G: Gearbox (Twin) Jumping into gear

[tom wilson]

I have now stripped out the gearbox, the only fault I can see is that the selector fork pins are at differant heights, 1 is flush with the cam plate the other is pertrudingthrough the cam plate by almost 1/4". What is the correct hight of the pins out of the forks. ..... I have just found the previous comments regarding the modded (shoulderd) pins, I shall fit these the shoulder should give me the height many many thanks to all ... ride safe and enjoy

 

[clevtrev]

Slightly underflush, otherwise the top of the pin can hinder the selector arms as they slide on that top surface in operation. I`m referring to the top of the shoulder on your new pin.

 

[greg brillus]

Must be more to this...........The height of the pins in relation to the cam plate would still not cause it to jump into gear unless the pin was not engaged at all. Are you sure the two selector forks are the right way around, the blade one meshed with the double gear on the mainshaft at the rear and the slotted one sitting over both 1st and 2nd sliding gears on the forward lay shaft. Something in the gears themselves must not be engaged with the selector forks to cause this problem.

 

[oexing]

Hmm, I cannot see how to jump into second gear when the neutral notch was definitely engaged. So I guess the gearchange mechanics were poorly set or the detent spring broken. In case the selector fork pin had a shoulder I would not want that to protrude supposing the cam plate rests on the top face of the selectors by design ?
I did not like the pointed detent plunger - nor the camplate resting on the selectors so came up with another mod that should provide a slick change. The camplate is bolted to the top of the gearbox so no friction from selector fork top faces there, only from pins in their slots.
Vic

third gear:

neutral position:

 

[greg brillus]

Nicely done, But I can see the shift being very heavy and notchy, as your lever detent set up is a very precise fit to the "V" grooves in the cam plate. you are better off with a large ball shape and leading/trailing ramps in the camplate. If I were going to that trouble I would alter the design like the Horner's do and run a "Barrel" type selector over a cam plate, I have seen pictures of theirs and it does not look that difficult to do. Remember that probably 90 % of gear shifting issues is a poorly operating clutch, causing drag in the system and overloading the shift.

 

[oexing]

Greg,
you are quite right about dragging clutches as a cause for poor gear changes. I did not care to get the original type working after a lot of efforts, had only bits for one but needed two sets for two engines. Luckily I had several sets from Kawasaki and tricked these into the HRD covers, intending to run them semi-wet. Did same exercise for the four-valve Horex 600.
As to my lever type indexing, it is not as notchy as you´d believe, at least not in this state when compared to the pointy barrel type that puts a lot of rubbing to the barrel in its bore from side loads. I am quite positive so far, once again sort of copy from BMW boxes I admit.

Vic

 

[Bill Thomas]

Tom, When you say it falls into gear, Does the indicator move, Which tells you this ?.
So you can easy put it back to neutral ?.
If so, I think you may be right when you said, Detent spring, But I have never heard of this.
As Trev has said before, Not all camplates are right !, He said some bikes have been wrong from new.
I wonder if at some time, The alloy Boss in the top of the gearbox has been repaired.
It only has to be a nat's out, To mess things up.
We have had the boss welded on 2 Bikes and had to re grind the camplate a touch !.
Good Luck, Bill.

 

[tom wilson]

Hi guys I have ridden this C Rapide for 30 odd years (many miles) and never had this fault unitl last year.
I do not think it is the fork pins causing the problem even though one is raised, I still think its the de-temp spring (I shall fita new one) If you read the gearbox item in 'Paul Richardsons Vincent' he too discribes the same problem .... jumping into gear. I shall re-inspect every part before I re-assemble and hope I see some thing else.

 

[tom wilson]

Tom, When you say it falls into gear, Does the indicator move, Which tells you this ?.
So you can easy put it back to neutral ?.
If so, I think you may be right when you said, Detent spring, But I have never heard of this.
As Trev has said before, Not all camplates are right !, He said some bikes have been wrong from new.
I wonder if at some time, The alloy Boss in the top of the gearbox has been repaired.
It only has to be a nat's out, To mess things up.
We have had the boss welded on 2 Bikes and had to re grind the camplate a touch !.
Good Luck, Bill.

Yes Bill The indicator does move and it easyly goes back into neutral and rides without fault, see last reply from me regarding Paul Richardson.

 

[tom wilson]

Hmm, I cannot see how to jump into second gear when the neutral notch was definitely engaged. So I guess the gearchange mechanics were poorly set or the detent spring broken. In case the selector fork pin had a shoulder I would not want that to protrude supposing the cam plate rests on the top face of the selectors by design ?
I did not like the pointed detent plunger - nor the camplate resting on the selectors so came up with another mod that should provide a slick change. The camplate is bolted to the top of the gearbox so no friction from selector fork top faces there, only from pins in their slots.
Vic

third gear:
View attachment 22039


neutral position:
View attachment 22040

Wow you are some engineer ... very very nice, class