38 Idler gear shaft tolerances

[Tom Beaver]

Does anyone have a listing for the fit and tolerances for the shaft that supports the bronze idler gear?  I can't find any dimensions or tolerances listed in the tank engine manual or the factory service manual.  I have two of the shaft supports and both shafts have ware on one side from the thrust of the idler gear.  I'm trying to figure out if they are useable or if I have to try and find a good one somewhere.

Tom Beaver

[Tom Beaver]

Still looking for idler gear/shaft tolerances, they must be written down somewhere but not in anything I have.

Tom Beaver

[Steve Passmore]

I cant find anything about this either Tom even in  the Manufacturing Information Book as this covers New assembly.        Have you considered turning the shaft around and having a good surface facing the thrust?          As I remember the oiling and locating groove is a complete circumference.  Personally I have never found one badly worn.

[Brad Ipsen CLC #737]

I'm with Steve on this.  I have never seen any wear on this shaft.  If you see any wear I should have an extra one some place.  The one dimension that is important are the bushings in the distributor tower.  This is supposed to be .002" and I have never seen one with less than .005".  The oil holes get plugged resulting in much wear.

[Tom Beaver]

Steve and Brad thank you for the reply.  The shaft on part that I have is tapered .0032" and is .0039" out of round.  There must be a significant thrust on the shaft because most of the wear occurs on one side of the shaft at the base with a lessor amount on the opposite side at the end of the shaft.  I do have a new bronze gear but the clearance I measure between it and the shaft is .0055", which I think is a bit excessive.  I could rotate the part around as Steve suggested to place the wear at a different place but I am concerned about to much clearance.

I thought of turning down the shaft and pressing on a sleeve but that's a fair bit of effort and I don't know how well that would even work.  Also, of course, don't know what the clearance should be in the first place.

It's odd that I can find the tolerances for the distributor shaft, the oil pump shaft, wrist pin bushings and etc. but no mention at all for the idler gear.  Maybe it was an afterthought on Cadillacs part..

Tom Beaver

 

[Steve Passmore]

I thought of turning down the shaft and pressing on a sleeve but that's a fair bit of effort and I don't know how well that would even work. 
Tom Beaver
[/quote]

I had thought about suggesting that Tom but I think the shaft may be hardened and not workable on a lathe, it would need to be cam ground then the sleeve would not be hardened. As you say a fair effort. A replacement would be a better bet but if that clearance were on the opposite side to the thrust it would not be a problem as it would always be under pressure.

[Tom Beaver]

Brad, if you have an extra one that's in good shape that may be the easiest fix.  I haven't checked but I bet Steve is right that the part is hardened and that means machining out a whole new part and having it hardened which wouldn't be much fun at all.  I will talk to my machinist friend and see what he thinks but barring something easy its either find a replacement or, as Steve suggests, clock the part so that the gear is wearing on a new part of the shaft.

Tom Beaver