Timing pinion to gear cam, meshing OK? W/NG

[nevhunter]

Yes there's no change to the pushrod length The holes in the gear are an attempt at part balancing. Something is better than nothing I suppose. Nev

[stevewhitt]

Based on the pictures, I think I have the standard cam. Where can I buy the 664 version?

[stevewhitt]

Further to my last post today, I see on the forum that the standard 'F' cam's can be machined/ground to be the A6/664 profile.
I have access to an excellent retired engineer, so is this correct and is the correct terminology a 1.25" base circle?
If I get this done, my understanding is that I will not need different push rods?
Does the valve timing change?
Does the ignition timing change?
Are there any other parts required?

In terms of finding an A6/664, Drags do not have any and it would seem neither do the club.

This is a deviation for me from an 'authentic' restoration, but from what I have read, it would be very worthwhile.

Cheers

Steve W

[will_curry]

A6/664 should be directly interchangeable with the 'F' cam although I much prefer
to keep the followers with the cam they were running on.

Pushrods, valve clearances and ignition timing should all be the same.

I'd consider fitting a slightly larger carburettor to allow it to breathe better
at higher revs to get the best from the cam.

If I remember correctly, A6/664 was the 'fast' cam prewar but eventually
was only used in the VB postwar and continued to be right up until the end.

[stevewhitt]

Thanks Will,
I have a 76 carb with 1 1/16 bore.

Cheers

Steve W

[will_curry]

If you get the chance go for a 276 rather than a 76. The latter has 4 holes around the
base of the body to feed air into the pilot system which the original 275 wouldn't
have had. The functionality is pretty much the same between 276 and 76 except
the pilot air isn't filtered and, of course, the look.

Going to 1"1/16 you may have to blend the inlet port on the head as well to avoid a step.

[stevewhitt]

The carb body has 76/014 stamped on it.
The inlet on the head measures 1 1/8”
The corresponding part on the carb measures 1”

[stevewhitt]

Photo of carb

[will_curry]

At 1" the carb should be about right - I'd mis-read your earlier post of the
carb size as 1"1/16.

The carb seems to be in reasonable shape too - how are the threads at the top
where the top screws on? They can get decidedly mangled over the years.

[jj.palmer]

A simple method of checking the mashing/bedding of gear flanks is as follows, this was a method often used in the manufacture of gears, whether it is used today I am uncertain, my associated with gear manufacture ended some years ago.

1.0 Clean both gears, remove all deposits of oil etc..
2.0 Lightly coat the flanks of the driving gear with blue bedding compound, ensure the driving/pressure flanks are coated, ladies lipstick may be used
as a substitute.
3.0 Assemble and rotate the gears together in the direction of drive.
4.0 Check the flanks of the driven gear, the driven/pressure flanks should be evenly coated with bedding compound just short of the tooth root.

Hope that this will help,
John P.