Worn fork yoke stem (2015)

Hello all,

I took the front end off the Commando the other day, a 1973 750cc mkV interstate, fitted new steering head bearings, slid the top yoke back in, bit of play in the bottom bearing, enough to fail an MOT!, took it out, the new bearing inner race is a wee bit loose on the worn yoke stem, so....

I see RGM sell a fork yoke stem for the commando,

http://www.rgmnorton.co.uk/buy/fork-yok ... e_2214.htm

Has anyone changed one?, I assume its a case of heating the top yoke, push/drive out the old stem from above, push in the new stem, let it all cool down naturally, re paint.

I think placing the new stem in the freezer beforehand, and inserting it into the heated yoke, simple job?.

I see the photo of the RGM replacement stem, has a knurled portion where it fits into the yoke, I am guessing it must be a very tight interference fit?, I can not see any sign of any other fastening method on my yoke, a roll pin or such like.

Also, I have the following letters/numbers cast into my yokes, the top-ANG 064048, the bottom-ANG 064083, is this correct for a 1973 750cc mkV?,

Thanks in advance,

John

Hi John.
Do you have the 850 frame to suit those yokes?

Hello Needing,

To be honest, I do not know!, the bike is a bit of a bitza I am afraid, the numbers match, engine and frame, but of course, the frame plate is easy to change, is there an easy way to tell which frame I have?,

John

mkv750 said:

Hello all,
I see RGM sell a fork yoke stem for the commando,

http://www.rgmnorton.co.uk/buy/fork-yok ... e_2214.htm

Has anyone changed one?, I assume its a case of heating the top yoke, push/drive out the old stem from above, push in the new stem, let it all cool down naturally, re paint.

Click to expand...

Do RGM give any instructions for changing these.
I'd think they'd need 1000 degrees and a 1000 ton press, or they'd be tres dangerous to fall apart on the road ?

Be better to lightly knurl the stem to the required size so the bearing was a good firm fit. ?
Its not like they need to come apart too often....

Hi John.
All I know is that I ran an 850 frame with 750 yokes for decades which gossip/rumour/furphy has it that this is the no-no combination. Now that I have later frame matching ANG (for angle mod) yokes I BELIEVE I have lost some 'noddyhead' at speed. My 850 frame has the numbers stamped into left side of the frame steering stem tube.
Don't quote me but I BELIEVE a 750 frame with ANG yokes is acceptable (I am sure LAB or others will chime in soon to decry/support/qualify this passing comment). Further, I BELIEVE the 850 rake and trail were altered from the 750s by changing the frame steering stem tube angle and yoke geometry (1° perhaps) to better suit them to highway plodders when the company realised the jap boy racer competition.

needing said:

Further, I BELIEVE the 850 rake and trail were altered from the 750s by changing the frame steering stem tube angle (1° perhaps)

Click to expand...

You don't have to merely believe any longer - the workshop manual printed 1973 clearly spells this out.
The 850 frame has a quoted steering stem angle of 28 degrees, over the earlier 750 frames with 27 degrees.

needing said:

Further, I BELIEVE the 850 rake and trail were altered from the 750s by changing <snip> yoke geometry

Click to expand...

You don't need to merely believe this any longer either.
If you look at the ANG yokes for the 850 and disc brake models, the fork tubes point slightly 'backwards' in their yokes,
so clearly the trail was altered over the previous models...

You could just buy the complete yoke with stem ready fitted from RGM.

I did fit the RGM stem to my 1974 yoke .
You need a press .

Remember to order the circlip .

Michael

Egholt said:

I did fit the RGM stem to my 1974 yoke .
You need a press .

Remember to order the circlip .

Click to expand...

How much pressing did it take ?
Remind us where this circlip goes, and why it is important.

The circlip goes on the top off the stem .
You can see it in the top yoke .
I have access to a big press , it did the job .

Michael

Electroplate or sprayweld and turn to correct dimension?

Stephen Hill

Stephen Hill said:

Electroplate

Click to expand...

Dipping clean steel in copper sulphate solution (bluestone) is a quick-n-dirty way of putting down a (thin) layer of copper.
Not sure if this would be sufficient for the undefined wear here, but this is common practice for bearings/housings that have a shade of wear to make up.
The layer is reasonably uniform in thickness, if not pushed too far.
Bit soft for really heavy duty applications though

I have a spare RGM new spindle surplus to requirements you can have at a discount but finding a way to build up the diameter would be easier if you have someone nearby who can do it without disassembly, if they want to disassemble then a new spindle is easier.

Please go back to "...the new bearing inner race is a wee bit loose on the worn yoke stem, so....". Does this not beggar the question: how did the yoke stem 'wear' away against the inner race of the old bearing? Since the 'wear' is apparent only after the new bearing is fitted perhaps measure the inner race ID of the old and new bearing to quantify differences. Ta.

Need to know how much a wee bite is? The locktite 600 series bearing retaining compounds can fill gaps up to 0.010-0.015". That's what I'd go for. If it's more than that shrink a bush on it. Have to machine round first.

Thanks for all the input, very informative.

Needing, Rohan, so I have the 850 type angle mod yokes, so unless I have the 850 frame, no numbers stamped on the head tube, the geometry will be out, but the Norton always rode well, I have had the motorcycle for, must be 25 years now, been off road for a few years now, but I put enough miles on the road to be sure its a pretty good handling motorcycle!.

The old bearing is loose too, definitely wear on the yoke stem, I picked up on it when the Norton was last on the road, thinking it had to be done before the next MOT, very strange that it has worn, very apparent with the old bearing too, the top bearing, the stem is a nice fit, just the bottom worn.

I never noticed any slight backwards tilt to the fork tubes Rohan, but thanks for that, I shall have a closer look, I will measure both yokes, from the stem to the stanchions.

Thanks Egholt, good to know you changed the stem, of course its got a circlip!, the groove is very visible on the RGM photo, stops the stem from being possibly pulled back out, I can see that now you have pointed it out, thanks, the top of my yoke is full of paint, so difficult to see.

I do have access to a large press, think I will look into surface treatment first, maybe knurl the stem, and thanks Kommando, nice offer, shall see how I go, thank you.

I shall look into surface treatment Stephen, do not want to buy the whole assembly though Toppy, great that its available, but more than I can spend at the moment I think.

Thanks for all the good advice, I will update,

John

Good point Dean, its not much, I have not tried to measure it, just feel, I do believe the locktite would easily fill the gap, trouble is, I think it would be subject to a certain amount of shock, transmitted through the forks, from the road, would locktite hold up to that?, I might contact the company and see what they say.

Thanks,

John

Locktie might do it if holds race to turn with stem as locktie tends to harden to brittleness so basically turns to soft sand pack which stays jammed up unless motion slack enough to crumble to fine dust to flow away. This is how loctite is released w/o heat softening, just crushes to gritty dust that rolls as thread undone. Main issue with liquid flowing state of locktite might be it setting up with stem uncentered. If'n was me I'd rough up inner race, light oil stem then smear JBW & assemble to set up while held centered. OR rough up stem area, mask off, JBW smear, then hand sand till just slip in race nice, assemble on bike and forgetabout it till next fella some decades later can appreciate lasting JBW solution.

mkv750 said:

so I have the 850 type angle mod yokes, so unless I have the 850 frame, no numbers stamped on the head tube,

Click to expand...

850 frames usually have the part number stamped on the front face of the left hand fuel tank mounting bracket.

This can be either 064140 ('73), 065404 (late '73 & '74) or 066532 (MkIII).

Headstock bearings are metric with a 25mm bore. If you've managed to find some with a 1 inch bore, you would have 0.4mm slack to take up (or 0.012 inches in old money) I would buy a cheap digital vernier calliper (£7 on ebay) and do some measuring before pressing stems out etc. There should be nothing to wear on the stem, it shouldn't move inside the bearing