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Old 04-06-2015, 03:17 PM   #1
knary OP
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I need to fix these forks

Ok. It's time for another thread.

'77 R100s. Unknown miles. Frankenbike.

Now that the engine is actually working within my modest expectations, it's time to address other issues.

A couple threads:
The Punk's Bike (the general rehab)
What fork springs do I have?

The forks are ridiculously stiff and unresponsive. There's a clunk as the bike gets on the centerstand. The steering head isn't the source of the clunk.

Fork tubes
There is not insignificant wear. It is, as expected, not around the entire circumference but mostly on what I presume had been the front and back of the tubes. They are, however, nicely aligned and straight.

Damper unit
There is wear on the 'guide support' (name from fiche)
Both damper springs (ball and ring) move easily.
wiper rings are a bit grabby to my fingers, but I have no idea what they're supposed to feel like.

Fork Springs
I don't know which springs I have. They are progressively wound at both ends.
4mm wire diameter
26.4mm wide coil
551mm length
total coil count 71? (not sure how to count)


Any guesses? Too much wear? Missing parts? wrong springs? Idiot mechanic?











Help!


And just to piss me off, I dropped a wrench on top of the header and put a small ding in it.
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Old 04-06-2015, 03:41 PM   #2
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Well, that wear isn't necessarily going to create the "stiff and unresponsive" quality you described. It might create a bit of slop, as I'm sure the lowers look pretty bad, too. But, I bet a lot of us are riding on similarly worn parts.

How much fluid came out? Chunky style? I don't see any rubber bumpers in your photos.
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Old 04-06-2015, 03:48 PM   #3
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Quote:
Originally Posted by SculptD View Post
Well, that wear isn't necessarily going to create the "stiff and unresponsive" quality you described. It might create a bit of slop, as I'm sure the lowers look pretty bad, too. But, I bet a lot of us are riding on similarly worn parts.

How much fluid came out? Chunky style? I don't see any rubber bumpers in your photos.
Forks were overhauled a few years ago. Fluid has been changed a couple times as it's easy. Current oil is 5 wt. 235ml, if I recall correctly. Bumpers at bottom of sliders were replaced.
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Old 04-06-2015, 03:52 PM   #4
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It seems that the general consensus is that Progressive (brand) springs are too stiff.

That was my experience with a few airheads.

I'd source a set of used stock springs, throw them in with fresh oil and see where that gets you.

Any chance you measured the sag before taking the forks to bits? That might have answered your question right there.
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your bike is suitably dirty. Well done.
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Old 04-06-2015, 03:55 PM   #5
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Quote:
Originally Posted by Solo Lobo View Post
It seems that the general consensus is that Progressive (brand) springs are too stiff.

That was my experience with a few airheads.

I'd source a set of used stock springs, throw them in with fresh oil and see where that gets you.

Any chance you measured the sag before taking the forks to bits? That might have answered your question right there.
What is this "sag" you speak of?

There was maybe 3/4" at most from wheel off the ground to rider on the bike. Ridiculously stiff.

I have a second set of springs, as mentioned in the other thread. They have different dimensions but the results were the same which suggested to me, perhaps erroneously, that the issue wasn't the springs. I'm don't even know what springs I have.

Anyone have some old stock springs they want to sell for cheap?
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Old 04-06-2015, 03:57 PM   #6
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Here's some reading for you, it might help

http://www.advrider.com/forums/showthread.php?t=567741

I guess the point is to check both front and rear sag to make sure both are close to each other...
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Old 04-06-2015, 03:59 PM   #7
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Quote:
Originally Posted by knary View Post
Ok. It's time for another thread.



I'm looking at the wear on this part, and I'm backtracking on my previous comment. You may have enough wear that things are well out of line and creating a lot of stiction.
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Old 04-06-2015, 05:43 PM   #8
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Quote:
Originally Posted by SculptD View Post
I'm looking at the wear on this part, and I'm backtracking on my previous comment. You may have enough wear that things are well out of line and creating a lot of stiction.
It may be. That kind of wear is on that part of both forks. It doesn't seem particularly deep.
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Old 04-06-2015, 06:52 PM   #9
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That is a little more than normal wear on your stanchions. With that said you seem to be missing some parts. Number 7 and # 15 on the fiche are not shown in your pics.



The lack of # 7 may be causing the wear on your lower tubes. The guide support wear is negligible. But if those wiper rings feel notchy when you run your finger nail along the outside edge, replace them.
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Old 04-07-2015, 10:08 AM   #10
knary OP
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Quote:
Originally Posted by headtube View Post
That is a little more than normal wear on your stanchions. With that said you seem to be missing some parts. Number 7 and # 15 on the fiche are not shown in your pics.



The lack of # 7 may be causing the wear on your lower tubes. The guide support wear is negligible. But if those wiper rings feel notchy when you run your finger nail along the outside edge, replace them.
One aspect of the forks I find a tiny bit frustrating is that the diagrams are, to my eye, strangely drawn as they don't really show the parts as they relate to each other. The diagram makes it look like the damper rod is installed in the fork lower below that circlip (#11), rather then being retained in the tube by that clip. Obviously this isn't the case, but that parts diagram makes my head hurt.


I think I might have #7 in my collection of ordered parts. I have no idea about #15.

looking...
Found those bushings (#7). I'd ordered them way back and never installed them. I assume that the bushing goes above the threaded rings at the bottom of the tube and, when the forks are full extension, keep metal from hitting metal. Their ID is big enough that I doubt they do much to keep things lined up.

#15??
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Old 04-07-2015, 03:57 PM   #11
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You don't need #15. That was a fiber, or plastic washer added to later models to smother perceived metallic clicking that was coming from the valve. Sounds crazy to me. I certainly have more noises to contend with than whatever faint clicking that little ring could make.

And, you are correct that the rubber ring #7 serves no mechanical alignment function. It's just a cushion. And there should be another one (different part #) at the bottom of your fork lowers.
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Old 04-07-2015, 03:59 PM   #12
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The large doughnut is at the bottom of the forks. The originals had been reduced to plastic oatmeal.
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Old 04-08-2015, 05:17 AM   #13
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Quote:
Originally Posted by knary View Post
After looking again I would tend to agree with SculptD. I thought that shiny bit was camera glare. Have a look at your stanchion tubes. Roll them on a flat surface to check for warpage.
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Old 04-08-2015, 10:14 AM   #14
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Quote:
Originally Posted by knary View Post
What is this "sag" you speak of?

There was maybe 3/4" at most from wheel off the ground to rider on the bike. Ridiculously stiff.

I have a second set of springs, as mentioned in the other thread. They have different dimensions but the results were the same which suggested to me, perhaps erroneously, that the issue wasn't the springs. I'm don't even know what springs I have.
My guess is your problem is due to stiction somewhere.

See my response on the other thread for exact spring rates but your problem is not the springs as the rates are very close to stock and the extra .4mm in diameter mentioned in this thread means the spring rate is even lower and matches almost exactly with stock.

They are not Progressive springs as the usual Progressives fitted are very stiff and over double your spring rates - something like 40/60 lb/in

Laden sag should be compared with the forks at full extension on the centre stand and you should have approximately 1/3 of the forks full travel so something like 60 - 75mm. If you have less then remove any extra pre-load spacers that might have been fitted. Too little sag can result in the topping out clunk you mention.
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Old 04-08-2015, 01:11 PM   #15
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It's all buttoned back up and it is *much* better.

I believe the wear on the damper is from the wear on the fork tube. With so much stiction and that missing bumper (small though it is), there was enough clearance due to the wear that it allowed the lowers to rock a bit. This, of course, tilts the damper within the tubes. Even off the centerstand, the forks were nearly at full extension, not how they were designed to operate (there's a good bit of conjecture and hope in my reasoning). This reduced the bearing surface and moved that damper in one spot over and over again.


So what did I do?
First, the tubes are straight and aligned, but they are worn on the exterior face. I rotated the tubes to move the most worn area to the outside so that most of the forces of the forks are applied to a relatively clean area.

Second, I polished the interior of the tubes a bit (600 grit followed by 1200 grit). I was surprised to feel a bit of a burr on the lower weep hole of one of the tubes. The difference in how easily the damper rods moved was dramatic. Clearances are, between what I did and years of wear, undoubtedly not ideal but I can live with that for now.

There was an immediate difference just getting the bike off the centerstand. I went for a short ride in the neighborhood that included some unpaved and beaten roads. While it isn't as supple as I might like, and certainly isn't on par with a modern suspension, it is *far* better.

Ideally, I would be replacing, at the least, the fork tubes. But 'ideally' and this bike have little to do with each other. I'll put it on my list.

Thanks for the ear and advice.
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