Author Topic: Plain bearing vs roller conversion  (Read 1925 times)

Online Bsareg

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Re: Plain bearing vs roller conversion
« Reply #15 on: 29.10. 2017 22:15 »
The original bushes work fine but a few years ago there were a lot of two piece bushes about with poor fixings between the inner and outer. This allowed the inner to turn and close off the oil ways.  I always fit solid bushes then  blue and hand scrape them into  line. Not the recommended way but has proved reliable on all the families a10s (some of which get a right hammering by the young-uns.
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Online Greybeard

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Re: Plain bearing vs roller conversion
« Reply #16 on: 29.10. 2017 22:55 »
I always fit solid bushes then  blue and hand scrape them into  line.
I had to learn how to do that when I fitted a new crankshaft to my Austin Seven. The big ends were white metalled and had to be hand scraped to fit the journals. I hadn't realised one could do that with the BSA shaft bushes.

Offline Clive54bsa

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Re: Plain bearing vs roller conversion
« Reply #17 on: 30.10. 2017 00:29 »
 I agree with gpo746, both my A10s cover barely 2000 miles a year, so the bushing is probably adequate, especially as I change the oil, which is still relatively cheap, approx every 500 miles. But if you intend to use your A10 as a daily rider, covering many thousands per year or racing then perhaps the conversion is for you, unless you have a bearing failure as I did.


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Re: Plain bearing vs roller conversion
« Reply #18 on: 30.10. 2017 07:02 »
My Star Twin has now clocked up 40 years of use and abuse and absolute thrashing on its plain bearing. Failures of plain bearings are not a design fault. So much is down to the bush and how it is fitted. My wife's A10 has had even more years of thrashing (she's not a delicate flower when it come to the throttle hand) and has never had a problem with the timing side bush.
A lot of this discussion is down to personal experience or belief. It does worry me slightly that new BSA owners feel they must go for the SRM conversion before anything else. It's a lot of money for something that they most likely don't need. 
If you are going to hammer an A10, I would look to the ageing con rods as the most likely components to fail.

Yes a sore point there.
More than 1 person I know was ardent that their bike would grenade without an SRM conversion but were more than happy to put the old rods back in without as much as a simple dye pen test for cracking.
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Offline Sluggo

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Re: Plain bearing vs roller conversion
« Reply #19 on: 30.10. 2017 17:01 »
Horses for Courses,,,,,,,, But overall I agree with T20Racer,

Biggest REAL issue in my experience with many rebuilds of British engines, (Not many on A10s admittedly) is that the process of "Blueprinting" is the most important, followed by sensible time change parts replacements with basis of metallurgy and physics.

Blueprinting is the process of checking every surface and dimension and optimizing it to the best possible specs.  Not easy, but in my experience (And I am certified in Aerospace inspection and repair (FAA-A&P as well as multiple ratings in NDT-Non Destructive testing) is that many of these old bikes were built to rather loose and sloppy tolerances.  For their day they were pretty good and overall I think 1950s BSA stuff was some of the best on the market.  But lets be honest. Every manufacturer builds things to a cost, not an engineering/machining  ideal.     Secondly after 70 some years, dimensions change, especially aluminum castings.  In the BSA engines I have checked I have found significant dimensional changes that I am certain did not leave the factory with.  But I have also found some really sloppy work as well that was "Good enough to go out the door" and many that WERE NOT good enough to be installed on a bike.   
**Norton was probably the worst offender in that dept, and knowingly shipped junk that had to rectified at the dealer level, But all Brit manufacturers were guilty at times of this. 

Something that Edward Turner begrudgingly acknowledged after returning from a trip to Japan.

But I wholehearted agree on aged rods and other bits.  I bring it up often but in Stan Shentons book "Triumph Speed tuning", Triumphs engineers stated that the service life for a Triumph connecting rod was ONE,, thats 1,.... 500 mile  race.  Its simply physics that a alloy rod has a limited service life, Math is Brutal!

As to the specifics of a bush vs bearing, I have come to a middle of the road approach.  I agree that a low stressed engine will run fine on a bushing if tolerances are kept in line.  I also talked to a lot of racers who spent decades thrashing these old engines on their insights.  I believe that the bearing conversion done properly is a sound modification.
Triumph ran the early 500 unit twins on bush but they were not without failures (same with the gooseneck frames prior to 67).  As the 500 unit gained power it was necessary to upgrade all aspects of the engine.
(Gearbox too)  So the castings were improved as well as the bearing change. 

***CORRECTION: Ted Simons Triumph he rode around the world on was NOT a bushing model,, It was either a 72 or 73 Model which had many improvements over the early engines. So lets dispel that myth please ***

So, comparisons to cars always come up, and I have built a number of car engines and raced a few. But there is a BIG BIG difference and it comes down to design.   The more cylinders you have the smoother the power pulses, which is why for example Jaguar ran a V12,  A twin cylinder vertical twin without counterbalancers is a nasty enterprise, which is why Ducati and others ran a 270 deg crank. (Smooths out that nasty vibration)  Only Matchless/AJS really got the design right and then failed in execution with their  center main bearing. (Sloppy manuf tolerances).  This is why the modern Norton 952-961 engine has a center main bearing as that crankshaft whip is extreme.   I have the documentation on stress analysis equipment to prove this.

If you guys were to actually see how much these engines flex, whip and bend internally at speed you would never leave the driveway or garage.  Some feel that the vertical twin engines of BSA-Norton-Triumph are purposefully weak and flexible by design and some argue that by reinforcing them you invite breakage.  If there is any truth to that then you by extension have to acknowledge that  parts that flex can only do so for so long and how much. (IE: Time change)

But a bushing in a main bearing application CAN last a very long time in a 4-6-8-10-12 cyl configuration if properly supported.  Most of the small block chevy V8s I build are a high nickel cast iron block with 4 bolt main caps and substantial meat.  They get line bored and I use seasoned blocks.  They dont move or flex.

These old vertical twins dont have any of these benefits and the amount of flywheel flex and whip is extreme.   But dynamic balancing is critical.  Not the old static balance (Which is better than nothing) but true dynamic balancing is something I wont cut corners on.   I have found piston and pin weight discrepancies of several grams out of the box, rods mismatched,Cranks with different strokes between cyls, and then there is rocking couple. 

So a BSA A7-A10 puttering around under 4000rpm and intermittent usage will be fine on a bushing, but beyond that they need all  the help they can get.
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Online Rex

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Re: Plain bearing vs roller conversion
« Reply #20 on: 30.10. 2017 21:21 »
***CORRECTION: Ted Simons Triumph he rode around the world on was NOT a bushing model,, It was either a 72 or 73 Model which had many improvements over the early engines. So lets dispel that myth please ***
 

Turns out you are spot on, and it was a late police model with those nice big mains fitted.
Another old myth busted... *conf*

Offline Sluggo

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Re: Plain bearing vs roller conversion
« Reply #21 on: 30.10. 2017 21:29 »
Ted Simon was a guest many years ago at the Oregon vintage MC club annual banquet, seemed like a nice guy.
He gave a short talk and presentation.  I did not go that year but I heard it was good evening.

I rather like the later model Unit 500 Triumphs,  I would NOT want to travel the US interstate system for any length of time on one, but back roads they are a hoot. Torquey and just a lot of fun.  One of my long languishing projects is a Rickman Montessa missing  a motor.  I have a very nice 1972 Triumph Daytona motor for it and one of these days will see the road again as a enduro.  (I have a clear title and registration for the Rickman)  I wanted to run a BSA B50 motor in that chassis and BRG along the lines of a Jeff Smith bike but sadly the BSA engine is too tall for that frame.  The T100R is a tight squeeze but manageable.

To cut up the Rickman frame is unconscionable so Triumph it is.
Remember that any advice received on a free internet forum is generally worth about 1/2 of what you paid for it.
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Online Black Sheep

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Re: Plain bearing vs roller conversion
« Reply #22 on: 03.11. 2017 14:40 »
That's where you and Odgie differ...
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Online cyclobutch

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Re: Plain bearing vs roller conversion
« Reply #23 on: 03.11. 2017 15:53 »
A similar argument often rages among unit Triumph enthusiasts, until someone always points out that Ted Simon (he of "Jupiter's Travels") rode around the World on a bush motor, and with no problems.
How much bigger test can there be?

I thought he had a lot of problems. Not sure how many were with the bottom end though.
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Offline Colsbeeza

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Re: Plain bearing vs roller conversion
« Reply #24 on: 24.11. 2017 12:31 »
Lads,
I have attached an article of 20 years ago. Found it recently.
On topic up to a point. It restored my faith in the basic design of the Timing side bush.
Col
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Offline duTch

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Re: Plain bearing vs roller conversion
« Reply #25 on: 24.11. 2017 19:32 »

 So now you have to come up with the follow up story... :!
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
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Offline harvey mushman

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Re: Plain bearing vs roller conversion
« Reply #26 on: 24.11. 2017 20:19 »
Lads,
I have attached an article of 20 years ago. Found it recently.
On topic up to a point. It restored my faith in the basic design of the Timing side bush.
Col

couldn't agree more!

thanks for sharing article.

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Re: Plain bearing vs roller conversion
« Reply #27 on: 25.11. 2017 17:29 »
Lads,
I have attached an article of 20 years ago. Found it recently.
On topic up to a point. It restored my faith in the basic design of the Timing side bush.
Col

couldn't agree more!

thanks for sharing article.

I could only find this; there are a couple of pics if you scroll down, and it seems to be talking more of '85 than '86 I think.

http://zhumoristenouveau.eklablog.com/a-versailles-louis-xiv-recoit-le-paris-dakar-85-a117369820
Various, including ...
'58 Iron Head Flash Bitza


Offline harvey mushman

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Re: Plain bearing vs roller conversion
« Reply #28 on: 25.11. 2017 18:27 »
Looks good in the husky frame, you could do a double take and almost think it belonged there! done up with its black paint job.

cheers  ;)

http://www.parisdakar.it/category/piloti/#/?playlistId=0&videoId=0

more pics

Offline harvey mushman

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Re: Plain bearing vs roller conversion
« Reply #29 on: 25.11. 2017 18:50 »
sorry a bit off topic  *conf*