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Roller bearing cages - full size

Ideas on how to make.....

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IanH10/04/2010 10:19:37
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129 forum posts
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Hi,
I am approaching a big end rebuild on my JAP LTOWZ engine (1000cc water cooled V Twin from the 30s). The original big end bearing was a crowded roller bearing (loads of rollers no cage) but I would like to modify this to add a light alloy cage.
The cage then is an annular ring with a series of rectangular slots to take the rollers.
Phil Irving in his seminal work "Tuning for Speed" recommends milling out the slots with a woodruffe cutter then filing the ends square but I am afraid I don't have it in me to do all that filing.
Do we have any alternative techniques for forming the cages without the filing? I have milling (manual and CNC) and turning of course.
I have wondered about making the cage in two pieces - a plain ring on one end to close off all the slots, but am not sure about how to secure it.
Ian
John Stevenson10/04/2010 10:48:00
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Hi Ian,
 
I also make a new flywheel assembly for a JAP some years ago including new pin and bearing.
 
I plunge cut the slots in phosphor bronze, parted it off and uses a floating washer of the same material to close the slots off.
 

This was a for a racing Morgan and it's still running today with no problems.
 
John S.
 

 
IanH10/04/2010 11:03:43
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Thanks very much for this John,
This was the idea I had in mind talking about a two piece cage but I wasn't thinking of leaving the washer floating.
Reducing the inertia by going into a lighter material might be an idea?
What did you do in terms of clearance between the cage and the crank pin and the cage and the big end sleeve for both the cage and the floating washer? I am thinking of "Tuning for Speed" where there is discussion about the cage wearing the pin away,
What clearance did you use between each roller and its slot? I am thinking that using shaped slots like this you could keep the cage off the pin and sleeve, but the washer would be free to run on the crank pin.
What do you think of giving the washer a register to held it in position on the cage - the register would need to be deeper than the end float on the big end to keep it in place.?
Lots of questions I am sorry!
Ian   
John Stevenson10/04/2010 11:34:17
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Can't remember the clearance now, it was a few years ago, if I had to do the job tomorrow I'd probably allow 5 thou on both.
The roller slots were done with a 1/4" slot drill for 1/4"  x 1/4" rollers, two rows and just plunged in making the roller a snug fit but still free to move.
 
In quite a few designs I have seen hardened washers with the ID at flywheel cheek diameter not bearing diameter so they are held fast when pressed up.
 
I usually allow 10 to 15 thou end clearance on these old racing engines to give they a bit of bag to allow everything to line up when running.
From experience trying to get everything to tight tolerances on these engines is a waste of time because they were never built to tight tolerances and they need the bit of bag to allow everything to catch up.
Ian S C10/04/2010 13:51:12
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If you did decide the end washer needed to be fixed , could it be pinned to the ends of the cage pieces? The pins could be quite small, say 1.5- 2mm dia.Ian S C
mgj10/04/2010 14:45:43
1017 forum posts
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I'm a little puzzled about "all that filing"?
 
You put the blank in a dividing head, with the potential cage aligned on the y axis. The woodruffe cutter is at centre height, and you plunge cut on the side on the cutter using the x axis. You finish with a perfectly rectangular slot with a tiddly little bevel at each end? (assuming you have chosen or made the woodruffe cutter correctly and can plunge to near centre. Too big a cutter and you'll finish with a shallow bevel).
 
To keep the finished weight down you want it as thin as possible, which the cutter wont like, so the blank needs to be overthick on the ID, and once you have the slots, one could return it to the lathe, because one won't have taken it out of the chuck, you can size the ID and part to length.
 
It might take as much as a minute with a needle file to square those bevels. 
 
Or have I misunderstood the set-up?. I agree, with a vertical plunge cut with a slot drill or FC3 cutter, you will have rounded semicircular ends which will have to be filed out, but not with a side cut off a woodruffe cutter.
 
 

Edited By mgj on 10/04/2010 14:50:17

Circlip10/04/2010 16:38:00
1723 forum posts
Wouldn't take much to make a "Broach" and die to take the corners out.
 
  Regards  Ian.
IanH11/04/2010 18:14:34
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129 forum posts
72 photos
Thanks for all the information - I would love to see a sketch of the broach and die set up Ian is suggesting - any chance of this Ian?
I have sent a message to mgj to check out the woodruffe cutter proposal - I think we have different ideas of what a woodruffe cutter is although I suspect it is because the cage is relatively thick compared with its diameter rather than being a thin shell as he suggests.
At the Three Wheeler Opening run today concensus of opinion amongst the racing fraternity was to use an INA caged needle roller bearing running directly on the crank pin. The proposal for the crank pin is to go to a parallel pin with .004" interference and press it together in the hydraulic press - no tapers, no threads! I have to admit that this is tempting......
Question is whether the blade rod will be ok on its bronze bush or should this be sleeved and a crowded needle roller arrangement be put in place - it only rocks back and forth when all is said and done.
Ian
IanH17/04/2010 20:00:41
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129 forum posts
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I think a final scheme is emerging. Moving up to a 40mm od crank pin and using a stock needle roller bearing get you up to 45mm od. If you then add in a hardened ring in the conrod eye you are looking at boring the conrod something like 0.15" over the iriginal dimension. At ths size the conrod is looking rather delicate and as this all started with a fork rod failure,,,,,

New conrods with a bigger "big end" would be required.
Plan B then is to go to a 35mm crank pin allowing me to use 42mm od needle roller bearings which can be accommodated by opening out the existing big end sleeve by only .030 on diameter. I am pretty sure the sleeve is hardened right through so this should be achievable. The od of the sleeve doesn't change so the original pattern conrods will do. If I stick with the bronze bush in the blade rod then it should be straighforward.
Ian  
IanH17/04/2010 20:03:08
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129 forum posts
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Another attempt at the photo....

Bowber19/04/2010 14:01:40
169 forum posts
24 photos
Oh dear
My dad used to race an 84S on grasstrack, they were fast but a little delicate, the Jawa's always won on reliability.
 
A few years later and I was racing and while watching a race an 84S went past just as it blew up, peices of crank case flew into the crowd (no one was injured) I kept a lump with one of the case bolts stil in it holding 2 halves together.
 
Steve

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