Main roller bearing

[bikerboy]

So as I am making a start on a basket case I got a couple of years ago I thought I would aks the question.

Main bearing, traditionally I have always used the two part bearing that is about £50 but I see draganfly are offering a ball bearing set that they say is fine for a lot less.

The main bearing which has the nylon surround is also a fair bit cheaper than the traditional one what are the differences and why should I just not use the cheaper ball type?

If it stays in the crankcase it would also be a lot easier to set the float on the crank as well.

[Brian]

you are probably going to get a variety of reasons to use or not to use a particular bearing so I am not going to recommend either but rather to tell about one of my bikes, the one in the attached pic.

It was a 53' plunger A10 which I owned for about 20 years. when I bought it I pulled the motor down to inspect and freshen up anything that required attention. The engine was in excellent condition but I put rings in, valve grind and a good check over. It was fitted with a ball main bearing which I replaced just to be sure, it had a white metal timing bush which was like new. Anyway I owned the bike for about 20 years and did 46,000 miles on it. Just before I sold it I pulled the motor down again as the timing bush was starting to break up, small pieces of white metal in the sump. The ball main bearing was still like new.

The early A7's used a ball bearing and they went back to a ball bearing for the first year of the A65.

My current 61' A10 has a roller in it at the moment but when its due a rebuild I will be putting a ball bearing in.

Everyone has all sorts of theories about the bottom ends of these motors, personally I believe not having a captive crank is probably the biggest design fault.

[Swarfcut]

 Just had a looky at Drags.  The two bearings listed are not the same size. The ball race only fits the Longstroke pre 1950 A7 and is an oddball imperial size.

   Standard roller is 30 x 62 x 16 mm*, so a deep groove ball race (C3 internal clearance) of this size is the jobbie.

   Plenty about this already on the Forum, along with the change to the roller type, history, development, pros and cons of the various types of roller race available.

  For a bike running solo, lightly loaded, a ball race is fine. A good deal cheaper, and eliminates crank float. I'd say Brian's experience nails it for pussyfoots like me.

 Swarfy

 * Source Roy Bacon

[bikerboy]

I looked at draganfly and read it as you can use either but after another look I am not so sure. I will probably go with what I know to be honest but if I can save £30 I will

[Swarfcut]

     Back in the day, drive side bearings were replaced as a matter of course. These days they are expensive, and experience shows  that there is plenty of life left in the most neglected examples. Replacing is likely to bring about a minor improvement, if any.
   If the present bearing seems reasonable, it will be good enough for the sort of leisure use these bikes get now.

 More important is attention to the timing side bush and the crank sludge trap. The drive side has a relatively easy time.

 Swarfy.

[bikerboy]

The bush will be done as a matter of course a grind if need be on the crank and line bored to suit altho I am thinking of the roller bearing conversion

[spottycat]

Just reading this after posting my topic showing how my drive side bearing is cracked - quite weird! I see there are many bearing available of the correct size, roller or ball. The idea of a ball bearing that stays in the casing appeals to me if it means end float is not an issue - maybe someone can explain to me why this is. Are you suggesting that one could fit the ball race bearing and just forget about end float measurements? I plan to do lots of miles on my A10 but it they will be steady so maybe ball is the answer? I see that SKF make a ball race of the correct dimension. I fit SKF wheel bearings to my 2CV and have always thought they were good quality. Cheers, Chris

[berger]

the drive side needs the load bearing roller race and not just for expansion and contraction, engineers didn't throw a well made expensive roller in that case when a ball race costing a 3rd of the price would do, ball races ground at different angles like wheel bearing races do their job and the drive side roller in the BSA engines do their job.

[groily]

While a lot of trouble-free miles with my own A convinced me that a plain bush on the timing side is OK, the only reason my engine had to come down in 50K odd miles was because of the drive side shimming breaking up. As Brian says above, a floating crank is a weak design feature.
So if long-term / decent mileage experience has shown that a ball can be capable of doing the job, at least in engines in standard sorts of tune, I wouldn't be against giving it a shot Bergs, if I had another A to play with.
If sticking with the roller, I'd definitely go for a single one-off shim rather than a collection of flimsies. Which is what I did with mine in the end (after an abortive attempt to have the outer face of the drive side of the crank built up accurately so as to eliminate ANY shim at all. Consigned to the dustbin of history, although it didn't seem too mad an idea at the time).

An age-old debate, hence the Devimead now SRM conversions, and the many discussions.
End of the day, A bottom ends can last as long as most others of the day  . . . it's just that apprehensive feeling whenever the primary outer is off and you give the crank a good yank, praying it won't move much or pretending it hasn't!

[limeyrob]

My bearing has spun on the crank and worn a 5 thou recess in the face.  I looked at ways to fix this and after discussions with the machine shop I made a shim to fit in the recess (by cutting down and std one) to bring the surface back, then shimmed as normal.  Wary of shim break up I used bearing fit, bought an SRM drive nut and heaved it all up to 70 odd lbft and left it to set.