BSA Owners' Club Forum

The BSA Workshop => Twins => Topic started by: LIONELSMITH on 02 April, 2017, 18:13:38

Title: Gearbox play
Post by: LIONELSMITH on 02 April, 2017, 18:13:38
The lower engine is back from SRM and turning beautifully. I started changing the worn Gearbox sprocket and when off including the spring ring, rotated the mainshaft. I am convinced like the engine, it has never been touched. There is a little rotational play but pulling the shaft, probably nearly 1.5 to 2mm of lateral play. Is this excessive, as I suspect an indication of worn bearings? It is not absolutely quiet in rotation either. I am happy stripping the box and replacing gears in situ where necessary, but drifting bearings in and out, then I think it could be going away. Please reassure me the movement is not a cause for concern. Like the engine I want to do EVERYTHING now, as I do not want to strip it completely again.

Does anyone have any simple tricks to get the oil seal out.

As always, any help is gratefully received.

Lionel (not the Lionel Smith in this month's Star!)
Title: Re: Gearbox play
Post by: JulianS on 02 April, 2017, 18:47:21
There should be no end float on the mainshaft. It is locked in position by the ballrace and kickstart pinion in the inner timing cover. If the nut retaining kickstart pinion is loose it may let the mainshaft (first photo)  There may be a little fore and aft movement of the sleeve pinion until the sprocket nut is retightened to pull it into position.

The inner cover ballrace is easy enough to remove - it is held in position by a circlip - remove circlip heat cover and press ballrace out. You can see the circlip in second photo. Similar for the large ballrace in the maincase.

To remove the oilseal first remove the large circlip it usually has a cutaway for a screw drive but if not there will be two holes for circlip pliers. The seal then just pulls out.

Replacing the seal is sometimes more difficult because the current new seals have an outside diameter which is just a little too much to fit properly and the outside edge may need to be eased with a file so it fits square against the ballrace and allows the circlip to be refitted fully in its groove. The new seals are usually about 0.5 mm larger diameter than the original.
Title: Re: Gearbox play
Post by: LIONELSMITH on 19 April, 2017, 18:23:35
Thank you Julian

I have got the Gearbox stripped some of the gears are a little rounded on one side. How worn is too worn? The main problem, however, seems to be that the Mainshaft bearings on the kickstart end is well and truly shot, (the clutch end looks OK). The layshaft at the clutch end is ridged, so I can renew the layshaft and bush, get SRM to machine the layshaft and fit an oversized bush or as this seems to be a regular problem, has anyone had the Goldstar and later model needle roller bearing conversion? If so, does the case have to be machined or is this a straight fit?
Title: Re: Gearbox play
Post by: JulianS on 19 April, 2017, 20:31:47
If the small mainshaft pinion has rounded dogs then it is likely to cause the box to jump out of third gear when put under pressure such as a third gear overtake or pulling hard up a slope. Over the years I have changed a number of these. First photo shows one which jumped out.

The small journal of the layshaft is frequently scored in bushed boxes, I think due to dirty oil and its small diameter. Photo 2 shows one fit for scrap only.

New layshafts and bushes seem readily available.

I got fed up with worn bushes many years ago and fitted an STDT box to my A10. The layshaft journal does not seem to wear so badly as the bushed ones. The needle roller layshaft small journal is plain, no oil scroll which is found on bushed boxes. The other end looks the same, except for provision for a circlip between ground portion and speedo gear.

The maincase bush can be replaced with a needle roller without modification, though you would, of course need the hardened thrust washer, and the case would not be machined in the outside to take a core plug - which you wont need with a closed end needle roller.

At the other end you would need to machine the bearing housing to accept the needle roller which has a larger outside diameter than the bush. You sometimes see needle roller inner covers on e bay. You would also need the thrust washer.

You can also machine the sleeve pinion, which is very hard, to accept the RRT2 needle roller bearing but you would need the RRT2 mainshaft because it is stepped due to the inside diameter of the needle roller being a few thou larger than the bush. I had this done on one box but concluded it was not really worth the effort.

I would replace both ball bearings whilst it is dismantled.

I would also check the kickstart stop in the inner cover, these have often fretted in the hole due to the nut coming undone.
Title: Re: Gearbox play
Post by: LIONELSMITH on 20 April, 2017, 21:47:47
Julian, thanks again.

I am fairly clear looking at your examples my box marked STD is not in bad condition, by slight rounding I meant profile of the teeth not the dog itself. I have priced the parts from Draganfly and have 2 further questions. I think my layshaft is machinable but for longevity, I will buy new.

However, Draganfly provide a layshaft and specifically say it is one without the fourth gear attached. I have not TRIED to remove mine, but it seems fairly rigidly attached. Are there two versions or do I just need releasing fluid and elbow grease?

Second question, it is the clutch end of the layshaft that has much worse ribbing. Has anyone tried a mix of the close ended needle bearing, including a thrust washer, in the clutch end and a brass bush in the inner cover end? this would seem to resolve the ridging issue whilst negating machining. Is there an issue I have not thought about? If any further work is needed, like the other needle roller bearing, I will be able to do it with the box still in the bike.

Finally, I will of course replace both mainshaft bearings, it would be remiss not to.
Title: Re: Gearbox play
Post by: JulianS on 20 April, 2017, 22:37:17
The fixed pinion on layshft is a press fit. (the only pinion which is machined as part of a shaft is the small pinion on the scrambles box mainshaft)

I have removed one by  use of a vice and copper mallet, but have also found one so tight that it needed to be popped off with a hydraulic press. When refitting it needs to be right up against the circlip and it is best to do it before you replace the speedo gear (which is unlikely to come fitted to the new shaft). When refitting the spedo gear you may have to redrill it so it aligns with the drilling in the layshaft.

Some years ago I ran a box with needle roller just on the clutch end with no issues, if you decide on this you might want to consider using a needle roller type layshaft.