Shifting becomes difficult when engine is hot

[rshane53]

Hey all, I haven't posted in a while. I have my 71 apart for some maintenance and have a few questions. I have been experiencing difficulty shifting into 1st gear when downshifting after the engine is hot. When the bike is cold it shifts no problem. I have removed the clutch and after inspection it appears to be in great shape. When I removed the clutch plates so that I could spin the clutch boss with my hand I found that in 1st gear there is a lot of backlash. With the transmission is 1st gear there is about 50-60 degrees of rotation of the main transmission shaft before the rear wheel begins to turn. As I shift up through the gears, the backlash becomes markedly less. In 3rd, 4th and 5th there is very little backlash. Could the excess backlash in 1st gear be causing the difficult shifting when the engine is hot, and does anyone know how much backlash is normal?

 

[TwoManyXS1Bs]

Due to the large clearances between tranny gear dogs/cogs and slots, the backlash you're observing is quite normal. Those large clearances allow for effective shifting.

One item to check would be your neutral detent spring and plunger. The plunger tip should be rounded and smooth...

 

[XSLeo]

Often the clutch adjustment changes from cold to hot.
As it warms up the cases expand, this causes the clutch to not open as much, this creates more clutch drag.
Go for a ride, once it gets warm adjust the lever a bit tighter.
One thing I do is when adjusting the clutch worm I don't back off the adjuster a full 1/4 turn as the book says . I use the lock nut and turn it back one flat of the nut. This gives it a bit less free play. Then adjust the lever for 1/8 to 1/4 inch of free play. This snugs up the clutch so there is less change from cold to hot.
Leo

 

[TwoManyXS1Bs]

Here's a similar thread:

http://www.xs650.com/forum/showthread.php?t=9347

 

[peanut]

I thought the same as you when I was assembling my engine a couple of years back.
I made this short vid showing exactly where the lash occurs.
I assume it is to soften the take up impact on the transmission from the first gear ?
The other gears don't need so much lash for engagement because the transmission is being turned by the rear wheel which is why you can change gear without using the clutch if you match the revs to the gear speed correctly
I may have this all wrong though lol

 

[TwoManyXS1Bs]

Excellent video, peanut!

If you consider the event timing aspect, maybe it'll make sense.

It takes a certain number of milliseconds for the fork to slide the adjacent gear's dogs over and into the 1st's slots.

At idle rpms (1200), the 1st gear 'wheel' is spinning about 200 rpms, and the engagement opportunity "windows" provided by those slots also occur within milliseconds.

If the slots were shorter, the opportunity 'window' shortens, and excessive corner-catching of the adjacent dog would occur, leading to premature rounding wear...

 

[peanut]

thanks for that explanation twomany

I initially wrote that the extended slot was to allow greater opportunity for the first gear dogs to engage and then not being sure of what I wrote I erased it.

Your explanation of the difference in speeds between the stationary output shaft /gears and the input shaft /gears at 1200prm engine speed explains the engagement problem clearly .

 

[rshane53]

I checked the neutral detent this evening and it is in good condition. The end that engages the transmission shaft is round and the spring is intact.There have been several posts regarding the clutch adjustment. Several members replied that they adjust the clutch cable at the handlebar after riding a while to allow easier shifting. It just seems that when new, you would not need to do this adjust on the fly to keep shifting normal. But considering that the parts are all 45 yrs. old with 23000 miles on them, I suppose I may just have to live with it.

 

[rshane53]

Great video Peanut, after watching I now know what goes on inside that causes the difference in lash. I believe Two Many is right in saying that mine seems normal. This is my first experience with the transmission, I only rebuilt the top end when re-conditioning the bike.