progressive springs - less oil? - K-Bikes.com - Excellence in Motion
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post #1 of 14 (permalink) Old Sep 4th, 2010, 7:27 am Thread Starter
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progressive springs - less oil?

Hello all,
Has anyone here done the swap to progressive springs (mine bought from motorworks in UK) and could give me an idea of how much less fork oil (if any) is needed than with standard springs?

I understand the progressives displace more oil than standard so you should use less. I'm wondering about weight of oil too. My forks take 360cc of roughly SAE 7.5 in standard trim.

As I'm getting the seals done at the same time it won't be diy so no chance to experiment measuring the difference in displacement myself beforehand.

Any hints appreciated.

Alex
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post #2 of 14 (permalink) Old Sep 4th, 2010, 11:35 am
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Interesting question, I used to have progressive springs on my K100RS and always used the specified amount recommended by BMW, albeit with slightly thicker oils,and those springs were installed by a very good dealer who made no mention of adjusting the oil quantity because the springs were larger. Same deal with my R100GS, no changes in quantity.

But them early K100s, described as "A slave kissing the feet of its master" by one publication in the 80's from the handling with the OEM springs.......I replaced the springs and rear shock within 2-3 weeks of buying that bike in 85, altogether with a fork brace,certainly the best mod I ever did to it.

But just to make sure you may want to make a dipstick out of some steel wire and check the oil levels before and after and compare,, that is how we used to fill a lot of the earlier bikes, by height of fluid instead of quantity.

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Honda V45 Sabre at 24
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post #3 of 14 (permalink) Old Sep 4th, 2010, 6:28 pm Thread Starter
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thanks very much H
I'll get the mech to do a before and after airgap check on the non-leaking leg, but assume that 360cc will probably be near enough anyway.

I've read the spec for Hagon progressive springs and was surprised to see they recommended 15w oil for my K100rs 2-valve non-sport forks - up from 5w standard - but their springs are different as far as I can tell, with all the tight coils at one end, rather than some top, some bottom, like the one's I've bought.

Getting a new tyre too ahead of winter so looking forward to happy handling.
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post #4 of 14 (permalink) Old Sep 7th, 2010, 10:01 am
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Let me know how this goes, I was looking at the hagon progressive springs to match the shock I have in the back. Are you going to end up putting the 15w oil in there? Seems pretty thick, but might stiffen things up.

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Current: 1985 K100RT Stripped.
See it here DC to Gaspe

Past: 1985 K100
See it here on my trip from DC to Panama
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post #5 of 14 (permalink) Old Sep 7th, 2010, 4:36 pm Thread Starter
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ended up going with 360cc of 10w.

First impressions, Lukeman:

- front end definitely feels more springy less saggy.
- hasn't cured my fork 'oscilation' (back and forth vibe) at 80mph - didn't really expect it to...
- noisy in operation, clunky, worse than before (there was always some clunk on bad roads at low speed). I'll give them some time to bed in then start fiddling the oil levels.
- much more planted feel coming to stops, less dive.

overall a bit mnah, definitely not a magic handling cure for my old bus, but my shock's far past its best. More miles needed, I think.

BTW The chap who fitted them (while doing the seals) lined up the old spring, spacer and alloy 'cup' against the new springs, found them to be the same length, so left out the spacer and cup. The spacer I can understand, the cup I'm less sure about.

Hagon springs will prob be different though.
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post #6 of 14 (permalink) Old Sep 9th, 2010, 12:29 pm
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It sounds like its a decent improvement, thanks for the write up. The clunkiness isn't good though, can't say that either of my bikes had a clunky front end. I wonder whats up with that?

------------------------------------------------------------------------------------
Current: 1985 K100RT Stripped.
See it here DC to Gaspe

Past: 1985 K100
See it here on my trip from DC to Panama
DC to Panama City

Last edited by lukeman; Sep 9th, 2010 at 4:34 pm.
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post #7 of 14 (permalink) Old Sep 9th, 2010, 3:14 pm Thread Starter
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I've sorted it. A previous owner had reassembled the fork internals wrong (with the valve housing in the wrong place...), the mechanic replicated it, but left the valve housing out entirely to get the length right! Clymer to the rescue.

BTW For the motorworks springs, which are ground flat at the ends, you chuck out the oem spring end caps AND the nylon spacer. These end caps, which have a sort of thread on them, are required for the oem springs (which aren't ground flat) to give them flat ends, but obviously a flat-ended spring won't sit right on them.

Now all is in order, clunkiness completely gone, progressive springs a definite improvement. More springy, osscilation greatly reduced and moved higher up the mph range. Feels like a bike, rather than just a collection of parts...

Last edited by Dayglo; Sep 10th, 2010 at 3:31 am.
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post #8 of 14 (permalink) Old Nov 4th, 2010, 1:50 pm
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Whats the best way to get the circleclip out to release the spring at the top of the fork? I just had a look as at the setup as my Hyperpro springs are getting delivered today and wanted to see if there were any tips. Is it just a matter of sticking a narrow tool down and jarring it lose? Is the spring going to shoot up once released? Never done any fork work.

------------------------------------------------------------------------------------
Current: 1985 K100RT Stripped.
See it here DC to Gaspe

Past: 1985 K100
See it here on my trip from DC to Panama
DC to Panama City
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post #9 of 14 (permalink) Old Nov 4th, 2010, 5:19 pm
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Quote:
Originally Posted by lukeman
Whats the best way to get the circleclip out to release the spring at the top of the fork? I just had a look as at the setup as my Hyperpro springs are getting delivered today and wanted to see if there were any tips. Is it just a matter of sticking a narrow tool down and jarring it lose? Is the spring going to shoot up once released? Never done any fork work.

It is best done with two people. Disassembly can be done with one person ... but getting it back together is real tough without four hands.

Remove the black plastic cap. Get the appropriate sized allen for the filler allen screw. I like to use a T handle to get good leverage. Push straight down on the cap... while pulling up on the tube ... it has a sealing O-ring and will be tough to move ... but it will. Push it an inch or so into the tube. Then push one side of the clip into the tube and get a screwdriver in there to pry it out.

There will be a bit of spring pressure, but not much if you have the original springs in there. Make new spacers so you have a good 25mm of preload with your new springs.

Two people to reassemble is really needed.Push the cap back into the tube and get the clip back in place.

'85 K100RS
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post #10 of 14 (permalink) Old Nov 5th, 2010, 12:27 pm
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Ok thanks, going to give it a whirl this afternoon.

Edit: Hyperpro recommends 20sae at 190mm

I'll give it a try and see what happens, hopefully drastically better

------------------------------------------------------------------------------------
Current: 1985 K100RT Stripped.
See it here DC to Gaspe

Past: 1985 K100
See it here on my trip from DC to Panama
DC to Panama City

Last edited by lukeman; Nov 5th, 2010 at 7:26 pm.
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