1962 Corvette 340 Hp Question

[Bruce B.]

Re: 1962 Corvette 340 Hp Question

Bruce------


What creates the problem with the fitment of the 3858533 mounting to the original style 3817173 balancer?

Joe,
On the back of the pulley is a raised lip or flange around the large center hole, it is about 1 1/4" in OD and about 1/8" high.
The balancer has the machined hole in the center (the mounting hole for the crankshaft) which is approx. 1 3/16" in diameter, therefore the pulley will not fit flat on the front of the balancer.

[Joe L.]

Re: 1962 Corvette 340 Hp Question

Joe,
On the back of the pulley is a raised lip or flange around the large center hole, it is about 1 1/4" in OD and about 1/8" high.
The balancer has the machined hole in the center (the mounting hole for the crankshaft) which is approx. 1 3/16" in diameter, therefore the pulley will not fit flat on the front of the balancer.

Bruce-------


From what I can see in your pictures, it looks like both of the balancers may have been "beat on" for installation purposes at some point in their lives (this is a DUMB thing for some previous "mechanic" to do since all crankshafts originally using this balancer were also equipped with a snout bolt tapping making the use of a balancer installation tool the way to go). This may have "mushroomed out" the material surrounding the hole and, effectively, reduced the diameter.

What the above does not explain, though, is even if this did occur, why the 3756328 indexing flange will fit in the hole and the 3858533 will not. The indexing flange is critical to centering of the pulley on the balancer as the bolts will not precisely center the pulley. The indexing flange MUST fit very snugly into the orifice in the balancer or it won't properly center the pulley, so if there is any "mushrooming" of the material surrounding the orifice, the pulley won't fit properly. I always thought that all small block balancers had the same orifice size and all small block crank pullies had the same corresponding size indexing flange OD. Maybe not, though. I can't say that I've ever really precisely measured any. I'll have to check some balancers and pullies in my collection.

Could you measure the indexing flange OD on the 3756328 and 3858533 pullies you have?

[Bruce B.]

Re: 1962 Corvette 340 Hp Question

Joe,
Here is what I found using a good Starrett stainless steel 6 inch caliper for measuring. Since I don't have any gauge blocks I just set the pointer to zero when fully closed.
The orange balancer center hole measured as follows; 1.225", 1.225", 1.229" and 1.225" from 4 random measurements. The variation in the dimensions might be due to hammer damage. The same hole when measured from the back of the balancer measured 1.250" indicating to me a lead or taper is machined into the hole from the back side.

The other balancer center hole measured 1.227", 1.222", 1.220" and 1.220" ,again 4 random measurements with no obvious hammer damage. The same hole when measured from the back measured 1.250".

The indexing flange on the 3858533 pulley OD measured 1.232" and 1.235" with the paint removed.

The 2 3756328 pulleys at the flange measured 1.225" to 1.226" and the other measured 1.220 to 1.221"

The 2 3756328 pulleys fit both balancers, the 3858533 will not seat on either balancer. Which makes sense based on the measured dimensions.

Measuring errors are obviously present but the test fit of the parts helps to confirm the measurements in general.

Hope this information helps.

[Joe L.]

Re: 1962 Corvette 340 Hp Question

Joe,
Here is what I found using a good Starrett stainless steel 6 inch caliper for measuring. Since I don't have any gauge blocks I just set the pointer to zero when fully closed.
The orange balancer center hole measured as follows; 1.225", 1.225", 1.229" and 1.225" from 4 random measurements. The variation in the dimensions might be due to hammer damage. The same hole when measured from the back of the balancer measured 1.250" indicating to me a lead or taper is machined into the hole from the back side.

The other balancer center hole measured 1.227", 1.222", 1.220" and 1.220" ,again 4 random measurements with no obvious hammer damage. The same hole when measured from the back measured 1.250".

The indexing flange on the 3858533 pulley OD measured 1.232" and 1.235" with the paint removed.

The 2 3756328 pulleys at the flange measured 1.225" to 1.226" and the other measured 1.220 to 1.221"

The 2 3756328 pulleys fit both balancers, the 3858533 will not seat on either balancer. Which makes sense based on the measured dimensions.

Measuring errors are obviously present but the test fit of the parts helps to confirm the measurements in general.

Hope this information helps.

Bruce------


Excellent information. Thanks for the careful measurements.

The thing I can't figure out is how the 3858533 pulley was used for 1965-66 Corvette SHP small blocks? They used the same configuration GM #3817173 as you have. In fact, one of yours confirms that this style was still being used as late as mid-1966.