'68 L-79 Pulleys

[Richard D.]

Hello All -

Going to start getting all the front engine pulleys (correct) done for my car soon.

Car is 68, no PS, no A/C, L-79.

In looking at the AIM for my car, I see that the Crank Pulley, and Water Pump Pulley has double groove, for 2 belts.

I have the part Number for the pulleys from the AIM, but was wondering what diameter they are, as aftermarket replacements go from 6.25 inch diameter, to 7 inch.

I measured the crank pulley (looks orginal to me, 2 groove for 2 belts), and it is 7 inch. Is this diameter correct? It has the original finned harmonic damper in place, which is in good condition.

Previous owner put an aftermarket 7" water pump pulley on it (looks like a Mr. Gasket one). It has a 3" backspace that works with the WP and alternator, but is single groove for one belt.

So, questions are -

1. Correct diameter for the WP pulley
2. Verification of the Crank Pulley diameter to make sure I have the correct one on there now.
3. How is the 2nd belt (runs from Crank pulley to WP pulley) put on, as there is not idler pulley for this belt (as far as I can acertain from the AIM drawing).

After this is accomplished, will start the search (expensive, I know), for the AIR stuff to finish the engine.

Thanks in adavance for any info./advise.

Regards,

Rich

[Joe L.]

Re: '68 L-79 Pulleys

Rich-----

One of 2 different waterpump pullies could have been used for your application depending upon when the car was built. Early cars without C-60 or N-40 MAY have used pulley GM #3770245. This is a 2 groove pulley of 7-1/8" diameter. Later 1968's with L-79 and without C-60 or N-40 used pulley GM #3848904. This pulley is also a 2 groove pulley but of 6-9/32" OD. It was discontinued years ago and replaced by GM #3995641 which is also a 2 groove pulley but of 5-7/8" OD.

So, which belongs on your car----the 3770245 or the 3848904? I don't know, but my guess would be the 3848904.

The crankshaft pulley should be GM #3858533. This is a 2 groove pulley of 6-3/4" OD.

How is the captive belt installed? With difficulty. There is a special tool available in the aftermarket (or, at least used to be available) which aids in the installation of the belt. Otherwise, I recommend removing the CRANK pulley, installing the captive belt over both pullies, and forcing the crank pulley down until the inner, central lip "snaps" into the center hole on the balancer. Then, align the bolt holes and install the 3 bolts.

As far as the smog stuff goes, most of the components you need are rather easily available used, rebuilt, or reproduction. The exceptions are the diverter valve (1968-only piece), diverter valve bracket (1968-only piece), and diverter valve elbow. Those are the challenging and EXPENSIVE parts.

[Jim T.]

Re: '68 L-79 Pulleys

I replaced my original owner 68 L79's AIR pump with a rebuilt unit from Auto Zone almost 4 years ago. The part was a Cardone Whitaker #32-105 is an exact replacement. All I had to do was paint the cast iron back of the pump because it was unpainted. In 1973 I went to a Chevrolet dealership to purchase a new diverter valve for my 68. I was told that the original was not available any longer and was sold a replacement version of the diverter valve. My original water pump pully is actually two individual pullys. My 68 was built in FEB.

[Joe L.]

Re: '68 L-79 Pulleys

Jim and Rich-----

All 1968 Corvette small blocks used a "sandwich" waterpump pulley arrangement. The rear, 2 groove pulley for the L-79 application was as I previously mentioned.

The front, single groove pulley was of GM #3883235 for the 1968 L-79 application. It's long-since GM-discontinued, but available in reproduction.

The 1968 diverter valve for Corvette small blocks was originally GM #7028469 which was stamped "28469". However, I believe that prior to the end of 1968 production, the number changed to GM #7036449, stamped "36449". In any event, the GM #7028469 valve was discontinued in January, 1968 and replaced by the GM #7036449 at that time. That valve remained available in SERVICE until it was discontinued without supercession in 1982.

[Richard D.]

Re: '68 L-79 Pulleys

Thanks Joe and Jim for the info.

My car is an "early" one, Nov. 67 build.

I see that the GM #3995641 (2 groove pulley but of 5-7/8" OD) is still listed on GM Parts Direct. I wonder if they have the AIR pulley also, I will check. Joe, does this pulley (and all the others you mentioned have a 3 inch depth (or "backspace").

One other question - Does the Crank Pulley and the WP pulley need to be the same diameter size?

I would guess it would not matter, but thought I'd check.

Thanks again,

Rich

[Richard D.]

Re: '68 L-79 Pulleys

Oops - Just noticed that you already said that "The front, single groove pulley was of GM #3883235 for the 1968 L-79 application. It's long-since GM-discontinued, but available in reproduction"

Rich

[Joe L.]

Re: '68 L-79 Pulleys

Rich-----

I don't know what the "back spacing" is for the 3995641 pulley. I'd have to go and get one out and measure it and I'm not too interested in tackling that right now. However, from memory, I would say it's about 3". In any event, it should be functional, if not correct, for your application.

GM Parts Direct or any other GM dealer will not have the front pulley (GM #3883235). That pulley was discontinued without supercession about 20 years ago.

The crank pulley and the waterpump pulley DO NOT need to be the same OD. In fact, in most instances, they are not the same OD. The relative sizes of the 2 pullies affects the drive speed of the waterpump pulley and, consequently, other "directly coupled" pullies, too (e.g. A.I.R. pulley).