Fork issue

I have not had a chance to test my rebuilt forks, (74 mk2) until now. The issue is that when I go to test them by locking the front brake and pushing down/forward with my weight on the bike the forks are stiff and then "stutter" to the compress position and return fine. In other words, there is no "smooth" compression on the way down.
Now I was very careful to follow all the correct advice when I rebuilt my forks, (new: seals, paper seals, progressive springs, bushings) & the proper fork oil weight & amount.
Any ideas?

Don't know if this still applies, but the original type fork bronze bushes were the 'sintered' type.
(reconstituted metal powder = porous = great for lubrication once oiled).
With these, it was very important that they be soaked in oil, at least overnight, before installing.
Or they could be dry, and resist movement...

Does that still apply these days ?

Also seen mention that the bushes/fork tubes supplied lately were a little tight.
Did they feel OK at install time ?

Something to try, before removing them and stripping them down again, is to drain the oil and try them again.

If the oil / damping is the problem, this will give you an indication. Before having them apart on the bench and wondering what the problem is....

You have done the basics, like loosen off all the fork clamping bolts and front axle nuts and mudguard stays, and bounced them up and down a few times ?

This is essential, to get them all aligned....

Rohan:

No, I didn't soak them overnight. Don't know either if this applies. I'll put the "drain em & try em" solution if no other obvious glitch is found.
Thanks for the reply!

Sky

Yes on the loosen all and bounce!

1up3down said:

Yes on the loosen all and bounce!

Click to expand...

Will try.

ugh. i hate doing takes twice on stuff but sure had to with my 2 Nortons.
Did ya roll stanchions together to make sure true straight.
Did ya beat around on the bushes to round them to the stanchions.
Did ya look inside stanchions to make sure rust knocked down smooth.
It will toss ya out saddle or off the road if not free to travel up/dn.
Did you put Convent kit bushes in?
Can't imagine ya put in too much fluid.

Another quick check is to remove the front wheel----make sure the axle is smooth--clean out the axle bores on the legs insert the axle all the way in as if the wheel was on and try spinning the axle. The axle should spin easily----if both legs are in alignment--vertically---if the axle does not spin---binds up--you got to double check from the top down---fork clamps could be bent--tapers on the top of the tubes not identical---not seating the same on both sides so one leg is higher than the other. This may not be the cause of your problem now but something else to consider if you want to check it out. Also---did you apply any grease to the seals--the center recess part which grips the tube?---I use a good thick silicone grease and they slide real nice---I also use a different m/c brand fork seal--double lipped---a little bit of work making them fit---but haven't had fork seal leaks in years.

hobot said:

ugh. i hate doing takes twice on stuff but sure had to with my 2 Nortons.
Did ya roll stanchions together to make sure true straight.

Click to expand...

-Yes, rolled em on glass

Did ya beat around on the bushes to round them to the stanchions.

Click to expand...

No, Didn't know ya had to beat new parts.

Did ya look inside stanchions to make sure rust knocked down smooth.

Click to expand...

No rust, made sure bores were glass smooth on insides.

It will toss ya out saddle or off the road if not free to travel up/dn.

Click to expand...

ugh! (to quote infamous Hobat.

Did you put Convent kit bushes in?

Click to expand...

I put the complete refurb kit from Old Britts.

Can't imagine ya put in too much fluid.

Click to expand...

Within one ML.

Ugh,

I did loosen up the fender mounts,axel & pinch bolt.
It seemed to behave a "little" better, but not much. Ugh.

Anything else.

Haven't emptied the fluid yet. If I put the exact amount, (*5 oz as I remember) then my confidence level is low that that would be the issue.
:|

Try loosening the big allen headed lower triple tree bolts and then also the pinch and axel bolts, then bounce up and down with the front brake on.

There IS a written procedure for doing this the correct way, maybe someone will remember and post it.

I've been putting them together by assembling the forks and leaving everything loose but the axle nut. Tighten the cap nuts on the tubes to seat them in the yoke then take them out and raise the wheel till the forks are completely compressed. Tighten the allen bolts on the bottom yoke and then tighten the axle clamp. Extend the forks and screw the caps back in.

Well in a word sydyguys. Ughhh..

I've order two set of new bushes the didn't slide on stanchion, 2nd because 1st didnt.
Then tired tapping on them using stanchion as a round anvil and suddenly I found both new set looser fit than my old worn ones to used those instead. ugh.

I've rolled stanchion on flat 5/8" thick tempered glass plate that showed good flat contact till put back in for binding, ugh, then rolled the tubes *Against Each Other*, to find them bent enough to matter, ugh, only after everything nipped up after the loose assembled thrust downs centering.

I was about to do the glass plate on mounted stanchions, strings and big beams and chain come along routine, till I rolled tube against each other and took to machinist who got em good enough they are in Trixie's factory forks now.

Peel got the brand new one's a tab over size measure that took up some the prior bush slack found. Bush slack has no effect I can tell on fork function but cause a blurring of axle when run fast enough the front is sliding till lift offs.
Can't feel it riding but can find it by back/froth wiggle unloaded full extension in shed.

Does not hurt to run an oil groove spiral in top bushes if ya care too.

I always assemble everything to snug, then back off just a touch. Compress, roll, bounce, compress a few times, slowly and carefully observing proper travel / alignment.

Then, tighten each level from the BOTTOM - UP (axle to top caps). That includes the brake and fender brackets which can tweak stuff out of line later.

Do some more compress, roll & bounce after each step to ensure you still have free movement. When it's all over, it should still be nice and free.

grandpaul said:

Then, tighten each level from the BOTTOM - UP (axle to top caps). That includes the brake and fender brackets which can tweak stuff out of line later.

Click to expand...

I think the idea behind using a clamp on one side is to be able to accommodate the variability in yokes and stanchions. No mass produced yokes are ever the same and nothing is ever completely straight, it just a matter of how much. By tightening the clamp first you eliminate the benefit of using a clamp in the first place.

The reason for undoing the caps and raising the wheel is to get the spacing of the sliders as accurate as possible when you tighten the clamp. The bushes are as far apart as possible and they are on the least worn sections that they bear on, the stanchion for the upper bush and the inside surface of the slider for the lower bush. It's the most likely position to get the distance between the ends of the slider right, then tighten the clamp.

If you followed the good advice in the previous posts and the issue is still not resolved, then you will have to dig deeper. I know it's messy and a pain to have to take the forks apart again but it is a safety issue.

You say it is stuttering or juddering on compression but not rebound?

Remove wheel, mudguard and fork springs, and work each fork leg up and down. It could be just one leg that is stiff. But if both legs feel smooth in both directions with the wheel off, then apply a fore and aft sideload. If a leg then gets stiff, maybe one or both bushes are too loose. If still smooth, then it could be an alignment issue, as previous posters have commented on.

Hopefully you can sort things without dismantling. Let us know what more you discover and we can go on from there.

Dave

Just bought a New pair of sliders for a Manx. made up some 30% graphite Nylon bush's ..they feel silky smooth! there is very little stiction . But with plastic bush's they are pron to cold weather nipping
I machined the limits to plus two thou, it was seven degrees in the afternoon and the assembly was sweet, BUt after a overnight frost next morning they where stiff/tight, placing them in the sun soon had them smooth again. I think the slider had contracted the "yeiding" bush onto the stanchion.
Makes me wonder what plus 35 degees will do...i would guess LOOSE!