1934 500 Blue Star primary chaincase

[David Samways]

I'm having some difficulties with my primary chaincase. The inner chaincase was pretty bashed and has had a rough hole cut in it where the sliding gearbox shaft plate should be. In fact, it was so stretched and deformed that I had to cut slits with a grinder and then weld while clamped to a flat surface. This has largely worked, although there's still some "oil-canning" toward the where the case is fixed to the engine.

My problem is that there seems to be very little clearance between the clutch and the rear drive-chain/sprocket and getting the chaincase into a position where neither the clutch nor the chain is rubbing is driving me mad. I wonder if this is due to the omission of the sliding gearbox shaft plate. Any thoughts/experience welcomed.

David

[David Samways]

Just an addendum: I should have asked if the omission of the slider could be the issue and whether anyone knows if the slider from the later B/C/M models might fit - Draganfly make them for a very reasonable 25 quid.

[David Samways]

OK, I've now got to the bottom of this and there's a salutary general lesson for all buying an unfished restoration project.

As you can see from the attached, when I bought my machine it looked pretty tidy (apart from truncated front guard) and had had a lot of important work carried out - reconditioned carb, mag, wheels rebuilt (shame not chrome rims), powder coated frame etc. The vendor was perfectly honest with me and said that the engine had been rebored and the head sorted but that the engine had been rebuilt by a couple of friends as had the gearbox. Unfortunately, these friends were not very bright as I will come to. I stripped the engine as a matter of course and found the crank wanted extensive work which set me back over a grand - that's OK, almost what I expected.

As I've gone through the machine I've found that just about everything has been very badly "rebuilt". The wheel bearings were completely knackered, the forks were dangerously worn, the mudguards were shockingly poor especially the rear which even had the wrong stay. Even the brand new rear chain was completly the wrong size. However, the gearbox seemed OK, that is until it came to fitting the primary chaincase.

I now realise that whoever rebuilt the gearbox decided to make their own gaskets from thick neoprene or similar and that the input shaft is consequently in the wrong position which not only makes the clutch sit too close to the output sprocket but also means that third gear doesn't fully engage. Hopefully the bearings will be OK and I can just make up some paper gaskets to set things right. As you can see from the photo, pushing the input shaft out to the correct position moves everything 2.2mm which makes a world of difference regarding clearance for the primary chaincase and also gives the correct engagement for third gear.

And the lesson is... all that glitters is not gold!

David

PS I'd still be interested to know if anyone thinks the slider from later models will fit and be of any benefit.
PPS I should add that I only paid £5K for the machine, so while it turned out to be less of a bargain than I'd hoped for, it's not such a bad deal and was certainly worth the punt of buying on the strength of the photos and a couple of conversations with the genuinely honest vendor.

[idie]

That looks really nice. Full marks for sticking with it.

[David Samways]

Thanks, the beauty in those photos is only skin deep, but I'm turning it around into a mechanically and aesthetically sound machine!

[Bicycle repair man]

I have been through the gearbox saga and no gaskets are shown in the parts book until 1937. Also in 1937 shims were listed for the mainshaft. Not for the layshaft though.

[David Samways]

Interesting. I'd not spotted the lack of gaskets in the parts book. Mind you, there are quite a few parts I can't find such as the stud that secures the outer primary chaincase cover to crankcase.

I'm inclined to fit gaskets and also shim as necessary. I've done a lot of geaboxes in my time - the performance of a Moto Guzzi gearbox is particularly dependent on careful endfloat shimming.

[David Samways]

Any thoughts on that slider plate btw? Looking at the parts books I have ('32 and '34) it doesn't appear to be shown. There are two holes in my chaincase which look like they're to hold it and Only British Austria have new chaincases which have the slider plate fitted.

[Bicycle repair man]

I have 2 hand change boxes, one with gaskets and one without. The one with is in the bike , no modifications to swimming and works fine. The one without is a rebuilt spare with new bushes etc and the end float on both shafts is perfect. I don't think that this is as critical as modern bikes.
With regard to the sliding plate, it is missing on mine also. The later ones are dimensions similar  but the flanged part in the middle is too deep. Without the plate, oil leakage is next to nothing. The main problem is that there is no seal on the outer case. The chain is lubricated from a breather pipe from one of the chaincase studs. This is adjustable from the screw and locknut on the crankcase. Once oil fills the chain dip on the inner case the oil leaks,  especially  on the side stand.
It is worth fitting a sealed type high gear bearing. Also I modified the kick-start shaft to take a thin o ring. The gearbox oil level is up to the mainshaft and theses mods stopped the oil running out both ends.

[David Samways]

Thanks. I think I can live without the slider plate. I modified my '32 Sunbeam 9 gearbox to take neoprene seals - worked a treat. The primary chaincase is like a Swiss cheese, so oil loss is an inevitablity. Given the very low mileage this machine will do, I'm inclined to close the oil-feed down to a minimum.

[Bicycle repair man]

The adjuster backed off from tight is sufficient to lubricate the chain without the bike embarrassing itself too much when parked.

[David Samways]

Thanks for the tip.

[Y13 Alan G]

I have two pre-war BSA Vee twins and both have the slider on the inner chaincase. The only contribution I can make is to advise using Thixotropic grease "Century EPLITH 00" in the gearbox. This grease becomes an oil under pressure between the meshing gears and provides excellent lubrication without leaking out of the gearbox which has no oil seals. I have been using this grease for over 50 years on several pre-war BSA;s with no problems at all. Hope this helps.

[David Samways]

Thanks Alan. How does the grease lubricate plain bushes? It obviously does otherwise you wouldn't be using it for all this time!

[David Samways]

BTW & FYI, Mark Quinney tells me that the inner gearbox gasket is the same as that fitted to M20/21 models. I've used ThreeBond 1184 Liquid Gasket which I can recommend for sealing crankcases etc. It's not silicone and better than old fashioned products like Hylomar (good in some circumstances) or Welseal (also has its advantages).