Velocette

Aah, Velo's.

They don't make 'em like that anymore.

Edward Turner would have had a shIt fit if one of his designers would have asked for a gear like that...

How much ????

Seriously, nothing wrong with making that gear out of alloy, it's ignition, not cams, so nothing will be harmed if it did go bang.

Presumably everything is getting covered in oil in the timing chest, so no biggie, In fact i'd prefer alloy over tufnol in that scenario.

My two Baht's worth...

The reason for possibly making it of aluminium was clearly explained in my post. Again, because you are altering the specification of the gear Helical/straight and the DP slightly, it is your risk should the cam gear get worn out as well- due to any possible mis-match. Especially if the engine is not a ‘safe engine’.

.

Presumably in your 'clear explanation' you did not really mean aluminium ... but some suitable alloy [as yet unspecified]

MichaelG.

I would be much more worried about microscopic (or larger) metal particles being rubbed from either meshing gear through any mismatch of tooth form, and then travelling around the engine. With aluminium as one of the gears you need to be alert to microscopic particles becoming embedded in its teeth, and those then forming a lap which wears the mating gear.

Deviation from specification is not always a sound idea unless you have a very firm grasp of the underlying design criteria and the likely consequences of changes.

I meant aluminium as a generic term. Just like steel is fairly generic, it obviously can be an alloy of variable composition, once there are other minor metal components in the recipe. Steel also has a variable carbon (non metal) content that can considerably alter its characteristics. Brasses, bronzes are common metal alloys but aluminium is also termed an alloy when only ‘alloyed’ with silicon (definitely not a metal).

I daresay the term ‘alloy’ has been diluted in the English language? They tend to class aluminium as different ‘grades’, dependent on the characteristics required and the other elements included - both metal and/or non-metal additions.

Got no worries about the use of a steel gear. Bikes fitted with manual a/r magnetos were fitted with steel gears as far as I remember ( based on the Clubman Viper my riding mate had) and the second hand BTH mag and wheel sourced by a local dealer that I fitted to my Viper.

The slight mismatch between module and DP was the worry as I'm no gear specialist just a t***t a**e and making the gear is keeping me away from her indoors who's decorating the kitchen.

Is there a Velo enthusiast out there who's desperate for a mag wheel that's willing to do an extended test, can let him/her have one cheap Lol.

Thanks for all your advice guys

I have made a lot of helical gears for stationary engine,timing and sideshaft,and one or two magdyno geas. What I have learnt is I now ask the customer if it is to drive a reconditioned magneto after one customer complained of gear wear,the mag was very difficult to turn the bearings were far too tight, Do not mix gears with different pressure angles ,fine teeth will really whine, eg Gardner ) 0 gas engine 14 dp ,not my gears. On course gears eg 10 and 8 dp where the engine has been well corroded in the past and the mag gear is missing ,pressure angle gears can be mixed as they run so slow. and hit and miss igniton will drown any noise.Do NOT cut the teeth at an angle they must be spiral cut, I would not use any soft material eg ali and tufnol ,try to use similar steel and the hardness of the original ,particularly when dealing with high perfomance Velo engine, they knew what the were doing. using a very close module gear does work sometimes as the difference is so small and all form gear cutters are a compromise.When copy ing spiral gears on a universal mill ,set up the spiral lead attach the old gear or a borrowed genuine gear, set a small dial gauge to a tooth and wind the table handle to ensurethat your gears are set up correctly spirals set to the various tables in Machineries handbook,sometimes a bit of adjustment of the gear ratios is worth trying to get the spiral the same or very close to the original.

Posted by
Graham Williams 11 16/08/2019 17:19:26

Wonder what a small gear hobber will cost to make........... where is this going?

An article published in MEW 193 Sept 2012 Shows an electronic system
which is still available from Richard Bartlett ,as of last year he still had 12 of these
available in pcb form.The article show the mechanical parts that i made and will cut
spur and helical gears of any tooth number.
Obviously this requires some amount of work and expense to complete to make
this unit and also finding an 0.8 mod or 32 dp hob.
These here sell hobs i have not bought from them so have no experience
of their service.
https://www.aliexpress.com/w/wholesale-gear-hobs-for-sale.html

Without knowing the exact specification of the gear ie 0.8 mod or 32 dp if the gears
can be hobbed the 0.8 can be cut using the pcd of the 32 dp ,i doubt you would be
able to tell the difference as the error will be less than the backlash.
The photo here is a 0.8 mod 17.5 deg helical gear for an align powerdrive unit.

The gear in your photo appears to have some damage on the flanks not unlike
the descriptions shown here in the second photo taken from a gear book, the
descriptions of abrasion and scuffing would seem to apply.
For this reason it would be unwise to make and fit some fudged gear and hope that
it will run in.

John

Thanks John and Nigel. Decided to cut the teeth as before but with the correct handed helix and as a test before trying it on a bike (no takers on a Velo enthusiast to try it out for me LoL) I'm going to make a test rig with an old intermediate gear driving the mag gear (will have to provide some resistance somewhere) and see if I can detect any of the potential problems outlined. After that may well look at a hobber as the next project after refurbing an old Mills aero engine as I'm giving the locos a rest for now.

Graham

Graham, in your Velo tatt box would you have a 3/4" x 0.040" wire circlip with "ears" for a KTT gudgeon pin ? or know where I can get one ? Most suppliers now just sell snap rings. Good luck with the gear cutting. Chris.

Chris.

Velo tat box sadly depleted as I sold every bit and bike I had a few years ago, regretted it ever since so got the MAC a couple of years ago, couldn't afford MSS/VM/VR and just buy bits when I see them at autojumbles.

Have you tried Ray Thurston, he's got loads of stuff and is on Facebook, Thames Valley member I think, his son Kevin runs KTT Services, easy to find on the web so might be able to help or even Martin Bratby who seems to have cornered the piston market.

Best of luck

Cheers

Graham W

Graham, thanks for the reply. Martin Bratby is based not to far from me so I will try him first.

I have not fitted circlips to a piston for years, preferring to use aluminium or Teflon/glass filled ptfe type buttons. From that you may well tell I am a pre war BSA man. I am doing some bits for a friend with a Velo and he wants me fit wire clips as original.

Chris.