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Old 06-02-2011, 12:12 PM   #106
Gangplank OP
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Hi OlyRider,
Ok, I'm not 100% sure exactly what he means by that lingo. Bottoming circtuit on road bikes can be a spring or a hydraulic device to give additional resistance as the fork bottoms or just before.

From here: Sportbikes.net

If I recall correctly what my guy did differently than -W-'s was that instead of making a solid spacer Ed used a small but heavy duty spring as the spacer to shorten the travel. That way it let the oil pass through it and also acted a bottom out spring.

In the end I trusted my suspension person and he did me right. If you are concerned about bottoming your forks (I rarely do with the new set up) then have him do the changes he suggests. If you are bottoming out that is usually due to an incorrect set up IMHO and can be fixed by tuning the fork to fit your riding style and application. If you bottom once because you come into a big hit too fast then you are not likely to repeat that err or you tune it to match where and what you ride.
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Old 06-02-2011, 09:46 PM   #107
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Quote:
Originally Posted by OlyRider View Post
Would you explain this in language I understand?
To piggyback on Gangplank, most bottom-out devices are hydraulic. There's a couple different designs, (some are actual oil lock pieces, some are based on where holes are in the damper tube) but in all cases once the 'circuit' engages it basically chokes up oil flow which ramps up the compression damping up and makes the fork much stiffer.

Most top out (and some bottom out) devices are short, heavy springs, which is pretty intuitive. When the suspension hits the spring (either way) it makes it much stiffer and thus slows the suspension down a lot.

I've seen rubber bump stops (like you see on cars and trucks) on motorcycle shocks, but never on forks...don't know that you'd want rubber sitting in the oil anyway, but I suppose some fork somewhere has a bump stop.

Whatever the actual method, the point is to prevent the suspension from slamming to a stop, mostly because that will significantly compromise traction.
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Old 06-14-2011, 11:56 AM   #108
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Quote:
Originally Posted by ChiTown View Post
OK, being lazy and short on time I need some help.
I can see with my huge TT tank I need to do something with my forks, on top of wanting to complete my ST bike build...
I've been scanning this thread, and am looking to upgrade my forks, problem is I'm on tour until mid-july - also why i want to get this done while I'm away.

The plan is to have a local independent mechanic pick up my bike, remove the forks, then ship them out to someone to do the conversion with them.

What parts to I need to compile, and can I send out the parts to McCoy's off road center to have all the work done? Since they've done it, it makes sense to use them...

Thank you!
The only parts you need at a set of forks off an Aprilia RXV. I am not 100% certain on the years but as long as they are a 46mm fork then you are all set. You will want stiffer springs I bet with the extra weight.

Give Ed McCoy at McCoy's off road center in Moundhouse, NV a call. I am sure he can find a place locally that can machine the feet of the BMW's to accept the bottom adjuster. Once that is done he can do the rest. He will remember my forks fromm my BMW F800GS.

I had mine done in Reno at JB Machine and then took them to Ed but I'd guess he knows a machinist that is worth his salt.
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Old 06-14-2011, 07:39 PM   #109
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Shivered forks

Gangplank helped me through the process. Forks went back on today. Haven't ridden the bike, but I will tomorrow. My donor forks were Shiver forks from a 2000 Husky WR250. Bought them on Cafehusky.org for $50. Then I had to buy new Marzocchi "caps" for them as the ones I received were all buggered up by visegrips. So that added $136. Paid $585 to have the forks put together per Gangplank"s experience. The shop I used doesn't matter because he said he only billed me for half the labor, and doesn't really want to do more. But he is a well-respected national caliber forks/suspension guru. He machined the fork feet himself. And he re-valved the forks in addition to the spacer. And installed quick bleeders. I decided to let the new progressive springs stay in. The mechanic that installed the forks today, in exchange for a ride, said he loves the way these forks feel compared to the old ones. (He just bought my '02 1150GS Adventure...so he wanted to compare)

So now I have a new Woody's front wheel, new Helbrakes MX brakelines, and new, ADJUSTABLE forks. I'm cool.
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Old 06-14-2011, 07:57 PM   #110
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Quote:
Originally Posted by ChiTown View Post
Thanks for the info, now I start looking... I already have Ohlins springs in my forks, would I want to go stiffer? I want the bike to handle properly when not fully fueled as that will be a rare occasion, but having a better feeling front end with some adjustment seems logical.
Are you happy with the Ohlins springs with the TT tank full? I have the HyperPro "Big Tank" progressive springs and they aren't really doin it for me. Input would be appreciated!
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Old 06-15-2011, 06:32 AM   #111
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Quote:
Originally Posted by bxr140 View Post
To piggyback on Gangplank, most bottom-out devices are hydraulic. There's a couple different designs, (some are actual oil lock pieces, some are based on where holes are in the damper tube) but in all cases once the 'circuit' engages it basically chokes up oil flow which ramps up the compression damping up and makes the fork much stiffer.

Most top out (and some bottom out) devices are short, heavy springs, which is pretty intuitive. When the suspension hits the spring (either way) it makes it much stiffer and thus slows the suspension down a lot.

I've seen rubber bump stops (like you see on cars and trucks) on motorcycle shocks, but never on forks...don't know that you'd want rubber sitting in the oil anyway, but I suppose some fork somewhere has a bump stop.

Whatever the actual method, the point is to prevent the suspension from slamming to a stop, mostly because that will significantly compromise traction.
Shiver 45 (ChiTown -> look for Shiver 45, not 46 like Gangplank said since there is no such Shiver) has bottom out "sircuit" which isn't "actual" sircuit. It is a conical cup at the top of the damping tube where the bushing attached to damping rod goes at the end of the fork stroke and forces the oil come out of that conical cup -> progressive borrom out resistant.

You can see that conical cup from one of the first pictures; it is that aluminum shiny part at the left side of the upper part (which is the damping tube itself). The bush which attach to rod (actually there is three steel parts in that "bush") isn't showed in this picture:



F800GS original forks don't have this bottom out "circuit" at all. I personally rode first 10tkm trip without it (didn't haver time to relocate the bushing to the rod when I originally made the conversion). After that I put the bottom out circuit to "work" (while servicing forks and tuning them to more agressive riding) and I have been riding with that last 20tkm. My forks (and shock) have currently both 250mm of travel and if you ride normal road based stuff you probaly don't need that bottom out circuit at all if you also have stiffer springs. But when you have the circuit working you can make the fork even a bit more plush/less compression damping (and preload) and you can also make proper hard jumps without braking anything.
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Old 06-15-2011, 09:35 AM   #112
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Ahhh... yes correct it is the Marzocchi Shiver 45 (45mm).

Sorry about that forgot/confused with my original plan of using the inter parts from a pair of 46mm forks off a Yamajaw. The Shiver 45's are easier as a conversion because the top caps already fit. All you have to is machine the bottom feet of the BMW fork tubes. Any inners will work (i.e. off a Yama YZ or similar dirtbike but you will have to have the top caps machined too or have a collar made = more work and cost).

Info re: Shiver 45's being the donor fork to use added to post #5.
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Old 06-15-2011, 11:25 AM   #113
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New forks

Just got back from a 60 mile test ride. Man, these forks are "plush"!! I looked for potholes to test the forks, and the difference is amazing. And this is with the middle-of-the-road settings the suspension guru theorized would work. I can make plenty of adjustments if necessary.

Money well spent.
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Old 06-15-2011, 08:34 PM   #114
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Quote:
Originally Posted by OlyRider View Post
Just got back from a 60 mile test ride. Man, these forks are "plush"!! I looked for potholes to test the forks, and the difference is amazing. And this is with the middle-of-the-road settings the suspension guru theorized would work. I can make plenty of adjustments if necessary.

Money well spent.
Hows your front dive under braking? You mentioned your progressive springs..HyperPros? I was thinking that's where my nasty dive came from. The ride is definitely plush and feels great until I grab a handful of front brake then it's scary!
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Old 06-15-2011, 09:28 PM   #115
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Hows your front dive under braking? You mentioned your progressive springs..HyperPros? I was thinking that's where my nasty dive came from. The ride is definitely plush and feels great until I grab a handful of front brake then it's scary!

Yep...Hyperpros. I wouldn't be so happy if I still had "the Dive". It was the first thing I checked...often. It's gone, gone, gone. Just like the "Guru" said it would be. How he managed that and plush at the same time, I'll never know. But he did.
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Old 06-15-2011, 09:32 PM   #116
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Good to hear you like it Oly. I was as amazed as you. Almost no dive & those potholes don't light up the abs all the time.
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Old 06-16-2011, 10:09 AM   #117
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I'm still trying to find a set of forks to do this conversion with. Twice I've had sales fall through. The first one the guy dropped off the face of the Earth and the second one didn't have top caps.


I have two weeks this summer where I won't be riding and I'd love to get everythig together by then.
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Old 06-23-2011, 04:29 PM   #118
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Thanks for all the info guys.



I'm having a hard time finding some donor forks myself...

Can I just buy just the parts I need new?
or is there any other options beside the not really an option Ohlins'?...
Yes, you can buy the parts you need new. I have emailed back and forth with Mike G. at Marzocchi a few times on some stuff. Good guy. I'm guessing it might be really expensive to order the bottom adjusters, internal cartridge, and fork caps... not sure. Check your PM for his contact info.

I know you can order the fork caps themselves. Not sure on the lead time tho...
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Old 06-23-2011, 04:41 PM   #119
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Ok, just saw both ChiTown and Yeti's posts on the AF1 forum.

No luck so far eh? Darn.... Well, I have a suggestion but you'd be guinne pig'n it.

Suggestion is to get a set of forks from a Yamaha YZ450F. They are a different make but since you are machining the feet to accept the bottoms there is no problem there. As long as there is enough room in the BMW fork foot it should work. The top caps will need to be machined to fit into the BMW fork tubes but any decent machine shop should be able to handle it. Once you have those two things sorted the rest of the job is pretty much just the same as -W- did it (and I copied).

If I had to do it now I'd try the YZ450F forks. Don't remember what year is a 46mm. Maybe 2001? A 46 would fit into our fork tubes and work according to the people I have talked to.

You'd have to find a set in decent shape. Prolly doesn't even matter if they are bent because normally the fork tubes bend and the internals are still straight. I had a set that I got off ebay for $125. I was planning to use those before I found the ones on AF-1 for cheap.
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Old 06-24-2011, 11:44 AM   #120
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Thanks for all the info guys.



I'm having a hard time finding some donor forks myself...

Can I just buy just the parts I need new?
or is there any other options beside the not really an option Ohlins'?...
I just bought a set of internals for mine! It was the set I almost bought before that doesn't have the top caps. The guy just randomly responded to an email I sent him back in March.


Gangplank, would you PM or email me the number for Mike G. so I can order me up some fork caps?
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