AMC Gearbox cam plate

Previously Barry Carson wrote:

looking into my gearbox without any cogs i focused in on the cam plate when i rotate it its buckled about 2mm ish. would it straighten up or is it a case of just renewing it .

Barry

If you are not experiencing any gear selecting issues I would be inclined to leave it alone. The selector dogs should slide around the tracks quite easily so look to see if there are any witness marks which would indicate misalignment. The selector cam plate has a long spigot which passes through the wall of the gearbox and is held in place by a bolt coming in from the outside. It possible that the spigot could be out of true but as I said if it's working ok leave well alone.

Barry

I would rotate the camplate and check the plunger locates in the notches enough to be secure, It may be only just hanging in there.Does the camplate rub against the inner cover because of the buckle?.If it works and is safe no problem, What bent it? I would take a close look around for other damage ,don't want a failure on the road.

I'm always worried about internal faults on gearboxes causing potential lockup. If the runout is enough it could possibly allow 2 gears to be selected at the same time.

If it was mine I would either investigate straightening it or replacing.

Hi Barry..I PM'd you but just in case you don't see it I suggested the Fork selectors could be reversed. (Pt No:040022) They are the same part and fitted back to back but one quite often has its selector pin (that operates in the cam plate cutouts) ground slightly shorter. If fitted the other way it quite often catches somewhere...can't remember where. Cure is to reverse the relative positions of the selector forks (Swap over)...Worth a check I reckon.

Don't think the slight wobble is any concern.

Les

Hi Les. thanks for the information i have taken a photo of what i have . i havent had the box completely built up as yet just testing the water to see what i need to replace or fix to complete it .

Thanks

Barry

Hello Barry to be safe here I would bit the bullet and buy new from RGM Motors Yours Anna J

Hello Barry looking at the photo gives me the impression that they are the same length as if the ruler is not laying straight? It would be easier to use one of those cheapish Digital micrometers you can get for about 35 quid or so, they measure depth as well as width and a "must have" tool nowadays. You can obviously swap them as I suggested as it takes only a few minutes to do. If you could paint some "engineers" blue on the pegs and operate the gear shift, you might end up with a tell tale mark on the tip of one and if you do you only need to grind off a couple of thou. Then again of course, the " catching" might be somewhere else. I was assuming too that this noise is when you operate the shift rather than when the cogs turn as per being driven by the input shaft?...Les

From the photo the pegs look near enough - within .10" or so although it's difficult to see whether the faces are in line - they looks slightly off but this is probably the photo.

WRT digital calipers you can get perfectly serviceable ones for £10 or so from Maplins and the like. I have to say that my M&W micrometers are now gathering dust (although I still use the old vernier caliper for measurements that don't need great accuracy) as I find the digital caliper easily accurate enough for my needs. I've checked them against the micrometers and they are spot on.

Thats interesting Les, does the selector peg thing also apply to Dommy boxes?,or is it a Commando/AMC thing only?. I had a well worn clutch center with plenty of wear from the plate tangs,but replacing it made absolutely no difference at all.Not what I was expecting.

I seem to remember my camplate had a slight buckle and rubbed at some point when it was misstimed,Not a problem though. If the bronze bush in the Kickstart shaft is worn or there is no end float on the kickstart when its all tightened up that won't help.

Previously Barry Carson wrote:

as i say its a gearbox i have out of the bike. just running through it to check things over to see what wants doing or renewing

...............................

Les . on the first photo the camera exaggerated the look of the gap slightly. the catching i can hear is the quadrant catching the cam plate as per photo. theres no play in the cam plate bush i have placed the selectors in position on the cam plate they don't protrude to cause any trouble. i have a digital micrometer but the battery is flat. think its just a case of renewing the plate.

Barry

On my laydown box I had the same problem. I removed the quadrant and found that it had moved on its splined shaft. I tapped it of and refitted with a smear of loctite, checked for squareness of fit and refitted. No more problem. Worth a try?

Hi Robert.. It will be the same for a Dommie box or Commando IF it's going to cause a problem but as said, I just can't remember where the pegs hit. I do have another AMC box to strip down soon which will remind me but it will be at least a week away.... It seems though that Barry's problem is caused by the quadrant slightly grazing the cam plate, probably caused by an unfortunate clash of wobbles. I imagine I would attempt to slightly flex the spindle of each part away from each other by tapping it as Charles said he did. You only want the sum change to be about 1mm, even a fraction of grinding will help and not weaken anything....Note don't lever or attempt any bending with the parts in situ. I would grip the protected spindle of each part in a vice and tap gently the area of contact to achieve the slight change to give the 1mm clearance...Les

If you have access to a lathe it would be easy to grip the shaft in a 3 jaw chuck and get a correct idea where the runout is - and possibly even tap it back into line whilst it is there.

The cam plate seems to be proud of the splines at one side (further from the camera) and not the other, which would obviously give the wobble you're experiencing (although a bit hard to tell from the photo).

The quadrant also appears to be quite a way off from right angles to the spindle.

I'm not sure if the plate and quadrant are pressed on to their spindles but given what we see there I would probably try Les's advice in the first instance.

The only concern I would have is that if it's relatively easy to move the cam plate on the spindle then what's stopping it from moving in service?

I suppose in theory the selector forks would hold the plate in place but like you I would not feel comfortable with what you have.

I would expect that if you used Bearing Fit on the splines it would keep everything together.....

i know you can get a new center but i think its best to renew the whole thing then again a new one will be fitted the same way. i will shelve it for now and have a think about it.

Barry