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Rohan Offline OP
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This project 'Fastback' obviously has tapered roller steering bearings.

https://i.ebayimg.com/images/g/AaMAAOSw7YRgRTKM/s-l1600.jpg

How has this been done, and what is involved with making this all work.
Bearing numbers ?

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Originally Posted by Rohan
This project 'Fastback' obviously has tapered roller steering bearings.

https://i.ebayimg.com/images/g/AaMAAOSw7YRgRTKM/s-l1600.jpg

How has this been done, and what is involved with making this all work.
Bearing numbers ?

I can see the series 1 Commando frame and incompatible Series 2 triple trees.This is in spite of roller bearings, it would require machining of the neck to remedy the bearing to bearing length mismatch..


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Rohan Offline OP
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Yes I wondered that.
How does the early frames steering neck differ in length from the later ones ?
Apart from the different bearing arrangements.

Hasn't the neck already been machined to take the tapered roller outer cones though..
The length could have been adjusted then ?

Or, it wasn't, and thats why this project is moving on !!

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The neck is the overall same length for S1 or S2.
However the bottom bearing pocket on S2 neck is counter bored over 3mm deeper to accommodate the late style triple trees.
The S1 steering tree offset is 2-1/4" and S2A (750) is 2-3/4" S2B (850) different again (series is my numbering)

Additionally S1 and S2 steering neck limit stops and triple trees are not compatible.
Of course anything can be machined, welded and rewoked if you want to...(bastardize it!) LOL


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All sounds kinda trivial - if you've got the machines to do the machining. !

There would be no problemo fitting disc brake yokes & forks either. ?
We've seen that before - Ludwigs P11 and various featherbeds.

So, what are those bearing numbers.
Anyone know ?

Edit.
Bearing # 30205 seems to get a mention or 3.
ID is listed as 25mm, is this going to cause a problem ?
Commonly used as wheel bearings, so priced at anywhere from $3 to $53

[Linked Image from nskbearingcatalogue.com]

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It is not that straight forward if done properly.

IMG_5811 - Copy.JPG
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Rohan Offline OP
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Originally Posted by Les P
It is not that straight forward if done properly.

Want to add to those words with some details ?

Obviously you can't use a bearing spacer tube with tapered rollers - or they can't be adjusted !
How do the outer races go into the frame steering head - its not just a drop in fit ??

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Only an idiot would leave the spacer tube out based on the design of the later Commando design

The spacer tube is obviously at the new length to set the bearings, the lower stem nut can then be tightened as per normal unlike the clowns who try and use it as some form of adjuster.
If the bearings needed adjustment some time in the next 50 years all it would take is lapping the tube end a 'thou or so.

If it had a fine thread adjuster between the lower bearing and triple clamp and the external nut that would be a different matter and would replicate (but inverted) bikes that come stock with tapered roller bearings (Moto Guzzi - Ducati and even my DR650SE)


Both bearings are standard off the shelf NSK30205J-L which fit as a drop in.
The stock spacer tube is to short so I faced both ends and machined a 4140 heavy shim washer then lapped the last thou or so to set the bearings with the lower nut tight.
The action is better than fantastic.
The bearings do space the triples out a little so that has an effect on the head light brackets, I simply machined the lower triple top to rectify that.

In hindsight I could have used a tapered lower for axial and radial load then a conventional ball top bearing for radial only have no real load.

Its an easy job and the bearings are probably not much more than the stock items that I recall, with a lathe and mill in the garage it was easy as said.

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With a simple spacer instead of the lower triple it was easy to set the nut and then lap the tube end for the final 0.001"
I also machined a Acetyl disc that is a weather/dust shield that fits over the lower triple.

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I hope idiots and clowns was not to direct.

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What ???

My BM doesn't have a spacer in its steering.
Or how can you adjust the tapered rollers !!
Why would you want a spacer in there - unless you plan not to adjust them.
BM actually have a special tool that lets you set the preload precisely to the value they specify..
You do need a locknut on the locknut.

My Guzzi doesn't have a spacer tube.
Or how can you set the preload on the tapered rollers ?

My Suzook front forks doesn't have a spacer tube in its steering.
Or how can you adjust the preload.

I had to replace the BM bearings, at about 200,000 miles, they had become a shade notched.
Probably all those wheelies the PO did ...
They were regreased and retensioned, more than once.

I'm losing confidence in your setup, totally.
A hot or cold day would adjust the bearings for you !
Is this really how its suggested to do this conversion ???

P.S. The spacer tube is REQUIRED with ball bearings, to AVOID preloading them.
Totally different kettle of fish.

PPS There is no spacer tube in the older dommie steering setup - it has loose balls and cup bearing rings.
You need to be able to tension down the bearings so there is no looseness, and no tightness.
About the same setup as tapered rollers ...

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Rohan Offline OP
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When you google and read up on this subject, OPINIONS are all over the shop !
Inc a number of accounts of using a spacer tube, or how to modify it to be 'useful', or why not. !!
And also that the coarse thread on a later Commando steering stem is not good for fine adjustment of tapered rollers.
As mentioned above.

It would be nice to see a set of precise instructions someplace.
This must be one of the most ambiguous subjects ever ... ?

And talk of sub-micron accuracy being required for a spacer is just !!!

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Bikes that come with steering head bearings that need setting have two threaded adjuster rings below the top triple clamp.

The bearing is set by the lower ring then the top is locked to it.

The triple clamp which usually has a top fastener then locks down on the two rings but they stop that upper Fasteners down force having any ill effect on the now set bearings.

The Commando or the version that had ball bearing units is not set up for tapered rollers for the above reason.

All retaining the spacer tube does is work around that from the opposite direction.

Both my Commando's have this set up.

Attached is a TL1000 triple clamp showing the adjuster rings which is common to many bikes.

stem - Copy.jpg
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They're not tapered rollers though.
What are they in fact.
Angular contact ball bearings ?

The adjustments on the steering head stem on many a british bike are quite substantial,
none of these slender little adjustment rings.

I'd suggest these above are too wimpy to serve as adjustments for a taper roller bearing in fact,
you'd have quite a high loading on just a few skimpy threads.
Even if the adjustment rings were made of kryptonite.

A slimline featherbed top stem and adjustment nut.
There is an inch of fine threaded nut there (and under the bearing inner).
Pardon the gunge in the thread, it pays to keep such things greased.

[Linked Image from i.postimg.cc]

There is another large nut that clamps down on the top of this, to lock it.
Also with a fair old threaded length.
Overkill ? Or fail safe ...

The more you read on this, the bigger the dogs breakfast of facts, opinions and just plain blather ??
"We demand rigidly defined areas of uncertainty" ...


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