The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Gearbox, Clutch, Primary => Topic started by: Bee-Za on 10.10. 2020 18:06
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Can I assume I’m right that this is the neutral on the camplate. See photo screw pointing to neutral
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Also this selector rod. I assume it’s held via a grub screw at the main bearing. But does the grub screw clamp the selector rod or does it stop sideways drift. Does anyone have a photo of the grub screw. see photo of selector
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Yes, that's the neutral detent.
Grubscrew is shown for the S/A gearbox, but the pic is not clear and BSA had the illustration numbers mixed up.
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Just screwed a bolt into the grub screw hole with the view to making my own grub screw. Out popped a ball bearing. Looks to me there should be a ball bearing inserted first then the grub screw which allows the selector rod to rotate. Should the selector rod be static per the A10 manual I have or should it be allowed to rotate via a ball bearing
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Here is the grub screw.
The rod should not rotate, if it does it may enlarge the hole and cause an oil leak.
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Thanks I’ll make and secure the selector shaft and secure the grub screw into the housing with a punch.
Out of interest I measured the ball bearing at 4.7mm and the groove at the end of the shaft is 5.6mm. Maybe someone tried a modification in the past. I’ve had this gearbox over 40 years.
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Sorry to go on a bit. But why have the shaft grooved all the way around when a flat on the shaft would make the shaft stronger and allow a flat for just the grub screw. Strange!!!
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Quicker to machine and avoids an assembler from missing the flat, causing eventual shaft misplacement.
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there's no reason for the shaft to be located radially is there, the grub screw is just to stop it moving longitudinally, correct? if so, I suspect the PO may have misplaced the original shouldered grub screw and used the ball bearing to locate in the groove with a standard flat grub screw locking it in place.....if it did happen to rotate for some reason, no harm done??
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Thanks all *smile*
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Couple more questions and photos
Firstly is this the correct selector to attach to the lay- shaft.
I’ll try and add 2 photos
No only allows one photo
Question 2 to follow
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This second photo shows lay shaft top and main shaft bottom. Question is. The gear at the end of the lay shaft slips on and off freely and when on the lay shaft it is stopped by the lay shaft circlip. But the gear at the end of the main shaft is stuck on and the circlip is underneath the gear.
Is this correct? Or should it slip off the end easily?
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Sorry guys every photo I post always rotates 90 degrees anticlockwise
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both those gears should be a very tight fit, they are pressed on and not normally easily removed. the circlips are stops for the gear position
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So main shaft gear is pressed too on too far. Is there a set distance from the end of each shaft to the gear.
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The gears press on until stopped by the circlip, the gears have a recess for it.
If the layshaft gear is a loose fit I suggest check it carefully for cracks.
Layshaft shown.
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no if you look close at it you will see that the gear has a relief to clear the circlip where it butts up to the circlip .. didn't see julians post
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Bee-Za... Julian's picture also shows the oil hole drilled in the gear. Locate the pinion gear on the splines so this hole coincides with the corresponding drilling in the layshaft. Do the same with the remaining sliding gears.
The fixed pinion gears are a tight press fit on the shafts. When correctly located (circlip acts as a stop) the spline on the shaft end should be level, or more usually very slightly below the face of the gear pinion. This allows the pinion face to act as a bearing surface against the blind bush top hat, in the case of the layshaft, and as a location against the inner race of the smaller ball bearing in the case of the mainshaft. Swing arm and plunger box layshafts have the circlip in different places, S/A circlip location stop groove is at the tip of the drive dogs, see bergs previous note, and as shown in Julian's picture. Plunger circlip is at the base of the dogs, adjacent to the gear teeth. The layshafts are machined with the locating groove holding the circlip positioned to match. S/A layshaft also has a scroll on the blind bush bearing surface, shown above, the plunger type is plain so you can tell at a glance which is which.
The layshaft you have shows a typical wear pattern. The remedy here is a new layshaft (rare/expensive), or re machining the bearing surface and a custom underside bush. In view of the problem with the loose fit of the pinion gear, a better used layshaft complete with pinion is another option.
The selector forks fit back to back, and it is easier to assemble the gearbox (Camplate set to neutral) by loading the complete layshaft and its selector fork but less the big bottom gear into the case first, positioning the selector fork against the camplate, followed by the mainshaft, gears and its selector fork. With both forks located in their respective tracks in the camplate, the fork shaft can then be added, but make sure the grub screw is removed completely. The grubscrew location cracks off when folks hammer the shaft into place, and the grubscrew is obstructing the hole. The selector fork shaft should slide in with little force when the selectors and case line up. Leave the grubscrew as the final finishing touch.
Swarfy.
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Lyashaft fixed gear pressed fully in position.
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Mainshaft gears pressed fully in position.
Note the rounded ends of the teeth on the lower pinion which caused the box to jump out of third gear when under load and needed replacement..
Top shaft with different machining is from a scrambles box, lower is from a STD box.