Harmonic Balancer

[Robert D.]

I have a 1957 250 hp corvette with 29k original miles. A few years back the balancer just about fell off. I had it replaced with a new one and since that time the car only had about 30 miles put on it. Last week I noticed it was coming off again. The engine is original to the car and never rebuilt. What is the proper way to address this ? I beleive the car has a steel crankshaft and unfortunately the balancer never had a bolt. Thanks in advance for the help.

Bob

[roy braatz]

Re: Harmonic Balancer

The KEY may be damaged if you used the old one again or the crank slot is warned or damaged, as you put the new one on, was it tight or hard to press on? I would look closly at this area. Also make sure the belt alignment is correct and not putting pressure on the balancer farward.

[Theodore K.]

Re: Harmonic Balancer

Bob,
I had the same problem with my 57 on a vacation trip up in northern Idaho. Going down the highway at 65Mph we heard a bang and wife saw the balancer rolling up a hillside. After recovering the balancer and getting the car towed to a shop that worked on old cars, we found the balancer now had a loose fit. Apparently it had cracked in the keyway and lost the interference fit. The replacement fit like it was supposed to and we used a lot of locktite on the shaft and balancer and it held. Then later the same week we had another problem. This time the bolts holding the pulley sheared off and ruined the pully. Got towed again and found it ruined the balancer by shearing off the rivit heads. Found the replacement balancer threaded holes for the pulley were not quite deep enough so the bolt bottomed out before the pulley was tight. Later got a third balancer and the holes were deeper. Again put the balancer on with locktite and it has held for 2 years now. Lesson learned!
My advice, check bolt hole depth for pulley and put on with locktite. If the balancer does not fit tight throw it away and get another one. They can be found at various salvage yards. If you can't find one please email me and I will assist you in finding one. By the way, the shop fixed mine in Idaho sent me another used one.

Good Luck,
Ted von Kampen

[Mike M.]

Re: Harmonic Balancer

If you ever have to pull and rebuild the lo horse FI, have machine shop drll and tap the crank snout so you can fasten the harm. bal. with a bolt like chevy did in the Hi horse C-2 small blocks. Lucky you didn't grenade the radiator when the assembly left the crank. good luck, mike

[Robert D.]

Re: Harmonic Balancer

Roy and Ted,
Thank you for your response. Is it possible to drill and tap the crank for a bolt ? I will always be wondering about the balancer because this is the second one.

Bob

[Robert D.]

Re: Harmonic Balancer

Thanks Mike.
Can this be done in the car without any damage to the engine ? I realize there are a variety of things I would have to remove ie grille, radiator etc.

[Theodore K.]

Re: Harmonic Balancer

Bob,
I addressed this a couple of years ago and I think if you go through the archeives you can find the responses. Honestly I don't think it can be done easily. You might get one to work but I think you could mess up a crank if not centered properly, etc. I had some of the same misgivings but the replacement seems to be holding okay. If the crank snout is worn and the fit is loose to start with then I would consider pulling the engine and redoing things properly.
Just my opinion. Yes Mike, I was lucky that it didn't take the radiator. Heck the fan belt was still laying in the compartment. Luckily I shut down immediately.
Ted

[Mike M.]

Re: Harmonic Balancer

Stick your index finger in the snout of the crank(engine off unless you'd like the visit the local E.R.) and feel if the crank is dimpled on its end. some are. it that's the case , you probably can drill and tap crank with engine in car but it would be a pisser.good luck, mike

[Joe L.]

Re: Harmonic Balancer

Bob-----

It would be very difficult to drill and tap the crankshaft with the engine installed in the car. You need to accomplish two things to do this right. First, you have to exactly center the drill in the crankshaft snout. If the crankshaft has a machining center as Mike described, this is pretty easy. Second, though, you have to drill the hole AND tap the hole, straight and true. That's NOT so easy.

If I were installing one of these crankshaft snout bolts on a crankshaft not originally so-equipped, I think that I would drill and tap for 3/8-24 threads. Cranks originally fitted with these bolts used 7/16-20 thread size, but the forgings were different than the earlier 283 cranks like yours. So, to be safe, I'd go with 3/8-24. This will result in less material being removed from the crank snout. A 3/8-24 SAE grade 8 bolt, torqued to proper spec, should have more than sufficient tensile strength to retain the balancer.

Another thing that you could also try is to modify the balancer to create a better interference fit. To do this, I would use a sharp center punch to craete as many punch marks as possible around the balancer hub crank snout hole's inner surface. You should do it on both sides of the hub in an area that contacts the crankshaft snout when the balancer is installed. This should upset enough material to create an acceptable interference fit. You only need to upset enough material to gain one or two thousandths of interference fit. Install with medium strength thread locking compound and all should be well. Keep in mind, though, that you will need to re-punch the balancer hub each time that you remove it. This sort of operation is a one-time-only thing, but you can re-do it.

[Robert D.]

Re: Harmonic Balancer

Roy, Theodore, Mike and Joe,
Thank you very much for the info. I don't want to take a chance on destroying the crank or the engine. Should I use the current baiancer ( which I nwas told was new) or should I go out and buy another ? This balancer is a very small ( narrow ) one. What is the best stuff to use to ensure it stays on. The miles that caused it to come off were idling and in and out of the garage unfortunately. So actually maybe this new one was not put on properly or it is worn. Again thank you all for your help.

Bob

[Joe L.]

Re: Harmonic Balancer

Bob-----

If the balancer is a GM piece, it's likely GM #3896904. If so, it's the correct SERVICE balancer for your application. If you have balancer GM #3896903, that's an INCORRECT balncer and may be the cause of your problem. Both balancers look exactly the same; you can only tell them apart by the numbers on the box they come in.

In any event, if you have the correct SERVICE balancer, I'd go ahead and use it with the mods I described. Then, as I mentioned, I'd use medium strength thread/sleeve locking compound on it prior to installation. I don't think that the locking compound, by itself, will be sufficient for the long-term.

[roy braatz]

Re: Harmonic Balancer

Did you check the key slot at the crank???? if it's worn then you can save the crank as others said by drilling the end for a bolt.If it's OK then locate a used one from Chevy guys, same as many early 283 blocks. I trust an original good used one more then todays new ones.If the key slots are good on both parts then a good mechanic can tell by the amount effort it takes to install it weather it's OK.

[John H.]

Re: Harmonic Balancer

Loctite "Bearing Mount" will do a good job of keeping it seated, but it will be a bitch to remove next time

[Ronnie Robertson # 36786]

Re: Harmonic Balancer

Bob,
I just went through this "exercise" with my '66 300 HP 327 last week. The ONLY way to correct the "General's mistake" is to have a reliable machine shop drill and tap the crank. They can give you the best advice. They will advice you whether the engine must be removed. There is equipment which can perform this operation without engine removal, but it is expensive and not available in smaller shops. I removed my engine and the drill and tapping operation took less than an hour. Now the new balancer is held in place with a 7/16 by 20 (the normally used bolt) with 60 Ft Lb of torque. The new balancer is not going anywhere, it can be easily installed and removed with normal methods and tools, and your engine can be serviced by most any professional with no surprises. Good Luck.

[Robert D.]

Re: Harmonic Balancer

Again thanks all for the information. Is there a balancer available from GM that will look and function like the original ? Is balancer # 3896904 ( thanks Joe )
still available ? I reaLLY do not want to mess with the crank. Again thanks for all your help.

Bob

the crank does have a deep dimple in the center.