Shimstack rework questions - Honda RC51 Forum : RC51 Motorcycle Forums
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post #1 of 12 (permalink) Old 01-13-2014, 05:14 PM Thread Starter
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Shimstack rework questions

I'm wondering if anyone on here has done any work restacking the shimstacks on their compression & rebound valves.
I've got standard SP1 forks on at the moment with Hyperpro progressive springs fitted.
I don't do much track work, mainly scratching with mates on newer machinery (Fireblades & R1's).
I've found the progressive springs help smooth things out over rough ground but I reckon there is improvements to be got from a rework of the shimstacks.
I don't want to go to the expense of buying new valves but I want to try improving what I've got.
I've just ordered a pair of SP2 forks which I'll be refurbishing before I fit, which want to rework the valves on.
Any advice on what shim sizes to use?
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post #2 of 12 (permalink) Old 01-17-2014, 08:43 AM Thread Starter
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Shit!
I suppose this is what you'd call a tumbleweed moment.
Never mind. I'll just go it alone I suppose.
Funny really. Usually everyones got an opinion where suspensions concerned.
But from what I've read it's usually limited to go buy this stuff or go buy that stuff cos it's good.
I've been trawling the Internet & there's some good information knocking about albeit a little hard to find. So I'll start with the info I've picked up so far.
Assortment of shims about to be ordered. Just waiting for the SP2 forks to arrive.
Looking forward to opening the Pandoras box that is suspension tuning.
I'll post my results good or bad later
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post #3 of 12 (permalink) Old 01-17-2014, 09:00 AM
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From what I understand, these suspension settings are like trial and error kinda thing.
Even if I had tried that, which I hadn't, I couldn't advise you on anything since our body structure is different, our driving habits are different, our environment and roads are different etc
So as far as I understand, you should go for an Ohlins front which guarantees you the best of performance if that's your goal, otherwise take your fork apart and start making one change at a time until you find what you're looking for.

However, don't expect much of that front. It's a 14 year's old technology plus it is manufacturer calibrated for 2 person riding.
Kinda like the rear suspension link swap we all need to do if we want our RC to dive by thought entering a corner.

I am really sorry I can't help more.

Anyway, if any discovery happens in your garage, I would like to see some pictures and read about it, if that's ok with you


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post #4 of 12 (permalink) Old 01-17-2014, 11:02 AM
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You know SP1 and SP2 forks are different, right? Is there a reason you're switching?

John, 2000 RC51 #000100

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post #5 of 12 (permalink) Old 01-17-2014, 11:50 AM
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I have a ktech compression shim stack in my sp1, night and day to the standard set up, i also have hyperpro springs, run 5w oil and 130mm air gap.
The shim stack i bought through perry at HM racing and he kindly (no charge!) assembled it for me saying "this should work" ..... it does, .
maybe worth asking k-tech if they will sell you a set and assemble them for you

You will need aftermarket valves, when you see them you will understand why the stock set up is so harsh, the holes in the valves are like a mouses quim, cant flow anything through them in a hurry

Last edited by dansp1; 01-17-2014 at 11:54 AM.
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post #6 of 12 (permalink) Old 01-17-2014, 11:57 AM
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FWIW IME most people consider restacking as different from reshimming. The first uses the oem shims, the second does not. And most people do the latter, not the former. Maybe that is why you never heard anything back.

I've had a few forks reshimmed (comp and rebound), and as mentioned makes a big difference. Not needed on the street imo, but a nice mod all the same.
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post #7 of 12 (permalink) Old 01-17-2014, 12:01 PM
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I have a set of (from memory) Bitubo valves if you are interested pbc0
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post #8 of 12 (permalink) Old 01-17-2014, 06:27 PM Thread Starter
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Reason for the new forks is so I have a pair I can mess with without taking my bike off the road.
SP1 forks would have been ideal but the SP2's were cheap & available.
I'm expecting to look at modifying the pistons to allow more flow but this is going to affect the shimstack design.
From what I've seen on some other guys sites. The Showa piston design is similar to the Ohlinswhich also has relatively small ports to limit the oil flow. Where most of the others have much larger porting therefore making the shimstack do more of the work. Therefore making the shimstack design more critical.
Of course this is all theory right now. But I want to understand more of what's happening by making changes & seeing what the effect is so I can come up with the setup that will suit me.
I'm not trying to end up a suspension expert. Just want to satisfy my curiosity.

Dan. I'd be interested in those valves.
I'll send you a pm later. Thanks.
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post #9 of 12 (permalink) Old 01-17-2014, 06:43 PM Thread Starter
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Also forgot to mention. Thanks for the responses guys.
Very constructive and helpful.
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post #10 of 12 (permalink) Old 01-17-2014, 08:02 PM
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I hope this will be helpful.

http://www.shimrestackor.com/index.htm

Best of luck
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