Mechanics?

[the_lone_wolf]

Righto, a friend of mine has recently done a complete strip of his triumph trophy engine, just been looking at the bits and noticed something i've never seen before

imagine the cog on the end of the balancer shaft, it's about 12mm wide. now immediately next to it, touching, is a cog of the same diameter, only about 4mm wide or so, but here's the kicker, there's fewer teeth on this cog than the larger one so if you turn the shaft the two sets of teeth go in and out of phase

but it gets better... the smaller width cog is on the inside of the larger width one from the point of view of the assembled engine, but it isn't actually connected to the balancer shaft, it's free to rotate around it

can someone please enlighten me as to what this arrangement of cogs is called and what purpose it serves, there was another one on the sprag clutch

[yorkie_chris]

Some type of accessory drive?

Can you get a pic, as I'm not entirely sure what you're on about

[the_lone_wolf]

Originally Posted by yorkie_chris

Some type of accessory drive?

Can you get a pic, as I'm not entirely sure what you're on about

yeah i know, it's hard to describe, haven't got a camera but as i'm not busy i'll knock something up in autocad and create a model

[the_lone_wolf]

image uploaded:



the larger cog is connected to the shaft, the smaller one rotates freely around it - if you look at the teeth you'll see the smaller cog has fewer so they go out of phase as you spin the shaft

[yorkie_chris]

Tis to eliminate backlash and chatter

Interesting....can you explain it a bit more for me YC? I havn't seen anything like this before

[the_lone_wolf]

oi, who moved my thread

i'd imagine because the tooth on the crackshaft cog has to slightly prise apart the two cogs it might help them mate better

do you know what it's called chris?

[yorkie_chris]

Seen them before on CNC machines, normally have equal number of teeth with springs to push them half a tooth apart, takes up the play between the gears.

I imagine the friction between the 2 (as small gear is rotating faster) will damp down gear noise.

Listen to a car in reverse to hear why you need to damp down the noise of straight cut gears.