Author Topic: Gearbox belt pulley  (Read 699 times)

0 Members and 1 Guest are viewing this topic.

Offline linksleyrover

  • Member
  • *
  • Join Date: Nov 2016
  • Posts: 4
  • Location: Sydney Australia
Gearbox belt pulley
« on: 15 Mar 2021 at 09:56 »
The belt pulley on the gearbox does not line up with the wheel belt rim.
My gearbox pulley runs close to the gearbox. (Approx 1/4 inch)
I have seen a pulley on a friends bike which has an offset and gives a gap to the gearbox of approx  3/4 inch.
Does anyone know where to obtain a pulley with a decent offset ?
Thank you, Hans 

Offline EW-Ron

  • Senior Member
  • ***
  • Join Date: Jan 2020
  • Posts: 199
  • Location: Oztralia
Re: Gearbox belt pulley
« Reply #1 on: 15 Mar 2021 at 22:36 »
That pic is a little too close-up to see much of what is going on,  but I've seen pulleys where the centre was bored out,
and a new suitable centre inserted and welded in with the taper, key etc suitably spaced to get the pulleys to line up.

This is often done where the taper has been damaged and is otherwise unusable.
The welds need only be not much more than minimal.
They do need to be evenly spaced and carefully done, to ensure continued good alignment.

Offline Hutch

  • Master Member
  • ****
  • Join Date: Nov 2012
  • Posts: 373
  • Location: Queensland, Australia
Re: Gearbox belt pulley
« Reply #2 on: 16 Mar 2021 at 01:43 »
Hi Hans and EW-Ron,

In the 2 3/4 parts I have seen and also in discussions with other 2 3/4  owners there appear to be two different offset plain gearbox belt pulleys for the 2 speed boxes. The ones for 1913-1919 2 speeds appear to have a  different offset to the later vintage TS ones. Not 100% certain but this might have come about by the increased use of 3 speeds from 1919-20 onwards and these gearboxes are wider than the 2 speed box and hence require a slightly wider belt line - ?? (more research to do, but I can take some pictures of the ones I have showing the difference in offset f you would like me to).

There was a guy called Stephen Sellar advertising 2 speed gearbox pulleys a while back on the forum and ebay. Not sure if he still has any, but probably worth contacting him. From my memory (which I don't trust anymore!) I think these pulleys might have been the later type (as opposed to the Bert Pol one I have which would appear to suit the veteran 2 3/4hp) and might suit the belt line you require??

https://www.douglasmotorcycles.net/index.php?topic=4662.msg16705#msg16705
https://www.douglasmotorcycles.net/index.php?topic=4384.msg15734#msg15734

(Edit: See reply 4 and 5 below)

Cheers

Ian

« Last Edit: 17 Mar 2021 at 06:06 by Hutch »

Offline linksleyrover

  • Member
  • *
  • Join Date: Nov 2016
  • Posts: 4
  • Location: Sydney Australia
Re: Gearbox belt pulley
« Reply #3 on: 16 Mar 2021 at 08:41 »
Hi Ian and Ron,

To make a new insert on the gearbox pulley  with a different offset seems a smart idea.
Bert Pol’s pulley have no offset. He also tells me that the one’s he sells are the only one’s in the part book.
The 1925 TS bike I am rebuilding for a friend is a “bitsa” . I had to modify quite a few parts to make them fit.

I saw a belt pulley on a Sydney friends 1926 bike which has a nice offset of about 3/4” . That would be perfect on my bike.
Will continue to look for an offset one. Otherwise have to modify mine with a new offset insert
Thanks for your input. hans

Offline Ian

  • Master Member
  • ****
  • Join Date: Jul 2004
  • Posts: 1287
  • Location: The Oaks, NSW, Australia
Re: Gearbox belt pulley
« Reply #4 on: 17 Mar 2021 at 03:48 »
The one you saw on my 23 was one of Stephen Sellar's ones. I dont think they are being made any more.

Offline Hutch

  • Master Member
  • ****
  • Join Date: Nov 2012
  • Posts: 373
  • Location: Queensland, Australia
Re: Gearbox belt pulley
« Reply #5 on: 17 Mar 2021 at 04:32 »
Hi Hans,



Bert Pol’s pulley have no offset. He also tells me that the one’s he sells are the only one’s in the part book.


Your comment got me thinking so I had a quick look through some 2 3/4hp parts books I have that are from different years and found something that might point toward there having been two different plain pulleys avail. for 2 3/4hp two speeds that wouldn't be obvious if you only looked at the common 1925 edition of the parts book.

I agree with Bert that the pulley he sells is the one shown in the picture in the parts book as the picture didn't change from at least 1922 onwards (I don't have any parts books between 1916 and 1922. The 1916 picture of the plain pulley for the two speed is different to the 1922 one but the pulley appears to be the same 781D part).

Gear Box Group - (Two Speed)

1916
Picture and description  - 781D Pulley (plain)

1922
Picture and description - 781D Pulley (plain)

1924
Picture shows part 781D

description;
781D Pulley (plain) 1912-20

and Douglas added;
748D Pulley (plain) 1921-24

(note: no picture of 748D)

1925
Picture shows part 781D

description;
748D Pulley (plain) 1912-25
781D Pulley (plain) 1912-20  See 748D

1927
(list only - no pictures)

description;
748D Pulley (plain) 1912-25

no part 781D listed

So did Douglas have  an additional plain pulley, 748D from 1920 onwards and discontinue 781D in 1925 or was 781D the same as 748D? My guess was that there were two different pulleys and Douglas rationalised their spare parts around 1925 at the end of the 2 3/4hp run when they were just trying to get rid of all the outdated models out the door as fast as possible(?). Not sure at all tho'.

I will measure the offset difference between the "748D" one I have (if that is what it is) and a 781D pulley and see if it matches what you need.

I guess the above information probably doesn't help you too much but hopefully you can find an original one to suit your needs rather than modify the 781D one you have.


EDIT: From Ian's post (which came through just as I added this post) it appears that Stephen Sellar's pulleys were possibly the "748D" pattern?? I have just found out from an old post that sadly Stephen is no longer with us.

Cheers

Hutch


« Last Edit: 17 Mar 2021 at 06:03 by Hutch »

Offline linksleyrover

  • Member
  • *
  • Join Date: Nov 2016
  • Posts: 4
  • Location: Sydney Australia
Re: Gearbox belt pulley
« Reply #6 on: 18 Mar 2021 at 11:21 »
Hutch,

Thanks so much for your research , a massive effort.
Very interested to see if you can measure the difference between the two pulley’s.

It must be a common issue that the wrong pulley will give you a very poor alignment of the drive belt.

Thanks again, Hans