The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: olev on 18.01. 2010 06:31
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Can someone please explain to me some things about the drive side bearing setup on my 52 plunger motor.
The bits working from the crank outwards are:
1. Crankshaft shim(s) (.005? or .010?) (67-671)
2. Roller bearing (67-670)
3. Bearing shim ? drive side (67-349)
4. Engine sprocket distance piece(s) (.005?or .010?or .030?) (67-2056, 67-2057, 67-2058)
5. Cush drive bearing. (67-2053)
There are no primary drive oil seals in these motors.
When the engine is running, does oil migrate between the primary drive chain case and the crankcase by suck and blow through the roller?
My engine didn?t have (3) - the bearing shim.
What is its role? It can?t be to set endplay. The crankshaft shims (1) obviously do that.
I?ll get a new one but what?s it do? The bearing is already wider than the housing.
The engine sprocket distance pieces (4) are obviously there to line up the clutch with the engine sprocket. How do you set this??
I suspect this alignment is important. I?ve seen 2 timing side bushes with chunks torn out that just might have been caused by the crank being pushed onto the bush. (pic of one attached) I understand the A65s had a thrust washer built into this bush.
Any thoughts??
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G'day Olev,
the bearing shim (don't think it should be called a shim) is to stop the oil coming through the bearing into the primary. It still gets in. Mine didn't have one either.
Once clutch is in, assemble the engine sprocket and cush on shaft (no need to tighten fully). Lay the edge of a 12" steel rule along the sprocket and towards the clutch. Add or sutract shims to line up with outer face of clutch chain wheel.
The bush pictured looks like a white metal or babbit coating over steel. They can do that through heat and hammering. Most new ones these days are bronze. A65 bushes are almost the same as ours, just different sizes. The bit that sits inside the case is the thrust surface and if the crank is shimmed correctly doesn't see too much wear.
Cheers
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Olev,
I feel that the "bearing shim" is in fact a chip guard to stop bits of primary muck getting mixed up with the rollers.
I have a new one in my '51 cases, the engine is yet to be built.
Have you found a source for these items? I need a couple.
The clutch alignment is supposedly set by differing thicknesses of the clutch thrust washer, there are three different ones listed. I suppose it is impossible to get the varying sizes now and what you have is what you use.
Trev.
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Thanks fellas,
trust you to muddy the water trev.
bl**dy clutch spacer shims. part no 67-3276, 77 & 78
and I don't have any of those either.
I guess you just *** about with shims and Muskrats steel rule until things line up.
and that timing bush face doesn't look too flash as a thrust surface.
I remember reading somewhere that the action of the oil pump drive is supposed to gently push the crank away from this bush.
but thats probably another BSA myth.
cheers
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Hi there Olev, the clutch spacer shim is the piece that goes behind the clutch that the split collets go in, you are not likely to need a different one of these. If it doesnt line up properly then you should be able to sort it with the shims that go behind the engine sprocket. They usually are pretty good and should only require a very small amount of shimming if any.
There are a couple of things to consider with all this, any end float in the crank will alter the alignment of the chain so even if you line it up perfectly if you have, say, .003" end float then the sprocket can move this much, assuming you are using a roller bearing in the drive side and not a ball bearing. (lots of theories on this subject but my plunger A10 has done 50,000 miles on a ball bearing)
So, assemble it all and see how it lines up, if it looks pretty close with a steel rule then it will be ok. It doesnt have to be perfect to the thou, chains are pretty forgiving things. If you do need to shift it one way or the other use the shims behind the sprocket.
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Brian,
Its interesting you seem to like the ball bearing main.
Beeza Bill had a ball bearing main in his A65 which covered a hundred billion miles with no problems. (RIP)
and there's a couple of interesting ball bearings floating about these days.
They are designed for use in transmissions which seem to have a rough life and are prefixed TM or TMB.
The most interesting one is the NTN TMB206JR2C3. This bearing is also used by KTM and Husaberg in their bikes.
Apparently they replaced a roller with this in the Husaberg as the roller kept breaking down???
google it and have a look.
If you read NTNs blurb, while the dynamic load stays the same, the life is 4 times better.
http://www.ntnamerica.com/pdf/Other/tmbspec.pdf
They even claim its a replacement for a 6306. I'd love to get one with a seal in one side.
Another one is the NSK TM206C3. This bearing has special seals to let oil in and keep particles out.
I've got one of these sitting on my desk. There is a temptation to fit the thing as the drive side main as its impossible get a sealed NTN in Aus for love or money.
Feel better after getting that lot out, time for a beer.
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Olev, its not so much that I like the ball bearing main its just that that particular bike has one and it has done a high mileage.
I have mixed feelings about them, BSA used ball bearings then rollers and then back to ball with the A65's and then back to roller again. As always there are several arguments either way. My 61' A10 has a roller but both A7's have ball's (ball bearings that is !) and the plunger A10 a ball.
At this stage I would use a roller in anything that was to have its performance increased but would be happy to use a ball bearing in a standard motor. I am in the throes of building another plunger A10 at the moment and are seriously considering a barrell roller bearing, in theory this would give the best of both worlds. Probably the biggest advantage of a ball is end float is not an issue, when using a roller you can shim it to whatever clearance you want but the clearance vary's with the temperature of the motor. If you ever have the primary cover off your bike when its hot feel the end float in the crank, when it cools down the end float will dissappear.
Like you say, all modern high performance motorcycles use ball bearing mains. If I do use a barrel roller in the A10 I am currently building I will post a topic on the forum about it and let everyone know what happens. This particular bike is a bitsa and I intend to use it as a sort of test bed for a few ideas I have.