Fork Stanchion Bend

Lovel

Lovel

Joined
Dec 28, 2021
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I stripped the front end fork assembly down for renovation of the yokes. After fitting everything thing back together I found that the steering was off centre when riding, prior to this work it used to steer quite straight. Off with the forks again today and i found that both stanchions have the same amount of bend on them perhaps .050” against a flat surface. Im assuming when i fitted them last time they were fitting in a random position hence the steering off centre. Assuming it is crash damage, but is there any chance that the stanchions could just be bent over a life of braking and they all start to bend over time. I dare say an order to AN is next move, or i fit the stantions back on in their original position before which the bike did steer straight?
 
Took the easy route and ordered a new pair from AN. Quite a lack of engineering skills in my part of the world today as we have farmed it all out. 🤨
 
take this FWIW -- determine which direction and side of each stanchion tube have the bend. mark the tubes and orient the tube bends perpendicular to the center line of the bike and opposite to each other, facing outward. when you tighten up the front axle, IN THEORY, the bends should cancel each other out. had a similar .050" bend issue with my BSA spitfire - when done, my fork tubes were within .009" parallel, fore and aft, and side to side.

Fork Stanchion Bend


might also work if you orient the bends facing each other and use the front hub assemble to cancel the bends, but that might put an axial load on the wheel bearings, although it may not be enough to be a concern.
 
Last edited:
concours said:
Crash damage. Normal use didn't cause it.

They can be pressed straight using V-blocks. (The scarety cats will be along soon, with fear of the unknown)
Or simply replace.
Click to expand...

New is always best! Your baby deserves it.

Slick
 
concours said:
Not by a long shot.

I have a big box of low quality garbage, not fit for purpose.
50 years ago, that statement would have been accurate.
Click to expand...
i tend to agree. for me, genuine factory NOS is the preferable. andover-norton seems to be the best replacement. with others, and there are acceptions, but most are hit or miss for form, fit, and function, they usually get 2 ort of 3 right.
 
joe czech said:
take this FWIW -- determine which direction and side of each stanchion tube have the bend. mark the tubes and orient the tube bends perpendicular to the center line of the bike and opposite to each other, facing outward. when you tighten up the front axle, IN THEORY, the bends should cancel each other out.


"As you tighten up on the axle it should pull the tubes together"
Click to expand...

When the axle nut is tightened it pulls the hub assembly to the disc-(or drum) side slider, not the opposing slider/leg which 'floats' on the larger diameter section of the axle and is clamped by the pinch bolt resulting in the gap between the slider and the hub assembly under normal conditions.

Fork Stanchion Bend

joe czech said:
might also work if you orient the bends facing each other and use the front hub assemble to cancel the bends, but that might put an axial load on the wheel bearings, although it may not be enough to be a concern.
Click to expand...

Once again, it wouldn't because even if the slider came into contact with the dust cover/spacer the inner bearing assembly is fully spaced and clamped by the axle.
 
L.A.B. said:
When the axle nut is tightened it pulls the hub assembly to the disc-(or drum) side slider, not the opposing slider/leg which 'floats' on the larger diameter section of the axle and is clamped by the pinch bolt resulting in the gap between the slider and the hub assembly under normal conditions.

Fork Stanchion Bend


Once again, it wouldn't because even if the slider came into contact with the dust cover/spacer the inner bearing assembly is fully spaced and clamped by the axle.
Click to expand...

yes, you are correct (as usual) . i should have noted that in detail. on my spitfire, i used a wood clamp to pull the fork tubes together parallel, set the axle, THEN SECURED EVERYTHING WITH THE PINCH BOLT. wasn't thinking things thru when i posted (memory issue). anyway, it seems to have worked - fork tubes, as best i can measure, appears to be parallel on two planes. steering, handling, and fork action also seem spot on - good enough that i have no complaints, and bottom line, that's all that matters.
 
New stanchions fitted and test ride all good, seems just that bit better handling too, wonder why? 😀 May try straightening my originals for the sake of it to see how close I can get.
 
Lovel said:
Took the easy route and ordered a new pair from AN. Quite a lack of engineering skills in my part of the world today as we have farmed it all out. 🤨
Click to expand...
That is the correct answer. I had a straightened pair of staunchions on one bike, and it was never right. There were press marks on the stanchions where they had been fitted into the yokes. Straightening them will not remove that. If the stanchions are rotated in the yokes, the slight offset moves. The result is the sliders stick when the forks are compressed.
When I bought the staunchions from a wrecker, I did not even notice the slight damage. After I installed them, I thought the binding was due to the bushes.
The staunchions need to be made of decent steel - NOT Asian ! - With Norton staunchions, you should not have a problem, but it depends on where they are made.
Many people must buy motorcycles without thinking about the steel which is used to make them.
In Australia we have an agency which sells Bohler steel - that is usually good enough - anything else is usually crap.
BHP and Comsteel are a joke.
Japanese steel is usually very clean so does not fail due to sulphide inclusions, but it is often lacking in alloying elements. The japanese seem to be minimalist. British is clumsy but better.
All of the steel in the Sydney Harbour Bridge was imported from Britain.
 
Last edited:
Lovel said:
New stanchions fitted and test ride all good, seems just that bit better handling too, wonder why? 😀 May try straightening my originals for the sake of it to see how close I can get.
Click to expand...
The bike was probably crashed and the forks bent. It changes the trail, so the bike handles differently. Even a fraction of a degree change in the rake, makes a difference. When you brake normally, or accelerate - how much does the rake on the steering head change ? It can be the difference between getting around a corner or running off the road.
 
I had a similar situation with a wrecked Sportster years ago. Both tubes were bent under the bottom tree and I couldn't get it perfect so ended up with the bend angling to the rear from side view, not noticeable but I knew it was there, from the front view the tubes were parallel, no binding.
 
acotrel said:
That is the correct answer. I had a straightened pair of staunchions on one bike, and it was never right. There were press marks on the stanchions where they had been fitted into the yokes. Straightening them will not remove that. If the stanchions are rotated in the yokes, the slight offset moves. The result is the sliders stick when the forks are compressed.
When I bought the staunchions from a wrecker, I did not even notice the slight damage. After I installed them, I thought the binding was due to the bushes.
The staunchions need to be made of decent steel - NOT Asian ! - With Norton staunchions, you should not have a problem, but it depends on where they are made.
Many people must buy motorcycles without thinking about the steel which is used to make them.
In Australia we have an agency which sells Bohler steel - that is usually good enough - anything else is usually crap.
BHP and Comsteel are a joke.
Japanese steel is usually very clean so does not fail due to sulphide inclusions, but it is often lacking in alloying elements. The japanese seem to be minimalist. British is clumsy but better.
All of the steel in the Sydney Harbour Bridge was imported from Britain.
Click to expand...
If the stanchions are damaged from press marks from the yokes I'm wondering just how tight the pinch bolts were done up?
Or were the press marks caused by the accident damage?
Either way the sliders don't run up to that part of the stanchions
 
acotrel said:
That is the correct answer. I had a straightened pair of staunchions on one bike, and it was never right. There were press marks on the stanchions where they had been fitted into the yokes. Straightening them will not remove that. If the stanchions are rotated in the yokes, the slight offset moves. The result is the sliders stick when the forks are compressed.
When I bought the staunchions from a wrecker, I did not even notice the slight damage. After I installed them, I thought the binding was due to the bushes.
The staunchions need to be made of decent steel - NOT Asian ! - With Norton staunchions, you should not have a problem, but it depends on where they are made.
Many people must buy motorcycles without thinking about the steel which is used to make them.
In Australia we have an agency which sells Bohler steel - that is usually good enough - anything else is usually crap.
BHP and Comsteel are a joke.
Japanese steel is usually very clean so does not fail due to sulphide inclusions, but it is often lacking in alloying elements. The japanese seem to be minimalist. British is clumsy but better.
All of the steel in the Sydney Harbour Bridge was imported from Britain.
Click to expand...
Purchased from Andover Norton look to be of decent quantity and finish, although if I compare the original chrome plating, the early ones have a deep lustre of chrome about them.

I’m afraid to say not even our latest Queensferry Bridge across the Firth of Forth was built with British steel, probably the case for the newer generation aircraft carriers QE & POW too, sadly from the far east most likely? All farmed out along with the engineering skills, a nation of bankers😂
 
I've seen V-blocks leave flats on stanchions.
Anything less than 100% straight and round will increase stiction, and I wouldn't even consider re-using tubes which have been through the stress of a bending/straightening cycle.
Replace, every time.
 
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