Rare Pulleys

[Joe R.]

Re: Rare Pulleys

Joe------


The only add-on pulleys I know of that will mate with the GM #3858533 are the GM #346290, used in PRODUCTION for most 1975-E1980, and the GM #14023153, used in PRODUCTION for most L1980-82, which you mentioned. The 14023153 also replaced the 346290 for 1975-1980 SERVICE. Actually, I do not understand why you found even a slight fitment problem when trying to mate the 14023153 to the 3858533 as that combination was used in PRODUCTION.

As far as alignment with the power steering pump pulley, that's another problem. While the 3858533 and 14023153 combination could be used on pre-1975 Corvettes, I don't think that combination would align with the pre-1975 pump pulleys. For 1975 and later, a different power steering pump was used which, in turn, required a different power steering pulley. Originally, that pulley was GM #346289 and later GM #14023175. If a 3858533 was mated with either a GM #346290 or GM #14023153 on a pre-1975 Corvette, I believe it would require using the 1975+ pump with either the GM #346289 or GM #14023175 pulleys for the crankshaft and power steering pump pulleys to align.

Hi Joe:

There might be a problem with the '533 that I have been using for my fitment checks. I have samples of both the 346290 and the 14023153 standard-groove add-on pulleys, and both of them fall slightly short of fully seating in the '533 I have on hand. Based on your findings, my guess is that simply tightening the three pulley bolts might close this gap without causing problems.

So, the good news is that anyone trying to replicate the appearance of the rare 1965 configuration has a couple options for the crank pulley that would be visually correct in terms of configuration. That leaves us with just the PS pump pulley to sort out.

Based on just comparing pulley offsets at my desk, it appears that the 3860457 PS pulley that I have comes the closest of any in my collection to providing the correct offset for the 1965 configuration. My measurements suggest that it will still be slightly off, but I have never mounted it on a mock-up to check. I'll try to do that soon and report back on what I find.

[Joe L.]

Re: Rare Pulleys

Joe------


The GM #3860457 power steering pump pulley was originally used for 1965-68 Chevrolet passenger cars and Camaros with small block and power steering. It is a narrow groove pulley as you mention and that's why it will not exactly align with the GM #346290 or GM #14023153 add-on crank pulleys which are deep groove. Also, while it might work for the 1965 Corvette with SHP application, it will not mimic the configuration of the GM #3868892.

Also, I've made a slight clarification to my previous post. I was not clear that the 346290 or 14023153 are the only pulleys in addition to the 3827843 that will mate to the 3858533.

[Joe R.]

Re: Rare Pulleys

Joe------


The GM #3860457 power steering pump pulley was originally used for 1965-68 Chevrolet passenger cars and Camaros with small block and power steering. It is a narrow groove pulley as you mention and that's why it will not exactly align with the GM #346290 or GM #14023153 add-on crank pulleys which are deep groove. Also, while it might work for the 1965 Corvette with SHP application, it will not mimic the configuration of the GM #3868892.

Also, I've made a slight clarification to my previous post. I was not clear that the 346290 or 14023153 are the only pulleys in addition to the 3827843 that will mate to the 3858533.

I have another project underway today in the garage, but I set aside an hour to try and quickly mock up the setup so that I could check the 3860457. Unfortunately, there seems to be something not right about my present setup, because the 3860457 comes out a bit *too far* to properly align with the 346290, when my table-top measurements suggest it should be "not far enough.*

I'm out of time to look at this further today, but I will get back to it and figure out the problem.

According to my table-top measurements of the pulley offsets, the belt center line of the 3860457 should end up about .100" too far back to align properly with the 346290.

One useful thing that I noticed as I mounted the PS pump on the block was that it would be very easy to shim the PS pump forward by .100". So, if the end result of my tests confirms that the 3860457 is just a tad too far back as expected, proper alignment could easily be achieved with some shims on the PS pump mounting bracket and a slight tweak to the third-arm bracket support that bolts to the side of the block.

[Joe R.]

Re: Rare Pulleys

I have another project underway today in the garage, but I set aside an hour to try and quickly mock up the setup so that I could check the 3860457. Unfortunately, there seems to be something not right about my present setup, because the 3860457 comes out a bit *too far* to properly align with the 346290, when my table-top measurements suggest it should be "not far enough.*

I'm out of time to look at this further today, but I will get back to it and figure out the problem.

According to my table-top measurements of the pulley offsets, the belt center line of the 3860457 should end up about .100" too far back to align properly with the 346290.

One useful thing that I noticed as I mounted the PS pump on the block was that it would be very easy to shim the PS pump forward by .100". So, if the end result of my tests confirms that the 3860457 is just a tad too far back as expected, proper alignment could easily be achieved with some shims on the PS pump mounting bracket and a slight tweak to the third-arm bracket support that bolts to the side of the block.

Apparently the error in my initial setup was that I used a 350 block and crank that were readily accessible. I had assumed that this would not make a difference, but when I installed a 1967 L79 damper, the face of the damper ended up closer to the face of the block than it should have been. The damper is so close to the block that it would have hit the timing cover if one had been present. Maybe this is unique to the specific 350 crank that I have, or due to some other GM change that I was not aware of.

I switched over to an assembled 1967 327 engine and now the measurements are what I expected. The 3860457 pulley belt center line is approximately .100" farther back than the center line of the 346290 standard-groove add-on pulley. This is much better than the Corvette base engine PS pulley 3770509 that is more than .200" back.

The sample 3860487 pulley that I'm using doesn't run completely true, so it's hard to determine the precise amount that it would need to be moved forward. I have another one on the way and will check that when it arrives.

[Joe R.]

Re: Rare Pulleys

Apparently the error in my initial setup was that I used a 350 block and crank that were readily accessible. I had assumed that this would not make a difference, but when I installed a 1967 L79 damper, the face of the damper ended up closer to the face of the block than it should have been. The damper is so close to the block that it would have hit the timing cover if one had been present. Maybe this is unique to the specific 350 crank that I have, or due to some other GM change that I was not aware of.

I switched over to an assembled 1967 327 engine and now the measurements are what I expected. The 3860457 pulley belt center line is approximately .100" farther back than the center line of the 346290 standard-groove add-on pulley. This is much better than the Corvette base engine PS pulley 3770509 that is more than .200" back.

The sample 3860487 pulley that I'm using doesn't run completely true, so it's hard to determine the precise amount that it would need to be moved forward. I have another one on the way and will check that when it arrives.

Okay, the mystery of the unexpected result of the initial test is solved. In my haste to do the mock-up quickly, I simply put a bare crank into a bare block and installed a damper on the crank. I forgot to install a timing sprocket on the crank before installing the damper, so when the damper bottomed out on the crank, it was more than a half inch farther back due to missing timing sprocket!

[Joe L.]

Re: Rare Pulleys

Apparently the error in my initial setup was that I used a 350 block and crank that were readily accessible. I had assumed that this would not make a difference, but when I installed a 1967 L79 damper, the face of the damper ended up closer to the face of the block than it should have been. The damper is so close to the block that it would have hit the timing cover if one had been present. Maybe this is unique to the specific 350 crank that I have, or due to some other GM change that I was not aware of.

I switched over to an assembled 1967 327 engine and now the measurements are what I expected. The 3860457 pulley belt center line is approximately .100" farther back than the center line of the 346290 standard-groove add-on pulley. This is much better than the Corvette base engine PS pulley 3770509 that is more than .200" back.

The sample 3860487 pulley that I'm using doesn't run completely true, so it's hard to determine the precise amount that it would need to be moved forward. I have another one on the way and will check that when it arrives.

Joe------


I don't recall the GM #346290/ GM #14023153 as being standard groove pulleys but they might be. I have NOS examples of both but I'm too lazy right now to dig them out. While I have had them for a long time, these were never pulleys that I was too interested in, so I never really studied them.

I don't understand the situation with the balancer that you described. As far as I know, all small block balancers are the same dimension from the face to the end of the snout (surface where they contact the crankshaft sprocket), regardless of the thickness of the outer ring. However, I've never really confirmed that by my own measurement (even though I've got most of the balancers). The only real difference in the balancers is the timing mark---pre-1969 balancers have the timing mark aligned with the keyway and post 1969 balancers have the mark several degrees displaced from the keyway.

[Joe R.]

Re: Rare Pulleys

Yes, the 346290 and 14023153 are standard-groove PS crank pulleys that nest with the deep-groove dual 3858533 crank pulley. So, in this respect, they are functional alternatives for duplicating the rather odd 1965 combination a standard-groove PS crank pulley used in combination with a deep-groove dual crank pulley.

As noted in my previous posts, the 3860457 PS pump pulley comes very close to lining up correctly with the above crankshaft pulley combination. I'll have a bit more info on this after I get another sample of the 3860457 (my current sample does not run true).

[Larry P.]

Re: Rare Pulleys

Joe,

The TIM&JG indicates the L75-300 hp & L79-350 hp uses a 5-3/4" OD compressor pulley, but the L76-365 hp uses a 6-3/8" OD pulley.
My 53-1975 Parts Catalog only lists the GM #5914745 (I assume 5-3/4"), so I don't know the PN of the 6-3/8".
Makes me wonder if the purpose of the larger pulley was for a deep groove. If it was, it just doesn't make sense that they would only use it on the L76.

Thanks,
Larry

[Loren L.]

Re: Rare Pulleys

The larger pulley would be to slow down the rotation of the compressor to "let it live" at higher RPM.

[Joe L.]

Re: Rare Pulleys

Joe,

The TIM&JG indicates the L75-300 hp & L79-350 hp uses a 5-3/4" OD compressor pulley, but the L76-365 hp uses a 6-3/8" OD pulley.
My 53-1975 Parts Catalog only lists the GM #5914745 (I assume 5-3/4"), so I don't know the PN of the 6-3/8".
Makes me wonder if the purpose of the larger pulley was for a deep groove. If it was, it just doesn't make sense that they would only use it on the L76.

Thanks,
Larry

Larry------


The purpose of the larger pulley for L-79 applications, assuming such a pulley was actually used, would undoubtedly be as Loren mentions. However, I have no GM-sourced information that such a larger pulley was actually used. It may well have been as it would make sense. But, I can find no GM information supporting that.

[Loren L.]

Re: Rare Pulleys

L-76, Joe. Red 65 coupe at San Diego Nationals.

[Larry P.]

Re: Rare Pulleys

Although, I realize it could only be viewed as visual reference only, there is one of the 6-3/8" OD compressor/pulley combinations currently listed on Ebay item# 262732019105.

I had read the higher RPM being the reason for using a larger OD pulley on the L-76, but had forgot. Thanks for the clarification.

[Joe L.]

Re: Rare Pulleys

L-76, Joe. Red 65 coupe at San Diego Nationals.

Loren-----


GM never cataloged the pulleys I originally described for 1965 L-76 applications with C-60 and N-40. The application they were cataloged for was L-79. It would make sense, though, that the same pulleys would have been used for L-76 with C-60 and N-40, assuming any such cars were built.

[Larry P.]

Re: Rare Pulleys

Would anyone have a photo of the 3850979 water pump pulley used for the L79 application with C60 & N40 they could post? I believe I had read in one forum where the pulley did not have the PN stamped on it. If that's the case, some dimensions would be greatly appreciated.

[Neal K.]

Re: Rare Pulleys

The larger pulley would be to slow down the rotation of the compressor to "let it live" at higher RPM.

LorenI am not that knowledgeable about pulley operation, but I thought that the larger the drive pulley is the faster the smaller driven pulley rotates. I am not sure I correctly understood the meaning of your comment. ThanksNeal