Broken bottom Yoke / Triple tree

worntorn said:
Since this issue could be deadly, it would be worthwhile investigating to see if there are other triple trees that could be retro-fitted. Simply putting a new part on that is made to the same design as the old broken one seems a recipe for trouble. Big question, has anyone at Norton redesigned this part to avoid the failure?
If it's just a not yet broken but identical to original part, I wouldn't trust my life with it.

Perhaps with a bit of modification there is a Suzuki , Yamaha Honda or Kawasaki part that will fit and work.
Those ones don't come apart unless you run into the back of a truck.
Or one could install an entire front end such as the Showa Big Piston unit and get the anti-dive feature, which is very nice.
These are fitted to late model GSXRs, Thruxton Rs and a few other bikes.
I installed a set on an original Commando frame, wasn't a bad job at all, bit of machining.
End result, it's a very light, high performance front end. And the triple trees won't break.
Another thought-
Perhaps it would be good to ask Ohlins about this. The front end is supposed to be Ohlins and they make quality items. Typically the triple trees come with the forks, so the triple trees ought to be Ohlins as well?

Glen
Click to expand...
I can’t believe you actually said the “S” word. Especially over Ohlins.
 
BritTwit said:
Egads, a double whammy!
Did this happen before Norton went belly-up last year?
Were you able to contact Norton about the failed unit?
The new triple tree looks well made.
Click to expand...
I bought my 961 in 2018 with the yoke already broken, the price took into account the repair I had personally done.
The seller contacted Norton for a warranty part but Norton declined.
When I disassembled the broken piece I saw that the original was of poor quality and the aluminum casting was uneven, the part I built is of really superior quality.

S.C.P. Special Parts

Negozio creato usando PrestaShop
www.scpspecialparts.com www.scpspecialparts.com
I think the problem of breakage is only on models with an inverted fork
 
As I posted way back in post #4, the pics of broken yokes tend to show a large gap where they’re broken. This, IMHO, is indicative of over tightening... the bolts are trying to pull the materiel apart.

If I still had my bike I’d be undoing these bolts and re torquing to a nice low figure. 12nm was mentioned previously.
 
At the very least worth a quick inspection before and after each ride, although I’m not sure there would be much warning for such a failure.
 
Stephen_Spencer said:
Top/bottom yokes are solid billet ally, along with many of the engine assemblies - much more expensive way to manufacture but you would have thought much stronger.
Click to expand...
Its a misnomer that billet alloy is stronger than cast or forged alloy, it all depends on the grain structure and in billet, even if you take the grain into account, you still cut through the grain before you answer the question, is it in line with the in use stresses or against it. Billet alloy is great for one offs where you have a CNC machine, design the part on cad/cam and load it into the cnc machine. No tooling costs but lots of swarf, cast and forged parts have the grain developed during manufacture and its not cut, little material waste but you need higher volumes to justify the tooling costs.

That Norton bottom yoke is a disaster waiting to happen, a sharp inner corner at the edge acting as a stress riser and a huge gap at the bolts allowing any over torque to stretch the part beyond its limits, and where does the stretch focus on, the sharp inner corner.
 
Stephen_Spencer said:
At the very least worth a quick inspection before and after each ride, although I’m not sure there would be much warning for such a failure.
Click to expand...
I don’t think you’d get any warning at all.

Hence the idea of loosening the bolts.

I‘d fit spring washers and tighten them a tweak past the point at which the washers are compressed flat. That IS something you can cover in a quick inspection.
 
Last edited:
Voodooo said:
I can’t believe you actually said the “S” word. Especially over Ohlins.
Click to expand...
I'm looking at the reality of the photos, not worrying too much about getting caught up in a name.
And the anti-dive really is nice to have.

Glen
 
Last edited:
kommando said:
Its a misnomer that billet alloy is stronger than cast or forged alloy, it all depends on the grain structure and in billet, even if you take the grain into account, you still cut through the grain before you answer the question, is it in line with the in use stresses or against it. Billet alloy is great for one offs where you have a CNC machine, design the part on cad/cam and load it into the cnc machine. No tooling costs but lots of swarf, cast and forged parts have the grain developed during manufacture and its not cut, little material waste but you need higher volumes to justify the tooling costs.

That Norton bottom yoke is a disaster waiting to happen, a sharp inner corner at the edge acting as a stress riser and a huge gap at the bolts allowing any over torque to stretch the part beyond its limits, and where does the stretch focus on, the sharp inner corner.
Click to expand...
Exactly. People love to say it has billet this or that as though it somehow makes it superior. I think this started with the Harley crowd with bolt on shiny bits. Small aftermarket companies made items out of aluminium bar stock as they didnt have the capital to operate any other way.

Glen
 
Fast Eddie said:
As I posted way back in post #4, the pics of broken yokes tend to show a large gap where they’re broken. This, IMHO, is indicative of over tightening... the bolts are trying to pull the materiel apart.

If I still had my bike I’d be undoing these bolts and re torquing to a nice low figure. 12nm was mentioned previously.
Click to expand...

961 manual lists 20nm torque for both top and bottom yoke bolts.
Same torque for RWU conventional yoke bolts as well.

Broken bottom Yoke / Triple tree
Hosted on Fotki
 
Checked my TL1000S and GSXR manuals and 23Nm for USD upper and lower yoke pinch bolts is standard.
20Nm Norton manual spec appears appropriate.
 
Kaw Z900RS is 20nm top , 20.1 nm bottom ~ 15 and 15.1 ft.lb.

HD XR1200 top and bottom 30 to 35 ft. lbs. ! And these are aluminum not steel or cast iron.
 
Last edited:
Interesting.
My CR is a 2013 model.
I checked my yoke clamps, and no visible signs of cracks.
When I get a chance I will check to see how tight the pinch bolts are and re-torque to Norton spec figure.
 
I contacted Norton directly with a request to help with a new bottom yoke. I got a reply fairly quickly. They would not warranty the part (2013 bike), but did give me a 15% discount for a replacement at around 300 pounds. I also requested the top yoke for the handlebar conversion, with all the clamps and hardware was another 500 pounds. I have paid the invoice and have not received notice of shipping as they are moving premises to Solihull and indicated shipping may be delayed slightly.

In my ownership I have not tightened the clamp bolts, they are still set at factory torque - bought the bike, out of warranty at 1700mils.
 
bushman said:
I contacted Norton directly with a request to help with a new bottom yoke. I got a reply fairly quickly. They would not warranty the part (2013 bike), but did give me a 15% discount for a replacement at around 300 pounds. I also requested the top yoke for the handlebar conversion, with all the clamps and hardware was another 500 pounds. I have paid the invoice and have not received notice of shipping as they are moving premises to Solihull and indicated shipping may be delayed slightly.

In my ownership I have not tightened the clamp bolts, they are still set at factory torque - bought the bike, out of warranty at 1700mils.
Click to expand...
Errrr excuse me - moving premises to Solihull (my home town)? Is this Christmas come early for me?

Oh duhhhh - just got round to looking at Russell's interview and Gurgling it. Turns out that the Solar Park site is within SpaceHopper distance from my house.

Now what is this Covid thing everyone seems to be talking about?
 
Last edited:
ntst8 said:
Its on the internet so it must be true :cool:
www.nortonmotorcycles.com

Get in Touch | Norton Motorcycles

Contact Norton here today - Fill in the online form and a member of our team will be in contact with your shortly.
www.nortonmotorcycles.com www.nortonmotorcycles.com
Click to expand...
This is where I start looking at the job pages on the Norton site! Staff discount and less than a mile commute! :D :D :D :D Can't believe this - I know must wake up eventually but I'm going to enjoy it while I can!
 
An issue like this would have been issued with a recall notice by any of the higher volume manufacturers. I can understand SG getting away with it based on his dishonesty and the very low volumes but you would have hoped TVS would have taken a different view. If the replacement bottom yoke has the same stress riser I would not fit it but send it straight back. To save its wasted journey I would ask for a picture to confirm the design flaw is not present.
 
kommando said:
An issue like this would have been issued with a recall notice by any of the higher volume manufacturers. I can understand SG getting away with it based on his dishonesty and the very low volumes but you would have hoped TVS would have taken a different view. If the replacement bottom yoke has the same stress riser I would not fit it but send it straight back. To save its wasted journey I would ask for a picture to confirm the design flaw is not present.
Click to expand...
Disintegrating clutch baskets, sprockets unscrewing and gearbox locking, eccentric spoked wheels, clutch rotor screws unscrewing, lights going out.........

I always said that you might get away with this on a 961 which will probably spend most of its time on a plinth in a living room or a leisurely Sunday pub run but a 180mph superbike? We've had a low speed spill already with just a minor pride injury but there's a real chance of a fatality here.
 
Clive said:
Disintegrating clutch baskets, sprockets unscrewing and gearbox locking, eccentric spoked wheels, clutch rotor screws unscrewing, lights going out.........

I always said that you might get away with this on a 961 which will probably spend most of its time on a plinth in a living room or a leisurely Sunday pub run but a 180mph superbike? We've had a low speed spill already with just a minor pride injury but there's a real chance of a fatality here.
Click to expand...
Agree, there is a real possibility of a (serious) adverse outcome if any number of these faults manifest themselves whilst at speed. I still love this bike and it’s a keeper, but that feeling I get before a ride about whether it will make it back to the garage is a little disheartening at times.

I’ll ride for a few months trouble free, gaining confidence points as I go. Then something small will occur (random change in tick over, failed gear change bar etc) and those points are spent and need to be built up again. I usually just glance across at the Kato (which never lets me down) before each ride, check I’ve got my RACQ Gold Membership card and we’re off! Gonna add checking the yokes/triple tree to my pre ride checklist.
 

Similar threads

DBT
Another broken bottom yoke/triple tree.
Replies
2
Views
1,122
DBT
DBT
C
  • Locked
lower fork yoke/triple tree allen bolt torque setting.
Replies
2
Views
999
Commando74
C
Back
Top