fan belt) and the very next weekend, drove across state to pick up a motor. Thats when the damper pulley parted company with the crankshaft and took out the radiator. Autopsy revealed that the pulley and damper were still in one piece, it had been flopping around and chewed up the keyway in the crank to the point where the key finally broke, and the pulley just worked its way off the end. A retaining bolt would have prevented this from ever happening.

My 302 engines are very prone to damper pulleys going loose. I guess the crank harmonics are more of a factor with the bigger motors. The factory recognized this and all 302 cranks are drilled & tapped for a BIG retaining bolt and washer. I have learned to recognize the sound, it's a subtle knock like a rod bearing going out. The bolt still seems tight, but a few more ft/lbs with a cheater bar pulls it down enough to stop the death rattle.

I am convinced that this (and flywheel bolts coming loose) are a message from above that these motors were rated at 3300 RPM and you exceed that at your peril.

The proper tools of an organized home builder makes quick work of damper installation. Factory tool and damper

Geez Tony, you're lucky. It's hard to find factory tools anymore..

I can't quite make out the Kent-Moore part number on that on. LOL

The organized home builder keeps all his spare parts in a neat well lit storage area climate contolled inventory storage area

Hey Oly, one of these days my truck will be all together and then I'll pay you a visit down that way. Or maybe at the swap meet in Albany coming up in a few months. I will eventually get it together, but I don't have a whole lot of time to work on it and am buying parts as I can. One thing is for sure, though, if I have to spend $, I can't think of anything I'd rather spend it on! Fred T and Tony, I'm not sure what all the fuss is about the difference between a car and a truck 235, but guess I'll find out. Mine came out of a Biscayne. Boyo, I'm liable to end up doing exactly what you suggested, although if I knew for sure a bolt could clear my fan when all is said and done, it sure makes sense to have it secured. I don't want to end up with what sixpack had for sure. And Tony, I assume the tool for the job is the sledge hammer next to the balancer. Right? Looks like overkill to me. I don't own a hammer that big! Anyway, thanks to all of you for the advice and the great feedback. That's what makes this web site the great place it is.