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Fitment of mainshaft 3rd gear and layshaft 2nd gear

Submitted by david_schandall on Sat, 25/02/2023
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Commando

History-gearbox had been used miles? with mismatched 2nd gears. I realized this the first time I reassembled the inner cover which of course bound everything, though obviously the previous owner forced it together and rode it like that. I have replaced 2nd gear and 3rd gear as matched pairs. The gears are Andover Norton. My concern is the "wobble of the splined gears. I have about 1200 miles on now and took the box apart to have a look around and I see apparent uneven wear of the teeth and one selector fork wearing noticeably. Below are the spline dimensions of the shafts and gears. Shafts are straight, some wear on mainshaft in area of sleeve gear, -.002" inboard and -.001" outboard.

Mainshaft 3rd gear spline .996"

Layshaft   2nd gear spline .997"

2nd and 3rd gear spline id 1.000"

All gearbox bearings are new, selector fork straight, no play in forks on shaft.

the gearbox works well, no problems with shifting, noise etc.

So the question is- Is some wobble ok in the aforementioned gears.

Thank you

Submitted by dave_taylor on Sun, 26/02/2023

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I would have thought that running with mismatched gears has a high probability to bend or damage something. The selector fork should not be showing signs of wear after only 1200 miles. Was the oil clean and free of gold dust, could it be an end float issue?

However, If the gearbox is quiet, smooth, shifting properly, and not jumping out of gear I think you going to have to recheck everything over and over again, or just ride it. To quote an old friend and mentor, "Let it develop it will tell you when it has had enough".

 

 

 

 

Submitted by david_schandall on Sun, 26/02/2023

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Good morning,

Thank you for your response. Oil is clean, no gold dust and a small amount of black paste on the magnetic plug. Your friends advice is well taken. 

Submitted by ashley_cutler1 on Sun, 26/02/2023

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David, 

Considering that there needs to be tolerances on these parts and the fact the tools that make them have also a wear tolerance there will always be differences in parts, this is acceptable. With gears the internal spline to shaft spline gets tighter as the tools wear. 

If the gearbox functions, shafts are straight, oil is clean then there is no problem. Uneven wear along the length of gear teeth is also not unusual and varies from one box to another as the shafts can be anything upto 11 thou from running parallel due to the old way of manufacturing the gearbox shell and inner cover.

Now the concerns, the wear on the area of the sleeve gear, did you take measurements prior to fitting the new items or is the 'wear' witnessed from the use of mismatched gears. The fact you have lost a thou suggests that your shaft will be shot in 10000 miles. Are the various areas on the shafts running concentric to their respective bearing areas.

Running mismatched gears is not ideal and I would not risk using the shafts as I doubt they are straight. There is also the little known issue of 4th gears being mismatched, a Domi layshaft 4th will run with a Commando sleeve gear, and vice versa, one combination will have lots of backlash but still work, the other will whine like mad letting you know something is wrong.

Selector fork, does this show wear in the 'throat' or on the sides of the fork, considerable wear would soon wear through the hard layer of the fork and gear. Does the fork have relieve in it on the outside edge, if not then it is not an AMC selector fork. 

Mr. Cutler,

Thank you for your insights and information.

The wear on the sleeve gear portion of the main shaft was there when I replaced the mismatched 2nd gears. I suspect the wear on one of the selector forks is from the mismatched 2nd gears, .007" deep on one side. The forks do have the relief. I don't have a set of v blocks so it is a little tricky to check the shafts re straightness and concentricity, however I did find a .002" bend in the area of the sleeve gear and a .001" in the lay shaft. The splines appear concentric. 

Sleeve gear has one chipped tooth, 4th gear lay gear is quite loose on the splines, and has an id +.008" larger than the od of the splines. Both 1st gears have some wear and nicks, main shaft gear much worse of course. All original gears marked "g". 

I prefer to replace the worn items in sets and also to replace the mainshaft. I am trying to rationalize the cost. I guess that's just part of the deal

thank you

d schandall

 


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