In this section I ll describe the modifications I made to the transmission pulley. The first thing I did was to remove all the electrical cables from the engine and drop it to expose the transmission and engine pulleys. I removed the two pulleys and the coil from behind the engine pulley, cleaned off the engine pulley, and reinstalled it. I left the magnets to preserve the balance. I was thinking of having it rebalanced but to do that I would need to have a custom mandrel made and that would drive the cost way up. So for now, I ll leave it alone. I also pulled the grounds off of the batteries as a precaution I cleaned off all the residual Loctite, reinstalled the socket head cap screws using fresh Loctite, and torqued them to 20 ft-lb. My screw database showed an advised torque of 25 ft-lb and a lubricated torque of 18 ft-lb. Since the screws were wet with Loctite I compromised on 20 ft-lb. That was about all I could muster anyway as the pulley is free to rotate and difficult to hold. Juan Rivera 8 August 2012 1
Since I can t lock these screws I torque striped them so I can look for any loosening during inspections. The next step is to machine the transmission pulley. It s critically important to mount the pulley so it is absolutely perpendicular to the tool. The fan tabs could be removed using a lathe or a mill, but it will take a mill to cleanup the mounting surfaces inside the pulley. The back side of the pulley is a machined surface so it could be placed flat on the work surface and clamped down on the inside while the tabs are milled off, then the clamps could be moved to the outside while cleaning up the mounting surfaces. If you chose to use a lathe you might need to make a special fixture to mount the pulley. In the photograph below you can see that the thickness of the sides of the sheaves vary slightly. The outer one is quite thin on my pulley (tabbed side.) The design of the alternator drive pulley is based on a maximum total width of 3.190 inches and a distance from the center of the outer sheave to the machined surface of 0.300. This will produce a symmetrical pulley. The alternator drive pulley design is based on the distance from the mounting surface in the center of the pulley to the outer edge. This in tern is based on that 3.190 width dimension. I don t want to reduce the width of that outer edge any more than I have to, but at the same time I need to machine those tabs off and keep going until the width is no more than 3.190. With my particular pulley I think I ll end up with some rough spots and some hard coat in a few areas that look especially thin. This is a purely cosmetic issue. I ll also be left with multiple fan blade mounting holes that protrude down below that 3.190 plane. I may elect to fill the holes and low spots with epoxy and then paint that surface. I ll have to see how it looks once I get going. Transmission Pulley Cross Section Juan Rivera 8 August 2012 2
Change of plans I was going to send this out to a machine shop but I ve decided that I want to do this myself. It s too delicate an operation to leave to strangers. My mill leaves a lot to be desired since it was inexpensive and made in China. I know the headstock is not exactly perpendicular to the table and there is a lot of slop in all of my adjustments, but with care I think I can overcome most of these issues. I ll start by removing the fan tabs and stop short of the final surface dimension while I reassess my progress. Here s a shot of my first pass with the mill. You can see the cross section of the tabs. The tapped hole in the upper tab stops short of the plane where I intend to stop, but the lower hole is deeper and will look ugly. Juan Rivera 8 August 2012 3
This picture shows my temporary stopping point. To get around the deficiencies in my mill I moved the table very little and instead, remounted the pulley in 90 degree increments. That way I was always machining in more or less the same position over the table. For my final cut I locked the quill and then rotated the pulley under the mill as I described. The width of the pulley is now sitting at 3.252 ±.001 across all twelve tabs which is pretty good, considering. Juan Rivera 8 August 2012 4
You can see that I still have material that will need to be removed since the belt clearance is tight, but I ll stop here and wait until I have the drive pulleys. I m currently.062 from my target pulley width. Ideally I d like to stop removing material before the twelve tabs start to blend together. Once that starts to happen I think the surface will start to look irregular. With luck I can remove enough material to allow sufficient belt clearance and still end up with twelve individual tabs sitting slightly above the hard coat background. Juan Rivera 8 August 2012 5
Here s a look at one of the twelve tapped holes from the lower fan tabs. They re defiantly unsightly. I ll clean them out with a reamer later. I ve already removed a lot of weight so I m worried about balance. There is a dynamic balancing shop in the area and I stopped by for a chat the other day. For each pulley they would need to make a custom mandrel. There are also limited locations to drill lightning holes now that the tabs are removed. Weight might have to be added instead. Now it s time to clean up the mounting surfaces where the alternator drive pulley will sit. I drafted the center area of the pulley from the drawings and pictures that I have and printed it out full scale on my cheap inkjet printer using AutoCAD. Modern printers are dimensionally extremely accurate since they re driven with stepping motors. I cut the drawing out and placed it as you see. Then I used the pattern to outline the areas I need to cleanup using a felt marker. Juan Rivera 8 August 2012 6
Here s a drawing showing the areas that need cleanup. Remember to stay away from the web fillets. I made the mistake of not waiting until I had the alternator drive pulley in my hand before starting. By mounting the two pulleys together with SHCS you can see just how close you need to get to the fillets to cleanup the mounting surfaces. I d suggest the following end mill for cleaning up the mounting pads. It has a 1/16-inch radius which will reduce stress concentrations: MSC part number (89338032) 1/2" diameter, 2 flute, 1" length of cut, 1/16 radius. ($37.25) Juan Rivera 8 August 2012 7
I set my mill to a depth of.005 and locked it down 1. I won t unlock it again until I get the drive pulleys and make sure my outer radius is large enough. A CNC mill would have made this a nice clean job, but I had to do it by hand. Going around corners is not easy and you can see the edge isn t a prefect arc. The good news is that.005 seems to be enough to cleanup the surface. The less I take off here, the less I have to remove from the fan tabs. I won t know if I ve removed enough from the tabs until I get the drive pulleys, but not enough is way better than too much. NOTE: MILLING INTO THE WEB FILLETS WAS A MISTAKE. IT COULD CASUE STRESS CRACKS LEADING TO PULLEY FAILURE. STAY AWAY FROM THE FILLETS! 1 I did not use the end mill I suggested on the previous page in these pictures. I went back later with that radiused mill to clean up the cuts shown above. Juan Rivera 8 August 2012 8
Here s the result after taking a.005 cut. You can see that there are a few areas that still have a bit of hard coat, so the.005 cut didn t go quite far enough for a completely smooth surface, but I m not sure that s really necessary. I ll have to wait until the drive pulleys arrive to finalize the depth of the pad cleanup and decide whether I took off enough of the fan tabs to allow the belt to clear properly. Altering those web fillets was a big mistake. I ll have to try to repair them by going deeper with an end mill that has a radius. I ll get to that once I have the drive pulley so I can gauge how much belt clearance I have. I ll write that up once I get started. Juan Rivera 8 August 2012 9
Ideally I d like to bring the entire assembly with both pulleys, the tail shaft, the spur gear and the attaching hardware and have it balanced as a unit. Aside from the cost of balancing the pulleys I left with the impression that the mandrels would cost around $200 a piece. If everyone doing this modification was willing to share the expense then it would be worth it, but then they would have to all send me their pulleys or I d have to send the mandrels all over the world. This is much more work than I want to take on. I think the only reasonable approach is to be as careful as possible and then try it. I already know that I had some engine vibration. If it feels worse then I ll have to deal with it. It is hasn t changed I ll probably live with it. Hold everything I think I can use my Spurling Pro-Drive dynamic balancer which might be perfect for the job. First I ll run the engine and see if I can feel any vibration. I may be worrying unnecessarily. Juan Rivera 8 August 2012 10