The BSA A7-A10 Forum

Technical => Clutch, Primary, Gearbox => Topic started by: KeithJ on 20.03. 2014 08:27

Title: Furrowed shaft equals furrowed brow
Post by: KeithJ on 20.03. 2014 08:27
Why do the shafts get so furrowed (chewed up) running in bronze bushes?  What options are there to minimise the problem?
Have rebuilt a couple of gearboxes and now doing another two.  Have always found the same problem with the shafts running in the bronze bushes.  Oil looks Ok.  No nasty debris.  Prefer not to go the needle roller route as I have good shafts to use.  Are there better bronzes to use than than used in the bushes available?  Is 0.002" clearance ok?  What is the optimum clearance on a bush?

Are Oilite bushes better?  http://www.bearingboys.co.uk/?catid=2568&page=2&att1=&att2=&att3=&att4=&att5=

Has anyone used needle rollers with "inner rings"?  http://www.bearingboys.co.uk/Inner_Rings-3665-c

Appreciate words of wisdom from those wiser than I.  *????*

ATB
Title: Re: Furrowed shaft equals furrowed brow
Post by: muskrat on 20.03. 2014 08:57
The old saying comes to mind "soft wears hard". Any grit embeds into the bronze/brass and wears the harder steel shaft. If the shaft is nitrided or case hardened it will wear the bush out first.
Another theory is the modern g/box oils eat brass/bronze bushes.
I haven't tryed those Oilite bushes but  sintered bronze is a good material as is Phosphor bronze. Not exactly sure what the material is that is used for the bushes we now buy off the shelf.
Use good (not cheap) oil and change yearly (10Kmiles).
Cheers
Title: Re: Furrowed shaft equals furrowed brow
Post by: bsa-bill on 20.03. 2014 09:03
Could be a similar situation as Copper, where my plumber remarked when replacing an immersion heater  " Copper is poor these days, been through the Scrap dealers too many times"
Title: Re: Furrowed shaft equals furrowed brow
Post by: KeithJ on 20.03. 2014 10:07
Another theory is the modern g/box oils eat brass/bronze bushes.

I think that was has been the case but believe it now is not.  Don't recall exactly but I think there used to be an additive in gearbox oils which attacked the copper but that is no longer used.
ATB
Title: Re: Furrowed shaft equals furrowed brow
Post by: BSA_54A10 on 20.03. 2014 10:25
Could be a similar situation as Copper, where my plumber remarked when replacing an immersion heater  " Copper is poor these days, been through the Scrap dealers too many times"
Rubbish, refined copper is just as good if not beter as virgin alloys. I used to make them.
Problem is poor quality Chineese material being passed off as good quality gear .
And cheapskates refusing to pay the extra for top quality heavy walled 99 copper tube although it will last 200 years
Title: Re: Furrowed shaft equals furrowed brow
Post by: BSA_54A10 on 20.03. 2014 10:33
Another theory is the modern g/box oils eat brass/bronze bushes.

I think that was has been the case but believe it now is not.  Don't recall exactly but I think there used to be an additive in gearbox oils which attacked the copper but that is no longer used.
ATB
Sulphur or rather sulphided compounds are the problem.
These are added to EP & Hypoid type oils and the sulphur attacks the copper grain boundaries. It also chemically reacts with the zinc rich phases which basically dissolve out of the brass.
Musky got it backwards, older oils were the big problem as newer oils were designed to be used in boxes with brass syncro cones.
Multigrade oils should also be avoided as these tend not to flow as well as mono grades.
And of course then we have "thicker oil or liquid grease" to slow oil leaks also not a good idea.
Title: Re: Furrowed shaft equals furrowed brow
Post by: bsa-bill on 20.03. 2014 11:18
Quote
Rubbish, refined copper is just as good if not beter as virgin alloys. I used to make them.
Problem is poor quality Chineese material being passed off as good quality gear .

Whatever the reason, I've had Three immersion heaters pack in in five years, all with the same fault, the copper corrodes - little holes appear - electric short - cold wash in the morning ( I no longer believe it's character building )

Plumber did say he'd order a stainless one for next time

thinking about it, our water is treated now since they backed up the supply by using a bore hole - could be them damn additives again
Title: Re: Furrowed shaft equals furrowed brow
Post by: coater87 on 20.03. 2014 23:07
 usill,

 I am an industrial electrician by trade, and can relate to your copper corrosion problem.

 We have areas with immersion heaters, and I can tell you for sure the less pure the water is,

 the faster they burn out. Some last 2-3 months in water used for QA samples. The heaters in

 De-ionized water seem to last forever. Matter of fact, there are some I have never even looked

 at in 15+ years.
Title: Re: Furrowed shaft equals furrowed brow
Post by: Flatboy 1950 on 21.03. 2014 08:07
I wrote a story about this years ago ... It was comprehensively ignored !!
My brother served his time at the Atomic Energy Board in Pretoria , South Africa , where they had the finest machining & measuring capability on Earth. During his apprenticeship they were allowed to do some practical work & he chose to rebuild an A10 gearbox. He owned 5 A10's at the time.
All 3 of the swing arm countershafts were scored on the inboard surface.
He was able to discover that the aperture for this inboard bush was not machined square to the gasket face using the fine measuring equipment available.
He bored the casing out slightly & made a new bush to suit & solved the problem.
His A10's were 56 to 61 , so over a 5 year period ALL the gearboxes made must have had the same problem !!!!
Nothing wrong with the material used ..... it is a machining error !!!
Title: Re: Furrowed shaft equals furrowed brow
Post by: KeithJ on 21.03. 2014 08:35
I can understand a bush being machined out of square but how does that give the furrowed wear pattern?  Also, during the years of manufacture of BSA A&B type gearboxes, the jigs, fixtures and machines will have been varied and many, so find it difficult to understand the same error will be on all gearboxes rather than on some?   *conf*
Title: Re: Furrowed shaft equals furrowed brow
Post by: bsa-bill on 21.03. 2014 09:22
Quote
and I can tell you for sure the less pure the water is, the faster they burn out.

That kind of fits  coater87 poorer copper and they've lasted no time at all since the change in water supply