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Okay, I was able to loosen both idler pulley bolts with the open end wrench, where there’s a will, there’s a way.
My water pump pulley is 5.5”, but my crank pulley is 7 5/8” diameter
Will have a video up in a moment showing what I’m seeing with the 7320 belt.
OK so you have a non-stock lower pulley. Makes sense for a police option. Would spin the alternator harder etc. Now you are into custom belt lengths, stock length belts will not work.
Or you could just get the correct pulley. The correct pulley at paragon is 119. I have an original somewhere in the attic Half that if you want it.
I thought of a way to figure out your custom belt size.
You have one that is too big correct?
So sacrifice it and use it for measuring. Cut it, put it in the grooves, and tape it where it overlaps.
Then take it to the shop.
If you have to measure it and order it online I think they measure them on the outside flat edge.
I thought of a way to figure out your custom belt size.
You have one that is too big correct?
So sacrifice it and use it for measuring. Cut it, put it in the grooves, and tape it where it overlaps.
Why not use the old PS belt? If the old PS belt is wider, you may have to subtract about 3/8" because the new belt will sit lower.
Originally Posted by leigh1322
If you have to measure it and order it online I think they measure them on the outside flat edge.
There are two length numbers shown in the Gates tables. One is effective length. That is the last three digits of the belt number. ie 7330 is 33.0" effective length. According to the Gates tech, we can't measure that. The OD is also listed in the table, but according to the Gates Rep that table is not maintained and was fractionally wrong for all the belts I used on my BB. I measured my belts using the cut belt method Leigh suggested and called Gates.
For the 7-5/8" pulley you will need a belt that is approximately 1-5/16" longer than the ones that we are all using 7315 (31.5") or 7320 (32.0"). The 7330 (33.0") should fit a little looser than a 7315 on ours unless there are other differences. Two things to remember: the belts will stretch a little when it is in-service so if it seems tight but you can get it on, it may be alright. It will take a lot of idler puller movement to take out a small amount of slop on that particular belt.
Aside from screwing up the belt size I need, what will having a larger crank pulley do or not do?
Assuming all your other pulleys are the original diameter. Your accessories will spin 13% faster. Powermaster has an RPM limit on their alternator. For me with the 6.75" pulley, I exceed this limit at 6000 engine RPM's (my rev limiter setting). You'll be 13% faster than me. Your water pump will require 44% power to spin 13% faster. Pump power is speed cubed. If you didn't have cavitation problems before, you are probably OK. . My guess is the same with the PS pump . I don't know about the power requirements with the fan. In theory it could be as much as 44% more but the viscous clutch my reduce those losses.
That being said, The post where I found the crank pulley diameters stated that GM went to 7-1/4" pulleys in the 74 vette to alleviate an overheat problem in '73. Air restriction with the plastic nose?
Agreed with the accessory speed increase from a larger 7 1/4" crank pulley. You mentioned a police engine. That would be a typical factory mod for a police car engine. More electrical / cooling needs.
When I was looking for a correct LS6 crank pulley I found out that one is a cast iron version, and there were in fact two diameters. A stock 6-3/4" diameter and an even smaller one, maybe 5-3/4" IIRC. The small one may have been used on high revving L88s or ZL1s or just available as an over the counter race part. But it's purpose would be to keep from over revving the alternator at extended 7k+ engine speeds, and perhaps save some HP from reduced WP/fan drag as well. You definately would not want to use that on a car that does low rpm a lot, it probably would not keep the battery charged or spin the water pump hard enough not to overheat. Old drag racing trick too.
Okay, Gates 7330 for the win.
It was pretty difficult to get on, and it’s pretty taught even without pushing the idler against it.
Also, I see why I was able to loosen the bottom idler bolt with my wrench…
No pulley or belt in the way. Now that ther’re installed I have to go buy a 9/16 inch socket.
I told you, I literally don’t own any tools I haven’t had to buy for something specific I’ve already done.
And my Miata is all metric.
I believe I did mention that it's a bit of a wrestle to get that belt on! It'll stretch out a little as you run it. Pick up an extension for the socket too.
Ok, one last thing. As 71 Green pointed out, your pulleys look misaligned. I don't know if it is just the way the picture is taken, but the pulleys look offset and the belt looks slightly twisted. Also, in your first picture all the belts look new. Did the PO not replace the WP belt when the others were replaced or did the car eat a new belt in a short time? Keep an eye on that belt. You may have to shim the WP pulley or possibly find a correct crank pulley.
EDIT OK, looking back on the last picture, I see the fan isn't on yet which will correct some of the misalignment, but from your original picture the pulleys do look misaligned. .
All belts back on. Went slightly smaller on the PS belt, which repositioned that pulley, which in turn gave me a little more play on the alt belt so it’s not maxed out anymore.
Wasn’t able to fit any tools up under the car other than my trusty little open end wrenches, so loosening and tightening the PS bolts was SUPER FUN.
Had to have my son hold the pump in place while I tightened the bolts.
Started her up and gave it a few revs up to about 1800 RPMs, no squealing.
I’ll take a quick video tomorrow. Gonna put the top up and brave the cold weather. Can’t wait to drive to work tomorrow and get the right kind of stares.
Sorry about all the run around about BB belt sizes, we were assuming you had the correct diameter crank pulley.
Glad you got the belts installed and have the satisfaction of doing the work yourself.
Hope you have a record of the 4 belt sizes for future reference.
Now it's time to enjoy your car...have fun!
I have a related question though.
Now that the screeching belt sound is gone the car sounds like a dump truck.
Pretty sure the main sound I hear is the transmission winding up while I accelerate.
Once I'm up to speed all I hear is wind, but the only time I get to hear the sweet sound of the engine burbling is when the car is idling.
Is that normal or what?
From: Loud, Raw and Dangerous 1968 327 4S in Southern California
Whew...I got dizzy reading this discussion. Congratulations sticking with and working out your issues. Big kudos also to the helpers on the forum. As far as the sound...stock mufflers perhaps? Slap some turbo mufflers on that puppy and you will hear the sound of the engine. Mine sounds like a dinosaur when I take off.
I have a related question though.
Now that the screeching belt sound is gone the car sounds like a dump truck.
Pretty sure the main sound I hear is the transmission winding up while I accelerate.
Once I'm up to speed all I hear is wind, but the only time I get to hear the sweet sound of the engine burbling is when the car is idling.
Is that normal or what?
Designer Imagines A Corvette That Looks More Like a Corvette Than the Corvette
Slideshow: A Jaguar designer's personal project imagines what a modern front-engined Corvette might look like if Chevrolet revisited the golden age of the Stingray.
It'll stretch out a little as you run it. Pick up an extension for the socket too.
