Author Topic: Dimensions of yokes for Yamahas with 36mm forks...?  (Read 181 times)

0 Members and 1 Guest are viewing this topic.

Offline James P

  • Novice
  • *
  • Posts: 27
    • View Profile
Dimensions of yokes for Yamahas with 36mm forks...?
« on: November 27, 2017, 07:29:54 PM »
I am looking for some dimensions of fork yokes from any Yamahas originally equipped with 36mm forks. My basic requirement is that the fork legs should be able to pass up through the top yoke without hitting the handlebar. Possible candidates so far include:

IT (all models except 125) - 1977 to 1980
YZ125 - 1977 to 1980

As far as I am aware, the above IT and YZ models all use practically identical yokes (after 1977, I believe the bottom yoke and steering column was supplied as one piece), but there are other Yamahas originally equipped with 36mm forks for which it may be handy to know details, particularly late 70s and early 80s TT and XT models.

For any set of 36mm yokes, I am looking for the following info:

1. Will the fork leg(s) pass up through the top yoke without hitting the handlebar?
2. If so, what is the distance between fork leg centres?
3. What is the offset (i.e. the perpendicular distance between the centre of the steering column and a straight line drawn through the fork leg centres)?
4. What is the inside diameter of the hole in the top yoke for the steering column?

I may have to modify positions of steering stops and make other minor adjustments to suit my application, but any basic info is welcome. If you are able to provide any details, please let me know the model and year of manufacture (if you know it) of the yokes you have measured, just in case there are any differences between models.

Mark Boddy has helpfully supplied dimensions for the 1977-1980 IT model yokes, but I'd be glad to know whether any of the TT or XT models have yokes which may be more suitable. If anyone can suggest any additional models from which suitable yokes may be sourced, please let me know!

Thanks in advance & regards,
James


Offline matcho mick

  • Legend
  • *****
  • Posts: 2192
    • View Profile
    • Moto Tumbi
Re: Dimensions of yokes for Yamahas with 36mm forks...?
« Reply #1 on: November 28, 2017, 06:33:54 PM »
just ran a ruler across XT/TT front end,the 36 forks will clear the h/bar clamps,just!,about 2mm innit,these are the "stepped" forks,(reduced between the triples), :P
work,the curse of the racing class!!
if a hammer dosn't fix it,you have a electrical problem!!

Offline James P

  • Novice
  • *
  • Posts: 27
    • View Profile
Re: Dimensions of yokes for Yamahas with 36mm forks...?
« Reply #2 on: November 28, 2017, 09:28:44 PM »
Thanks for that info Mick. Are the fork leg holes in the top yoke 35mm...or something else?

Whatever the case, can you easily measure the distance between fork leg centres and also the offset for the XT/TT yokes (I gather they are the same :-\ )? Oh, and the ID of the hole for the steering column too :) .

It appears so far that 1978 RM125/400 (or 1978.5 RM250) yokes are my best bet, but I've still got to find some! Until then, any further info on Yamaha parts would be most welcome.

Thanks again & regards,
James

Offline matcho mick

  • Legend
  • *****
  • Posts: 2192
    • View Profile
    • Moto Tumbi
Re: Dimensions of yokes for Yamahas with 36mm forks...?
« Reply #3 on: November 29, 2017, 11:26:52 AM »
forks are 36 in the trees!,centres 185,offsets 60,stems 25,(but bottom bearing surface is 30 dia),overall length is 230,it's removeable from lowers,(pressed?,& clamped), :P
work,the curse of the racing class!!
if a hammer dosn't fix it,you have a electrical problem!!

Offline James P

  • Novice
  • *
  • Posts: 27
    • View Profile
Re: Dimensions of yokes for Yamahas with 36mm forks...?
« Reply #4 on: November 29, 2017, 06:03:41 PM »
OK - thanks very much Mick. It seems that the XT/TT yokes make the fork centres a little wider than I really wanted. That in itself is not really a problem, but the offset is about double what I wanted. Nevertheless, thanks for taking the trouble to measure 8) .

Regards,
James

Offline LWC82PE

  • Superstar
  • ******
  • Posts: 5705
    • View Profile
    • PE motorcycles & SuzukiTS.com
Re: Dimensions of yokes for Yamahas with 36mm forks...?
« Reply #5 on: November 29, 2017, 10:46:38 PM »
The 60mm offset ones are from the inline axle forks. The leading axle TT/XT500 clamps will have  a lot less offset than 60mm.
Wanted - 1978 TS185 frame
Orange Don Vesco/MS/Windsor tank
ADB Mags (vol 2 no.2) nov/dec 77& jan/feb 78 (vol2 no.3)

Offline James P

  • Novice
  • *
  • Posts: 27
    • View Profile
Re: Dimensions of yokes for Yamahas with 36mm forks...?
« Reply #6 on: November 30, 2017, 04:40:32 PM »
The 60mm offset ones are from the inline axle forks. The leading axle TT/XT500 clamps will have  a lot less offset than 60mm.

Ah yes - I forgot about the difference in axle orientation. Some basic research suggests that the change to leading axle occurred in 1979 for the TT500 and in 1980 for the XT500.
It seems that the 1979-onwards (at least until 1981) TT500 used the same top yoke as the 1977-1980 IT175/250/400/425 (for which I have the dimensions), while the 1980-onwards XT500 used a top yoke which positions the handlebars almost directly above the fork legs (hence preventing the fork legs from being pushed very far through the yoke).
The IT/TT yokes are a possibility, but would require other modifications which I'd like to avoid if possible. There could be other Yamahas with yokes suitable for my purpose, so if anyone knows the details, please let me know!

Thanks & regards,
James

Offline matcho mick

  • Legend
  • *****
  • Posts: 2192
    • View Profile
    • Moto Tumbi
Re: Dimensions of yokes for Yamahas with 36mm forks...?
« Reply #7 on: November 30, 2017, 05:30:23 PM »
The 60mm offset ones are from the inline axle forks. The leading axle TT/XT500 clamps will have  a lot less offset than 60mm.
[/quote
onya LW,set me another task  ;),your'e correct,leading axle top trees 20mm offset, JP, the h/bars are angled back on fixed risers,with just enough fork clearance, :P
work,the curse of the racing class!!
if a hammer dosn't fix it,you have a electrical problem!!