68 L36 AIR pump mounting

[Douglas L.]

Looking at the 68 AIM UPC L36 A3 it shows a spacer, part#3877608 on the AIR pump longer mounting bolt. I've searched the internet for pics of engine with one installed but cant seem to find one and cant seem to remember ever seeing one. Does anyone know if the spacer was actually ever installed from St. Louis?

Thanks, Doug

[Henry J.]

Re: 68 L36 AIR pump mounting

My February-built 68 definitely has that spacer. I can't provide a picture, as my car has been put away for winter.

[Joe L.]

Re: 68 L36 AIR pump mounting

Looking at the 68 AIM UPC L36 A3 it shows a spacer, part#3877608 on the AIR pump longer mounting bolt. I've searched the internet for pics of engine with one installed but cant seem to find one and cant seem to remember ever seeing one. Does anyone know if the spacer was actually ever installed from St. Louis?

Thanks, Doug

Doug-------

I do not understand how this spacer could have been installed if within the bracket and I do not understand what purpose it would have served if installed outside the bracket.

Beyond that, I cannot find that the 3877608 spacer was ever a released part. It was never available in SERVICE.


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[Henry J.]

Re: 68 L36 AIR pump mounting

Going by memory, the BB through-bolt has a very long unthreaded portion and a short threaded portion. The unthreaded portion extends well past the rearmost leg of the BB AIR pump mounting bracket. The spacer takes up this space, and a little more. Without the spacer, the mating nut would reach the limit of the thread but not tighten anything.

I'm sorry. I would like to be more quantitative, with bolt dimensions, but I am unable to do so.

I have two examples of this bolt, one of which I purchased from a vendor at Carlisle and the second which I purchased from Bill Hodel, as I was unsure about the first. Again, going by memory, both proved identical!!!

[John C.]

Re: 68 L36 AIR pump mounting

Henry's answer is the only reason I can see for it. It is also shown in the 69 AIM. Attached is a picture I found of a well preserved 1969 20k mile car on Corvette Mike's website that shows it:

http://corvettemike.com/used-corvettes-for-sale/1969-Corvette-L-68-427/400hp-Coupe-2265

Neither my 68 or 69 have it, on my 68 it has a shorter bolt than shown in the attached picture, on my 69 it has a long bolt with a long threaded area. This is how the cars were when I bought them, but I don't know if the bolts are original.

John

[Joe L.]

Re: 68 L36 AIR pump mounting

Going by memory, the BB through-bolt has a very long unthreaded portion and a short threaded portion. The unthreaded portion extends well past the rearmost leg of the BB AIR pump mounting bracket. The spacer takes up this space, and a little more. Without the spacer, the mating nut would reach the limit of the thread but not tighten anything.

I'm sorry. I would like to be more quantitative, with bolt dimensions, but I am unable to do so.

I have two examples of this bolt, one of which I purchased from a vendor at Carlisle and the second which I purchased from Bill Hodel, as I was unsure about the first. Again, going by memory, both proved identical!!!

Henry------


Yes, that's what the case is but it sure is weird. The GM #3877606 bolt is 5-1/4" in length with a thread length of 13/16". The big block bracket is only 4-3/8" in total width. That means that about 1/16" of unthreaded shank would extend beyond the bracket. A thick washer would have sufficed to take this up. I can't imagine why GM chose to use a thick spacer.

The best solution would have been to use a shorter bolt with a little more thread length. However, the only reason that I can figure that GM went with the 3877606 bolt is so that it could be standardized with small blocks. The cast iron small block pump bracket had thicker ears and, thus, required a little longer bolt than the big block's stamped steel bracket.

[Terry M.]

Re: 68 L36 AIR pump mounting

A similar spacer is used on small blocks at the base of the AIR mounting bracket (Bolt is also to the water pump.) if no C60 is installed. I can't find that spacer in the AIM at the moment, so I can't verify if the part number is the same; but perhaps it is just a case of they had the spacer on hand and used it so they could use the common 606 bolt.

[Joe L.]

Re: 68 L36 AIR pump mounting

A similar spacer is used on small blocks at the base of the AIR mounting bracket (Bolt is also to the water pump.) if no C60 is installed. I can't find that spacer in the AIM at the moment, so I can't verify if the part number is the same; but perhaps it is just a case of they had the spacer on hand and used it so they could use the common 606 bolt.

Terry-------


Yes, there was a spacer used on small blocks but it was of a different part number. The small block spacer was GM #3877660. You won't find it in the AIM since the bracket and spacer were installed at Flint. The GM #3877660 was of 13/32" ID, 21/32" OD and 1/2" thick. It was once available in SERVICE.

The big block spacer was GM #3877608. It was to be installed at St. Louis. It was 13/32" ID, 3/4" OD and 3/8" thick. I cannot find that it was ever available in SERVICE.

[Terry M.]

Re: 68 L36 AIR pump mounting

Terry-------


Yes, there was a spacer used on small blocks but it was of a different part number. The small block spacer was GM #3877660. You won't find it in the AIM since the bracket and spacer were installed at Flint. The GM #3877660 was of 13/32" ID, 21/32" OD and 1/2" thick. It was once available in SERVICE.

The big block spacer was GM #3877608. It was to be installed at St. Louis. It was 13/32" ID, 3/4" OD and 3/8" thick. I cannot find that it was ever available in SERVICE.

I should have remembered that small block spacer was installed at Flint. All are, or should be, painted orange. I forgot that detail when I posted.

[Joe L.]

Re: 68 L36 AIR pump mounting

I should have remembered that small block spacer was installed at Flint. All are, or should be, painted orange. I forgot that detail when I posted.

Terry------


...and the original 3877600 spacer had very slight, circumferential raised machining marks on the OD.

[Douglas L.]

Re: 68 L36 AIR pump mounting

Thanks for all the info everyone. Seeing as at there at least 2 examples with the spacer out there I'm gonna assume they came with them. I also tend to believe(like others) that the reason for its use was so GM only had to spec one bolt for both small and big block applications. I was unable to source one(later found out AMK bolt makes them) so I purchased a 660 spacer, chucked it in the lathe and cut it down to 3/8" thick. Looks alot better than a thick washer and alot of extra threads past the nut.
Thanks again, Doug