Front forks won’t compress after fork rebuild

gatsby · Jan 7, 2023

Hi,
I am in the middle of a rebuild, and I have rebuilt my front shocks with new springs and seals. My bike is on a lift, and I installed each fork tube with the forks fully extended, poured in the proper amount of oil, and then screwed in the top forks nuts. With the bike still on the lift with the forks still extended, I installed the front fender and wheel. As I lower the bike down on the lift, the front forks will not compress. I can put all my weight on the front end, and it won’t compress. Did I miss something, or is something not lined up properly? Any help would be greatly appreciated.

Thanks!

Gatsby

Stephen Hill · Jan 7, 2023

I would start by undoing the pinch bolt on the bottom of the slider and making sure the two sliders are in parallel.

L.A.B. · Jan 7, 2023

gatsby said:
I installed each fork tube with the forks fully extended

When you say "each fork tube" do you mean each fork assembly?

If you built the assemblies before installing them then did you check each for free movement of the tubes/stanchions in the sliders?

I suggest you remove the wheel and mudguard/fender and check each leg for free movement with the cap bolts fully unscrewed from the stanchions.
Is the lower yoke/tree free to pivot on the stem (stem nut slackened)?

gatsby · Jan 7, 2023

L.A.B. said:
When you say "each fork tube" do you mean each fork assembly?

If you built the assemblies before installing them then did you check each for free movement of the tubes/stanchions in the sliders?

I suggest you remove the wheel and mudguard/fender and check each leg for free movement with the cap bolts fully unscrewed from the stanchions.
Is the lower yoke/tree free to pivot on the stem (stem nut slackened)?

Hi - I will check this and report back. Thanks!

marshg246 · Jan 7, 2023

gatsby said:
Hi,
I am in the middle of a rebuild, and I have rebuilt my front shocks with new springs and seals. My bike is on a lift, and I installed each fork tube with the forks fully extended, poured in the proper amount of oil, and then screwed in the top forks nuts. With the bike still on the lift with the forks still extended, I installed the front fender and wheel. As I lower the bike down on the lift, the front forks will not compress. I can put all my weight on the front end, and it won’t compress. Did I miss something, or is something not lined up properly? Any help would be greatly appreciated.

Thanks!

Gatsby

This might help you: https://www.gregmarsh.com/MC/Norton/FrontForks.aspx

Schwany · Jan 7, 2023

Too much fork oil will do it as well.

Chris · Jan 7, 2023

I'm a bit lost! With the fork fully extended, how do you attach the fork nut to the damper rod?

marshg246 · Jan 7, 2023

Chris said:
I'm a bit lost! With the fork fully extended, how do you attach the fork nut to the damper rod?

Are you asking about the thick washer and nut or the top bolt (06.0345)? The bolt should be no issue, but you probably want to compress the fork(s) a little to make it be easier. If the washer/nut, you need more room to work so compressing them will help. All is easier if the fender and wheel are not installed so they can be compressed individually.

Jdub · Jan 7, 2023

A related question on this - following Greg's instructions, what is the best way to remove misalignment of the fork tubes as you are going through the Top Bolts > Bottom Yoke Nut > Pinch Screws sequence? A deadblow hammer to move one tube, or a cheater bar across the two tubes ("H") to cross-flex them into alignment?

I had all three (Tops / Bottom / Pinches) reasonably snugged down and had planned to align once the bike was fully on the ground as I would with the head steady (i.e. fully loaded with suspension tension removed via "bouncing" compression and rider weight).

marshg246 · Jan 7, 2023

Jdub said:
A related question on this - following Greg's instructions, what is the best way to remove misalignment of the fork tubes as you are going through the Top Bolts > Bottom Yoke Nut > Pinch Screws sequence? A deadblow hammer to move one tube, or a cheater bar across the two tubes ("H") to cross-flex them into alignment?

I had all three (Tops / Bottom / Pinches) reasonably snugged down and had planned to align once the bike was fully on the ground as I would with the head steady (i.e. fully loaded with suspension tension removed via "bouncing" compression and rider weight).

I use a rubber hammer. Lets say you are facing the forks and the top right has a gap. Hit the fork at the bottom right. Usually does not need to be a hard hit. In truth, a perfect bottom yoke will give you perfect alignment unless other things are too tight with the forks out of line.

YING · Jan 8, 2023

marshg246 said:
I use a rubber hammer. Lets say you are facing the forks and the top right has a gap. Hit the fork at the bottom right. Usually does not need to be a hard hit. In truth, a perfect bottom yoke will give you perfect alignment unless other things are too tight with the forks out of line.

I really like the glass plate for this. I just have the top fork nuts and the pinch nuts a bit loose and use my legs to hold the tire and move the handlebars to get the plate hitting on all four corners then tighten it all up.
Mike

baz · Jan 8, 2023

I'm not sure from your post
But without having the bike on the floor and plunging the forks with every fastener loose the forks are unlikely to work properly
You have to start from the top and work your way down
Plunging the forks several times between each tightening sequence
The pinch bolt on the front axle being
Also check the slider pinch clamp is able to move sideways and not binding on the axle
If it's still binding try loosening the mudguard mounting bolts
See what happens

marshg246 · Jan 8, 2023

baz said:
I'm not sure from your post
But without having the bike on the floor and plunging the forks with every fastener loose the forks are unlikely to work properly
You have to start from the top and work your way down
Plunging the forks several times between each tightening sequence
The pinch bolt on the front axle being
Also check the slider pinch clamp is able to move sideways and not binding on the axle
If it's still binding try loosening the mudguard mounting bolts
See what happens

That is certainly to conventional wisdom and how I've done it on bikes with a pinch-bolt to allow adjustment (most other British bikes). But while thinking it over long ago, I realized that the Commando forks are locked into place and getting the fork tubes parallel (actually in a flat plane) is what you're trying to accomplish. If the fork tubes are correct the sliders must be. That only leaves the fender and front axle pinch bolts to be possible issues which are possible binding of the sliders - I'll update my page to mention that. The fender should be obvious - it should bolt on without flexing anything. I definitely need to mention that I don't tighten the front axle pinch bolt until on the ground and the axel nut is tight.

marshg246 · Jan 8, 2023

YING said:
I really like the glass plate for this. I just have the top fork nuts and the pinch nuts a bit loose and use my legs to hold the tire and move the handlebars to get the plate hitting on all four corners then tighten it all up.
Mike

Here's the one I use: Amazon product ASIN B07T7ZMGL2
I use it for lots of things and it's particularly good for forks alignment and flattening things like float bowls.

baz · Jan 8, 2023

marshg246 said:
That is certainly to conventional wisdom and how I've done it on bikes with a pinch-bolt to allow adjustment (most other British bikes). But while thinking it over long ago, I realized that the Commando forks are locked into place and getting the fork tubes parallel (actually in a flat plane) is what you're trying to accomplish. If the fork tubes are correct the sliders must be. That only leaves the fender and front axle pinch bolts to be possible issues which are possible binding of the sliders - I'll update my page to mention that. The fender should be obvious - it should bolt on without flexing anything. I definitely need to mention that I don't tighten the front axle pinch bolt until on the ground and the axel nut is tight.

I also think issues can arise with pattern components
I once bought some commando stanchions that had what I can only describe as blob of chrome on the end of one stanchion
I had to grind it off before it'd even fit into the bush/slider

marshg246 · Jan 8, 2023

baz said:
I also think issues can arise with pattern components
I once bought some commando stanchions that had what I can only describe as blob of chrome on the end of one stanchion
I had to grind it off before it'd even fit into the slider

The fork tubes I get from Wassel are excellent, but often the bottom bushing would have to be forced onto the tube if you don't deburr the circlip groove - I don't force things. Other pattern tubes I've bought are junk IMHO.

Matt Spencer · Jan 9, 2023

After assy , i left all the bolts ' nipped ' almost firmly . To let it all settle down BEFORE pulling it all down TIGHT ., after haveing gone for aspin . Aligned .

gatsby · Jan 11, 2023

Hi Everyone,

Many thanks for the replies and tip.This is what I have currently done:

checked alignment, and all was good
removed fender and stays.
Removed the front wheel
Removed top fork nuts

With the top fork nut removed, the left slider would plunge with little “stiction”. The right fork slider is not smooth at all when I try to plunge, and would require a lot of force. I removed the assembly, and am currently draining the oil. Im going to dismantle, and double check that the bush can fall freely over the stanchion (as per Norman White Book). My other thought is the condition of the internal valve rod and damper. This bike is a parts bike build, and I may have assumed these parts were serviceable and they may actually not be. I will post a picture once I have it disassembled.

Many thanks,

Gatsby

PS - @GregMarsh - Carbs made their way to Newfoundland safe and sound. Many thanks for the prompt service!

L.A.B. · Jan 11, 2023

gatsby said:
The right fork slider is not smooth at all when I try to plunge, and would require a lot of force.

My other thought is the condition of the internal valve rod and damper.

With the "top fork nut" (cap bolt) removed, the complete damper assembly and spring will rise and fall with the slider so that shouldn't be the cause of the resistance.

mdt-son · Jan 11, 2023

gatsby said:
With the top fork nut removed, the left slider would plunge with little “stiction”. The right fork slider is not smooth at all when I try to plunge, and would require a lot of force. ..... This bike is a parts bike build, and I may have assumed these parts were serviceable and they may actually not be.

Proviso your fork stanchion is straight, the fork slider may have been welded. This will cause the cross section to become elliptical, and there will be severe friction moving the slider up and down. In most cases, a welded slider requires a line boring operation and fitment of oversize bushes.
Another cause for stiction is mechanical damage to the slider (a dent) caused by a collision. This should be fairly evident if you examine the slider carefully.

- Knut

Front forks won’t compress after fork rebuild

gatsby

Stephen Hill

L.A.B.

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gatsby

marshg246

Schwany

Chris

marshg246

Jdub

marshg246

YING

Pittsboro,NC

baz

marshg246

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baz

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Matt Spencer

gatsby

L.A.B.

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mdt-son

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