Author Topic: Bush and Roller conversion questions  (Read 481 times)

Offline AnthonyA

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Bush and Roller conversion questions
« on: 24.12. 2019 16:39 »
Hi fellas !

I read a lot of stuff about the roller conversion for the timing side bush, and simply the bush itself. But that raised questions often left unanswered. I seek some guidance from you guys.

1- Since the oil to the crank comes from the plain bush, replacing it with a roller bearing means a mandatory crank end oil feed, right ?
 
2- Can someone have the tools and knowledge do the conversion in France ? (I live in Bourgogne, not far from Paris, I'd be easier to bring the engine than ship it to somewhere in England in a crate)

3- Is line reaming necessary if your crankcases are matching numbers ? If so, does it mean I can't buy a bush that is of the spec of the crank journals (because I'd have to make it larger to align it anyway) ?

4- Would nitriding the crank be easier / cheaper than doing the conversion ? (And maybe would it allow a phosphor-bronze bush since the crank would be more tough?)

5- Where do I order the right king of bush ? Do I start from a lump of bronze and if so, which kind ? I read somewhere "LG2" type...


Thanks for the help, I'm dying to finally put my hand in this engine.
A10 Road Rocket (swing-arm)

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Re: Bush and Roller conversion questions
« Reply #1 on: 24.12. 2019 16:59 »
Just a couple of answers:
1. yes.
2. pass
3. no
4. one can only nitride certain steels eg EN40B. If you want to have harder journals and less risk of crank stress failure, you'd need tuftriding. Trouble is, the latter requires a higher temp than nitriding, with more liklihood of warpage. Also it only penetrated around .005" whereas nitriding goes to around .040" meaning you can re-gring a nitrided shaft but a tuftrided one need re-tuftriding every time it's ground.
5. There's a zillion different types of bronze. One with a fair % of lead would be kind to the crank (phosphor bronze has 10% Lead and low Zinc).
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Re: Bush and Roller conversion questions
« Reply #2 on: 24.12. 2019 21:25 »
Cringing at the thought of the 'Trusties' tutting at my input:

I am of the belief that a clean sludge trap, a well fitting timing side bush and frequent oil changes are enough to keep the engine together. Mind you, I do not thrash the testicles off my bike.

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Re: Bush and Roller conversion questions
« Reply #3 on: 24.12. 2019 22:43 »
G'day Ant.
I have a foot in both camps. The roller set up in the A10 Cafe is great, road raced for 8 years and on the road for 10. The A7 plunger is bushed and flogged mercilessly. The bush is well past it's use by date but still going strong.
For a road tourer I'd stick with the bush. If the case has been flogged out (meaning the bush isn't a good fit) or the crank journal has been ground too many times I'd go for the roller.
1 = yes, 2 = groily may know, 3 = oversize bush's are available and yes, 4 = if I had the money everything would be nitrided but no, std journals last a loooong time. 5 = https://sites.google.com/site/priorymagnetos/crank-and-rods  number 83a
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Re: Bush and Roller conversion questions
« Reply #4 on: 25.12. 2019 01:12 »
Hi fellas !

I read a lot of stuff about the roller conversion for the timing side bush, and simply the bush itself. But that raised questions often left unanswered. I seek some guidance from you guys.

1- Since the oil to the crank comes from the plain bush, replacing it with a roller bearing means a mandatory crank end oil feed, right ?
 
2- Can someone have the tools and knowledge do the conversion in France ? (I live in Bourgogne, not far from Paris, I'd be easier to bring the engine than ship it to somewhere in England in a crate)

3- Is line reaming necessary if your crankcases are matching numbers ? If so, does it mean I can't buy a bush that is of the spec of the crank journals (because I'd have to make it larger to align it anyway) ?

4- Would nitriding the crank be easier / cheaper than doing the conversion ? (And maybe would it allow a phosphor-bronze bush since the crank would be more tough?)

5- Where do I order the right king of bush ? Do I start from a lump of bronze and if so, which kind ? I read somewhere "LG2" type...


Thanks for the help, I'm dying to finally put my hand in this engine.

On 5 measure the cases and see if you have an oval or oversize housing, it’s not uncommon, if you have either you will need a special journal made to suit yr newly machined case. Line boring of a new bush bought deliberately undersize is desirable I reckon, as is getting a worn crank journal ground back to round, rather than to the next undersize. All this is well covered elsewhere. Opinions vary but I’d only go for the roller bearing conversion if I was either rich, or racing it, in which case I’d be poor  *eek*
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1956 A10 Golden Flash (1st finished project)

1949 B31 rigid “400cc hot rod” (2nd finished project, + favourite bike)

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Re: Bush and Roller conversion questions
« Reply #5 on: 25.12. 2019 01:47 »
Read the reports on the A7's that won BSA the Maudes Trophy.
Standard ( well sort of ) bikes assembled from parts ridden all over Europe competed in a variety of races , won some then ridden back to the UK.
So the Std set up is good enough unless you are thinking of fitting 12:1 pistons & running on dope.

Yes they can & do suffer crank failures.
Nearly all of them were in the USA where you can get on a bike wind the throttle up full and ride till you just about run out of fuel.
In these situation they suffer from ring flutter and pump a lot of the oil strait out of the mufflers.
The remaining oil overheats, over thins and lubrication breaks down.
Most of the A65 ( not all ) big end failures had a similar back story.
HD's were made for doing 80 mph for 3 hours down long strait roads , BSA's are not .
Like all of these "known short commings" get exagerrated and blow  way out out proportion to the point where owners are terrified to touch their bikes lest they self destruct.
These bikes are tough.
Down here it is near impossible to get a good crank.
There are dozens of them , pulled from a running bike that are cracked all the way round the journals, yet they had been running just fine and probably would have continued to do so for the next 50 years, cracks & all.
A member just got caught buying a SR that the previous owner thrashed till his back gave out so he sold it.
he crank was cracked around both journals and the drive side yet it ran really well.

AS for carbo nitirding it can be done to a finished crank if it is furnace nitirded and all you need to do is polish off some discolouration when it comes out.
If done in a salt bath then it will require refinishing
Carbo nitirding should not harden the surface, it toughens the crank and prevents cracks forming and slows down the growth of cracks that are already there.
Carbourizing hardens the crank
The crank is hard enough as it is
IF hey can run 70 years, how hard do they need to be ?
you intend to ride yours for better than 70 years ?
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Re: Bush and Roller conversion questions
« Reply #6 on: 25.12. 2019 08:33 »
Re question 2, I am afraid I don't know Anthony.
My own bike runs a bush (which had a correct 1.5 thou of an inch clearance after about 40k km in my hands and don't know how many more before) - which I thought was pretty darn good, but like GB I don't thrash the A as there isn't much point with a 'soft' motor.
When I have needed jobs doing, I have shipped parts to the UK because I don't have enough info on French specialists. Whether anyone is doing the roller conversion here I very much doubt, except maybe as a complete 'one-off'. Not much incentive when there are already several ways to get it done elsewhere and it is a very small niche market! A query on the Amicales BSA forum might be useful? It's a friendly place with a lot of knowledge on tap.

Joyeuses Fêtes & Bonne Année and Happy Christmas & NY to one and all on the forum!
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Re: Bush and Roller conversion questions
« Reply #7 on: 01.01. 2020 04:59 »
Anthony,
 perhaps the least useful reply but as a fellow road rocket owner (I havent seen your intro post with a picture of yours... ) on my race (55) RR I did the conversion after several years on a white metal plain bush which finally started breaking up . On my (54) RR road bike I'm sticking with a bush. This second engine is stuck in a storage unit while I finish a house renovation .

On a side note when I did my race motor conversion I did a super rocket motor with the same conversion as a race motor back up: I sold it a few years back and it then changed hands again before the rocker oil feed by the oil tank cracked and the current owner (who hadnt noticed) ran the oil tank dry at open road speeds until it ground to a halt, the pistons were a real mess. Awful to see... But the bottom end was fine, no marking on the shells and all within clearance down below. The timing side combination bearing also mint. How would this dry motor have coped on a plain bush... I dont know but suspect it would have ruined the big ends.

So my 10c worth is plain bushes are fine for normal use and that's what my 54 road rocket will have even though I have successfully had a local engineer convert two A10 motors for my abuse in the past
Tim
A good rider periodically checks all nuts and bolts with a spanner to see that they are tight - Instruction Manual for BSA B series, p46, para 2.
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