1961 Harmonic Balancer Question

[Joel T.]

Guys,

I was driving down Route 22 here in NJ this afternoon in our 1961 283/245. All of a sudden I hear something bouncing under the car and look back in the mirror to see something left in the middle of the road!! My first reaction was that it was a piece of the exhaust system (a couple of hangars are broken). I stop the car to go back and pick up the debris and low and behold, it is my harmonic balancer!!! I quickly ran through my inventory of curse words... a couple of times...

I managed to the car home with a little running of the engine a lot of engine off coasting (she was WARM but OK).

Question, is there a bolt or something which holds the harmonic balancer in place on a 1961 (like my 1963)? I do not see any evidence of a bolt or washer being in place on this balancer/pulley assembly. There is a counter sink in the front end of the crank but it does not appear to be threaded.

What keeps the HB in place?

Thanks,

Joel

[John O.]

Re: 1961 Harmonic Balancer Question

Hi Joel

Like my 62 vette. The harmonic balancer is just pressed on. No bolt. Hope you did not get alot of damage.

John

[Joe L.]

Re: 1961 Harmonic Balancer Question

Joel-----

As John mentioned, the balancer on your engine is retained by an interference fit on the crankshaft snout and NO bolt was used. The balancer retaining bolt was first used for the 1962 model year for 340 and 360 hp engines. It's use was progressively expanded after that time until by 1969 all Chevrolet small blocks used it.

So, that still leaves open the question as to why your balancer "seperated" from your engine. There are two likely possibilities:

1) The crankshaft snout and/or balancer hub orifice had their interference fit degraded over time. If a balancer is repeatedly removed and re-installed, this can happen. With an interference fit type balancer, the ORIGINAL INTERFERENCE FIT SPECIFICATIONS MUST BE MAINTAINED. Just because a balancer retains SOME interference fit does not mean that it has the PROPER and NECESSARY interference fit. In simpler terms, just because you have to pound the balancer on does not mean that it fits tight enough.

2) An incorrect replacement balancer was used. This is VERY, VERY easy to occur if someone that's replacing the balancer (or, someone selling that person the balancer) doesn't "know their stuff". Here's the deal: since about 1967, Chevrolet has offered TWO balancers to SERVICE most pre-68 Corvette small blocks. These balancers are GM #3896903 and GM #3896904. These balancers APPEAR absolutely identical. But, appearances can be deceiving because they are NOT the same.

The SERVICE balancer applicable to ALL 1957-61 Corvette 283 engines as well as 62+ 327s which do not have the balncer retaining bolt is the GM #3896904. The balancer applicable to 62-67 327's without the balancer retaining bolt is the GM #3896903. The difference between these balancers is a VERY slight difference in the OD of the crankshaft orifice. This difference affects the DEGREE OF INTERFERENCE FIT between the balancers. BOTH balancers will exhibit an interference fit on the crankshaft snout, but it will not be the same interference fit. That's what "throws off" the installer; he thinks that it's just fine because he has to "pound it on".

So, if some hapless soul ends up with a GM #3896903 balancer on a 1957-61 283 (or, a 62-67 327 without the bolt), they'll eventually end up with just exactly the problem you have.