Ball bearing mains

Fast Eddie · Mar 8, 2016

Gents,

Most Triumph twins have a ball bearing timing side main and roller drive side main. This has the advantage of holding the crank in place, so end float exists primarily to facilitate expansion and contraction and is taken up via the drive side roller bearing.

It seems a logical idea, and in general, Triumphs do not suffer main bearing failure.

A ball bearing allows for a great deal of 'miss alignment' compared to a roller. A feature the 'superblend' is also famed for.

So my question is... Why not fit a top quality ball bearing to the timing side of a Commando engine along with the standard 'Superblend' on the drive side?

Onder · Mar 8, 2016

Are not Triumph rollers on the TS?

Fast Eddie · Mar 8, 2016

Onder said:
Are not Triumph rollers on the TS?

Only very late models. Even then I don't know why they did it as it seemed like overkill. Just about everything else would wear out before those bearings!

trident sam · Mar 8, 2016

Fast Eddie said:
Onder said:

Are not Triumph rollers on the TS?

Click to expand...

Only very late models. Even then I don't know why they did it as it seemed like overkill. Just about everything else would wear out before those bearings!

Nigel, how late is very late. Triples had a timing side roller from the start ?
sam

L.A.B. · Mar 8, 2016

trident sam said:
how late is very late.

From 1981 (NUP306E roller in place of the previous 6306 ball bearing). The roller bearing can also be fitted to earlier (late T120 and all T140 engines)

http://montysclassicmotorcyclesshop.co. ... -858-p.asp

comnoz · Mar 8, 2016

I don't know about a Triumph but on a Norton the ball bearing will not hold the crank in position once the engine is at operating temp. When the cases are hot the bearing will float in the bore unless it has been retained with added screws. Jim

Matchless · Mar 8, 2016

Jim,

I was under the impression that AMC had changed to C3 fit bearings in the mid 60s & reduced the size of bearing bore in the cases to suit,thus giving a tighter fit. Steve Maney makes his cases for C3 bearings in the same way.

Martyn.

comnoz · Mar 8, 2016

Matchless said:
Jim,

I was under the impression that AMC had changed to C3 fit bearings in the mid 60s & reduced the size of bearing bore in the cases to suit,thus giving a tighter fit. Steve Maney makes his cases for C3 bearings in the same way.

Martyn.

This is true -but they still move.

Check the temperature that the bearing can be pushed out of the engine case by hand and then check the temp of the engine case after a little time on the highway and you will see. Jim

Fast Eddie · Mar 8, 2016

Thanks for the input Gents.

commando6868 · Mar 8, 2016

comnoz said:
I don't know about a Triumph but on a Norton the ball bearing will not hold the crank in position once the engine is at operating temp. When the cases are hot the bearing will float in the bore unless it has been retained with added screws. Jim

So, on a 750 Commando, is it better to use roller bearings on both sides?

MF

comnoz · Mar 8, 2016

commando6868 said:
comnoz said:

I don't know about a Triumph but on a Norton the ball bearing will not hold the crank in position once the engine is at operating temp. When the cases are hot the bearing will float in the bore unless it has been retained with added screws. Jim

Click to expand...

So, on a 750 Commando, is it better to use roller bearings on both sides?

MF

Yes,
Commandos benefit from the high load capacity of a roller bearing. Jim

acotrel · Mar 8, 2016

If the bearings float in the crank case when the commando engine is hot, why do we even need superblend bearings to alleviate the alignment problems ? Do you think there would not be sufficient clearance around the outer race to allow the bearing to twist in the tunnel ?

marinatlas · Mar 8, 2016

why-ball-bearing-mains-t15270-105.html

some more to read.............!

comnoz · Mar 8, 2016

acotrel said:
If the bearings float in the crank case when the commando engine is hot, why do we even need superblend bearings to alleviate the alignment problems ? Do you think there would not be sufficient clearance around the outer race to allow the bearing to twist in the tunnel ?

Superblend bearings alleviate the alignment problem by two methods.

1. very high load capacity
2.They do "twist in the tunnel" The move enough to stay aligned with the bowed crankshaft. Look at the wear pattern on the outside of the bearing and measure a case bore after many miles and this becomes obvious. Jim

Rohan · Mar 8, 2016

Fast Eddie said:
Gents,

Most Triumph twins have a ball bearing timing side main and roller drive side main.

Its maybe worth pointing out that ALL Norton twins had a ball bearing on the timing side too, until somewhere in the 1960s ?
Triumph didn't do anything differently to Nortons for quite some decades in this respect.

Doesn't someone offer a heavy duty ball bearing for Commandos to revert to this setup...

comnoz · Mar 8, 2016

Rohan said:
Fast Eddie said:

Gents,

Most Triumph twins have a ball bearing timing side main and roller drive side main.

Click to expand...

Its maybe worth pointing out that ALL Norton twins had a ball bearing on the timing side too, until somewhere in the 1960s ?
Triumph didn't do anything differently to Nortons for quite some decades in this respect.

Doesn't someone offer a heavy duty ball bearing for Commandos to revert to this setup...

Sure- there is a heavy duty ball bearing that has been used on the timing side for quite some time. But it will not have the life expectancy of a roller -since it only has a fraction of the load capacity of the roller.

Rohan · Mar 8, 2016

comnoz said:
Sure- there is a heavy duty ball bearing that has been used on the timing side for quite some time. But it will not have the life expectancy of a roller -since it only has a fraction of the load capacity of the roller.

It was the roller bearing in dominators that wore out first, not the ball bearing ?
The ball bearing on the timing side only had to be a light duty bearing.

Commandos/Atlas's got a heavier flywheel and revved harder and made more hp,
so the bearing(s) needed to be beefed up - especially the drive side one ?

comnoz · Mar 8, 2016

Rohan said:
comnoz said:

Sure- there is a heavy duty ball bearing that has been used on the timing side for quite some time. But it will not have the life expectancy of a roller -since it only has a fraction of the load capacity of the roller.

Click to expand...

It was the roller bearing in dominators that wore out first, not the ball bearing ?
The ball bearing on the timing side only had to be a light duty bearing.

Commandos/Atlas's got a heavier flywheel and revved harder and made more hp,
so the bearing(s) needed to be beefed up - especially the drive side one ?

More reciprocating weight, longer stroke and more RPM meant the bearing load was much higher. Jim

Rohan · Mar 8, 2016

Rohan said:
Commandos/Atlas's got a heavier flywheel and revved harder and made more hp,
so the bearing(s) needed to be beefed up - especially the drive side one ?

comnoz said:
More reciprocating weight, longer stroke and more RPM meant the bearing load was much higher. Jim

Same way of saying the same thing !

Can't see that too much really changed between the Atlas and the Commando, when you look closely....

comnoz · Mar 8, 2016

Rohan said:
Rohan said:

Commandos/Atlas's got a heavier flywheel and revved harder and made more hp,
so the bearing(s) needed to be beefed up - especially the drive side one ?

Click to expand...

comnoz said:

More reciprocating weight, longer stroke and more RPM meant the bearing load was much higher. Jim

Click to expand...

Same way of saying the same thing !

Can't see that too much really changed between the Atlas and the Commando, when you look closely....

Yeah, as long as you tilt your head just right....

Ball bearing mains

Fast Eddie

Onder

Fast Eddie

trident sam

L.A.B.

Moderator

comnoz

Matchless

comnoz

Fast Eddie

commando6868

comnoz

acotrel

marinatlas

comnoz

Rohan

comnoz

Rohan

comnoz

Rohan

comnoz

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