Am I going to regret not buying this crank?

[morris]

Metal spraying and welding are totally different processes despite what an ill-informed Wikki ego posted.

Ok, maybe not the right terminology here. Strictly speaking, welding is the joining of two metals by the aid of a third (which can be three times the same metal), so in a sense the phrase " building up with weld" ain't right either...

In both processes the aim is to get the one metal to bond with the other by the aid of heat. Can we thus  agree on using the word "fusion" maybe?

[bsa-bill]

Can we thus  agree on using the word "fusion" maybe?

Only if we also agree that a hacksaw is a fission weapon

[Butch (cb)]

Ha - was that where Tony Blurr went wrong in his search?

[morris]

Only if we also agree that a hacksaw is a fission weapon

Let's meet under the Brussels Atomium and give it a try. 

[A10Boy]

Whether its right or wrong to buy and break up a good bike, has anyone noticed how Mr M B Transits' prices have gone through the roof recently? A good crank should only cost say £300.

[edboy]

h no, does it mean i will have to insure the crank separetely from the rest of the bike ? as its agreed value only

[BSA_54A10]

Metal spraying and welding are totally different processes despite what an ill-informed Wikki ego posted.

Ok, maybe not the right terminology here. Strictly speaking, welding is the joining of two metals by the aid of a third (which can be three times the same metal), so in a sense the phrase " building up with weld" ain't right either...

In both processes the aim is to get the one metal to bond with the other by the aid of heat. Can we thus  agree on using the word "fusion" maybe?

Well if this was a conversation down the pub, I would not give a wrinkled rats rectum about correctness,
However this is a conversation in cyber space and as such it will persist forever.
Even worse it is searchable and indexed so others will also find the wrong answers and thus an urban myth is born.

The defining thing about a weld is not how it is made.
It is the fact that the microstructure is CAST becuse all parties to the process are at some point in time were MOLTEN
The one and only exception to this is vacuum welding where neither pars get particularly hot and the microstructure of both parts is unchanged.

By definition flame spraying is a BRAISING process because the parent material is not molten at any time but the filler ( or build up material if you like ) is molten.
Thus the parent material more or less retains the microstructure that it had before the process

[morris]

Well if this was a conversation down the pub, I would not give a wrinkled rats rectum about correctness

Lucky we aren't in a pub then because we would now be somewhere at our tenth pint, and no one wouldn't understand anymore what we're babbling about...

However this is a conversation in cyber space and as such it will persist forever.

That's why we need to mind our language...

Even worse it is searchable and indexed so others will also find the wrong answers and thus an urban myth is born.

Forums like this one are there to discuss, learn, and correct, which, after your thorough explanation, made me come to the conclusion that I wouldn't really trust metal spraying on a cranck journal...
OTOH, don't know if I'd trust welding either.

[BSA_54A10]

I and only if and that is a very big IF it is done properly by a good well experienced operator it will be stronger than the welding build up method.
Note the if's.
Now days people who know what they are doing are few & far between.
modern equipment means you simply dial in the data and press the start button.
Fine if they actually know exactly what the crankshaft material is and how it was made.

[RichardL]

Trevor,

Is it safe to say that the materials and methods (forging, I think) used in making BSA crankshafts in the '50s and '60s were not so sophisticated in metallurgical structure (such as alloying) as to make fusing common welding media to the journals a big problem? Of course, the condition applies that the work be done by a professional using high-quality, purpose-built crankshaft welding equipment.

Richard L.

[BSA_54A10]

A yes and no type of question.
Twin cylinder BSA cranks were drop forged from a high strength forging alloy. which of course I will remember 2 minutes after I hit the post button.
They were also made from primary forging billet ( all virgin metals used to make the billet ) so would have been as good as they knew how.
A simple logic behind this as forging is very expensive so you want to reduce bad forgings to a minimum so you use good materials.
The two big things that have changed is better allys are now available and better heat treatments are now available.
The actual composition of most metals have become a lot tighter as assaying methods have become a lot cheaper and unbelievably fast.
You can do a mag resonance assay in real time as comparred to 6 hours by wet means.
Also computers have allowed real time TTT ( time temperature transformation ) analysis so I can now accurately manipulate the microstructure at any depth within the crank that I like.
Back in BSA's days every time you wanted to change some thing you had to cut a good crank up polish, etch & examine the structure under a microscope to see if it worked.
Now it can be modled on a computer with 100% accuracy.

However a casting is a casting is a casting and weld build up will always have a cast microstructure so the grains will run from the old crank face up towards the air / weld surface.
Some of it will be dead perpendicular to the journal and some will be at an angle in the direction of build up.
The very best you can do is to solutions heat treat then recrystalize to a  finner grain structure with no directional orientation.
This, engineering wise adds no strength to the crank, unless it was originally a cast crank, you are just building up coating on the outside so it will never have the same strength as it did when new .
Unless welding has changed a lot you used to need a weld pool 3 times the depth you were trying to build up so to add 1mm you need a 3mm pool depth so 2 mm of old forged structure will get replaced with weaker cast structure.

Metal spraying will not cause the loss of any of the original forged microstructure if done properly so if you were building up the same 1 mm you would only have 1mm of cast microstructure and around 0.5 to 1 mm of modified forged structure so it should be stronger when done properly.

[terryg]

Re. crank materials and processing - I've seen references to BSA having had a very competent metallurgical group.  Does anyone have any further information on this?

The 'Triple' crankshaft, twisted into shape when hot, may be a testament to the capability.

Just curious - as the large company in which I worked originally had huge in-house technical breadth dating from WWII and just after.  Sadly all dismantled to assuage the wrath of the bean counters in the 1970/80s (at about that time the apprentice school was closed too).

[RichardL]

Trevor,

Thanks for that great answer. Very intereisting discussion of grain structure and testing methods. Takes me back to the one materials class required when your major is Electriclal Engineering. This brings me to another question. I'm digging down because my next rebuild will most likely include journal welding. If I understand it correctly, forging changes grain size, shape and orientation to increase strength. In a crank, I assume the added strength is for both torsion and bending. So, the question: would 2mm (or, even more) of grain-structure change due to weld penetration make much difference in the overall strength that has been added core-deep by forging?

Sorry if seems I'm trying wear out your fingers with typing.

Richard L.

[a101960]

Sadly all dismantled to assuage the wrath of the bean counters in the 1970/80s (at about that time the apprentice school was closed too).

Yes, I too saw all this happen when I worked at Thorn EMI. Sir Jules Thorn built the company up from nothing, and while he was alive he had a policy of expansion and aquisition. Now there is nothing left of this once great company. In quick succsession the apprentice school, and the research and development department was closed, followed by the sell off of all the assets. That is the British business model unforunately. Now the only thing that we make in the UK is redundancies. If you wanted to bring Honda for example to is knees, then all you have to do is hand over the management of the company to to British managers and accountants. Job done!

[bsa-bill]

can't recall at the mo just what did come out of the ashes of BSA. BSA Regal still do stuff (other than the attempt to get back into bikes)
http://www.bsa-regal.co.uk/?category=none&page=aboutus
and I had an idea alloy wheels came about from BSA-  could be way off tho
I've read somewhere that Dennis Poore hived of the metal expertise the BSA were known for although I think he himself knew a bit about that side of things - dunno.
Yes management went from brilliant from   WW1 and WW11 to allowing the follies of the Dockers.
BSA were way ahead of government in both wars, having  foreseen hostilities and pre ordered vast amounts of stock.