From: "Stoodley: Jon & Martha" 
Subject: Re: Shifting Problems
Date: Tue, 5 Oct 1999 20:23:15 -0500


-----Original Message-----
From: Chris L Johnson Subject: Re: Shifting Problems


>I have noticed the same on my `74 250.  It does not like to go from
>neutral to first.  I press down, and the gear dogs partially engage with
>a pop pop pop then clunk and in it goes.  Sometimes pops out again.  My
>guess is that I and you have a bent shift fork from bashing the lever in
>1st or 2nd.  Thus the dogs come up short in first, for example.  The fix
>would be to either re-bend or replace that fork.  Since the other gears
>are fine, my guess is the engagement mechanism that engages the pins on
>the rotary drum is not the problem.
>
>But,  I don't know for sure.  I don't recall ever having this problem on
>any of my CT, DT, or RT-1s in the `70s.  Anybody on this list know for
>sure?
>Chris Johnson

Randy Lantz >writes:
>> Would you happen to know of any solutions to the terrible shifting of
>> gears on the Vintage TY 175 Yamaha's (1975 / 76 models). I have 2 of
>them
>> and a friend of mine has 4, and every one of them has inconsistant
>shifts,
>> mostly from 1st to 2nd. Any help, suggestions greatly appreciated.
>Thanks
>> in advance.

My guess is that the engagement "dogs" (those series of protrusions that
slide over and into the holes on the next gear) and the slot edges on the
gears are worn, causing the dogs to bounce off rather than slide into the
slots. They need to have relatively sharp edges so that they catch and the
"undercut" causes the gear to lock in to the other. Unless you have
sophisticated machine tools they should be replaced.

A bent shift fork is a good possibility. A bent fork will have the shiny
(engagement) area on the flat part of the fingers at the top or bottom of
the flat machined area that rides in the groove of the gearset- rather than
the engagement area evenly distributed over the machined area. Most bent
forks will look fine as they need only be bent a few degrees to cause
problems. In order to straighten them you will need to be able to measure
off the bore to get them 90 degrees absolute. You will probably better off
replacing them if bent.

Other possibilities are: weak spring on the little engagement roller that
drops into the "star" slots (that star shaped thingie on the end of the
shift drum)- a combination of worn thrust washers, spacers, shaft bearings
and circlips-

I'd go with the first possibility. I think the early TY series had a shallow
undercut on the gearsets that eventually results in shifting problems. If
you are going to have the cases split, make sure the mechanic is not just a
"parts-replacer" but really knows how to read the entrails correctly. The
parts and the location (or not) of all the polished areas of the
transmission will "talk" to a good mechanic and tell him/her whats wrong.

Jon Stoodley
JSE Racing

------------------------------------------------------------------------

  Alas, if only I could remember 1/2 of what I have forgotten , I would be
close to a half wit. Somewhere in the murky depths of this cluttered mind of
mine recalls a possible solution to this problem. First let us recall the
days of yesteryear. Being a purpose built machine, it was desired to
engineer a 'long throw' in the shifting mechanism so as to prevent
disengagement by incidental contact subjected to the machine during
competition. Remember that most duties were served in 1st and sometimes 2nd
gear was called upon, however deliberate. Definitley in contrast to todays
standards. However, cutting to the chase before the vision fades, there is a
shifter adjustment in which if you were to pull the primary[clutch] cover,
you would be able to access. There is a plate[so to speak] attached to the
shift shaft that is relieved [slot in it] with a slotted stud in the middle
of it. This is actually an eccentric in design to allow/limit travel.
Observe the attached linkage at the exposed outer shift drum. There is an
opposing [hopefully] symetrical 'fingers' that engage the shift drum. The
idea is to have equal 'throw' in both directions. You can adjust this by the
aforementioned eccentric stud. A repair manual covering that era/similar
machine should utilized if you should elect to perform the
inspection/adjustment on your own. Proper clutch adjustment and gear oil are
also contributing variables.
 The fact that both you and associate are experiencing similar maladies with
multiple/like machines, raises suspect. It's entirely possible that the two
of you need to travel to the nearest 'Pub' , get a good 'edge on ' and
admit to being 'Shifting Deficient' !
 Just Kidding ! :^)
Have one for me !
 Guluk, Scott