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Just went out to measure my belt position. My belt is in the rear position on the PS pulley. 4 rib belt on a 5 rib pulley, so one empty groove at the front of the pulley. I measured 1.015" from the rear edge of the belt to the machined surface of the adjustment carrier that the idler bracket sets against.
Thanks from me too. I think Darien is running his belt in the front grooves of the PS Pully. With two 16th inch spacer washers under my pully the distance from the lower mounting face of the Base to the inside edge of the rim on the pully is 1.165 inches. I wonder if Darien can figure out just what it means in terms of shims under the pully for mounting this new Idler.
Then there is still the question of which mounting surface was the measurement made from. On my engine that I am designing from, the two mounting surfaces are about 50 thou different with the lower one being closer to the belt than the upper one by that much. If I were going to mount one of these on my engine I would need to shim the upper mounting surface by that much to have the idler to be mounted flush to both surfaces.
Last edited by Jerry Feather; 11-18-2023 at 10:48 AM.
Thanks from me too. I think Darien is running his belt in the front grooves of the PS Pully. With one 16th inch spacer washer under my pully the distance from the lower mounting face of the Base to the inside edge of the rim on the pully is 1.165 inches. I wonder if Darien can figure out just what it means in terms of shims under the pully for mounting this new Idler.
Then there is still the question of which mounting surface was the measurement made from. On my engine that I am designing from, the two mounting surfaces are about 50 thou different with the lower one being closer to the belt than the upper one by that much. If I were going to mount one of these on my engine I would need to shim the upper mounting surface by that much to have the idler to be mounted flush to both surfaces.
I made my measurement from the upper surface. In all honesty, When I made my bracket/idler assembly I assumed the two machined surfaces were coplaner. My idler pulley is flat all the way across (doesn't have raised edges) and much wider than my belt, so fore/aft positioning isn't that critical, though alignment may be, to keep the belt tracking straight..
I made my measurement from the upper surface. In all honesty, When I made my bracket/idler assembly I assumed the two machined surfaces were coplaner. My idler pulley is flat all the way across (doesn't have raised edges) and much wider than my belt, so fore/aft positioning isn't that critical, though alignment may be, to keep the belt tracking straight..
Thanks, Simon, for staying with us on this and for helping out with the information you are providing. I tend to be concluding that the surfaces of the mounting places are just about random in respect to their relative planes and even the relative resulting thicknesses. What I am going to have to do is provide a small group of thin shims in order to accommodate proper mounting of the idler base.
I have the bolts figured out for these Idlers. I am using a 38 by 24 schedule 8 bolt that is 2 1/4 inches long for the pully axel bolt. In that length it will be able to use from zero to about 4 1/16-inch-thick spacer washers to get the belt and pully lined up. I think that is an advantage over putting the pully on the bottom bolt for holding the PS base in place since that is only 8mm. The 3/8 bolt is about 43% heavier than 8mm. I have also ordered the 8mm bolts to hold the base in place that are about 50mm long and that are countersunk with a socket head. I wont be able to test fit my Base on my engine until I get the bolts to mount it.
Last edited by Jerry Feather; 11-18-2023 at 11:03 AM.
I made a few shims that I think might be necessary to properly mount this idler Base. They are in thicknesses as follows: .020, .025, .032, and .050. I had hoped to include some in .040, but I could not find any of that material in my stash. I guess I had used it up in the 928 door hinge shims that I have made before.
Last edited by Jerry Feather; 11-19-2023 at 08:23 PM.
I assume the bracket is symmetrical about the tensioner groove so that the shims are capable of mounting on the upper or lower bolt position?
Is the intent to use spacer at the top and bottom bracket bolts to account for the offset between the mounting surfaces and simultaneously adjust the idler position to be centered on the belt (narrow, flanged pulley, so so positioning is critical), or are you planning on shimming one bolt location and then still providing additional (geometrically different, 3/8" ID) shims for pulley mount bolt for positioning?
The shims will work at either or both mounting points. The shims are not intended for pully positioning. The pully will be positioned for belt alignment only with the washers under the pully on the pully axel bolt. There is about a 32nd of an inch of extra width on the pully compared to the width of the belt. That, together with the 16th inch washers, should be enough to get perfect alignment. However, I am going to see if my fastener supplier has some thinner washers to also include with the idler.
I finally received the mounting bolts that I had ordered a few weeks ago and am now sending a complete idler to Darien. I have three more from this little project if anyone is interest
11-15-2023, 11:33 PM
