Author Topic: 1971 GTR 350 Not Shifting  (Read 1145 times)

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Online Bridgestoneboy

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1971 GTR 350 Not Shifting
« on: March 08, 2018, 11:57:08 AM »
Howdy,
Finally got my bridgestone running the other day only to find that the bike shifted into first but then wouldn't shift back into neutral or into second gear. I disabled the entire engine and didn't seem to find much. However, I stumbled across one of my shifting forks with some serious wear around second gear where the gear had been hitting/wearing on the fork. Is this common, what could cause this, and could this possibly be the answer to my issue of shifting. Any help is appreciated. Below are two pictures, one with an unworn fork and where it is hitting on the gear, and another photo where the fork that I believe was in that position was worn. I have a feeling that when I reassembled the engine previously that I maybe put a different fork that was unworn in the position where the work fork used to be, but that still would not explain why the shifter drum wouldn't not spin inside the cases. Either way I would like to get this issue straightened out so I don't have to disassemble the motor a 10th time lol. Regards

Offline OldSwartout

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Re: 1971 GTR 350 Not Shifting
« Reply #1 on: March 08, 2018, 03:38:23 PM »
You can put the assembled transmission in the bottom half of the case along with the shift drum and forks, then slowly spin the drum while watching the gears engage/disengage.  It may be necessary to spin the gear shafts a little to get dogs to line up as the gears move.  Any binding or misalignment should be visible.
Karl Swartout
Mooresville, IN
BS175 Roadracer
BS350 GTR

Offline vinny g

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Re: 1971 GTR 350 Not Shifting
« Reply #2 on: March 08, 2018, 05:24:10 PM »
Engine mount bolts? I'm sure someone has mentioned that has been an issue on the 350. I think if they're over-tightened/ a bit long/wrong washer then they can force the crankcase up against the fork.

Offline BRT-GTR

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Re: 1971 GTR 350 Not Shifting
« Reply #3 on: March 09, 2018, 10:51:53 AM »
         Bridgestone didn't get everything quite right, the shift fork/second gear interference you have found is not unusual.  The engine I'm currently rebuilding has it. Not helped by a bit of wobble on the second gear pinion. Suggest you file some clearance in the web or maybe reshim the gear to move it over. ( Fork blueing was also a common issue on early gearboxes due to inaccurate factory shimming of the gears). This is probably not the cause of the shift problem.

    The drum guide bolt (bottom of crankcase) can jam the box if it's aluminium washer is missing or flattened.
    More likely is an issue with the ratchet pawls on the end of the shifter drum. Check the springs are not squashed and the pawls are installed the right way up, see manual for guidance.
    Most likely cause is the over-run stopper plate (item 12 on gear change page, Parts Manual) being installed 180 degs out of position, very easily done, it has an odd number of teeth 7.     See Figs 34 & 35 in the engine rebuild section of the Service Manual, with the change mechanism centered at rest a single tooth(marked C3 on drawing) should point toward the centre of the change arm. Drawing shows the flats on the shift drum in a vertical position, this corresponds to the box being in third gear but it is not essential to have the box in third before installing the stopper plate because it self centres after each gear change. As long as it centres on a single tooth it will be correct. Put it in 180 degs out and the box won't change !!  Hope you can follow this.

   As  Karl Swartout says above, carefully put it back together, checking at each stage that everything is free and you can shift through all the gears, particularly before bolting the cases up and it will be fine.                   Brian.

    An after thought, (was sometimes called 'Columbo' at work  ;D) you have obviously identified the correct fork for the 1st/2nd gear. You should find one of the other forks has rather crude grooves ground into the tip of the longer fork end. This is the 5th/6th gear fork and was a factory mod to improve oil supply and reduce blueing of the tip. That ensures all the forks are replaced as factory assembled.
« Last Edit: March 09, 2018, 05:27:03 PM by BRT-GTR »
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Online moonpup

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Re: 1971 GTR 350 Not Shifting
« Reply #4 on: March 10, 2018, 07:20:37 PM »
       
.....snip....

You should find one of the other forks has rather crude grooves ground into the tip of the longer fork end. This is the 5th/6th gear fork and was a factory mod to improve oil supply and reduce blueing of the tip. That ensures all the forks are replaced as factory assembled.


Brian, is this documented somewhere or is it your personal observation?  Didn't see anything in the service letters about this, but it's possible I may not have that one if it's in there.

Service manual maybe? I haven't read that one front to back yet.  :o
« Last Edit: March 10, 2018, 07:23:08 PM by moonpup »
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Offline BRT-GTR

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Re: 1971 GTR 350 Not Shifting
« Reply #5 on: March 12, 2018, 06:28:10 PM »
        Hi Mike,
         Fork groove mod was detailed in a BS Service Bulletin dated August 67 and was effective from  No. 21S01001.  Was intended to prevent fork scoring (blueing?) when in 5th gear.
       Not sure where I came across the bulletin, may have come with one of the bikes. We lost access to a number of BS service bulletins and Rockford service letters when Ray Oliver closed his Redimport web site.  Would be nice if they could be transfered to this forum.                                     Brian.
« Last Edit: March 13, 2018, 09:42:46 AM by BRT-GTR »
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Re: 1971 GTR 350 Not Shifting
« Reply #6 on: March 12, 2018, 07:04:46 PM »
Do you have the number for that service letter?

I'm missing letters # 9, 12, 40, 71, 72, 73 (all of which are listed as cancelled on the "Service Letter Index") and # 76 which shows subject matter of "Semi-sealed beam headlight"

The highest number I have is BSG-0078. Are there higher numbered letters out there?

I'd like to have a complete list one day.....
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Offline BRT-GTR

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Re: 1971 GTR 350 Not Shifting
« Reply #7 on: March 13, 2018, 07:56:13 AM »
           Mike,
         I assume the number series above refers to the 'Rockford service letters'

    The shift fork document is a 'Bridgestone Service Bulletin, which I guess were factory issued.
 Unfortunately, it has been printed or copied off centre and it's number has been chopped off.
       Never noticed before but these carry a 'Ref No' in the form 'MC-69-xxx' and may have been numbered from zero in each date year of issue.  Serial number is missing on most of them.                  Brian.
 
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Re: 1971 GTR 350 Not Shifting
« Reply #8 on: March 18, 2018, 04:30:47 PM »
 For starters I'd like to thank everyone who has provided some feedback on what the issue might be. Since then I have double checked everything but I am somehow still having the issue. It seems that it will not shift once the cases are pressed together, even with the shift drum alignment bolt loose and not overtightened. Even with the bolts just snug, nothing more, it binds up and will not shift. Of course I'm am attempting to shift the gears by hand but I am constantly rotating the transmission as I shift through the gears so I don't think it's as simple as the gears not locking into each other. I am lost at this point  :o Thoughts...?

Offline BRT-GTR

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Re: 1971 GTR 350 Not Shifting
« Reply #9 on: March 19, 2018, 10:27:36 AM »
           Something similar has been reported before but the cause was never fully pinpointed, see here :-
                       http://bridgestonemotorcycleparts.com/index.php?topic=4217.msg24418
       A few long shots :-
       Could the crankcases be distorted ?  This could happen if they have been bolted up with a knock pin not seated in the bearing recess, particularly the one that locates the smaller needle bearing on the gearbox output shaft. It's close to the shift dum. Any evidence of the knock pins being pushed down, cracked boss below ?

      Are the bearing 'c' rings correctly located. The 3 thicker ones look very similar but one of them is slightly larger diameter and goes on the right side of the crankshaft. The other two fit the 6305N bearings for the gear box.

     It has recently come to light (to me), via an article in the VJMC magazine, that the modern spec for the groove machined into Ntype bearing outer ring has changed since the late 60s when our bikes were built.  The groove is now narrower and the BS 'C' ring will not fit, being too thick ( checked on some modern KOYO 6305N gearbox bearings, I've recently bought). Article referred to the 6205N bearing  for a Kawasaki  H1 clutch shaft. The thin outer rim of the modern bearing had been broken off by the old 'C' ring being forced into the groove when the cases were bolted together.
    This could distort the cases and jam the shift drum if modern 6305N bearing is used with original 'C' ring on a BS 350 engine. Something to be aware of and bear in mind.                                                                   Brian.
     
« Last Edit: March 19, 2018, 06:31:08 PM by BRT-GTR »
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Re: 1971 GTR 350 Not Shifting
« Reply #10 on: March 25, 2018, 11:13:29 AM »
I do know that all of the bearings I purchased were from Richard so I believe they are all to OEM spec. I also don't believe that the c rings are in the wrong place, but I will make sure to check when I get back, since I am currently on vacation.

My worry however came up when you mentioned distorted cases. In fact, when I originally tore my motor apart I found signs of the cases having been torn apart in the past, possibly by someone who had no knowledge of the inner workings of motors. Actually, the A dowel for the driveshaft bushing had been pushed down to far and cracked the boss just above the shift drum. Maybe this is an issue I need to look more in to....I had the boss welded so the dowel doesn't slide right through but who knows what might have gone wrong. Is there any way for me to visually see the distortion?

Offline BRT-GTR

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Re: 1971 GTR 350 Not Shifting
« Reply #11 on: March 25, 2018, 05:02:21 PM »
           Regarding the link I gave above, the owner had previously reported that two of the R/H side gearbox knock pins had been forced down, which he also had welded. So, maybe there is a common cause here. Hope this does not spoil your vacation ;).
        Couple of ways to check the cases :-
     A good straight edge along the right side of the cases, any daylight showing or gaps ?

     Better still would be to check case joints on a flat plate with feeler gauges. Hang the tubular case dowels off the edge of the plate, (I'm not sure how you would get them out). An old ground plate glass mirror can make a good substitute for a proper engineering surface plate.

    Not much you can do if they are distorted. They can't be skimmed, this would upset the bearing fits and destroy the joint seal.
    But, assuming it's the shift drum wedging up on the right side, assemble the cases with just the drum in place and see if it tightens up.  Rotate the drum back and forth a few times and remove. That should show up any high spots on the large case hole for the drum. Carefully remove high spots with wet/dry paper and repeat until drum is free. Worth a try.          Brian.
« Last Edit: March 25, 2018, 06:10:15 PM by BRT-GTR »
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Re: 1971 GTR 350 Not Shifting
« Reply #12 on: April 02, 2018, 07:39:29 PM »
Through process of elimination and my brothers second set of eyes, I was finally able to determine what I believe the issue is, and so far I have success with fixing. Below I attached a quick drawing I made with hopes of this helping others in the future. What I found was that when the guide pin hole was welded after previously being pushed through the case, the hole directly above the welded area would warp upwards, making what once was a perfect radius no longer. This "warping" on my case was actually so minute that it could not be seen by the naked eye. However, when the drive shaft bushing was placed in the cases without the transmission drive shaft itself, the shifting shaft'/drum would not rotate. I will continue to post updates as I verify this is positively the issue, but so far with some light abrasive sanding the bottom of the drive shaft bushing seat, I have seen great progress the drum/shaft slowly becoming easier to rotate. Please refer to my drawing if my verbal explanation was confusing. Thanks for all of the help so far, and with luck I will be posting a restoration overview soon!

Offline BRT-GTR

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Re: 1971 GTR 350 Not Shifting
« Reply #13 on: April 03, 2018, 10:33:50 AM »
          Excellent detective work !!       Many members would have tossed the cases and sought a replacement.  We now have a better understanding of what happens when the cases are forced together against a knock pin. Not quite what I would have anticipated but you have the evidence in front of you. Keep up the good work and hope you can recover and continue to use these cases. This issue is sure to crop up again in the future.
        Have you checked the OD of the drive shaft bushing, if original it may have been slightly flattened when forcing the pin through the case boss. Might be worth replacing to be on the safe side.                                                           Brian

     
« Last Edit: April 03, 2018, 05:24:12 PM by BRT-GTR »
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Re: 1971 GTR 350 Not Shifting
« Reply #14 on: April 06, 2018, 04:21:58 PM »
I have two sets of cases where the pin has been driven through by someone also where there's been engine seizures and someone with a hefty foot has managed to smash the kick gear through the rear of the casing
my welder mate said that aluminium cases have to be heated in a oven evenly  to be able to weld them to prevent distortion   

 


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