Tech 39mm Forks

Tech 39mm Aluminum Forks

As received, I was not satisfied with how the front end worked.  The bike did not turn as well as my EFI OSSAs.  I was not using all the fork travel, and it was harsh near the end of the stroke.

I improved the turning behavior by sliding the fork tubes up so that 10mm protruded above the clamp (this is roughly double the standard protrusion) but it still does not turn as well as my OSSAs.

The ePure's previous owner is a big guy who had installed stiffer springs at both ends.  I replaced them with standard and set the preload at the minimum to get the sag in the ballpark.  I still did not use all the travel, and the ride height of the bike was now such that the side stand became useless (causing the bike to be too upright for safe parking).  The rear seemed to be working pretty well, and I increased the front preload to mid-scale to get the sag closer to ideal.

EM claims the front has 175mm of travel. I have only been able to measure 165mm, and am only using 150mm.  A 165-mm travel is more in keeping with other modern trials bikes.  Chris at SplatShop informed me that GasGas also states the Tech fork has 175mm of travel.  He guessed the 175 number is from “metal stop to metal stop” and that the top-out spring will provide the missing 10mm.  He added that you'd have to run a very stiff spring with a lot of preload to get anywhere near 175mm. 

The Race's front forks are 39mm Tech made by Formula in Italy.  Tech forks come in 3 grades.

• Base: Steel stanchions

• Mid-Range: Aluminum stanchions

• High-End: Aluminum stanchions with adjustable compression damping

All have adjustable rebound damping (right side) and spring preload (left side).  Adjsuters are at the top of each fork tube.

Six(!) manuals were produced by Formula for servicing their Tech forks.  You can download them from the rideformula.com website.  SX and DX refer to the right and left sides, respectively.

Tech recommends an initial oil change at 20 hours and then every 6 months thereafter.  An informed estimate is that my forks had about 50 hours on them.  The photo below shows the oil I got out of each side, along with virgin 5-weight Maxima.

The rightmost container is from the right fork (damping side).  It looked like used fork oil.  The center container is from the left (spring) side.  It was very dirty, probably from the spring sliding against the ID of the tube.  The photo does not show the true difference in color.  The leftmost container is virgin 5-weight Maxima.

It is interesting to note that I got pretty nearly exactly 250cc out of each side (which is the volume Tech says to put in prior to setting the level).  Initially, I only got 180cc out of the right (damping) side.  The cartridge contained the rest and could only be drained by removing the M14-1.0 bolt at the bottom of the fork leg.  I could not find a torque specification for that fastener and simply measured the break-away torque during removal at about 200 inch-pounds.  (Later I read the spec is 16.9 - 23.5 Nm.)

Prior to draining, I measured the air gap at the top of each fork tube.  The right side oil level measured 75mm with the stanchion collapsed, the fork cap removed, and the cartridge rod at the bottom.  In the Tech service manual, the range is 55mm to 75mm for various trials bikes.  75mm is the spec for the 2018-2019 Electric Motion (latest listed).

The left (spring) side oil level measured only 144mm.  The manual says 130mm for 2018-2019 Electric Motion.  The range is 100mm for older Montesas to 130mm for most of the newer bikes.   It's possible that some oil was lost when my springs were exchanged, twice.

My go-to suspension oil is Maxima.  Their 5-weight viscosity is very close at 15.9 cSt.  (For forks, I only care about the 40-degree C spec.)  I hate to be cheap with suspension, but I doubt there is any noticeable difference between the Yamalube and the Maxima.  Long ago, I had an excellent exchange with the president of Maxima – he was actually doing their technical support at the time.  I came away with a high regard for their products and his knowledge.  I suspect most of the higher cost of the Yamalube 01 is just profit and getting the product into the USA in small quantities.

Again, I used my timed flow test and got the following results for the oils I had on hand.

• Fresh Maxima 5 weight (85 - 150 SUS) took 25.5 seconds

• Fresh Maxima 7 weight (125 - 150 SUS) took 45 seconds

In thinking about the oil that came out of the left side, the viscosity is certainly more than even a fresh 7-weight, maybe nearly 10-weight.  I can see where that would have made the bottoming behavior harsh.

It's really too bad Tech did not provide variable compression damping with the high-end aluminum fork.  The red M14 x 1.0 bolt at the bottom contains a needle valve to change the damping.   That's really the only manufacturing change, other than a few holes in the red cup.   The cost difference at the time of manufacture would have been insignificant.  

Note that a 2mm hex key is needed to make the compression adjustment.  It has slightly less than 5.5 turns of range.

Although not visible in the compression-side cartridge photo, the circlip had some plating that chipped off as I was removing it.  It would probably be fine if left alone, but is the kind of thing that can foul a shim stack.  I used a wire wheel to remove all the plating.

As well as the circlip, there is a tiny setscrew that must be removed.  The photo shows a 1.5mm hex key in that setscrew.

This next photo shows the damper rod on the spring side.  The gold anodized bolt is also the bottoming adjustment, which is just a needle valve.  It has about 7 turns of total range and can completely shut off the flow.  Tech calls it the “end-stroke governor.”  It requires a 2mm hex key for adjustment.

Quoting the Tech manual: “Below the left leg, you find the end-stroke governor.  This setting works only over the last 45 mm of the stroke.  Usually, we use this adjuster completely closed, but in case of very thin riders who can’t reach the end-stroke position, it is possible to have a better feeling unscrewing it.”

Discussion

The Tech forks have some advantages over the excellent Marzocchis that came on my OSSAs.  For one thing, they are still being manufactured!  The Techs are much easier to work on.  They have no propensity to shoot a geyser in your eye when bleeding the cartridges.  And, the bottom-out adjustment is nice – assuming I can get it to work.  Plus, a design using a single spring is very tolerant of fork tube height discrepancies during installation.  They are probably lighter, too.

Unfortunately, it's winter where I live so I won't get a chance to do any testing for a while.

Although I could attribute the poor bottoming performance to the very dirty (high viscosity) oil, it's possible the air spring is too stiff even though the left side had a lower oil volume than standard.

My suspension guru reminded me to leave the air volume large.  I kept the air gap at 144mm on the left side and increased it to 89mm on the right side. It's far easier to add fluid than to remove it.  While the fork is on the bike just by unscrewing the cap, I can use a syringe to add fluid.

Changing the fork oil level on the right side requires 0.66cc / millimeter change in level.  On the left side, it is 0.74cc / millimeter.

I'm a bit puzzled about the oil viscosity on the right side being more than that of the virgin 5-weight.  Usually, I think of oil shearing down (losing viscosity with use).  But I guess it's equally possible that contamination will increase the viscosity. 

I'm also considering polishing the OD of the fork spring so that it slides easier inside the fork tube.  This should help keep the fluid cleaner as well.  But I'm not sure if I'll want to use a softer spring, and would prefer not to go to that much trouble.  So I did 50% of the job with 10% of the work by running the spring against a wire wheel.

Replacing Fork Seals

Eventually, all forks seals leak and must be replaced.  It's best to do this at the first sign of trouble because fork fluid will contaminate the brake pads.

The Tech fork seals have a 39mm ID and a 51mm OD.  The thickness dimension is usually written “8/10.5”.  Looking at a side view of the seal reveals a step.  The part of the seal that goes under the retaining circlip is 8mm tall, and the overall height of the seal is 10.5mm (or sometimes 10mm).

As can be seen in the adjacent photo, the original equipment seal uses a spring not present in the K&S aftermarket seal. Aftermarket seals are usually much cheaper than OE, and more readily available.  It's typical to replace both seals at the same time, but I wanted to conduct an experiment by replacing only the leaking left seal with a K&S 16-1034.

The premium solution is to use SKF's low-friction green seals.  Decreasing fork seal friction provides better compliance over small bumps.  SKF's part number KITGT-39T would appear to fit.  I have used SKF's seals on my EFI OSSAs and like them very well.

Fork Seal Installation Tips

The following is not intended to replace Tech's fork maintenance instruction manuals -- it's just some tips you may find helpful.

• Seals are easy to install on conventional forks.  That's because, unlike with upside-down forks, the seal driver can be a simple shop-made item (although commercial fork seal drivers are readily available if you prefer).

• The outer dust seal is typically removed using a dull wood chisel.  I begin this way, but then use a soft plastic gasket scraper to pry the dust seal out completely. 

• The seal retention circlip is not a complete circle, so it's easy to pop out with a small screwdriver. 

• The cartridge retaining bolt at the bottom of the fork leg must be removed prior to the next step.

• Use the “slide hammer technique” to remove the old fork seal.  This is described in the Tech fork maintenance manual. Now is the time to inspect/replace any worn bushing (bush outside the USA). 

• Fork seals need lubrication on their inside surface prior to installation.  I always use Race Tech's USSG 01 (ultra slick seal grease), but other greases may well be satisfactory.

• I made a seal driver from 1.5-inch size PVC plumbing pipe.  This plastic pipe has an OD of about 48mm and an ID of about 40mm.  Note that it's necessary to machine a small recess at the end to clear the protruding part of the seal. (Just as when installing a bearing, you want to apply force near the OD rather than the ID.)

• A much longer piece of the same PVC pipe can then be used as a “hammer” to seat the fork seal in the fork leg.

• When refilling with fork fluid, the air gap measurement is made with the stanchion tube fully collapsed and the cartridge rod at the bottom of its travel.