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Something that doesn't seem to have been addressed here before (possibly because the answer is so obvious that I'll be embarrassed when it's pointed out), but the timing-side cases from the ZB through DBD all look identical, at least in the parts books, and all use bearing 24-722. However, since all of them are listed with "with fixed fittings," not as the bare cases only, the parts manuals don't reveal what, if any, differences those bare cases have with each other, or with B33, M33, or others that also look identical in the parts books.

So, are the bare timing-side cases of these various engines identical? At a minimum, for that to be the, ahem, case it would require that at least the holes for the tappet guides have the same threads. Leaving aside "minor" issues like alignment of the bearings, with a different set of "fixed fittings" could a, say, ZB33 timing-side case be readily made to work with a DBD drive-side case?

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MM: I cannot get at many cases just now but comparing a photo of the inside of a ZB34 GS timing side case with an actual BB34A and a BB33 timing side case I see no difference. I think the real early cases had a narrower mating surface and the CB 34 GS engines had the extra threaded hole for the long head bolt.

However I have a photo of the inside of a DBD timing side case and it is different with four small ribs at the top above the bearing and there is more metal around the bearing area.

The BB34A case is cast number 66-1617 and the DBD 66-1678.

Photos sent

Gordo

Last edited by Gordo in Comox; 05/09/21 5:02 pm. Reason: added info

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MM: In the BMS parts section for the early machines, (appear to be BB types) the 500 timing side case is 66-1648 and the 350 timing side case is listed as 66-1650.

On drive side the 500 case is 66-1654 and the 350 drive side is 66-1652. A difference makes sense there as the 350 still had the small drive side roller bearing, It makes no sense to have a different timing side case in my mind.

Gordo


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There is a definite physical difference between the iron barrel timing side case and the alloy timing side case. the base of the cylinders were different and needed different support area. Here's the difference showing the iron barrel case first.


[Linked Image from i.postimg.cc]


[Linked Image from i.postimg.cc]



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Not so cut and dried.
This is an iron barrel (B31) case
[Linked Image from live.staticflickr.com]20210511_095320 by Sigma Projects, on Flickr


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I think the curved case in Boomer's first photo is more about the year than the model.

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Given the differences in the timing-side cases, documenting those internal and external differences seems like a very worthwhile communal project. I've been planning to photograph the cases I have, and hope that I have photos of the inside of my BB "Alloy Clipper" to add to the thread, but several matters have kept me from working on this project as yet. However, I certainly plan to do so. Meanwhile, please, especially those of you who are able to photograph the insides of timing-side cases, please do so and post them along with the number stamped on the front lug (e.g. 66 1658 on BB and 5000-series ZB Gold Stars).

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Originally Posted by Gordo in Comox
I think the curved case in Boomer's first photo is more about the year than the model.

Gordo


Well it would have to be post alloy barrel then as the curved corner case would not support an alloy barrel but the later case, as in Andy's instance, could fit an iron or alloy barrel.


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In my experience of looking at case sets in a generic sense, the more curved timing side 'under barrel' area did seem to be true to early iron engines and coincident with the weaker drive side internal (small) bearing support webs.

All later more-heavily-supported-but-still-small-bearing B31-style cases summed (generally) to have the squared-off step for the alloy barrels.

Hazarding a guess, I'd say the change, simplifying production of timing side cases for all heavyweight singles, was probably around the time of the 'late ZB' engines.

Anyone got a known early ZB engine to look at? I'll see if I can dig out photos of a known ZB34 (iron) engine I sold a few years ago..


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Resurrecting a somewhat gone to sleep thread, partly as I am working on a timing side case repair at the mo'.

In direct response to Magnetoman, I know for certain that DB/DBD timing side cases at least, are quite different to the more cooking engines. They have more metal around the bearing housing & strengthening ribs running away from the bearing area. I would assume that CB34 castings are the same. Other B31-33 (& 32/34) castings I have seen have been, internally, nominally identical to each other, with less metal around the bearing & no strengthening ribs, although there may be some other very slight casting differences between them. MM probably knew this anyway :-) All the B cases in the entire run from 39-63 used the same timing side bearing & all the tappet guides are the same thread into the case AFAIK

I have used mixed cases - DBD drive side with B31-3 type timing side with no major issues. The only quirk I did once have to overcome was the magneto seal in the timing chest, which was in one ahem :-) case, completely out of line with the magneto spindle centreline, no matter how I tried to set it. As a result I machined an eccentric sleeve to take a smaller OD seal & after some experimental aligning of the mag, press fitted the sleeve into the housing. It was a perfectly adequate solution & the smaller seals were easily available. I don't know if this case was originally mis-machined or that it was from an earlier batch where the set up was marginally different to later cases...
There are all sorts of differences with various other details of both cases, several variations of bearing bracing casting in drive sides, sometimes with thick (as per post ZB GS) centreline lugs/ribbing & sometimes thin, with no apparent logic.

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And to continue...
Re. Boomer's "iron" cases;
I will try & post a photo sometime but until then I can confirm that the very early small-fin ZB32 GS ('49) has a timing side crankcase identical to Boomer's.
The GS small-fin barrel does overhang this case type, very slightly at the tappet cover & corner of the angled face of the case. It doesn't particularly ;-) leak oil from here. The barrel is adequately supported where it counts. Of course it could be that some earlier barrels were slightly different & fitted the early T side case better & that only later barrel castings overhang. It's just a thought, I have no proof that this could be the case; the small fin ZB32 barrels I have seen, have all been the same.

These early Timing-side crankcase castings are what we can call the (immediate) pre-war to post-war design; as the '39 pre-war KM Goldie timing side cases are in this area, of this casting type. I have seen many earlier X/Y/Z B31-33 T-side cases that are also of this type, as was the early ZB34. A much later ZB34 I have has the later square cast case.
At what exact point they moved to the extended / squared off case I don't know but case variants I've seen suggest this to be somewhere (mid-way?) through the ZB production runs, as Kerry W also says. BB31 cases are definitely squared.
However... as cases get worn or broken & paired with replacement halves - particularly where any number stampings are not clear on the lugs(they are often filed off) it's more than possible that the pairs we have are not how they came from BSA works.

Another detail of this "pre-war" type casting, also seen on early post-war, is a steel screw head fitted below the timing chest & above the oil pump bulge. This drilling was used on some (but possibly not all) KM24's for an oil pressure indicator. It can been seen on photographs of the '39 ISDT army bikes.
Post-war it was simply capped off with the blanking screw. I've only seen one case with this screw removed which might suggest it will by now be very difficult to remove by hand! Eventually this drilling was omitted, possibly while BSA were still using the early angled case castings. It is not seen on later ZB "square" castings.

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Here's three pictures of of the ZB alloy barrel sitting of both types of cases. All speculation and assumptions aside I don't think BSA would have cast a new barrel to not fit the cases it's sitting on. The overlap shown is approximately .080, more then "a little bit", with no support on the corner of the barrel base. With the squared off corner case the barrel is completely supported, fits the case and leaves just enough room to make a flush fit with the inspection cover in place. I have two very early alloy ZB's, one a '49 and one an early '51 and they both have the square corner cases.


[Linked Image from i.postimg.cc]


[Linked Image from i.postimg.cc]


[Linked Image from i.postimg.cc]


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I suppose Boomer it would depnd upon just how serious one was about weight reduction
Lots of room to remove a lot of metal from that cover seat area
Now the actual weight would not be much except in the mind of the owner .


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Every ounce counts!
In general it is easier to lose weight from the rider than the bike... ;-)

Interesting Boomer. Our ZB32 looks like your first pic. As far as I know ours has original cases.
BTW those last cases are the most polished ones I've seen!
Interestingly this bike came up for sale in 2014 & *appears* to be completely original
http://suprememotos.com/bsa/34500-bsa-gold-star-1949.html
The TS case is as Boomer's with squared extension (note later timing cover). But I don't like the look of the number stampings on the drive side; maybe the cases aren't original at all...
My favourites are in the book "BSA Competition History". On page 90, 97, 98 are period photos of Bill Nicholson & other riders on rigid & plunger '49 GS's showing fairly clearly to my eye, the rounded/angled TS case like ours.

I should just add that our ZB32GS is in the first 20 produced so it is very early - as works riders would have access to them before general production or public release, the Nicholson photos referenced above may also be showing very early engines. It would be interesting to see what number sequence forum member's ZB32's have & what TS casting.

Last edited by flowboy; 12/01/21 6:40 pm. Reason: more info
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I made this thread a sticky type thread. Lots of good info here.


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Period photos: Early 1949 ZB32 GS showing timing side crankcase casting

[img]http://https://app.photobucket.com/u/Flowboy/a/c9693c49-2f6c-466d-b09b-6fb2d42af79b/p/4f72bd1b-e50f-4b32-b15c-ceb4defc7268[/img]

[img]http://https://app.photobucket.com/u/Flowboy/p/c9f07e96-201a-4aec-a8d0-000d68e14725[/img]

Last edited by flowboy; 12/02/21 9:13 pm.
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In addition on Boomer his ZB crankcases

My very early ZB34GS is/was shipped to Rich Child,USA on 6.5.1949.
Competition/race spec..

And has the “round” corner… cases are still original with the correct numbering, both casing numbers and engine number..
[Linked Image from download.motolab.nl]


Image is from my own libary, ofcourse i can make a detail image if wanted…

Last edited by Motolab; 12/06/21 12:48 am.

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Motolab,
I'm interested to know if your tappet cover overhangs the case as per Boomer's 1st pic.
Also what number range both yours & Boomer's are in

How many of the early ZB's were actually built in '48, (with the early cases) given that's when the bike was first displayed at the Earls Court show?

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Well overhang…tbh that is very very minimal… it is there but on a fully assembled engine, barely to be seen….
It is dark here now… so measuring is for daylight… but i doubt if it it is more than 2 or 3 mm just on the corner (i use a decompression plate who slightly influences the look/feel..

It is no 48 so quite early in the 500 line

As far as i know the 500 was first displayed /presented at Earls Court show ‘49 to the public (correct me if i am wrong)
And 3 of them raced in February ‘49 i believe…


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According to Ian Jackson of the UK Gold Star Owners Club, holder of the BSA Gold Star dispatch list, says the first Gold Star listed in the dispatch list was ZB34GS105, dispatched on April 5th 1949. The Daytona races were held the first weekend of March 1949 and it is believed 101 to 104 were sent to Rich Child for that race.


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By that, I assume Ian J meant ZB34GS105 was the first 500cc dispatched, rather than the "first post war Gold Star".
The ZB32GS appeared in Nov '48 & was available for some months prior to the appearance of the 500.
April '49 seems quite early for the 500 - AFAIK they weren't generally available until much later in the the year, after the Earls Court MC show in late '49? Although it doesn't surprise me that some will have been supplied early to favoured dealers etc. BSA were of course chasing export dollars in the US market.

Anyway, having now contributed to a hijack, this is a thread about crankcases, rather than dispatches & exports! Shall we keep it neat? smile

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If they were available in late '49 that would make them a '50 model as the model year always started after the summer break in late August. Here is the email that Ian sent me several years ago:


"Bill – Thanks for all this. I think you may have found an interesting one. I’d welcome any photos of it.
I noticed that the stamping is not the same as some of those I sent. I wonder if BSA hadn’t settled on the stamps – I’m sure the engines would have been stamped at the factory before despatch.
ZB34 GS 105 was despatched to a dealer in the West Country on 5 April 1949. I suspect that 101 – 104 would have been despatched at this time = late March – early April, which would have given plenty of time to have got them across the Atlantic for the 1950 Daytona.
I have never been told about the Tommy McDermott Daytona ZB but I have led a sheltered life. I’ll ask about it!
I find all this fascinating!
Keep in touch!
Ian"


Bill B...


I should clarify that 101 to 104 were dispatched for the '49 race and not the '50.

Last edited by Boomer; 12/15/21 10:24 pm. Reason: clarification

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