BSA Owners' Club Forum

The BSA Workshop => Twins => Topic started by: robin smith on 04 August, 2017, 16:51:34

Title: RGS inner primary chain case
Post by: robin smith on 04 August, 2017, 16:51:34
As far as I am aware, despite the many RGS options offered by the factory, a fully enclosed final drive chain case was not one of them!

Therefore, why would the short inner primary chain case 42-7515 with the drilled boss to accommodate such a case be fitted, as seen on some RGS labelled machines, apposed to the longer type with the un-drilled boss 42-7505? 
Title: Re: RGS inner primary chain case
Post by: JulianS on 04 August, 2017, 18:56:31
Perhaps the owners of the bikes you have seen could tell you?

I think you will find that all the swinging arm twin chaincase backs have a casting number 42 7503 on them.

The 1954-55 A7 A10 (rod brake) parts book shows the part number as 42 7503.

The 1954-57 book shows it as 42 7515.

The 1958-59 book shows it as 42 7515.

Same in the 1960-63.

The RGS parts service bulletin, G21,  also shows it as 42 7515. (see photo)

So which part number is short and which is long?

I suppose if the owner is happy with his bike does it actually matter?
Title: Re: RGS inner primary chain case
Post by: robin smith on 05 August, 2017, 10:18:06
Having owned and ridden a Gold Star fitted with Super Rocket engine for almost 40 years. During that time, having lost count of the times I have had to explain, this is not in fact Rocket Gold Star!

Then attempting to point out the difference between a genuine RGS and my GSR! Consequently, the question of what is the correct type of inner primary case as arisen at times, hence my enquiry on this forum.

I totally agree with you “If the owner is happy with his bike does it actually matter?”

But obviously to some it does!  Particularly with so many so called replicas in circulation.
Title: Re: RGS inner primary chain case
Post by: robin smith on 16 September, 2017, 08:58:14
It would appear surprisingly, by the lack of response on this particular subject. I should merely shrug my shoulders when asked this question. 

In spite of the wealth of knowledge you guy’s have out there!
Title: Re: RGS inner primary chain case
Post by: DEAN SOUTHALL on 16 September, 2017, 19:28:08
The RGS was the end of the line for the pre-unit twin and I would not be at all surprisd if the answer is that they use the last stocks of whatever chaincase was avaible in the latter days if the production run to get bikes out of the door for the least cost.
Title: Re: RGS inner primary chain case
Post by: robin smith on 16 September, 2017, 22:12:43
I am aware the RGS was more or less a shelf clearing exercise of  the remaining parts from the out of production Gold Star, and later the Super Rocket.

However, the question remains, which models were fitted with the un-drilled extended inner chain guard and why?
Title: Re: RGS inner primary chain case
Post by: JulianS on 17 September, 2017, 09:39:35
One of those things which may never be known for sure.

However logic would suggest that the drilled part is only needed for full width hub models which could be fitted with a rear chaincase.

Parts book shows 42 7503 for 1954/55 half width hub models. The other books show 42 7715 as does the RGS supplement shown above.

They all have cast in part number 42 7503.

The 1970 master parts price list shows that when stocks of 42 7503 are exhausted it will be replaced with 42 7515 (At £3.59)
Title: Re: RGS inner primary chain case
Post by: robin smith on 01 October, 2017, 18:05:36
A month has passed since posting this question in the “twins” section of the BSA workshop:

What type of inner primary chain case was fitted to a Rocket Gold Star?   

Amazingly just two fellow members have offered up plausible but not definitive answers, despite well over 200 views!

With the asking price of an RGS now often exceeding £20,000, it would be good to know precisely what a prospective buyer should look out for, which is not easily faked.
Title: Re: RGS inner primary chain case
Post by: SLIPPERY SAM on 02 October, 2017, 23:11:21
Robin, I think your lack of quantity on answers is probably because the one or two guys that have more knowledge than you could ever imagine have already answered your question.
I doubt if you'll get much more on the subject on the forum.  I suspect the majority of BSAOC members are not glued to their phone, tablet or MacBook and may well be draining their sump or applying fresh sealant to their primary outer case as we speak.
Try a couple of forums there are other busier ones (frequented by members on here too) where you might get an RGS owner pop up with something definitive.  Also if you are a member there's a list of contacts for technical questions in your monthly magazine (think jules who you've already had an answer from is one).
Seen it a few times (on other forums) where new forum members are highly expectant of instant fixes to hard question the let rip cause no-one has fixed it for them.  Remember you get out what you put in.
What's your thinking on the cases. Is it not just early and later cases and RGS being later = later case?
Are you going to build one? Or convert your GSR or buy one? What case are you running?
Hope you get to a landing place soon.
Cheers Raymond.