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#713333 - 10/31/17 12:06 pm Pre-Unit Transmission Info, Swing Arm Models  
Joined: Aug 2001
Posts: 4,950
Rich B Online happy
Rich B  Online Happy



Joined: Aug 2001
Posts: 4,950
Stone Creek OH USA
This is not my work, I believe it was the work of Dave Kath some years ago. GStar Ron may have contributed as well. I keep a copy of this in my book with all of my pre-unit printed information. Lots of good information here. I will make it a sticky thread since questions about pre-unit gearboxes come up from time to time. grin

Through the magic of cut & paste, here are the wise words from a number of years ago:

"I frequently come across problems of the incorrect assembly of the layshaft thrust washers in the swing arm type gearbox, of the type with the needle roller layshaft.

There are four large hardened washers used in the gearbox, three on the layshaft and one behind the ratchet pinion bush and it's possible to assemble the gearbox with some of these four in the wrong position. Unfortunately the BSA spares list illustration does not show clearly the correct assembly.

Working from the clutch end of the gearbox, the washers should be assembled on the layshaft in the following positions.

42-3078 ... 1.156" OD, 0.687" ID, o.108" thick
fits between main shell and layshaft 'B' gear.

67-3203 ... 1.094" OD, 0.750" ID, 0.093" thick
fits between the 'F'
layshaft 3rd and 'H' 1st gears.

42-3079 ... 1.250" OD, 0.750" ID, 0.113" thick
fitted between the 'H' layshaft 1st and the middle 'sandwich' case.

67-3161 ... 1.162" OD, 0.750" ID, 0.075" or 0.068" thick
fitted behind the kickstart ratchet pinion bushing.

Pay particular attention to the washer p/n 67-3203, which is also used on the gearboxes fitted with bronze layshaft bushes. The bore of the washer often only has a chamfer on one side only. If this is the case, the washer must go onto the layshaft with the chamfer against the spline to give clearance for the small radius on the shaft at the start of the spline.

Be very very careful of the improperly sold repop 'T' layshafts. There are a couple of subtle dimensional differences between the STD bushing layshafts and the STD T needle roller shafts but some suppliers want to sell a 'one part fits all'.

'Bushing' Box info
The 42-3019 'bushing' lay shaft has oil grooves on the end adjacent to the clutch.
bearing surface diameters:
clutch end ... ~ 0683"
speedo drive end ... 0.7475"

'B' gear, aka 'layshaft 4th' tooth width is 0.660"

'A' gear, aka mainshaft sleeve gear, tooth width is 0.560"
note: both are narrower than the 'T' box gears.

'T' Box info
The 42-3094 Timken needle bearing lay shaft used in 'T' Gold Star boxes is almost identical to the shaft in a bushing box, but there is Never a oil groove in the bearing ends. The bearing ends are also 2.5 thou larger than the bushing shaft. Measure.
bearing surface diameters:
clutch end ... 0.686"
speedo drive end ... 0.750"

'B' gear, aka 'lay shaft 4th gear' is 0.740" wide across the teeth.
'A' gear, aka 'mainshaft sleeve gear, is 0.603" across the teeth.
note both gears are wider than the 'bushing' box gears.

'T' box thrust washer info:
42-3078 - Fitted between main shell and the layshaft fixed 'B' gear.
1.156" OD, 0'687" ID, 0.108" thick

67-3203 - Fitted between the layshaft 3rd 'F' and layshaft 1st 'H' gears.
1.094" OD, 0.750" ID, 0.093" thick

42-3079 - Fitted between the layshaft 1st 'H' gear and the middle case.
1.250" OD, 0.750" ID, 0.113" thick

67-3161 - Fitted behind the kickstart ratchet pinion bushing.
1.1625" OD, 0.750" ID, 0.075" (or 0.068") thick

Note:
67-3203 is also used in bushing boxes. If this washer has only one chamfer on the ID, fit the chamfer against the layshaft splines to give clearance for the radius.

Mainshaft Info
There were 4 different mainshafts used in these gearboxes.
RRT2 shaft 42-3131 for use with needle bearings in the 'A' sleeve gear

STD(T),RR(T),DAY(T) 67-330 shaft used in both the bushing and 'T' boxes

SC(T) shaft 67-3315 is slightly different than the STD shaft. This shaft can be used in a STD box, but not visa versa.

TRI(T), STB(T) shaft 67-3313 identical to the SC shaft except the 'G' 1st gear is made as part of the shaft vs pressed on.

There are 17 gear sets listed to make up the 7 different ratio transmissions both with and without the Timken bearings. Some gears are used in multiple applications, but some are unique to a particular box. And you can create your own ratios with a bit of 'mix and match' of the gear sets."

Last edited by Rich B; 10/31/17 12:08 pm.

Life is too short to drink cheap, bad beer.
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#713684 - 11/03/17 2:53 am Re: Pre-Unit Transmission Info, Swing Arm Models [Re: Rich B]  
Joined: Nov 2011
Posts: 3,972
Magnetoman Online content
BritBike Forum member
Magnetoman  Online Content

BritBike Forum member

Joined: Nov 2011
Posts: 3,972
U.S.
For anyone getting ready to rebuild a complete T-type gearbox (STDT, SCT, etc.), it will cost a minimum of ~$25 if everything inside is in good shape. Which, of course, it won't be. If the gears are in reasonable condition but all the bearings and bushes need replacing the rebuild cost could be as much as $250. Although a few parts are different, the cost to rebuild a bushing gearbox or an RRT2/SCT2 will be about the same.

Before you open your gearbox you might arrange to have the first set of items below on hand because even if you find nothing broken or worn inside you will need these to put it back together. You also should have $150 in your bank account and a further $100 line of credit in order to be ready for the worst case eventuality. The numbers come from Plate 3 (Gearbox) of the DBD parts manual.

Every rebuild definitely will require:

No.__Part No.__ Description
2____67-3067__ Gearbox sprocket oil seal
46___67-3346__Gearbox inner cover joint washer
53___24-8504__Gearbox casing plug washer
59___29-3449__Gearbox inspection cover washer
105__67-3354__Gearbox outer cover joint washer
116__64-3106__Inspection cover joint washer
Yamabond 4 or your favorite equivalent gasket sealant
approx. total $25

Your rebuild also may or may not need some or all of the following bearings:

3___24-4065__Constant mesh gear ball bearing
14__24-4217__Mainshaft bearing
72__42-3074__Layshaft needle roller bearing
75__42-3075__Layshaft needle roller bearing (cover end)
approx. total $75

Repeating some of the information from a different thread, a caged needle bearing will have only ~20% the lifetime of a full complement uncaged bearing of the same quality so it is well worthwhile to use the latter.

You also may need some or all of the bushes:

4____67-3073__Constant mesh gear bush
6____67-3080__Constant mesh gear bush (drilled)
17___67-3169__Kickstart ratchet pinion bush
101__67-3093__Layshaft gear bush
approx. total $80

You only will need the following if they missing from your gearbox or excessively worn:

16___67-3161__Kickstarter ratchet pinion sleeve washer
73___42-3078__Layshaft thrust washer (clutch end)
74___42-3079__Layshaft thrust washer (cover end)
99___ 67-3203 (replaced by 57-1962)__Layshaft thrust washer
approx. $70


Moderated by  Rich B 


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