Manitou 2 Coil/Elastomer FrankenFork Build Thread

Juanabe · Apr 27, 2014

Hey there everyone.. thought i would share a recent project i have been working on. I picked up a few manitou forks about a year or so ago and have been playing around with various configurations regarding internals. I built up a manitou 2 to factory specs just to start with in order to see what the original ride characteristics should be like with a rider of my size. Riding the factory setup (elastomer stack only), i was generally pleased with the ride but experienced much fluctuation in handling characteristics when the cold weather rolled around. Cold and stiff polyurethane proved to be rather useless during the later winter/early spring time, rendering my fork more or less fully rigid at times. My biggest gripe with the factory setup was that low speed compression was virtually non existent. The fork seemed to work well with medium to big hits, but showed very little give on the fire trails. I first started thinking about a spring/coil setup when i came across some photos on google of someone installing a coil/rubber combo for street riding. I was fond of the simplicity and the supposed efficacy of such a crude stack and embarked on my own path to try and emulate something similar, but perhaps with more modularity. Here are some photos of the setup that i just finished installing. This is an initial run that i suppose will require some tweaking here and there but the basic concept is simple. Following will be some photos and a basic breakdown of componentry.

Here is the front end with the stanchions and lowers removed completely from the fork. I went with the manitou 4/eft crown because they have some nicely machined flat spots right below the top of the crown. This allows you seat the stanchions right to the top with confidence and no guess work.

Here are the essentials spread out and ready for setup.

Using Sram butter for this one.. non lithium grease is an elastomer's best friend

Here we start with the stanchion tubes from a manitou 3. I chucked these up in the lathe and machined away some material in order to fit the oem aluminium manitou 2 top caps. This makes for a clean setup that looks as if they were made for one another. I used the manitou 3 stanchion tubes for 2 reasons, the first being that the tubes are not externally butted, leaving more surface area for contact against the seals, and the second being that these stanchions are drawn from 7076 aluminium (at least thats what the graining revealed to my eyes after machining), and that an aluminium to aluminium concact makes much more sense (being that the two grades of 6065 [the easton e9 lowers], and 7076 [stanchions tubes] have similar hardness) and will give rise to far less scoring and thus increase longevity as opposed to 4130 chromoly riding inside of a far softer aluminium. I'm not sure why exact ally, but there appears to be scoring inside the lowers from use with the chromo stanchions. This could possibly be warn bushings exposing the inner walls to the steel. I will use a newer set of lower bushings and hope that the wear does not continue

Here we have the new dust seals i just recieved in the mail. These are not factory but are molded to spec by a third party company i found on ebay. These are advertised as manitou 3 fork seals, but the first four iterations, as well as the efc, magnum, comp, and sport forks accept this seal. Its always refreshing when companies produce products that have interchangeable bits like this. Here is the link to the seals.

http://www.ebay.com/itm/NOS-Answer-Manitou-Three-3-Four-4-Fork-Dust-Seal-Wiper-Boot-SOFT-Rubber-VTG-NEW-/221244795663?pt=Cycling_Parts_Accessories&hash=item338337ab0f

Here we have the main bolts to be used. These bolts were installed on one of the blown manitou 2 forks i purchased on ebay for parts. I opened them up to find these beautifully machined 4al6v looking titanium main bolts. [Edit] These are aluminum anodized as clarified by Elite504. Thanks you for the bit of info. I have the oem steel bolts as well but these should do the trick as well as lightening up the equation.

Here is a photo of one of the lower tubes to be used. The manitou 2 lowers are by far the most aesthetically pleasing to me and i will be using these as well as the factory preload adjustment setup fork this fork. Everything in this photo is true to the factory oem setup for the manitou 2 forks.

This is a photo of the coil/elastomer stack combo that i settled on. The springs are something that i dug up in a box of parts we had laying around at the shop. For my weight (130) these seemed to be perfect. The only stress testing that went into my having decided to use these springs was me pushing down on them with one in each hand against a table. The red elastomer that you see inside the springs came from a manitou comp. These bits nestled perfectly into the springs and serve as a guide to prevent the spring from moving around and scoring the walls of the lowers, as well as providing some minimal bottom out mitigation if ever needed. The washers that contact the springs were sourced from a specialty bolt and washer shop locally. These washers are slightly thicker than the oem aluminium washers provided with some of the manitou forks as well as being all stainless in design. After looking at the factory washers i was convinced that not only would the metal to aluminum contact of the two give rise to serious wear and tear, but that due to the thinness of the factory washers some bending issues might be incurred. The upper elastomer seated above the spring is a very soft manitou 2 replacement bit and is used to achieve the correct stack height needed as well as accurate preload to minimize excessive sag. I used the oem aluminium washer on the top of the stack underneath the bottom of the stanchion and delrin bushing.

Here we have the aftermarket dust seals and bushings seated, lubed up, and ready for stanchion insertion.

In this picture you can see that the main bolts are penetrating the stanchion tubes, but not depicted are the short elastomers i used for rebound. Following the elastomer is another factory aluminium washer seated beneath the top of the main bolt. Being that i am achieving roughly 1.5" (close to oem spec) of travel, this elastomer, though slightly taller than the ones outfitted to the factory manitou 2, should provide sufficient damping.

Here we have the stack mounted to the bolt, lubed up, and ready to be inserted into the lowers.

The fork has been compressed and the bolts have been tightened down adequately for compression. The fork is now ready to go (^_^)

After a quick ride around the block to make sure everything was feeling good, you can see the line of my max travel. 1.5" +/- .1/.2 seems to be where i stand at this point. I am hoping that this setup will be perfect for the all round style of riding that i do with this bike. I really needed something more substantial to negotiate the poor infrastructure of the city as well as all of the hard pack/sandy/gravel roads that i find myself riding on. I would liken the feel of this fork to a very plush short travel xc fork, with good low speed compression. Some miles and testing are now in check as well as working out whatever kinks i run into with this setup. I will keep you all updated as to how this setup works in various conditions, as well as noting irregularities that i need to address. I hope this thread proves helpfull to those who have taken a similar interest when it comes to rehabilitating and reconfiguring wonderful old forks that have lots of life ahead of them. Please feel free to ask questions and make suggestions as this is all just a big experiment that will be refined over time.

To those interested, here is a link to the album on flicker containing all the photos linked above in higher resolution. https://www.flickr.com/photos/juanm_pho ... 353148972/

If anyone is interested in setting up something similar i will happily take the caliper to some of the bits for exact measurements. This was all eyeballed so i don't know most of the dimensions off hand.

Here is a blow up diagram of the original maintou 2 setup.

[edit] Had some image link issues with the initial post but have since worked them out. Cheers (^_^)

phill77 · Apr 27, 2014

Re: Manitou 2/3/4 Coil/Elastomer FrankenFork Build Thread

A top quality write up, good to see someone trying hard to keep these classic forks in reliable regular use!
I don't get why you prefer the alu stanchions to the steel ones - surely the wear is the same as that is what the bushings are for?

Juanabe · Apr 27, 2014

Thanks for the kind words

I went with the aluminium stanchions because they are lighter, provide greater contact surface area, and have no external butting that limits my stack height. The metal to metal wear might be minimal, but you will see scoring in all of the early manitou forks. My logic was that if there was to be any metal to metal contact, better it be two alloys of a similar hardness vs steel riding up against aluminium.

sho220 · Apr 27, 2014

If you're drinking those beers straight out of the bottle, I believe that's considered a "Crime Against Humanity"...just sayin'...

Juanabe · Apr 28, 2014

Oh gawd.. *smacks forehead* ;D

elite504 · Apr 28, 2014

Hi there Juanabe. Sincerely, thanks for taking the time for a detailed write up.
Such a detailed write up deserves some time to be taken with the response!

Juanabe":3hjq17ia said:
Cold and stiff polyurethane proved to be rather useless during the later winter/early spring time, rendering my fork more or less fully rigid at times.

Yup, but in fairness it is what they made the soft ride kits and cold whether kits for. But I also appreciate that for the "two", these are no longer available. SO, it's down to the tinkerers to find solutions!

Juanabe":3hjq17ia said:
My biggest gripe with the factory setup was that low speed compression was virtually non existent. The fork seemed to work well with medium to big hits, but showed very little give on the fire trails.

This is the inverse of how elastomer forks conventionally behave. Usually they're considered supple on the small stuff, and then get out of their depth on the bigger stuff. However, having seen elastomers over time in various forks either go to chewing-gum, or to what feels like wooden dowels, perhaps the elastomers were too hard or past their best. I'm assuming you're 130lb (being stateside) and not 130 metric Kg, so you should be on a soft and supple elastomer...

Juanabe":3hjq17ia said:
Using Sram butter for this one.. non lithium grease is an elastomer's best friend

Amen.
And Thanks for sharing the seal link!

Juanabe":3hjq17ia said:
The tubes are not externally butted, leaving more surface area for contact,

Nope. The only contact points of the system are the two bushes.
The small one on the end of the stanchion is static on the stanchion and slides in the bore of the slider (hence on internally butted slider).
The large bush at the top of the sliders under the seal is static on the slider, and slides on the OD of the stanchion, but only at the top, above the butted portion. The only time the butted "two" stanchion becomes an issue is if you're trying to extend the fork with a DIY long travel kit.

Not trying to score points at all I promise, just trying to be crystal with how the system functions.
Nothing wrong with using the "three" stanchions modified as you have done. There is a big hole in the bottom of the stanchion for the "three" pushrod, that is far larger than the bolt. Achieving stack control without buckling is an important issue here, and we'll continue to touch on.

Juanabe":3hjq17ia said:
... aluminium to aluminium contact makes much more sense (et al.

Nope. This is why Aluminium pistons run in iron cylinder bores in car engines. A hard thing in a soft thing or vice versa gives best slide and wear characteristics (vast metallurgical generalisation, but good point in principal). However, it's a moot point as there is never metal-to-metal contact. The slider and the stanchion always have the bush keeping them apart.
... unless the spring stack destabilises, then the spring will contact...

Juanabe":3hjq17ia said:
I opened them up to find these beautifully machined 4al6v looking titanium main bolts. I believe these are srp bolts but im not certain.

These are hard anodised aluminium.

Juanabe":3hjq17ia said:
The red elastomer that you see inside the springs came from a manitou comp. These bits nestled perfectly into the springs and serve as a guide to prevent the spring from moving around and scoring the walls of the lowers, as well as providing some minimal bottom out mitigation if ever needed.

Good call.

Juanabe":3hjq17ia said:
The washers that contact the springs were sourced from a specialty bolt and washer shop locally. These washers are slightly thicker than the oem aluminium washers provided with some of the manitou forks as well as being all stainless in design. After looking at the factory washers i was convinced that not only would the metal to aluminum contact of the two give rise to serious wear and tear, but that due to the thinness of the factory washers some bending issues might be incurred. The upper elastomer seated above the spring is a very soft manitou 2 replacement bit and is used to achieve the correct stack height needed as well as accurate preload to minimize excessive sag. I used the oem aluminium washer on the top of the stack underneath the bottom of the stanchion and delrin bushing.

Yup the aluminium washer will fold as you say. However you need to control the spring at the top too, for all the reasons you state. If you look at something like a judy topcap, you can see it had an external keeper for the spring on the type II system or with Speed SPrings. Internal will work too. Perhaps if you have a lathe machining up a washer with integrated keeper is the way forwards. As you say, the bore of that lower leg is the bearing surface for the stanchion bush.

Also, because the M6 is running through the (10 or 12mm IIRC) pushrod bore in the "three" stanchions, you bolt isn't guided as carefully as it could be. Perfect candidate for you to machine a little bronze or delrin tophat to press into the bottom of the stanchion bore at the bottom to keep that stack under control; and keep the washer off the slider bore.

-- --

Good write-up and thanks for sharing.
My main concernwith spring conversions on early manitou series forks is that the damping disappears. Whilst the fork may be supple for your commute or fire roads (which may be all you want), it will kick back HARD on g-outs and gulleys and this is a serious control issue.
The decent spring forks that emerged (look at the early judy evolution), utilised some sort of damper to control the spring. Whatever the spring medium, there is always a damping medium. look at race cars, cart sprung (leaf spring) trucks and mustangs, and even vintage vehicles with star washer friction dampers, there is always a damping medium (even if not concentrically located).

Keep up the fettling. Share the results, and between us all we can be more confident modifying old parts to keep them running.

lrh · Apr 28, 2014

Re:

Very similar to what I've done to a couple of pairs of early Manitou's: http://www.retrobike.co.uk/forum/viewto ... p;t=285021

Your springs look softer/longer than mine and I would grind the ends of the springs flat so the load is spread more evenly. I created seats to keep the springs central at both ends but it's a mission to get the stack into the first-gen forks and screwed down!

Can you post the link to the seals again as you accidentally posted an image link instead

Juanabe · Apr 29, 2014

Elite504 thanks a bunch for the awesome reply, and shedding some light on a few concerns and questions I had.

Juanabe":2uex2oo6 said:
My biggest gripe with the factory setup was that low speed compression was virtually non existent. The fork seemed to work well with medium to big hits, but showed very little give on the fire trails.

Elite504":2uex2oo6 said:
This is the inverse of how elastomer forks conventionally behave. Usually they're considered supple on the small stuff, and then get out of their depth on the bigger stuff. However, having seen elastomers over time in various forks either go to chewing-gum, or to what feels like wooden dowels, perhaps the elastomers were too hard or past their best. I'm assuming you're 130lb (being stateside) and not 130 metric Kg, so you should be on a soft and supple elastomer...

I think this was due in part to possibly receiving the wrong elastomer kit. I ordered the soft but I feel that what I received was the firm. These elastomers were very firm out of the box.

Juanabe":2uex2oo6 said:
The tubes are not externally butted, leaving more surface area for contact,

Elite504":2uex2oo6 said:
Nope. The only contact points of the system are the two bushes.
The small one on the end of the stanchion is static on the stanchion and slides in the bore of the slider (hence on internally butted slider).
The large bush at the top of the sliders under the seal is static on the slider, and slides on the OD of the stanchion, but only at the top, above the butted portion. The only time the butted "two" stanchion becomes an issue is if you're trying to extend the fork with a DIY long travel kit.

When speaking of surface area I was speaking strictly in terms of the amount of distance the stanchions were capable of being inserted into, or removed from the lowers while still clearing the seals. I knew that the butted stanchions might leave me with minimal material to ride against if my stack was much higher than the factory spec when all was said and done.

Elite504":2uex2oo6 said:
Not trying to score points at all I promise, just trying to be crystal with how the system functions.
Nothing wrong with using the "three" stanchions modified as you have done. There is a big hole in the bottom of the stanchion for the "three" pushrod, that is far larger than the bolt. Achieving stack control without buckling is an important issue here, and we'll continue to touch on.

This is something that I hope is not going to be an issue, I did noticea tiny bit of slack in between the bore and the bolt but not much more than the original Manitou 2 stanchions. At least not much with this bolt set i am using. I am hoping that the compression as well as good alignment with the spring and stack will be enough to keep things in order, especially once i add another guide to the lower as i will speak more of after a quote below. Some more riding will bring the reality of the matter to light.

Juanabe":2uex2oo6 said:
... aluminium to aluminium contact makes much more sense (et al.

Elite504":2uex2oo6 said:
Nope. This is why Aluminium pistons run in iron cylinder bores in car engines. A hard thing in a soft thing or vice versa gives best slide and wear characteristics (vast metallurgical generalisation, but good point in principal). However, it's a moot point as there is never metal-to-metal contact. The slider and the stanchion always have the bush keeping them apart.
... unless the spring stack destabilises, then the spring will contact...

I was initially considering the same principle, but when i looked inside a few of the lowers i had that utilized the cromo stanchions i noticed scoring and thought to myself that if there was to be irregular, somewhat angular contact of any sort, better it be from aluminium than from cromo that appeared to be scoring the lowers. I understand that in theory the bushings will keep the tubes seperate from one another, but upon further inspection i unfortunatly found this not to be the case. Perhaps worn bushings might be the culprit? I have another set i can throw in the forks soon when i reconfigure the stack.

Juanabe":2uex2oo6 said:
I opened them up to find these beautifully machined 4al6v looking titanium main bolts. I believe these are srp bolts but im not certain.

Elite504":2uex2oo6 said:
These are hard anodised aluminium.

Thank you for the info

These things felt and looked like lower grade ti in the hand. That old anno had me totally fooled.

Juanabe":2uex2oo6 said:
The washers that contact the springs were sourced from a specialty bolt and washer shop locally. These washers are slightly thicker than the oem aluminium washers provided with some of the manitou forks as well as being all stainless in design. After looking at the factory washers i was convinced that not only would the metal to aluminum contact of the two give rise to serious wear and tear, but that due to the thinness of the factory washers some bending issues might be incurred. The upper elastomer seated above the spring is a very soft manitou 2 replacement bit and is used to achieve the correct stack height needed as well as accurate preload to minimize excessive sag. I used the oem aluminium washer on the top of the stack underneath the bottom of the stanchion and delrin bushing.

Elite504":2uex2oo6 said:
Yup the aluminium washer will fold as you say. However you need to control the spring at the top too, for all the reasons you state. If you look at something like a judy topcap, you can see it had an external keeper for the spring on the type II system or with Speed SPrings. Internal will work too. Perhaps if you have a lathe machining up a washer with integrated keeper is the way forwards. As you say, the bore of that lower leg is the bearing surface for the stanchion bush.

I will totally take your advice as i have already felt a bit of movement in the stack from playing around on the forks this morning. I was thinking about turning some nylon on the lathe and drilling it out for spacer guides to sit at the base of the spring stack, and have the old manitou comp elastomers (thanks for clearing that up by the way) sit up higher for better alignment. I will also play with the idea of turning some mushings with the keeper as well.. i like that idea alot.

Elite504":2uex2oo6 said:
Also, because the M6 is running through the (10 or 12mm IIRC) pushrod bore in the "three" stanchions, you bolt isn't guided as carefully as it could be. Perfect candidate for you to machine a little bronze or delrin tophat to press into the bottom of the stanchion bore at the bottom to keep that stack under control; and keep the washer off the slider bore.

This is a great idea. If i run into stack wobble issues i will definately consider this. If you take a look at the picture again, you will see how the tolerance between the bore and the rod seems to be tight. Fairly snug i would say.

Elite504":2uex2oo6 said:
Good write-up and thanks for sharing.
My main concernwith spring conversions on early manitou series forks is that the damping disappears. Whilst the fork may be supple for your commute or fire roads (which may be all you want), it will kick back HARD on g-outs and gulleys and this is a serious control issue.

I hope that the elastomers i used for the rebound will be sufficient for such short travel. If not i might consider a short spring inside the stanchion for rebound damping.

Elite504":2uex2oo6 said:
Keep up the fettling. Share the results, and between us all we can be more confident modifying old parts to keep them running.

Thank you again so much for your time and input. It is very much considerd and i hope to compare and contrast more ideas as i continue to refine this.

Juanabe · Apr 29, 2014

Re: Re:

lrh":1lla8asw said:
Very similar to what I've done to a couple of pairs of early Manitou's: http://www.retrobike.co.uk/forum/viewto ... p;t=285021

Your springs look softer/longer than mine and I would grind the ends of the springs flat so the load is spread more evenly. I created seats to keep the springs central at both ends but it's a mission to get the stack into the first-gen forks and screwed down!

Can you post the link to the seals again as you accidentally posted an image link instead

Thanks for sharing that picture of your setup. Im curious about your coils. Who made those springs? I am particularly interested in the ones on the left. By the way i like your idea regarding the ends of the coils, although i might try gently rounding them to keep them more stout at the contact points. Thank you for the suggestion.

I reUped the link by the way

thanks for letting me know it was bad.

drcarlos · Apr 29, 2014

You do know that springs have no damping properties at all right?

This mean that what elite says about them kicking back hard cannot be cured with another spring to replace the rebound bumper you need a damper in there which is usually hydraulic fluid. The beauty of the elastomer was that they had inherent damping properties (ie they don't just return to the same shape as quickly as they deformed, like a spring does, the energy is dissipated through the material and they return slower to their original shape) which kept these early forks light as it serves as both spring and damper in one light unit. They were far from perfect but springs change them for the worse, which is not just my opinion it's a scientific fact.

Easy case in point is have you ever seen a car or motorbike with no dampers?

Sorry, you have just created this:

Carl.

Manitou 2 Coil/Elastomer FrankenFork Build Thread

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sho220

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Juanabe

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Juanabe

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drcarlos

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