Unit 650 Timing Gears

[Grewth]

I've got a 1970 unit 650 engine to build up from a basket case.
I've got a box full of timing gears to work from, but I can remember reading somewhere that timing gears should be kept as a matched set for some reason.
Any truth in this ?
Or another Triumph myth ?

 

[speedrattle]

if you can, yes. triumph had worn machine tools, and so fitters would hand-select timing pinions that fit well during assembly.

if you mix em up, there is supposed to be the possibility of more noise and maybe? a bit more backlash.

but that was then. i mix em up without anything exploding these days.

if you have a buch of gears, its possible you may have some with keyways that were machined a bit off. these are valuable because they allow timing adjustments a bit more precisely than what the average gears offer. but most all the ones i measure are pretty accurate.

 

[Grewth]

if you can, yes. triumph had worn machine tools, and so fitters would hand-select timing pinions that fit well during assembly.

if you mix em up, there is supposed to be the possibility of more noise and maybe? a bit more backlash.

but that was then. i mix em up without anything exploding these days.

if you have a buch of gears, its possible you may have some with keyways that were machined a bit off. these are valuable because they allow timing adjustments a bit more precisely than what the average gears offer. but most all the ones i measure are pretty accurate.

Thanks for that.
No chance of me keeping a matching set I'm afraid, I've just got the cam pinions that were still on the cams, that's all.
The rest I have are off other bikes mostly T140 I suspect.
My best guess is that the PO didn't have the correct tool to remove them so left the cams where they were.
I can live with a little extra backlash and gear noise

 

[speedrattle]

^^^that is odd. the cam pinions are an press-fit on the cams., and you cant take the cams out without removing the cam pinions. did someone remove the pinions, take the cams out, and then re-install the pinions on the bare cams? if he did, its a good bet that the pinions go with those cams.

if something else is going on, i wouldnt worry about maintaining a matched set. its a good thing to do if you are lucky enough to buy some together-- then mark them and use them that way. but to be honest, after this many decades, the ordinary wear on the cam pinions is likely to be greater than the closeness of fit of any pair when they were new.

T140 cam pinions interchange with T120, but have puller holes and different marks.

 

[Grewth]

^^^that is odd. the cam pinions are an press-fit on the cams., and you cant take the cams out without removing the cam pinions. did someone remove the pinions, take the cams out, and then re-install the pinions on the bare cams? if he did, its a good bet that the pinions go with those cams.

if something else is going on, i wouldnt worry about maintaining a matched set. its a good thing to do if you are lucky enough to buy some together-- then mark them and use them that way. but to be honest, after this many decades, the ordinary wear on the cam pinions is likely to be greater than the closeness of fit of any pair when they were new.

T140 cam pinions interchange with T120, but have puller holes and different marks.

No, the cams were still in the cases when I got them.
But the crank and rods were long gone.
Looks like someone split the cases to remove the crank, but couldn't figure out how to get the cams out of the TS case.
Cams are a little rusty, but probably worth saving as they should be the T120 type (3134 ?)
Same goes for the high gear pinion and sprocket in the gearbox.
But apart from those bits, I've got to fill the rest of it with my own parts.
Should provide hours of fun

 

[speedrattle]

i see. theres typically no reason to remove the cam pinions during a rebuild. th ebushes almost never need to be replaced, and you can split the cases and re-assemble without disconnecting them.

new cams are available from megacycle that give you lots of options if the ones you have dont pass inspection.

ebay is your friend. study up in advance on what you need so you dont end up with boxes of stuff that isnt worth anything to you, like i do.

 

[Lordmac]

Cam pinions? There's cam pinions s'posed to be in there? So THAT'S what those little wheels are for . . . No wonder my bike won't start . . .

 

[Bloodknot]

Don’t forget that the timing cogs have a Hunting configuration which means that every tooth on one cog will eventually mate with every valley in it’s adjacent cog so over time any slight mismatch will bed in.

 

[Grewth]

Don’t forget that the timing cogs have a Hunting configuration which means that every tooth on one cog will eventually mate with every valley in it’s adjacent cog so over time any slight mismatch will bed in.

Thanks for that!
I never actually bothered counting the teeth myself, but I can understand the advantage.
Old Triumphs are full of little touches like that