THOR LAWSON'S
VINTAGE and EVOLUTION SUSPENSION PRODUCTS

SIMONS FORK PARTS

NEWS FLASH for Owners of Conventional Seal Forks!!!
I am now offering a modification to replace the seals with a Seal Carrier (Patent Pending) that uses the 1/4" Pneumatic Seal/Wiper combination.
This will allow the Forks to be used as originally intended, as Air Forks, without the problem of seal failure due to the pressures needed.
Cost is $200 plus rebuild labor and seal parts.

Simons documents:  (Specs and Tips on Simons)  (Not sure which way the seal/wiper goes in?  Click here for JPG diagram)
Normal setup is 5wt oil at 6" starting at 15 psi.

Fork Leg color: Safety Yellow, I use powder, but Krylon Safety Yellow in the can is a match.  Lemon Yellow is close but appears to
be slightly lighter.  Later in production, legs could be ordered to closely match all of the major manufactures brand color.

Tubes and legs are all the same length unless modified after production, overall length and travel is adjusted by varying the length of the damper rods.
See the Specs and Tips sheet above for how to determine travel by rod length.

 

Left-pneumatic seal/wiper leg, Right-conventional 50mm oil seal leg. Photo of a leg using pneumatic seal/wiper on left, conventional canned oil seal leg on right.

 

 

SimonsSealKit.JPG (189681 bytes) SIMONS FORK SEAL KIT*- consist of 2 Seals, 2 Wipers, 2 Bottom Cap O-rings, and 2 O-rings for the air caps.

* I don't mind doing exchanges if you order the wrong set, provided they are not damaged.  If you have never had your forks apart before, please disassemble one and see what you have and save yourself time and postage.  Don't assume.... from the top, the 1/4" and 3/8" appear the same.  However, the 50mm conventional canned oil seal is readily viewable from the top and is held in by a circlip.  Seal size can usually be determined by the Serial Number, up to 2969 should be 1/4", 2970 and up is 3/8"  Caution on early 1/4" numbers, I have seen a few sets that someone had upgraded thru a machine shop, but they are rare.

How long will your seals last?
First, it is normal for hydraulic seal/wipers to leave a trace amount of oil on the fork tubes that you can just barely feel, this indicates there is positive pressure in the forks that helps keep dirt out and protects the tubes from corrosion.  When it gets to the point where enough oil collects to start running down the fork leg it is the first stage of a leak and is called weeping, this should be treated as a warning sign to replace as soon as possible, you may or may not get 1 or 2 more rides out of them before they blow and you are sidelined.
Simons recommendation back in the day, was to replace annually, regardless of whether they are leaking or not.  The reasoning behind this is so that you do not have a failure while riding or racing.  I tried to go into the 2nd season on my Simons in 79 without a rebuild, the seals failed after 2 races.
When the fork legs and tubes are in perfect condition, the seals will start to weep before completely blowing out, this will usually buy time to replace before your next event.  Condition of the legs, tubes, and piston rings will effect life expectancy.  Worn parts will result in play that will shorten seal life.  On my own set a couple years ago, the seal on one fork would only last maybe 3 months.  I found extreme wear in the fork leg where the tube dug into the lower part of the leg, replaced the leg, but the seal still failed in 3 months.  At this point I suspected the fork tube even thou there was no damage to the chrome.  Tooling marks or coil like swirls were just barely visible under some of the chrome which is only about 0.002" thick.  Measuring the tube with a micrometer showed 0.001" deviation in the OD of the tube.  I then had both fork tubes re-chromed, (hard chroming, not the same as show chrome), and the problem was solved.
The next factor on life is the material itself, the seals and wipers are polyurethane, this material has a shelf life of 5 years, once installed, this is immediately reduced by half, and further reduced by condition of parts as noted above and by riding conditions they are exposed to such as fine gritty sand and extreme mud being the worst.  Even in the package, polyurethane parts will naturally deteriorate over time just as you may have noticed when doing a rebuild on a set that has not been touched in years.  The parts first start to harden, then become brittle, white seals and wipers will discolor to yellow or brown.  Buying original seal kits from back in the day is a waste of money unless it is just for display on the wall.
Even if the forks are never used, the bike is a show or museum piece, the seals will eventually fail.  After 2 to 5 years, take the bike off the stand, compress the forks, they will most likely weep or leak.
.
The rubber coated canned seals used in the 50mm kit in the first production of the Simons has a 15 year shelf life, but there is major flaw in the design, if they last a year, they're doing good.  The canned seals are not designed for high pressure applications and thus the reason Simons changed to the hydraulic wiper/seal combination.  My recommendation is to convert the forks to a conventional setup like the OEM's, replace the air springs with a standard rate for your weight and riding.  Install RaceTech Emulators for damping as this was controlled by the air pressure setting.  Use no air or just a few pounds to set sag if needed.

Bottom line, one year is the norm, less then that is an indication of a wear issue that is effecting the seals.

SIMONS 1/4" REBUILD PACKAGE,  up to serial # 2969 (a letter usually preceded numbers), 1/4" Seal Kit, Orange Decal Set (or specify other color), and the Manual at 50% off. #909-510A$43.50


SIMONS 3/8" REBUILD PACKAGE,  from serial # 2970 on (a letter usually preceded numbers), 3/8" Seal Kit, Orange Decal Set (or specify other color), and the Manual at 50% off. #909-511A$43.50


SIMONS 50mm REBUILD PACKAGE,  50mm Seal Kit, Orange Decal Set (or specify other color), and the Manual at 50% off. #909-512A$40.50


1/4" Seal Height, usually found in Aluminum Lower Legs up to serial #2969 (a letter usually preceded numbers), a few customers have aluminum legs with 3/8" seals, you have to check, fits early to late 70's, most commonly produced, the weight of one leg is 2 lbs and 5-1/2 oz. #909-510$29


3/8" Seal Height for Forks with Magnesium Lower Legs from serial #2970 on (a letter usually preceded numbers), ultra light legs used in the late 70's, limited production, the weight of one leg is app. 1 lb and 7 oz. #909-511 $29

SIMONS 50mm FORK SEAL KIT, used in 1st year production, utilizing a OEM style canned (metal rubber coated casing) seal retained by a snap ring, maximum pressure is 15 psi, above that you can expect to replace the seals more frequently then stock OEM forks, thus the reason Simons went to the hydraulic setup above.  O.D. of seal is 50mm, kit consists of 2 Seals, 2 Bottom Cap O-rings, and 2 Air Cap O-rings.   #909-512 $26

NEW, SIMONS OEM FORK TUBES, new re-production, due to the increasing cost of having old tubes repaired and replated, it is now more cost effective to purchase new tubes.   #909-504 $369 Set of 2

SIMONS DUST BOOT SET, zip tie around base might be needed if they slide up,   #909-506, $39 set


SIMONS RaceTech Gold Valve Emulator Setup, upgrade your forks to the performance level of modern forks with a progressive response, includes RT valving package, 26 lb valve springs installed, spacer set to go between valves and damper rods, requires drilling of lower damper rod ports and shortening main springs by 15mm.   #909-508, $189.99 set


SIMONS Air Cap, gold anodized, does not include Air Valve #11-110 $24 each


Critical part!!!  SIMONS Slit Spacer, do not tighten your axle clamps without these, you will crack or break the clamps  #11-151 $5.00 each


Simons Floating Valve

SIMONS Floating Valve,  #11-112 $15 each


Simons Valve Stop

SIMONS Valve Stop,  hand made from harden washers, a few Dremel cuts, some die grinding, then filed by hand, not pretty, but they work  #11-113 $30 each


SIMONS 50mm SNAP RING SET,  #909-585 $3.95 pair


SIMONS BOTTOM FORK LEG CAP,  #11-116 $56 each


SIMONS PISTON RING SET,  #11-132, wear limit is 1.245", depending on wear inside the tube, this may be slightly higher, there should be a very slight drag or you will get blow-by, new rings seat at about 1.255" $30 pair


SIMONS HANDLEBAR CLAMP SET,  #11-146/150 $120 pair set


SIMONS HANDLEBAR 1x Top & Bottom, HALF SET,  #11-146/150-1, tops and bottoms are machined together and only offered as a matched set due to slight variations in machining, tops only will be available at a later date when time permits,  $70 half set


SIMONS HANDLEBAR CLAMP BOLT SET, set of 6x Allen bolts for handlebar clamps only (included in complete set below), zinc plated . #909-558 $6


SIMONS BOLT SET, complete set of 20x Allen bolts and 4x nuts for steering, handlebar and axle clamps, zinc plated . #909-524 $22


SIMONS AXLE (stainless steel) & spacer-nut (aluminum), Honda CR125R & CR250R ,  #11-155-04 $150.00 Working on now.

SIMONS BRAKE STAY with spacer & hardware, Honda CR125R & CR250R ,  #11-166-01 $90


SIMONS AXLE & spacer-nut, Honda CR125M ,  #11-155-01 $150.00 Out of Stock until new shop is running.

SIMONS BRAKE STAY with spacer & hardware, Honda CR125M ,  #11-166-02 $90 Out of Stock until new shop is running.


SIMONS T-Stem Nut, CR125&250R with Simons Stem, 1"x20 thread, #11-202 $55
 

SIMONS T-Stem Nut, CR250R with stock Honda Stem, 24mm x 1.0 thread, #11-202 $65


Simons Fork Springs

SIMONS FORK SPRINGS, 26" length, 6.1 lb or .11 kg/mm rate #11-177 $140 set of 2


SIMONS NEGATIVE REBOUND SPRINGS, goes around the damper rod in the lower legs and eliminates harsh rebounds and makes for a softer ride on the small stuff. Compressed length 1.2", (note: OEM springs are 1.94"), subtract from overall travel without. #11-173 $49 set of 2
 


SIMONS STEERING STOP, stainless steel, #11-159 $15.00 each
 


SIMONS SNAP RING for Air Caps, zinc plated,  Set of 2, #909-580 $4.00 set
 


SIMONS SNAP RING for Damper Valve, black phosphate coated,  Set of 2, #909-581 $3.00 set
 


Simons Manual, scanned & printed from the original, covers installation, maintenance, tuning, machining blueprints for CR250R brake panel and steering nut modification.   #909-501 $9


 


SIMONS FORK STICKERS, Orange, Set of 2, #D-75 $10 pair


SIMONS FORK STICKERS, Yellow, Set of 2, #D-345 $10 pair


SIMONS FORK STICKERS, Red, Set of 2, #D-75R $10 pair


SIMONS FORK STICKERS, Blue, Set of 2, #D-75B $10 pair


SIMONS UDX-60, majority of the UDX-60's use seals with a 66.5 mm (2.623") or 67mm (2.638") OD, recently a customer reported a set with a 68mm (2.677") OD, whether by design or modified is undetermined at this time.  You must measure the seal bore before ordering.  Oil type is 2-1/2wt at approximately 750cc.  Seals are installed app. 3/8" from top.  The reason for the gap is to allow you to use a punch to drive in one side of the seal when replacing, this will cock the seal allowing for easier removal.

  SIMONS UDX-60 Fork Seals, 50x66.5mm (2.623"), seals will have a red coating on outer ring, wiper not available at the moment but working on it, Set of 2, #909-509 $18 pair


  SIMONS UDX-60 Fork Seals, 50x67mm (2.638"), wiper not available at the moment but working on it, Set of 2, #909-513 $18 pair
 


  SIMONS UDX-60 Fork Seals, 50x68mm (2.677"), Set of 2, #909-518 $22 pair
 

 SIMONS UDX-60 Wipers, 50x68mm, this is a single lip seal that is installed inverted to serve as a scraper, Set of 2, #909-519 $18 pair
 


  SIMONS UDX-60 Owners Manual, scanned & printed from the original,  #909-502 $14


  SIMONS UDX-60 Primary Spring Set, #14-341 $170 pair
 


  SIMONS UDX-60 Primary Spring Washer Set, #14-344 $8 pair
 


  SIMONS UDX-60 Spring Tube with internal clip,#14-340 Out of Stock--On order $26 each
 


  SIMONS UDX-60 Spring Tube Center,#14-342 $15 each
 


  SIMONS UDX-60 Spring Tube Clip,#14-345 $6 pair
 



Air Valves, Cores, and Caps

Air Valves with Low Pressure Core, Original replacement, Nickel-Plated, metal cap, always install with a fresh layer of plumbers tape which can be found in the Tool section,  #909-060,  $4.80 each

Low Pressure Air Valve Cores, 10 psi opening, 50 psi sustained, 300 psi peak, lighter opening value makes tuning easier, #909-052, 2 for $2.50
 


Original Style Nickel Plated Air Caps, long skirt for easy threading, o-ring seal, measures 0.513" long by 0.350" O.D. #909-056-4 2 for $1.40
Nickel Plated Air Caps, similar to original in appearance but wall is thicker, long skirt for easy threading, o-ring seal, measures 0.559" long by 0.423" O.D.,  #909-058-2 2 for $1.40
Chrome Hex Air Caps, fiber ring seal,  #909-055-2 2 for $1
 

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