Hello from Australia,

I have a ZB33 500cc which i've had in storage for a few years due to work commitments. When i first purchased the bike it was complete, but very rough and had sat for two decades- i got it running for half an hour, but decide it'd be best that I pull the bike to bits and sort all the issues out properly.

Yesterday I finally got around to the motor- after splitting the cases I found a hairline crack from near the driveside mains bearing on the case exterior, which ran down to the bottom of the cases near the drain plug. The underside of the cases were caked in ancient gasket cement and once i cleaned all that away i discovered a large crack and a self tapping wood screw which had been inserted somehow to pin it, and filled off flush with the case sealing edge.

The timing side case is undamaged, but i'm wondering if this drive side case is possibly salvageable?

Has anyone had experience welding or brazing a crack of this extent?

regards,
Nick

G'day Nick,

I wonder how that happened?

Does the crack extend into the bearing housing?
The cases can be welded, sure, but if the crack extends to the bearing then there will be a whole lot more work to get that case usable.

Most of the crack is isolated to the last photo where it goes through an inch of the lowest section of the case. The hairline crack on the exterior of the case goes up to just before the main bearing but not too it, or into it.

I would guess hitting a curb, when there is no guard fitted there is nothing protecting the cases in the B serie frames....

Shame, good luck, can't advise in welding but personally would look out for replacements.

Michiel / NL

What a great shame this happened to a nice old thumper motor.
I to would like to know how best to go about an effective repair, as I have a few similar repairs needing attention.
I suppose an important part would be to have all contamination removed from the pores of the metal, soaking in a suitable solvent, and or boiling the part in a strong detergent solution for a long time.
When the crack is cleaned out ready for TIG welding, or whatever method is most suitable, would it be a good idea to use every available bolt hole to clamp it down onto a thick steel plate to prevent warpage when cooling. This would only do the outside of the case though. Would the crack need to be completely gouged out to allow full penetration of the filler rod or just a bead along both sides of the crack.
Thanks Keith
Ps Great photos!!!

yes a repairable case But it won't be pretty or cheap.
You will have a scar for the full length of the crack which can only be obsurred by polishing the whole crank.
Personnaly I like to see scars like this left as the extra thichness of metal will add to the strength and it gives the bike a sort of authenticity.
It screams out I HAVE BEEN RIDDEN.

As for the rest, I would look for some one who will torch weld as torch wlding is far more tollerant of porosity and oil ( a small amount will just float off with the flux ).
You will have to clean it thoroughly & I would opt for ultrasound after degreasing.
Heed previous warnings about jigging up

email (option): bsansw1@tpg.com.au

Not the subject of your posting, but...

The timing cover looks like it might have come off an M20..It appears to have a home made breather pipe fitting added and something is going on with the anti drain valve...It doesn't have the right fitting in place....

If you can find one I'd be inclined to replace that with the correct cover that has the right breather assembly fitted and an anti drain valve...Ian

email (option): ian@wright52.plus.com

Hi Nick,
I recognize that engine! You'll be pleased to know that most of the cycle parts have been put to good use on my project. I'm not sure how different M20 cases are to your B33 but I've got some M20 spares if you need some.

['I'm not sure how different M20 cases are to your B33 but I've got some M20 spares if you need some...']


Not interchangeable unfortunately..Ian

email (option): ian@wright52.plus.com

Nigel - Hello mate! Glad to hear the plunger frame has been put to good use, I'm living back in Melbourne after some time interstate and overseas. I must get along to the BSA club again soon.

Ian - very astute observations, though I'd expect nothing less of you my friend, I also have a ZM21 motor which has a different timing cover to this one on my B33, and I wondered which, if either, were correct. My bike is near on 40 years older than I am so I'll have a lot of questions for you down the track I'm sure. It appears as though i shave a short rod on B31 flywheels, what is the difference between the 350cc and 500cc flywheels?

The case is going to a very experienced precision welder for appraisal, he will be the judge on the matter as my welding skills are very basic.

The basic difference between B31 and B33 flywheels is the weight...Specifically the bob weight section is heavier for the B33..

Theoretically the B31 flywheel assembly should be rebalanced to suit the increased (B33) piston weight but in practice this combination runs OK, if not quite as smoothly as with the correct balance factor...

It's really down to how fussy you are and whether the increased vibration occurs in the part of the rev range you frequently use...

Many years ago I converted an alternator B31 to a B33 without bothering to look at the bottom end, ran it like that for a few years and still had the fillings in my teeth and the use of all my limbs afterwards... ...

If the timing cover fitted to you ZM21 engine has the breather assembly fitted to it, it's the right one for the B33 motor...

Basically the M and B engines either had the breather fitted to the crank case or to the cover...I notice your B33 engine has 'wide flange' crank cases which makes it ZB or later so it should have the breather in the cover...Ian

email (option): ian@wright52.plus.com

What is the difference in the cases that make this a "wide flange" engine.
Keith

BSA crank cases were strengthened from late 'ZB' engines onwards..

This was probably a spin off from the increasing power outputs obtained from Gold Star engines and the introduction of the larger capacity ZB34 500 Gold Star...

Where the two crank case halves join there is a 'flange' that runs around the periphery of the cases, between the joining bolt bosses and the frame mounting bosses...M20/21s, early B31s and early ZB engines had a flange approximately 3/16" wide to stiffen the cases here...

This was nearer 1/2" wide from late OHV 'ZB' motors onwards..M Series engines always retained the earlier narrow flange..

Along with this mod. support for the drive side main bearing was much improved with the introduction of additional stiffening ribs around the bearing housing..

Also the area around the cam followers was thickened up...

Externally the wider flange is the quick identifier for these later cases. When purchasing cases, particularly for highly tuned B Series engines, they are the ones to have ideally...
They are also much in demand at the moment as donor cases for DBD34 'lookalike' engines and by the racing fraternity for the same use...

Expect to pay £150-£200 for these late cases now, which is maybe three times as much as the earlier ones are likely to fetch..

It's worth noting that on more than one occasion I've seen early cases being sold at inflated prices for Gold Star conversions and I've even seen early ones numbered as 'ZB' or the later 'BB' casings...

It seems there are no limits for the desire to make money and in doing so to set these traps for the unwary... ....Ian

email (option): ian@wright52.plus.com

That's a lot..but I guess you can ask what you like...

I've yet to see them fetch anything like that much on e bay and it is sales I have seen there along with what I've seen at jumbles that lead me to the figure I mentioned..

Mind you, it seems the price of anything can rise rapidly these days...Ian

email (option): ian@wright52.plus.com

One option for successful repair of aluminium alloy, might be
HTS 2000 second generation fluxless brazing rod for non ferrous metals.
There is some good demonstration videos on you tube.
Anyone tried this??
Keith

It is a zinc based solder and calling it a braizing rod is a down right lie.
There is no deep penetration as happens with real braizing and the rod does not for a new alloy phase with the parent metal.
While the rod itself has reasonable mechanical properties a join made with it does not so it is not suitable for use anywhere that is stressed,
It is really good for filling corrosion holes , although it has a slight blue tinge and cracks in non stressed places like a footpeg hole in a primary cover.

It is just a variation of Lumiweld that has been around since the 60's.
Somewhere amongst the 1000's of digital images I have is one of an A 10 rocker cover repaired with a similar material that blew out on the first long trip the owner took it on around 200 miles from nowhere.
We did some very interesting things to that head to get it & the rider back to base

email (option): bsansw1@tpg.com.au

You could try and repair this yourself with HTS-2000, I have used this and had some good results with it, I think when I sent for this it was about £60 but it has paid for itself over the time I've had it.
Watch the video hts2000@msn.com

Regards TTJohn

email (option): Jomichael@aol.com

After going to some great lengths to clean all the oil from the pores of the casting (boiling in water, soaking in acetone, ultrasonic cleaning etc) the case was able to be welded up with the help of a specialist who used his TIG after carefully V'ing out the crack at the bottom and the small hairlines extending from it on the inside and outside of the case, I argued the mark on the inside of the case was just a casting mark, but we welded over it anyway. The bead on the case exterior has been roughly cleaned up and I'm testing for any pinholes now with some penetrine sitting in the case. Fingers crossed it holds together.