Author Topic: Gear selection problem  (Read 3908 times)

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Offline Sye

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Gear selection problem
« on: November 29, 2015, 07:27:57 AM »
When i rebuilt bike number two's engine I checked that every gear could be selected before joining the two halves but now the engine is in the frame there's a problem. I could select a few gears, then nothing, everything went tight and I was unable to move the gear lever up or down.

I have stripped the right hand side and taken a look and everything looks as it should except the drum centre doesn't turn when selecting a gear. The drum shifter doesnt move unless I push the sprung ratchet manually and the central stopper plate doesn't move either, which means that the drum isn't turning. I can turn the drum using a pair of pliers but it's very stiff so I have stopped in case I cause any damage.

Any ideas please? I was really hoping I didn't have to remove and split the engine but it's looking likely.  :'(
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Offline jawman1234

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Re: Gear selection problem
« Reply #1 on: November 29, 2015, 10:13:19 AM »
Make sure you have a washer on your drum guide bolt the bolt might currently be sitting to far up into the shift drum you can look at the manuals I had this happen on my 350 gtr and it wouldnt allow it to shift through any of the gears until I put a new washer on because previous owner had disassembled the motor and forgot to put a new one back on.

Offline fiction

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Re: Gear selection problem
« Reply #2 on: November 29, 2015, 12:07:42 PM »
Hi sye,try taking bottom engine mount bolts out,I had an engine and the bolts had gone through the crankcase locking the gears up .long shot but worth a look.

Offline Sye

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Re: Gear selection problem
« Reply #3 on: November 29, 2015, 12:45:38 PM »
Thanks Jawman and Fiction. I will try both suggestions tomorrow and see where that gets me.

If I do have to split the cases, how far do I need to strip the motor? Can I leave the cylinders, pistons and con rods in place or is it a full strip down?
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Offline jawman1234

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Re: Gear selection problem
« Reply #4 on: November 29, 2015, 02:06:46 PM »
If you have to split the cases you will have to take the cylinders off and the piston out at least as well as the clutch so it will be a full strip down basically but if you completly disassemble the motor I would go head and put a new top end on it as well as any other components needed. Also make sure you clean everything super good because its hard to find replacement parts for these motors.

Offline Sye

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Re: Gear selection problem
« Reply #5 on: November 30, 2015, 11:14:06 AM »
Fiction hit the nail on the head. I used the supplied bottom bolts without checking their length and guess what, they were too long. They didn't go all the way through but have caused the metal to balloon inside which is jamming the shift drum. So, it's a grind down and weld job unless I can source a decent bottom half crank case?

Jawman, it has been completely rebuilt. New rings, con rods, seals, bearings, gaskets, the lot has been replaced. I'm really pissed off that this has happened but I should have checked the bolt lengths first, so I've only got myself to blame. The supplied ones are 7mm too long.  :'(
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Offline Sye

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Re: Gear selection problem
« Reply #6 on: November 30, 2015, 11:56:05 AM »
Right ho, I may have been a bit premature there. I found a picture of the bottom end after I had cleaned it up before assembly and the bulge was already there. I have attached the picture of it and can say that it doesn't leak or snag anything, so I now have to look elsewhere.

The drum stopper seems to be very strong, should it be? It takes quite a lot of effort to turn the drum once the spring is in place. I can't think of anything else it might be at the moment, so I will assemble the gearbox and see what I find.
« Last Edit: November 30, 2015, 12:00:40 PM by Sye »
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Offline dcr

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Re: Gear selection problem
« Reply #7 on: November 30, 2015, 03:19:06 PM »
Sye,

I believe the case halves aren't interchangeable as they are machined as a set.

Dan
1966 175 DT and 1968 350 GTR

Offline slawsonb

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Re: Gear selection problem
« Reply #8 on: November 30, 2015, 03:40:37 PM »
Sye,

I believe the case halves aren't interchangeable as they are machined as a set.

Dan
Good catch Dan! On 350s the cases are stamped with matching numbers to avoid inadvertent mismatch. The cases I am currently working on are S277 for example. These stamps are on the rear of the cases close to the mating surfaces.
...bert
« Last Edit: November 30, 2015, 03:45:51 PM by slawsonb »

Offline Sye

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Re: Gear selection problem
« Reply #9 on: December 01, 2015, 07:40:13 AM »
Has anyone got a gear stooper boss spring they can measure please? I'm reasonably sure that mine is too long/strong.

Thanks.
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Offline BRT-GTR

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Re: Gear selection problem
« Reply #10 on: December 01, 2015, 10:43:13 AM »
       Hi Sye,
                   Can appreciate how teed off you feel, I'd be seething, especially as you checked the gears before bolting up. 
             First the good news, the little dome on the crankcase bottom is part of the original casting, so I guess your cases should be OK. The correct bottom engine mounting bolts have a 45 degree taper machined on the inner end, IE , they are pointed. Found one of mine in the lower fork bridge !

       The drum stopper spring is 33mm long  X 7mm dia. Does the gear box select ok with the drum stopper removed ?
    Apologies if I'm teaching you to suck eggs here but one possible cause :-
 When the drum stopper is correctly inserted, the roller has to sit in the slot in the outer boss. This stops it twisting and keeps it in line with the star wheel on the shifter drum. If the drum stopper arm and roller are slightly twisted when the boss is inserted in the case, it will go in but cannot then fully retract into the slot and jams the shifter drum. With the bottom case sitting on the bench , it's easy to see if its gone in straight and into it's slot, not quite so easy when done under the engine in the frame.  Might need a few attempts.
     Can post you a replacement spring if needed, it's one I made but then found an original. Would you have a pair of 57mm crank seals amongst your spares ?

   Brian.
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Offline ziggy stardust

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Re: Gear selection problem
« Reply #11 on: December 01, 2015, 04:20:14 PM »
Sye, I'm away at the moment so can't look at my parts book for the correct name for the star fish shaped thing that should turn as you move the gear change lever on the drum' you can fit that 180 degrees out by mistake which gives no gear change. Check it.
Z
P.s. it may be called the stopper plate?
« Last Edit: December 01, 2015, 05:35:47 PM by ziggy stardust »
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Offline Sye

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Re: Gear selection problem
« Reply #12 on: December 02, 2015, 03:56:59 AM »
       Hi Sye,
                   Can appreciate how teed off you feel, I'd be seething, especially as you checked the gears before bolting up. 
             First the good news, the little dome on the crankcase bottom is part of the original casting, so I guess your cases should be OK. The correct bottom engine mounting bolts have a 45 degree taper machined on the inner end, IE , they are pointed. Found one of mine in the lower fork bridge !

       The drum stopper spring is 33mm long  X 7mm dia. Does the gear box select ok with the drum stopper removed ?
    Apologies if I'm teaching you to suck eggs here but one possible cause :-
 When the drum stopper is correctly inserted, the roller has to sit in the slot in the outer boss. This stops it twisting and keeps it in line with the star wheel on the shifter drum. If the drum stopper arm and roller are slightly twisted when the boss is inserted in the case, it will go in but cannot then fully retract into the slot and jams the shifter drum. With the bottom case sitting on the bench , it's easy to see if its gone in straight and into it's slot, not quite so easy when done under the engine in the frame.  Might need a few attempts.
     Can post you a replacement spring if needed, it's one I made but then found an original. Would you have a pair of 57mm crank seals amongst your spares ?

   Brian.

Measured mine Brian and it's the correct one, thanks for the offer. If you mean the crank web seals then I only have one pair that I bought with the rebuild kit, sorry.

I'll double check the roller and drum stopper, thanks for the tip.
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Offline Sye

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Re: Gear selection problem
« Reply #13 on: December 02, 2015, 03:58:44 AM »
Sye, I'm away at the moment so can't look at my parts book for the correct name for the star fish shaped thing that should turn as you move the gear change lever on the drum' you can fit that 180 degrees out by mistake which gives no gear change. Check it.
Z
P.s. it may be called the stopper plate?

Hmmm, thanks Lee. It is the stopper plate but ISTR it looked the same both sides but I'm at work ATM and going by memory.

How do I know which way round it goes as there's no clue in the manual?
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Offline BRT-GTR

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Re: Gear selection problem
« Reply #14 on: December 02, 2015, 08:54:51 AM »
      Good call Z, enjoy your hols.   :D

 Sye, there is a clue in the manual but you have to look darned hard to notice it. I only know this because it was pointed out to me (thanks Alan T). Must have got lucky last time I assembled a box

   See Manual, Page 19, Fig 35, titled Setting over-run stopper or P33, Fig 65-1. With the change arm at rest , the stopper plate should be fitted with a tooth pointing towards the change arm centre, the opposite side has a recess  between the teeth.
   Also check the pawl springs are working properly, they can become squashed in their holes. The pawls can also be fitted the wrong way round. Not east to explain which way round they go. The pawl ends are not square but have a slight slope. The bottom of the slope should be facing outwards to contact the grooves in the shift drum. Think there was a post recently about the kick starter which uses the same pawl, that explains it better, will put up a link if I can find it.
   I really hope you can sort this one without having to split the engine again. Spin the gears using the chain sprocket when checking the gear operation.               Brian. 
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Offline BRT-GTR

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Re: Gear selection problem
« Reply #15 on: December 02, 2015, 09:19:54 AM »
      Link to drawing  showing pawl orientation , see 2nd page. Same pawl used on shifter drum and kickstart.               

              http://bridgestonemotorcycleparts.com/index.php?topic=3971.20                                     Brian
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Offline Sye

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Re: Gear selection problem
« Reply #16 on: December 02, 2015, 09:50:09 AM »
     Good call Z, enjoy your hols.   :D

 Sye, there is a clue in the manual but you have to look darned hard to notice it. I only know this because it was pointed out to me (thanks Alan T). Must have got lucky last time I assembled a box

   See Manual, Page 19, Fig 35, titled Setting over-run stopper or P33, Fig 65-1. With the change arm at rest , the stopper plate should be fitted with a tooth pointing towards the change arm centre, the opposite side has a recess  between the teeth.
   Also check the pawl springs are working properly, they can become squashed in their holes. The pawls can also be fitted the wrong way round. Not east to explain which way round they go. The pawl ends are not square but have a slight slope. The bottom of the slope should be facing outwards to contact the grooves in the shift drum. Think there was a post recently about the kick starter which uses the same pawl, that explains it better, will put up a link if I can find it.
   I really hope you can sort this one without having to split the engine again. Spin the gears using the chain sprocket when checking the gear operation.               Brian.  

Too late Brian, I had already split it. I have this sussed now and you are half-way there above. The link shows a picture of the kick-start ratchet, not the gear stopper.

The key to setting up the stopper is that the holder must be vertical when you set it up. I've been setting it up in neutral. To get it vertical means selecting 3rd gear and then the holder is in the correct position. In this position the starfish wheel is installed with the tooth pointing horizontally to the left as you look at it. If it's the wrong way round then two teeth align to the left.

It does show you this in a very poor picture in the manual but does not tell you that the vertical alignment is critical. The clue is in the attached picture from the service manual.
« Last Edit: December 02, 2015, 09:53:43 AM by Sye »
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Offline BRT-GTR

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Re: Gear selection problem
« Reply #17 on: December 03, 2015, 12:23:30 PM »
   Sye,
          Glad you got it sussed.
        Agreed, the 350 manual is poor when it comes to setting up the change mechanism (and engine timing for that)  your post above should help many others in the future and will be going in my reference folder.  Have a look at the 175 manual, it's far more comprehensive. I think BS  did a minimum job on the GTR manual (it's full of errors, wrongly labelled drawings etc)) and were already considering the future of their bike production when the GTR went into production. 

           The kickstart drawing link was only included  to highlight the slope on the end of the pawl and which way round it goes. The gearchange mechanism drawings in the manual do not show this feature clearly. The pawls used in both the kick start and the shift drum are the same item with the same part number.
     
   Good luck with the rebuild, Brian.
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