K2 / Proflex Riders Group
General => Tech Forum => Topic started by: DugB on October 01, 2008, 09:44:54 am
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Hello all,
So I tried to make the ball bearing conversion axle for my K2 4000 a few days ago...but there must be some small degree of misalignment to my small lathe, because I kept turning slightly tapered shafts...also, with my setup it's difficult to know when to stop...I accidentally shaved the shaft slightly below 12mm, at which point there was not enough lip to prevent the bearings from sliding all the way to the center of the shaft.
Anyway, that's not my question. :-) So I'm always looking around for shocks that will work on the rear of my 856's...and let's be honest, there aren't many out there that end with a female-threaded shaft or bolt hole. I know I can get new Risse's that will work...but new shock = new price, and I'm hoping to leverage the poor resale value of the used air shocks going on eBay.
Have any of the machinists on this list considered making an eyelet adapter for the X56/X57 rear strut so an eyelet-to-eyelet shock can be used? My mind envisions something like a block (with a threaded hole for attaching it to the strut top), with arms on each side that reach up to a cylindrical piece (positioned horizontally). The cylindrical piece would be removable (attached through the "arms" with a bolt), onto which the bottom eyelet for the shock could be mounted.
Such a piece would enable us to use many of the 7.87" (or smaller...realizing that the shock length doesn't *have* to be exact) rear shocks available. Anyone have the facilities to fabricate something like this?
- Doug :-)
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Yep, I'm sure these have been made and I'm pretty sure there's some pictures on here of them!
But.......IMHO.........I don't think the "cylindrical" piece should be horizontal or else it will allow a pivot point to occur at the base of the shock...............not good................I think it should be vertically aligned to allow a little bit of lateral flex but no vertical.
Col.
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Hmmm...I was thinking of a U-shaped piece of billet mounted to the top of the strut, with the rod going between the two uprights...the rod would go through the bottom eyelet to provide the lower mounting point. Are you saying that this isn't a good idea? OH WAIT...duh...I forgot that would mean three hinged points along the entire length of the strut/shock...yeah, that would be a bad idea without an additional, supporting link to the frame.
Another idea: drill a hole into the bottom of the shock eyelet...something large enough to support the shock well with no flex along the strut/shock combination. Then, insert into the shock eyelet a short section of rod tapped for bolt that will go up through the strut top, through the hole in the shock eyelet and thread into the tapped section of rod. The icing on the cake would be a piece similar to the black plastic pieces on either side of the ODS's top mount - with a semi-cylindrical cut in it to match the bottom curve of the shock's bottom eyelet.
Thoughts?
- Doug
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If your lathe is making tapered cylinders it means that the tailstock is misaligned. There should be a way to adjust it back into place to get a perfect cylinder. If the workpiece comes out too small on the tailstock end it means that the tailstock is positioned too far out (toward the operator).
I don't know exactly how most shocks are put togeter, but the eyelet probably comes off somehow. If you remove the eyelet entirely the shaft is probably threaded on its OD or ID. Either way it is easy to make an aluminum adapter that is a cone on one end and threaded on the other.
Post some pictures of the particular shock you want to make an adapter for and a sketch of the part you want to make. I have a shop and can make the prototype.
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Guys,
Over the years, lots of your forebears have had great results building these U-shaped adapters for the top of the strut. And yes, the bolt MUST go fore-n-aft and it MUST NOT go side-to-side. I've tried other tricks and failed.
If you can find any of pictures of the work done by FrankD3000 he was a great Canadian machinist on the forum. If you IM him, he might answer.
Go get 'em!
Will
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Hi,
I'm also interested in attaching a new shock to a Proflex. In my case it's an 857 (medium so probably ok for conversion). I've done a (tiny) bit of research:
http://idriders.com/proflex/smf/index.php?topic=3034.msg21801#msg21801
Shows adapting the rear strut with two plates so you can bolt a shock to it. There's no (or minimal) lateral support for the shock so personally I'd not be comfortable with this. I'm also not able to weld so a bolt on adaptor would be better for me.
There's also posts from jazclrint who seems to have fitted a Fox shock on the back but I don't think he's ever posted any pictures.
I'm having problems finding older conversions as the links to the pictures have gone but the Frank3000 link I found was him talking about fitting a front shock which doesn't have the same problems.
Anyway, my idea would be to create an aluminium 'cup' for the end of the shock to go into, then screw a rod through the shock eyelet. The other side of the aluminium piece would be a cone that would screw into the strut.
Things that've occured to me:
1) It's pretty simple so why has no one else done it? (I'd have thought a small aluminium adaptor like this would sell as well as the replacement shock springs you see on here).
2) Would probably help to rotate one of the eyelets on the shock so the were at 90 degrees to each other. Not sure if this is possible, I'd been thinking about using a Fox float R or similar.
3) The length of the adaptor could be modified to cope with different shock lengths.
4) Presumably an air can will save a fair chunk of weight over the spring shock on it now?
5) Not sure where to find accurate dimensions of air cans to see if they'll fit in the gap in the frame.
Anyone else got ideas? All of the stuff I've searched on seems pretty old/incomplete/broken links.
Cheers,
Stuart.
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Ah, that's great! Nice to see the pics! The adaptor I was considering making wouldn't involve welding the strut, but would involve more precise machining of the adaptor (to match the face of the shock's lower eyelet) as well as drilling a hole in the end of the shock (through to the eyelet, but not out the other side). I'll try to draw some pics of what I'm talking about, but in general I like the designs in the linked thread much better! :-)
- Doug
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Also found some links from somewhere in Spanish (my Spanish is rubbish):
http://www.forumbtt.net/index.php?action=printpage;topic=11574.0
Which linked to this:
http://img172.imageshack.us/img172/4719/proflex1legendatg6.jpg
Keep getting the link to Frankd3000's gallery but it's not there any more.
Also found a link to Simon's Proflex, which he seems to have changed into a linkage system. Looks lovely but I think that would be somewhat further than I could manage. Frankd3000's previous posts are here:
http://idriders.com/proflex/smf/index.php?action=profile;u=441;sa=showPosts
One of the threads was saying that it's probably best to have the cone that fits into the strut for strength.
Stu.
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Stu,
You wrote "There's no (or minimal) lateral support for the shock so personally I'd not be comfortable with this. "
This is a regrettable shortcoming of the strut design. Whether you weld the shock to the strut or have complete lateral flexibility, your shock will not prevent side flexing of the rear swingarm.
If you get the vertical flex under control, you'll be fine.
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Hmmm...the idea I had would still reduce the side to side flexing because the shock would be rigidle mounted on the bottom. The U-shaped piece I'm envisioning is one where the u-shaped indentation in the block matches the outer curvature of the shock's lower eyelet. Then the mounting bolt comes up from underneath, through the bottom of the shock eyelet (requires a hole to be drilled) and then into a rod segment matching the shock eyelet's inner diameter and with a hole drilled and tapped through it to accept the mounting bolt coming up from underneath. This would provide a rigid mounting point.
As for what shock I'm talking about...well, that's the tough part. There are so many air shocks on the market and in different sized I'm not really sure which would be best. What air shock would YOU choose?
Ideally it'd be one that...
- could be used on the front as well (or a similar one from the same manufacturer)
- with the proper or slightly longer length (when including the extra .5 inch or so for the mount)
- is plentiful enough so that resale values are reasonable (and therefore I'd be able to find one cheap on eBay ;-)
- with readily available parts
Thoughts? If you can recommend one and I can find it cheap I'll give this idea a shot.
- Doug
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if someone invents something that works well - and can get me an example. I'll pay for the design and the work you've done so that I can get a few hundred made up and put them on sale.
Any of these frames:
+ World Cup Frame 955. 855
+ World Cup frame mk 2, 757, 856, 956, XP Serries, 96 beast
+ 97 Frame: 857, 957, 97 beast and 97 animal
cheers
callum
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One of the other threads has a picture of a bent strut and there is a question of whether the shock is ruined too. Given that, it seems like attaching the shock rigidly to the strut is a bad idea; it can't take the sideload, so it doesn't add any stiffness to the frame.
Making a pivot on top of the strut that lets the shock move in the left-right direction might be the way to go.
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Just changed a broken seat post. the seat clamp off the broken post is a threaded lug and a bolt. Was thinking of shaping the lug to fit the eye of a shock I have,drilling the bottom of the shock eye and bolting through the seat stay into the lug.Would this work? All feedback welcome
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(http://i275.photobucket.com/albums/jj313/efc_rule/DSC00083.jpg)
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Just changed a broken seat post. the seat clamp off the broken post is a threaded lug and a bolt. Was thinking of shaping the lug to fit the eye of a shock I have,drilling the bottom of the shock eye and bolting through the seat stay into the lug.Would this work? All feedback welcome
Hi Keith,
That was what I was getting at in the posts above...but I was proposing also creating a U-shaped block to better support the eyelet where it would mount to the strut top. The bolt would pass through the hole in the strut, through the u-shaped block, through the hole drilled in the end of the shock eyelet and screwed into the threaded hole in the cylindrical piece that fits through the shock eyelet (similar to what you were thinking). I wanted to do this to fit one of the widely available air shocks that frequently go for cheap on eBay...but I don't know enough about them to know which would be best for the Proflex. Any ideas?
- Doug
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([url]http://i275.photobucket.com/albums/jj313/efc_rule/DSC00083.jpg[/url])
Keith, I totally get it. :o I can see that it would prevent any side to side play.
A 7.5 inch i2i shock drops right into the cone of the strut, and mimicks the 8.25 inch cone to eye length of the stock shock.
Would you plan to enlarge the hole in the strut?
Terry
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Doug, I am a big fan of the Manitou Swinger shocks. They are pretty cheap on Fleabay, and are pretty durable. They just make the Proflex design even better in my opinion.
One grip I have with Noleens is they have to be overdamped to overcome bobbing. 50 to 75 lbs. pressure in the platform chamber prevents bobbing, then is buttery smooth when broken thru on big hits.
Some clearance of the frame or swingarm may be necessary, but only slight.
Terry
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I am reluctant to drill the frame ,will probably shape lug and use a nut on top of it with original bolt.If that doesn't appear too clever will drill larger hole and use a washer to spread the load
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I am reluctant to drill the frame ,will probably shape lug and use a nut on top of it with original bolt.If that doesn't appear too clever will drill larger hole and use a washer to spread the load
The only think I worry about is that the bolt along is not enough to prevent flexing and the eventual bolt snap where the strut meets the shock eyelet. The original design uses the conical insert to provide additional linear stability. That was the reason for the u-shaped piece in my approach...to cradle the eyelet as snugly as possible, and maybe even allow for additional attachments to the cylindrical piece running through the eyelet. I just doubt an M6 bolt, no matter how torqued, will be enough to prevent the shock/strut combination from buckling in the middle on the first heavy hit.
Just my $0.02...
- Doug
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The eyelet appears to fit the shape of the seatstay cradle perfectly without any extra packing.
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The eyelet appears to fit the shape of the seatstay cradle perfectly without any extra packing.
Oh, right, if you're talking about the top/seatstay mounting then it should be fine. I was talking about where the shock's lower eyelet would meet the top of the strut. A single M6 bolt going up through the bottom of the eyelet and keeping that connection rigid would not be enough.
- Doug
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It's the lower eyelet top of strut I mean,seems to fit pretty well.Given the original shock was secured with a m6 bolt,why would it not be sufficient now?
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It's the lower eyelet top of strut I mean,seems to fit pretty well.Given the original shock was secured with a m6 bolt,why would it not be sufficient now?
You're talking about an X56 or X57, right? It wouldn't be sufficient with an unsupported lower mounting point because the shaft of the original shock fit into a conical sleeve that nestled into the strut top to provide extra support, like a collett one might use for machining a rod. Because of that sleeve the shock was not only supported by the M6 bolt bot also on the size by the sleeve, adding linear rigidity. Linear rigidity was further reinforced by the pressure of the elastomers/springs down onto the top of the strut (which I'm trying to replicate with the u-shaped piece) which helped to prevent the shock/strut combination from folding in half.
These are just my thoughts...I've been thinking about this for a couple weeks now, trying to devise a solution. Maybe it is as easy as drilling a hole in the bottom eyelet and screwing into a threaded piece inside the eyelet...but with it being less common to see a spare strut for sale, and the likelihood of other damage/injury if the rear support folded on you while riding, wouldn't you want that connection to be as rigid as possible?
Seriously, though, I'm a web designer not a structural engineer... ;-)
- Doug
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I'm a carpenter Dug,Don't have much idea of this,just kicking ideas around at the moment.
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Anyone know how the eyelet on the thin end of the shock is attached? Was wondering if it would be possible to remove the eye and fix it as per origonal?
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DugB -- Making a u-shaped socket that is a tight fit for the eyelet is not a trivial thing. The socket would have to be made in three pieces and welded together, or it would have to be done on a CNC machine. Maybe you could make the socket a loose fit and line it with a thin piece of rubber.
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DugB -- Making a u-shaped socket that is a tight fit for the eyelet is not a trivial thing. The socket would have to be made in three pieces and welded together, or it would have to be done on a CNC machine. Maybe you could make the socket a loose fit and line it with a thin piece of rubber.
Hey!
Yeah, I figured it'd be no small matter. I pretty much assumed I'd take the shock to my local machine shop and have them match the eyelet profile. They're a small outfit but very competent and pretty cheap, too. That said, after reading the MTBR reviews for the Risse shocks, I'm thinking that I'll spend little to no additional cash on the shocks I have now, and possibly spring for some Risses at some point. Would be nice to have a Genesis for the front, and one with lockout for the rear.
- Doug :-)
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Yeah, I figured it'd be no small matter. I pretty much assumed I'd take the shock to my local machine shop and have them match the eyelet profile. They're a small outfit but very competent and pretty cheap, too.
- Doug :-)
Doug, you make 2 sets of mounts, one for you and one for me. And in exchange, I will weld it on your strut.
Terry
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Hmmm, I seem to have been away for a while! This is all looking quite promising. I'm still quite interested in getting something like this for my 857 so if it works, count me in!
I think a good shock for this would be the bottom of the range Fox. You can pick it up new from chainreactioncycles for about £150 eBay prices seem to be 50-100 ish for used ones. Personally I'd prefer a fox shock with Pro-pedal to a Risse shock and Fox servicing is much easier to get too.
The talk of snapping an M6 bolt makes sense so we'd need something stronger connecting the shock to the swingarm.
I have no idea if this is possible but how about "threading" the end of the shock and making the adaptor with a threaded hole/sleeve it slides into? Or just making the adaptor deep enough that it supports the shock?
The adaptor would look like a "cup" that maybe 3 centimetres+ of the end of the shock would go into. We could drill through the sides of the "cup" so a bolt could pass through the eyelet making it secure. Failing that we could go back to the idea of drilling through the bottom of the shock eyelet and the adaptor to provide a secure attachement for the M6 bolt.
Also, not sure if I ever got an answer to this: Can anyone who's used a rear shock tell me if it's possible to rotate the bottom eyelet of the shock through 90 degrees?
Cheers,
Stuart.
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Hmmm, I seem to have been away for a while! This is all looking quite promising. I'm still quite interested in getting something like this for my 857 so if it works, count me in!
I think a good shock for this would be the bottom of the range Fox. You can pick it up new from chainreactioncycles for about £150 eBay prices seem to be 50-100 ish for used ones. Personally I'd prefer a fox shock with Pro-pedal to a Risse shock and Fox servicing is much easier to get too.
The talk of snapping an M6 bolt makes sense so we'd need something stronger connecting the shock to the swingarm.
I have no idea if this is possible but how about "threading" the end of the shock and making the adaptor with a threaded hole/sleeve it slides into? Or just making the adaptor deep enough that it supports the shock?
The adaptor would look like a "cup" that maybe 3 centimetres+ of the end of the shock would go into. We could drill through the sides of the "cup" so a bolt could pass through the eyelet making it secure. Failing that we could go back to the idea of drilling through the bottom of the shock eyelet and the adaptor to provide a secure attachement for the M6 bolt.
Also, not sure if I ever got an answer to this: Can anyone who's used a rear shock tell me if it's possible to rotate the bottom eyelet of the shock through 90 degrees?
Cheers,
Stuart.
Hey there Stuart.
Rotating the bottom eyelet has been done often. Here is my current config.
(http://img.villagephotos.com/p/2005-6/1036595/957strutmounted.JPG)
(http://img.villagephotos.com/p/2005-6/1036595/Proflexwithmods,Aug.31.JPG)
(Disregard the front fork, as I have moved on to a slider). The eyelet of the shock drops right into the taper of the strut. Many comments have been made that without boxing in the shock there may be some flexing of the swingarm, but the improvement of the shock action cancels that out(in my mind at least. I have been toying with the notion of making some side pieces and welding them in.
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Thanks Shovelon. I'm not that confident with welding so I'd prefer to have some kind of adaptor for me. I like your mod though it looks great. Did you find the air shock to be better than the original Noleen?
Cheers,
Stuart.
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Thanks Shovelon. I'm not that confident with welding so I'd prefer to have some kind of adaptor for me. I like your mod though it looks great. Did you find the air shock to be better than the original Noleen?
Cheers,
Stuart.
Stuart, I did find the airshock to be better, and I will tell you how. The factory noleen shocks are overdamped in my opinion to prevent bobing. I did have one redamped before and it was much better but sag distance was critical.
The Swingers that I like, have the intial platform setting that limits bobing, then it is correctly damped through it's stroke. I can also adjust the ride hieght infinately. And the airshock is less than half the weight and gives a tad more travel too. The difference in comfort on both my Oz and 957 were immediately noticable.
Another note, when I had Simon's sealed bearing conversions done on both my Oz and 957, the travel was noticably less restricted. The Oz drove me nuts until I reset the platform pressure from 50 psi to 70 psi. The Oz felt like something was loose in fact.
On the other hand, many comments have been made that I would get some side to side movement of the strut on my 957, but honestly the much improved travel has cancelled out any feeling of that. The Oz has been observed by some people to have swingarm side to side flex that feels unnerving, but the same has occured in that the improved travel characteristics have absorbed that too.
Terry