E: Engine Half time pinion specification

[Bill Thomas]

Remember, the drive gear for the ignition must have .008" backlash. Ignition must be timed with the gear resting back against the driving pinion.

Bit worried about that !,
After a disaster with my Special, I found the new Fibre pinion was a snug fit !!, "D" distributor,
Wanted it back running quick, So took a chance.
Greg later told us that we could use a Half time pinion , On the breather tube ?,
For me a smaller size ?, And that would sort the problem,
Good idea, Thanks Greg, I have never needed before, And didn't know of,
Not sure if I should take it apart again, Not keen !.
Worried of Ruislip .

 

[Robert Watson]

That's what happens when you try and trust a 70 something year old memory, I'm sure you are correct at .108!

Also Bill I had a new tufnol ATD pinion a few years ago (unused but could have been years old) that was great on the pitch dia, but the outside dia was about 30 thou over spec and bottomed and got bound on the breather pinion. Chucked it in the lathe and took 60 thou of it. Problem solved, it bound tight enough to stop the ATD (even with new heavy springs) from returning to full retard at an idle.

 

[Bill Thomas]

I have been known to worry too much !,
Just wanted it back on the road , An AGE thing, Mine !,
I had not touched the engine in 38 years, Don't go far !,
A lot of new owners tend to over think things , These being Old Bikes,
Mine was not as bad as yours, Just a bit snug, Which I know is not right,
Was thinking it was NEW old stock, Maybe swelled with age ?,
That Breakdown nearly DONE for me, Hottest day etc !,
Must dig it out next year, And give it a good Talking to !! ,
I was enjoying it so much before it went Bang !.
Cheers Bill.

 

[bmetcalf]

There was quite a series in MPH about that measuring technique. Very glad mine came to me in 1980 in fine shape in that department.

 

[vibrac]

On a fixed drive my thinking is that backlash is not so critical what is important is that all the clearance in the drive direction is taken up when setting the timing not unlike the days of chain drive mags