Here is the scoop: I am designing a custom crank pulley to run my supercharger. It will be mounted to the harmonic balancer. It is a 3 bolt balancer on a ford 300 inline 6. I have measured this thing about a hundred times, at least 3-4 different ways. I am going to take it to my machinist and have plot it but I honestly don't think he can get it any tighter than what I have it due to the variance in the puller holes. Center to center on about 15 measurements I am varying .015" or 15 thousandths, with a low of 2.3965, and a high of 2.4115, and an average of 2.398 over the 15.........Is that tight enough? My 3/8 grade 8 bolt shoulders measure .3705, what diameter should I spec the bolt holes in the pulleys?
Can you post a picture of the pulley and balancer? My 300 is in storage and I can't see it in my head. Is the position of the pulley defined only by the bolts on the balancer? You may need to have your balancer machined with a toleranced mating (pilot or bore) feature to hold your pulley concentric. Then you don't have to depend on bolt hole tolerances to define your two parts concentricity. Check this out: http://en.wikipedia.org/wiki/Geometric_dimensioning_and_tolerancing
I have been thinking about buying a longer balancer bolt, and run it through both pulleys... have the center hole a thousandth over the bolt shoulder diameter.... Would that work?
I would suggest having that first step off of the pulley bolt mating surface cleaned up and made concentric with the crank bore. Then on your new pulley, have a pilot machined to mate with that larger concentric bore. I'll post a picture of what I mean when I get a chance.
I understand what you are saying.... If I do that, should I still get a loner bolt for the center or leave it bored out and use the stock bolt... boring it out would save me some weight....
By cleaned up I mean machined concentric with the crank bore. Probably want to check the mating surface so that it's perpendicular to the crank bore as well, just to be sure. But no, I don't see a problem and blasting it to clean in general.
Im not really sure what your asking but if its a size for clearance for the bolt I would use a letter "V" drill which is .377 factor in the drill running out and cutting a bit over-sized should probally cut another .003" out giving you .007 to .009" clearance for your bolt. I imagine you want a tight fit. You could always run .250" locator dowel to get a good allignment and not have to rely on the srews for location. Brent
After seeing the picture of the pulley I dont think my idea will help you. I had something else in mind.
are you commited to using the stock damper? you should be able to buy a hub and pullies for less than a custom pulley could cost
Would you post pic's of what you are mating to the crank balancer? It will give me some things to consider and before I give an opinion. Any machinist can figure the bolt circle for you.
I don't have a picture, I am designing it, and sending the CAD files to have it cut. It is just a 8 rib serpentine pulley that will set in front of the harmonic balancer seen above. I think I have figured out how to do it. GrimGreasers idea will work perfectly, that way I won't have to rely on the bolts for lining it up, just holding it in place. Only question I am still left with is should I get a longer Harmonic Balancer bolt and thread it through everything, or bore out the pulley.....
I would bore the center of the pulley out. By boring the pulley out you are not having to rely on the back wall of the newly machined pulley to hold the balancer in place, plus less material means a lighter pulley. Just my opinion.
I had a hub and pulley made to turn a McCulloch on an early Olds drew them up in CAD and took the pictures and measurements to a good shop the hub was not too expensive to make but the pulley was not cheap.
Yeah i was quoted at $250.00 for my pulley.... Those look really nice, who made them? The other thing I am having concerns over is the length of mine, I first wanted to sandwich the pulley right up to the harmonic balancer leaving about .01" between them. Well the waterpump pulley sticks out farther than the balancer so I am going to have to put close to an inch between them... putting the overall distance from the face of the balancer something like 2.375", which is about 5.75" from the front bearing........ I hope its not too much stress.
I can look up the required tolerances at work tomorrow, my Machinery Design handbook is there, to provide to your machinist. I will need the dimension of that step feature, though. And yes, I would keep the regular balancer bolt and bore the pulley to minimize mass.
Don't have it here, but i recollect the old B&M blower book had a section on pulleys that said .005" out. If you look at B&M blower pulleys they stick out about 3" so no problem for anticipated load.
The Jalopy Journal
