1967 water pump belt headaches

[Gary B.]

…I do not understand how there can be different lengths applicable to the GM #3837810 belt. Originally, they were all the same length….

Joe,

Rather than Quanta having two belt lengths for the same application, my guess is that their belts have an average length equal to some manufacturing spec, but there is a distribution of length around that mean value due to some manufacturing issue or allowed tolerance. With the crank to water pump captive belt Quanta may examine each belt they receive from their supplier and then sort them into either a short bin or a long bin. And within each bin, there is still a distribution of lengths about a short and a long mean value. Obviously, I don’t know this for certain.

But here’s a similar example. The alternator belt for my ‘66 L79 no-option car is GM #3861946. The corresponding Quanta belt is 29-B-061. I bought a Quanta 29-B-061 for my car and I was able to install it, but the alternator brace adjusting bolt was at the extreme end of the adjust slot, toward the engine side. So, it was functional, but in my opinion too short and not typical of original GM belts. After talking with another person who had the same issue I called Quanta and told them of my problem and they looked thru their inventory of 29-B-061 belts and they found a longer one, which I bought. All of the markings on the two Quanta belts were identical, so they were the same Quanta part. But they were clearly different lengths. The longer belt they sent me allows me to have the alternator adjusting bolt at least 3” closer to the center of the adjusting slot. For the alternator belt, Quanta could also separate the same belt into two bins and sell a short version and long version. But for whatever reason they don’t do that for the alternator belt, whereas that might be what they do for the captive crank/water pump belt. Just speculating.

Gary

[Joe L.]

And the story continues:
the pulley that is on his car is a two groove 3900434AB 7 1/8" diameter. A quick search says Camaro and Corvette big block but obviously not the numbers that Joe L. put out.

Thank you all for the comments. The short 3837810 is on its way back to Quanta and we are hoping that we don't suffer the same issues that some of you have had with irregular measurements. The one we got was 34 1/2". here's hoping that Gary B's "goldilocks thing" isn't happening.

Gary-----


GM #3900434 had many applications including some Corvette small block applications. However, I cannot find that it was ever used for any Corvette big block. It was NEVER catalogued in SERVICE for any Corvette big block application and is not shown in any of the AIM's I've looked at. It may be the same 7-1/8" OD but that does not mean that it's EXACTLY the same. It was discontinued from SERVICE in May, 1990. In addition, I do not think that the 3900434 is a deep groove pulley like the 3906656. That, by itself, would account for your belt problem even if the two pulleys are exactly the same OD. If it is a standard groove pulley (which I'm virtually certain it is), I'm surprised that it would even properly align with the GM #3863108 balancer pulley. Have you confirmed that you have that balancer pulley?

I would recommend getting a correct pulley. The GM #3906656 is discontinued but you should be able to find one, NOS, used, or reproduction

By the way, this car does not have K-19 does it?

[Gary S.]

No K-19. I will pass your information to the owner. I did search for the 656 pulley and see that it is readily available. I have not confirmed what is on the balancer but we will do that.

This is one of the problems I have with this owner's car. He bought it on one of the usual auction sites, had it inspected but apparently not inspected well enough. The engine was rebuilt but there aren't any details on the build and this pulley situation is a prime example. I will have put a mirror in the engine bay and see if he can pull the number up.

Thank you, Joe.

[Tim S.]

[QUOTE=Patrick Hulst (16386)
Note that old style (Quanta) belts might be thinner than modern ones, resulting in a different belt length because of how it rides the pulley.[/QUOTE]

^^^^^^^^^^
That is a large part of the problem IMO

[Joe L.]

^^^^^^^^^^
That is a large part of the problem IMO

Tim------

The GM #3837810 belt was a 3/8" wide belt. Many modern belts are 7/16", including the GM #9433722 which replaced the 3837810. If the Quanta belts are actually 7/16" (which could be because that's what belt manufacturers are tooled up to manufacture) and are simply embossed to mimic the original 3837810, that could be the root of the fitment problem that many folks seem to have.

For the vast majority of belt applications, this width difference or, even, a slight difference in length from originals would not be a problem. That's because the vast majority of belts are used in applications for which there is an adjustment . Captive belts are the exception.

[Gary S.]

lots to pass on to the owner. I have my suggestions - we will see what he does.

Great comments and feedback as always. Thank you

[Gary B.]

Tim------

The GM #3837810 belt was a 3/8" wide belt. Many modern belts are 7/16", including the GM #9433722 which replaced the 3837810. If the Quanta belts are actually 7/16" (which could be because that's what belt manufacturers are tooled up to manufacture) and are simply embossed to mimic the original 3837810, that could be the root of the fitment problem that many folks seem to have.

For the vast majority of belt applications, this width difference or, even, a slight difference in length from originals would not be a problem. That's because the vast majority of belts are used in applications for which there is an adjustment . Captive belts are the exception.

Joe,

On their home webpage, Quanta says: “Our belts are made to blueprint specifications for top width…”.

Gary

[Robert P.]

The gates belt number i posted is 34+1/2" by 3/8 belt

[Gary S.]

here's a follow-up. My friend exchanged the short version of the Quanta belt for the 3/8" longer version (I think that was the number they gave me) but it of course didn't go on any easier than the short version. So he ordered a repro GM #3906656 water pump pulley and the depth of the groove is significantly deeper than the incorrect one that was installed. Once that came in a few days, the rest went relatively well.

I am handicapped because I don't have access to the books that he should have but doesn't. So, thank you Joe and others for helping sort this out with advice, part numbers, and similar stories of difficulties.