Crankshaft pinion H3 - L3 - B31

[douglas1947]

Hi,
I have recently bought an 1930 H3; original (unrestored) condition, but with missing engine.
I had bought also a right type ER engine from on Ebay, but several parts are in a bad state.
One of the problems is a worn crankshaft cam drive pinion (3 teeth are part broken).
Outside dia 31mm, inside dia 15,9mm, high 12,7mm, 20 teeth.

I think the disc is used for crankcase breathing, the bore is worn, but I think it is repairable.
Would like to get advise.

Michael

[Doug]

Michael,

It is the crankcase breather. The same arrangement can be seen in this post of a 1935 engine:

https://www.douglasmotorcycles.net/index.php?topic=6027.msg22209#msg22209

There is also a wave-washer required to press the disk against the crankcase.

The disk should have a D-shaped hole, and is driven by a corresponding flat on the crankshaft. Both the disk and the crankshaft tend to get worn. The disk is easy to re-make, but he groove worn in the crankshaft (if significant) has to be welded up.

Other than variations on width, a pinion for any of the 1930-37 250-350cc engines ought to be the correct bore and tooth profile.

-Doug

[hoejmark]

Hi Michael
A few years ago I made new gear wheels for the cams and the small centre spur gear wheel for my B29.
I had a local tool maker shop to make the holes for the cams. The centre spur wheel, I adapted in my small lathe to fit the shaft. After 3 years the system still runs perfect.
I did buy the spur gears from HPC Gears in England in Imperial dimensions. Cam wheels: XG18-40, Centre wheel: XG18-20. In my opinion they were not expensive.

 http://www.hpcgears.com/pdf_c33/23.114-23.119.pdf

Regards
Soren

[hoejmark]

You can see the gear wheels in the thread that Doug refer to.
Soren

[douglas1947]

Thanks  for the advises.

Doug, on the breather of my engine the spring washer was not fitted.
I think that caused the wear massiv.

Sören,
thanks for the link to the pinion shop, I could not find model XG18-20, is the first letter wrong.
I should be able to do the inner dia on the pinion, but may be the slot for the key is difficult?

Michael

[hoejmark]

If you scroll down until the YG type, you will have the XG type in the column far right.
The YG and XG type are heavy duty steel.
Soren

[eddie]

Michael,
            For just the one pinion, you should be able to set a parting tool on it's side and use it to cut the keyway by hand (winding the carriage back and forward). If you set the new pinion to the back of the jaws, you should also be able to nip the old pinion with it's teeth in alignment, to give the correct indexing for the keyway.

  Regards,
                Eddie.

[douglas1947]

Hi Eddie,
thanks for the advise to do a keyway. Do you make a special tool to scrape the keyway?

Michael

[douglas1947]

Hi Sören,

sorry, I  had not noticed that the pinion (without boss, far right ) has it own XG number!

Michael

[eddie]

Hi Michael,
                Use an ordinary parting tool that is the same width as the keyway. Mount it on it's side so that it points directly at the chuck, and pack it up so that the middle of the tool is exactly at the lathe's centre height. Use the carriage on the lathe to move the tool in and out of the gear, taking light cuts by moving the cross slide out in .05mm increments until the keyway depth is correct. By the way, all this is done with the lathe stationary - you are just using the lathe as a makeshift slotting machine.

  Regards,
               Eddie.

[douglas1947]

Eddie,

many thanks again, now I understandhow to do!

Michael