I have the dual sheave main and alternator pulleys from what I believe to be Mazdacomp/Racing Beat and was using a stock water pump pulley. Purchased the S5 water pump pulley (S5 one is $79 and the S4 one $163) from Mazdacomp and it doesn't fit. The pulley rubs on the main pulley so tight that you can't even turn the water pump pulley. Is the single sheave pulley smaller than the dual sheave? Is the S4 water pump different than an S5 water pump? Based upon the gasket N326-15-116 that I am using it appears to be an S4 water pump. I really wanted to try it out this weekend and should have checked fitment before I got to the track.

Edit: Just discovered S4 pump has 7 holes and S5 has 8 holes. Is the propeller shaft in a different location?

 

Remember when I mentioned modifying one to fit whatever combo I have on the front of my engine...

I just turned a little off the OD, the hard part was chucking it up in the lathe. I tried grabbing it from the ID first and ended up tearing apart an old water pump to use the shaft as a fixture.

 

I remembered you had to enlarge the center hole but had forgot you also had to turn the OD down. The center hole on mine is plenty large and actually could be a tad smaller. Guess I'll need to have a machine shop turn the OD down after I figure out why the motor quit running this weekend.

 

that is one of the differences in the stock parts too. the S5 has a larger pulley boss, and center hole in the pulley.

 

Anyone want a new S5 Mazdacomp water pump pulley? Make an offer so I can just go pay 2x the price for an S4 pulley and be done with it.

 

I had this exact fitment issue using the s5 Mazdacomp w/p pulley with an s5 pump and the RB deal-sheave main & alt pulleys. A trip to the machine shop solved the problem. They shaved down the OD and also deepened the V-belt groove so the belt is flush. Installed it last Thursday on my way to the track. I'll post a pic when I can.

 

Makes me wonder if the S4 pulley is any different than the S5 other than the price. I'll try and give them a call today to find out.

 

What's the purpose of the dual sheave main and alt?

I am running single main mazdacomp, S5 water pump single mazdacomp (on an s5 waterpump), and stock single alt. No interference issues at all. Also never heard the belt slip once, temps have been perfect.

 

^ With the air pump deleted, the remaining belt makes little contact with the *stock* water pump pulley. The dual sheave main and alt pulleys allow the water pump to be driven by two belts, thus doubling the contact area. (In addition, they are both underdrive pulleys - alt larger and main smaller). See pic from RB site attached.

Due to its larger OD, the mazdacomp water pump pulley has more contact area with the belt, so dual belt grooves are not necessary.

To answer SCCAITS's original question:

The mazdacomp main single pulley is smaller than the RB dual-sheave. Thus, you won't have interference issues if you use both mazdacomp pulleys (main + w/p). I started out with the RB alt & main duals, and wanted to utilize the mazdacomp w/p pulley without spending $ and replacing the main with the mazdacomp piece.

Also, the RB main drive pulley has bolt holes so you can attach the outer stock pulley and drive power steering and/or A/C, if desired, in a street-driven application. Finally, RB makes a single-sheave main pulley, but I don't know if its OD is different than mazdacomp's.

 

SCCAITS:

just run the engine for a while, it'll self clearance

 

One of my favorite quotes:

"It'll wear in before it wears out"

Of course, this is from the same guy who often says....

"BAH, run it till it rains parts!"

 

Yep, that's well known, my turbo runs that setup. But once you have that massive water pump pully there is really no reason for a dual sheave setup, like you said, so why keep the dual, sheave main (and by association) alt pullys.... cost?

 

Yeah, didn't want to spend the money on two mazdacomp main pulleys, as I have two of the RB mains already (one for current engine, one for the spare). Also, I'm experimenting -- wanted to find out if the big w/p pulley helps my water temps (it didn't), so no reason on replacing the entire pulley set yet.

 

My 2hr old motor quit running this past weekend (no joke) or I'd consider it


Excellent, thank you! That is exactly my situation. Guess I'll just get the Mazdacomp single sheave main/alt pulleys and sell the RB ones and do it right.

As far as the S4/S5 water pump pulleys , I called Mazdacomp today and was told "the S4 pulley is different than S5 but I don't know how, corporate won't give us dimensions or specs" ...and there's a 20% restocking fee if I wanted to send it back.

 

Speaking for stock parts, S3 and S4 and S5 all have different pilot bore sizes.

 

/\ and for alts spigot size similar changes , s1/s2/s3 is different to s4/s5 ,, which is different to s6

 

I just run the stock double angle washers for the Alt pully (with the mazda comp single main and S5 waterpump underdrive single). I have not found a reason yet to run anything fancier.

 

Pulley OD was taken down to 4.90". The clearance between the main and water pump pulleys is now a hair over 1/32". So the fitment issue was solved, but created a new problem -- the belt wasn't fully seated because the groove was shallower. I had the machine shop deepen the groove sufficiently to get the top of the belt flush with the groove (there was quite a bit of material available to dredge it out). In retrospect, this was a little too much because the belt sunk in about 1/64" by the end of one race weekend. i.e., it would have been ok for the belt to stick out, say 1/32", when new. Although the pulley body has a conical taper, it isn't bulky enough to interfere with running the power steering belt (not sure if it would get in the way of the inner A/C pulley on a street car -- untested).

 

I thought there was a dual belt water pump pulley to go with the alternator and main pulley that fits???

 

The stock one. No aftermarket dual sheave waterpump.

 

I finally got my hands on a Mazdacomp main pulley which is the correct pulley to use with the Mazdacomp water pump pulley. The Mazdacomp main pulley is approximately 3 1/4" in diameter and the Racing Beat dual sheave pulley (single sheave would be the same) is approximately 3 7/8" in diameter. That explains why the RB main pulley won't work. When I get around to it I'll have a RB dual sheave main and alt pulley set for sale.