twin cam question

[32 coupe]

Hey all,
While looking at my Ashwamegh 2/25 cam I have noticed that the cam carrier (the bearing) is sized at 2.495 while the hole in the case measures 2.510 that leaves about .015 of play between the two.

It seems like alot of "slop" to me.  Wont' the cam "walk" with this much play ? I was wondering if I should make up a shim to take out some of the excess play. A soda can looks like about .004 to .005 and I'm thinking a "band" shim would be about right ??

I have read all the archived reading about the twins breaking cams , etc. and am concerned about this matter.

What do you guys think ?? Am I worried about something that I should not be ??

I hope I have written this so everyone understands the question.

32 coupe   

[listard-jp2]

Oh the joys of Indian Listeriod ownership  

I can only speak from a standpoint of owning and operating genuine Lister 16-2 engines. In so far that there should be a  precision clearance between the intermediate bearing housing in crankcase and the outside diameter of the  intermediate camshaft bearing. The situation that you describe if left unchecked could possibly lead to camshaft failure due to a fatigue fracture [because of lack of support at the intermediate bearing housing] caused by constant flexing of the camshaft when the engine is running.

The intermediate bearing plays no part in controlling end float, this is achieved on genuine Lister engines by having axial clearance between the last two cam lobes and the bearing on the non gear end of the camshaft, I would think it would be a similar arrangement on a Listeriod engine.

I would consider your suggestion to be a temporary solution at best, because you will have problems with retaining the shim in position, and due to the soft nature of your proposed shim material it may be susceptible too wear away quickly.

I know its a pain but I would consider the best solution would be having the intermediate bearing housing remade, but with an increased outside diameter to more closely match the corresponding crankcase bearing housing.

[BruceM]

There have been a number of reported camshaft failures on listeroid twins, and I suspect what 32coupe has found might account for some of them.  Some steel shim stock (mcmaster.com)  Weld-Bonded (steel filled epoxy) in place might suffice, but I'd also be concerned about camshaft alignment.  In my admittedly poor memory, there were 3 bearings for the twin camshaft, and I'm thinking - what are the chances that they are located accurately, in line with each other, given Rajkot typical practice?  If they are not aligned, then the constant flexing of the camshaft with each revolution over time will cause it to fail at some weakest point. Which is pretty much what the broken twin camshaft pictures I recall have shown.  Somehow, I'd want to check the alignment before shimming anything, as one might wish to use the loose tolerance to correct for misalignment.

Dave (XYZer) has already shown us years ago that case boring of critical locations (cam, idler, crank) for listeroids are way off spec, and vary considerably.  This was the underlying cause of idler gear failures.  I wonder if the same underlying cause might be the problem with twin camshaft failures.

Just speculation...

[38ac]

Bruce you are almost spot on in my opinion. I only differ in that I would say "part of" the problem instead of the problem. One thing that must be known to all who strive to fix the twin's cam problems is this is not entirely an Indian clone problem, there were also issues with the originals. The same drive gear, intermediate gear and cam gear designed for the singles was given double duty in the twins and given the added burden of lack of lubrication on the #2 side. There was a parts 10-2 at an auction I attended a few years ago and the gear train was a mess in it.  I have a 1924 Lister model L twin or TL  in my shop. (This was the basis for the CS diesels) and the cam gear, crank gear and idler gear are a total mess in it also.  Point here being ( I think?  ) is that the need for good fit, finish and material is much more paramount with a twin than a single. Make sure you get some specs for the clearances and carefully check your gears for defects and personally I would install a bronze idler even though the You Tube Listerboob disagrees.

[BruceM]

A very good point to raise on the original Lister twin cam design, 38coupe.
 

[Tom]

If you really want to do it right and if $'s are not an issue and if I understand the problem correctly. The thing to do might be to have it align bored and have over sized bushings made to fit.