Author Topic: Plain bearing vs roller conversion  (Read 1924 times)

Online Greybeard

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Plain bearing vs roller conversion
« on: 27.10. 2017 11:20 »
I've obtained permission from Barry Huron from Ontario to copy and post his comment on Facebook. He says he has more to say about this in Real Classic magazine, October 2017.
Barry was answering a chap who was trying to find a cheaper way to get a roller conversion than SRM.
 
...modern oil is far better than the old stuff and tolerances for bearings has not changed since the beginning of the industrial revolution. the plain bearing is much stronger and more durable than a roller and is universally used in all engines. the fly in the ointment is the sludge trap in the crankshaft-it is always the left big end that siezes due to it filling up if there is any oil in the tank. i have an A65 engine that ran just fine with .009" clearance and .035" end play so it is clearly a good design. the idea that a modification of dubious durability worth as much as the whole bike is more a matter of marketing hype than engineering excellence. clean out the sludge trap and add a filter and it is a bulletproof design. spending money on a modification will only win you garage races and ultimately devalue a bike in the eyes of the rivit counters that have the money to buy it at your estate sale.

Online JulianS

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Re: Plain bearing vs roller conversion
« Reply #1 on: 27.10. 2017 12:21 »
Interesting point of view.

I went SRM conversion back in 1984. Got fed up with end float and poor quality pattern bushes. Replaced the combined needle roller/ball thrust bearing in 2009 after many many miles. So for me the durability is proven and not dubious. Would not want to go back to a bush.

First photo is one of the horrors which persuaded me to convert.

On the other hand see second photo the defence of the Vandervell bush from BSA back in 1964. Unfortuately Vandervell dont make them anymore.

So it is all a matter of personal choice.

Online Rex

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Re: Plain bearing vs roller conversion
« Reply #2 on: 27.10. 2017 13:02 »
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?

Offline Clive54bsa

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Re: Plain bearing vs roller conversion
« Reply #3 on: 27.10. 2017 20:34 »
I've done 2 engines with the SRM conversion and 1 without. In hind sight I think I wasted my money on the conversions.
Firstly I'm in So Cal U.S. so obviously the freight charges add a lot to the total cost, and secondly I had one of the SRM bearings fail, I found little shiny flecks in the oil and after removing the timing cover, discovered the small ball bearings were breaking up after 13,000 miles. I sent the bearing back to SRM, as I thought it might be of interest to them and within a month I got a new one in the post...no note. I had already purchased a new bearing from a supplier in Canada, so now I have a spare.
My local bearing supplier told me that a 1% failure rate in bearings is quite common, so I suppose I was just unlucky...didn't play the lottery that week.


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Offline wortluck

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Re: Plain bearing vs roller conversion
« Reply #4 on: 27.10. 2017 20:48 »
Back in the 50s and 60s, bikers used thick coffee and washing up liquid for oil, never changed it only topped it up, and never fitted fancy modern filters - just made do with the tea strainer to filter out the chunks of metal.  Nowadays, we use engineered oil and change it in half the recommended time or less.  Some of us have magnetic sump plugs and are meticulous at cleaning everything.  Do we really need to change the original bikes.  I'm not fitting a filter, just changing the oil more often - and no conversions!!

Rant over - with the winter lay-up coming, do I leave the old oil in the bike and change it when the rabbits start breeding, do I change it now and leave the new oil in the bike, or do I drain the whole lot off and leave it empty? *dunno2* :-\
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Online Triton Thrasher

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Re: Plain bearing vs roller conversion
« Reply #5 on: 27.10. 2017 20:52 »
Many A65s had disastrous problems shortly after new purchase. Sloppy factory build may have contributed to that.

The Devimead/SRM end feed conversion had a market because of all those disgraceful A65 breakdowns. The similar conversions for A10s and unit Triumph 500s were tacked on to the range and people bought and keep
on buying them.

Offline t20racerman

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Re: Plain bearing vs roller conversion
« Reply #6 on: 27.10. 2017 21:26 »
There is simply no comparison - the SRM conversion is far, far superior to the original bush. If you ride an A10 or A7 in a low level of tune and are not prone to thrashing it, then fine, the bush will usually suffice. Once BSA uprated the power though on the late A10s and the later unit twins, the bush was at the absolute limit of acceptability. BSA had loads of warranty claims, and many unimpressed customers. The bush can't cope with high revs & power.
My A10 is tuned up, and has been thrashed continuously for the past 34 years. The bush lasted two years, but the SRM conversion has managed 32 years so far - with one replacement a few years back as I'd stripped it anyway.
My bike does a lot of miles, cruises at 80mph on faster roads, and gets revved high through the gears all the time. No bush could cope with what I've put my engine through. You might consider me a philistine for treating my BSA like this, but it's built to take it. If you only potter round on yours (and there's nothing wrong with that) then don't waste your money on an SRM conversion. If you want a bullet proof engine like mine, get the SRM conversion, and nitride your crank at the same time.
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Offline wortluck

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Re: Plain bearing vs roller conversion
« Reply #7 on: 28.10. 2017 10:43 »
Point taken t20racerman - can't argue with that!
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Offline coater87

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Re: Plain bearing vs roller conversion
« Reply #8 on: 28.10. 2017 14:55 »
Back in the 50s and 60s, bikers used thick coffee and washing up liquid for oil, never changed it only topped it up, and never fitted fancy modern filters - just made do with the tea strainer to filter out the chunks of metal.  Nowadays, we use engineered oil and change it in half the recommended time or less.  Some of us have magnetic sump plugs and are meticulous at cleaning everything.  Do we really need to change the original bikes.  I'm not fitting a filter, just changing the oil more often - and no conversions!!

Rant over - with the winter lay-up coming, do I leave the old oil in the bike and change it when the rabbits start breeding, do I change it now and leave the new oil in the bike, or do I drain the whole lot off and leave it empty? *dunno2* :-\

 Used oil has some acidic qualities, I believe this is a byproduct combustion.

 I dont think a three or four month lay-up would make any difference, but I would change it out than store it. Its one less thing to do when you bring it back out.

 Lee

Central Wisconsin in the U.S.

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Re: Plain bearing vs roller conversion
« Reply #9 on: 28.10. 2017 15:20 »
I'm with t20. My A10 Cafe gets flogged (raced for 9 years) and no problems with the conversion. My A7 plunger is on it's third bush and needs replacing now.
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Offline coater87

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Re: Plain bearing vs roller conversion
« Reply #10 on: 28.10. 2017 16:48 »
 The big advantage I can see from a distance is the fact the bearing can be changed by anyone.

 I can get my own bushes close by setting up in the mill, but I don't own a Sunnen hone much less the mandrels needed to do the job correctly.

 I think if I was to ever do another A10 motor, I may do this conversion and think deeply about converting the rest of the bushings over to bearings.

 Dont get me wrong, there is nothing at all wrong with bushings. Its just that if your not set up with the right tooling it gets pricey quickly and you have to rely on other peoples time line.

 Lee
Central Wisconsin in the U.S.

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Re: Plain bearing vs roller conversion
« Reply #11 on: 29.10. 2017 13:58 »
To a large extent, the problem wit the bush is way way way over rated.
back when we were young and used the bikes as daily transport we were always looking for reasons not to pull down the engines and accepted that they missed a bit , dropped some oil, blew a bit of smoke, vibrated and did not throw the front wheel skyward the instant you looked at the twist grip.

Now days when they get used once every forest fortnight we are desperate to find reasons , any reason to tear the engine apart.

Now my first BSa was a horrid mix of long & short stroke parts, over carbed & filled with pistons that made a church steeple look flat.
I thrashed that bike without mercy for 3 years till eventually it locked a rod , chewed out the barrel spigot then proceeded to rip the barrels off the flange.

Now there is no such thing as an engine that can not be made to work better by spending a lot of money on it, the question is , do you need to spend the money & will it be good value.
While there were quite a few warranty claims attributed to the plain bush on A 65's. remember that engine is putting out near double what a std A 10 puts out and is a high reving over square engine and not a A7.10 that developes peak power way before an A 65 gets onto its cam.

 
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Offline gpo746

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Re: Plain bearing vs roller conversion
« Reply #12 on: 29.10. 2017 14:31 »
The big advantage I can see from a distance is the fact the bearing can be changed by anyone.


 Lee

The fact that you could do your own bearing and could be changed by anyone with basic tools is a BIG advantage. The pain of having to strip down and then find an engineering company to hone and prat about with a plain bush..
What about cost???... How much does it cost to get a bearing conversion done? What is the difference in price Plain vs Bearing?

Online Black Sheep

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Re: Plain bearing vs roller conversion
« Reply #13 on: 29.10. 2017 15:19 »
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.   
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Offline gpo746

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Re: Plain bearing vs roller conversion
« Reply #14 on: 29.10. 2017 19:25 »
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.

I do not intend hammering my A7 . I just want it right and reliable (as can be!) . I will use it , not mollycoddle it , defo not thrash it. I may stick to a plain bush then......BUT..it is getting the RIGHT part (C&D Autos?) AND having someone who KNOWS how to machine it correctly .That is my concern.