HopFrog's 1980 KDX175 Build Log

Discussion specific to the various air-cooled KDX models sold in the USA
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HopFrog175
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Re: HopFrog's 1980 KDX175 Build Log

Post by HopFrog175 »


Thanks for the feedback everyone, saving an old runner is especially rewarding and I hope to get a reliable bike by the end :grin:

I have pulled a number of stems apart and this one seem pretty normal. A little rust on the shaft but nothing to worry about. The top bearing slid right off as expected and the lower was a press fit. I worked it a little with a tapered chisel then got the pickle fork started and off popped the bearing.


KDX175 steering stem bearing removal
_click image to zoom_
kdx175_00_steering_stem.jpg
kdx175_00_steering_stem.jpg (172.56 KiB) Viewed 11039 times
kdx175_01_steering_stem.jpg
kdx175_01_steering_stem.jpg (181.33 KiB) Viewed 11039 times
kdx175_02_steering_stem.jpg
kdx175_02_steering_stem.jpg (169.52 KiB) Viewed 11039 times
kdx175_03_steering_stem.jpg
kdx175_03_steering_stem.jpg (127.91 KiB) Viewed 11039 times


With the bearing out, I was able to get dimensions and evaluate the various bearing sources. For the KDX175, the same size bearing is used top/bottom and it appears that Koyo supplies it to Kawasaki. It looks like a good bearing with an integrated rubber seal on the exteral facing side. Other sources offer the bearing but they may have separate seals or may not have a seal at all. I ended up ordering Koyos from a bearing supply and expect them to be exact replacements when they get here in a couple of days. Here are the details:


KDX175 Steering Stem Bearing Details

Quick list
Mar 10, 2021


OPTION 1
--------
Steering Bearings and Seal Kit - 22-1022
    source - AllBallsRacing.com - $32.91
      https://www.allballsracing.com/22-1022.html

total for AllBallsRAcing - $32.91


OPTION 2
--------
Individual Bearings
(priced each)                                                                      Koyo
                    Part numbers                                                   from
            ------------------------------                   Part-   Kawasaki     Quality
Size        Kawasaki    General  Koyo*      #  Description   zilla   Parts House  Bearing
----------  ---------   -------  ---------  -  ------------  ------  -----------  -------
25x47x15mm  92047-017   32005    32005JRRS  2  Stem Bearing  $35.33  $36.18       $22.74

*"Koyo taper roller bearing, rubber seals"

totals for 2 bearings (steering stem top and bottom)         $70.66  $72.36       $45.48

Links:

Steering stem bearing sources:
https://www.partzilla.com/product/kawasaki/92047-017

https://www.kawasakipartshouse.com/oemparts/partsearch/kawasaki?partsearch=92047-017%20

https://www.qualitybearingsonline.com/32005jrrs-koyo-25x47x15mm/


I like going with a bearing supply house as it makes me feel like I know what I am getting. A little more than the cheapest but, I like to think, worth it!

hf175w.jpg
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Re: HopFrog's 1980 KDX175 Build Log

Post by KDXGarage »

Same as always, good job!

Be sure to get the old bearing races out of the frame and install the new ones. I doubt that is something you were planning at this level of a rebuild, but just throwing it out there since I have seen several people do it.
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Re: HopFrog's 1980 KDX175 Build Log

Post by Goofaroo »

It looks like he already has them out.

Nice job on the build and the patience to document it so well. It’s coming along nicely!
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Re: HopFrog's 1980 KDX175 Build Log

Post by HopFrog175 »


Thanks! I am trying to do a decent job without going overboard (on time and $$$)! I try and do at least something most days just to keep the momentum up.

The steering stem is apart and new bearings ordered so on to the forks. The tube protrusion above the upper triple clamp is in the book but I like to take photos. Looks around 1-1/8" or 28mm / 29mm. That rust is the top of the tube is the only instance that I can see. The rubber boot is in pieces but the tube looks fine underneath.


Tube on the throttle side
_click image to zoom_
kdx175_00_front_forks_part1.jpg
kdx175_00_front_forks_part1.jpg (155.68 KiB) Viewed 11023 times


It seemed reasonable to remove the fork springs at this point so I took the cap off of the rusty tube. Nothing came out; the spring stayed in place so I looked down the tube.


Inside of the top tube
kdx175_01_front_forks_part1.jpg
kdx175_01_front_forks_part1.jpg (206.02 KiB) Viewed 11023 times


The spacer on the top of the spring was stuck to the inside of the tube - reeeaaallly stuck. Whacking, hammering, pushing, pulling - nothing budged it so I had to resort to task-specific tools :-)


Spring spacer unsticker tool set
kdx175_02_front_forks_part1.jpg
kdx175_02_front_forks_part1.jpg (179.77 KiB) Viewed 11023 times


This got me started but the spacer was so thoroughly adhered to the inside of the tube that I had to resort to small vice-grips. Once they gripped, the spacer did not have a chance - the result is not pretty and I may not be able to reuse it :hmm:


Spring spacer removed
kdx175_03_front_forks_part1.jpg
kdx175_03_front_forks_part1.jpg (193.98 KiB) Viewed 11023 times


I might beat on it for a bit and see but, that failing, it will be replaced with a piece of metal tubing or pvc. (I think pvc will work.)

The other spacer slid right out :-)

Well behaved spring spacer
kdx175_04_front_forks_part1.jpg
kdx175_04_front_forks_part1.jpg (40.02 KiB) Viewed 11023 times


I followed up with fork leg disassembly and I will post it next.
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Re: HopFrog's 1980 KDX175 Build Log

Post by Goofaroo »

It always seems like the simple jobs can be the most difficult.

You can use pvc for the spacers and you’ll probably want to make them a bit longer than the factory ones. If your plan is to use the stock springs they would benefit from some additional preload.
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Re: HopFrog's 1980 KDX175 Build Log

Post by KDXGarage »

Wow. That's odd that they were stuck, but I guess forks setting straight up for years has all the oil drain down. Next time, spray some penetrating oil and go take a break. Let it do its thing. It might help.

PVC will work fine as spacers if they have a size that will fit. Measure the stock amount of preload and go from there.

If the springs are too soft, buy the correct rate springs or just ride it slowly. :grin:
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Re: HopFrog's 1980 KDX175 Build Log

Post by HopFrog175 »

Hmm, I have not really thought through springs yet. On the front, each side can be aired up. Is this to help avoid bottoming? I am guessing this is the case as the force from the spring is fairly linear whereas the force from the psi seems like it would be exponential. That is, the spring force would be about the same from start to finish but the psi increase would start slowly then go up quickly at the end (full compression).

I think my approach will be to go with factory settings to start with and add if/when needed. By add, I am thinking adding more preload, psi and/or up the oil viscosity if my speed/abilities get to the point where the forks are bottoming a lot.

On the rear, I did read a little somewhere and I figured to just set the sag and try it. The stock shock has no adjustments. It still has pressure and I can feel damping if I work it by hand but it it starts to leak, or if the damping is to slight, I will have to figure out what to do at that point. Probably check around a find a shock that is a dimensional match and try to dial it in to work (or check with one of the shock outfits but they are likely too $$$ to really consider).

Does this sound like a reasonable approach? I weigh in at 155lbs and figure about 20lbs for gear, tools, water plus extra gas on occasion.
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Re: HopFrog's 1980 KDX175 Build Log

Post by Goofaroo »

That’ll work. You can modify it later if you want to.

You can pretty much assume the fork springs are somewhat fatigued by now. I’d add about an inch of preload with a longer spacer. It’ll put you in the ballpark and certainly good enough to go hit the trails. You don’t want to add air. You control the amount of compression of the captured air in the forks with the oil level. More oil equals faster compression of the lesser amount of air. Use the highest volume of oil recommended. I don’t know what viscosity is recommend but I would start with 10 or 15wt.

Even in stock form your bike will run a brisk pace if it has the right person on it. It’ll be a really fun bike when you get it done.
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Re: HopFrog's 1980 KDX175 Build Log

Post by KDXGarage »

Skip adding air if you can. It does ramp up as you stated. More oil will mean less air volume. If you put too much oil, it will not be a pretty sight when it blows past the seals. :-)

On damping rod forks, heavy oil is used to control rebound. I think Fredette used to say 7.5 weight on the 86 - 88 forks (maybe 1989 - 1992 also? not sure)
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Re: HopFrog's 1980 KDX175 Build Log

Post by HopFrog175 »


I did some work on the forks waiting for the steering stem bearings to come in.

Each fork assembly slid out of the triple clamps pretty easily and a close inspection I did not find any bad damage. The upper (inner) tubes had no rust or dents and slid smoothly into the lowers. The drain screws are frozen, the impact screwdriver did not budge them. That small parts order that came in had some new ones along with seals so I just need to not damage the threads or seat removing the old ones.


Fork tube assemblies removed
kdx175_00_front_forks_part2.jpg
kdx175_00_front_forks_part2.jpg (187.53 KiB) Viewed 10995 times


While inspecting I found a hex-head bolt in the bottom. I did not have a socket-hex that size so found a hex wrench that fit, slipped an extension over it and used a strap wrench on the lower outer tube.


Trying to disassemble a fork tube
kdx175_01_front_forks_part2.jpg
kdx175_01_front_forks_part2.jpg (281.66 KiB) Viewed 10995 times


Turned and turned, nothing came apart tho :hmm: time to consult the manual and read the internet. It turns out this is not the way to do it - oops :lol:

Following online advice, dug out a 5/8" hex-head bolt with a 15/16" head and pinned it into the end of a four-foot piece of emt (the pin held but just). I could feel the receiving end but the 15/16" head would not quite fit but a little grinding fixed it;


Fork disassembly tool
kdx175_02_front_forks_part2.jpg
kdx175_02_front_forks_part2.jpg (292.56 KiB) Viewed 10995 times


Ok, try number two worked!


A fork disassembly technique that worked
kdx175_03_front_forks_part2.jpg
kdx175_03_front_forks_part2.jpg (108.83 KiB) Viewed 10995 times

The other assembly was much quicker to disassemble :grin:

Forks apart and ready for cleaning
kdx175_04_front_forks_part2.jpg
kdx175_04_front_forks_part2.jpg (348.17 KiB) Viewed 10995 times
I need to measure the springs too - if they are too sagged out I might have an excuse to look for a new set.
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Re: HopFrog's 1980 KDX175 Build Log

Post by KDXGarage »

Thanks for the pics. It is pretty wild to see springs with the coils so close together.
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Re: HopFrog's 1980 KDX175 Build Log

Post by HopFrog175 »


Steering stem, part 2

The Koyo bearings came in so I jumped back to the stem in order to finish it up (having too many half-finished sections of a project is a sure way to throw me off stride!). The bearings looked great with the rubber seals nicely attached.


New Koyo bearings
_click image to zoom_
kdx175_00_steering_stem2.jpg
kdx175_00_steering_stem2.jpg (194.68 KiB) Viewed 10972 times


The bearing races got recycled as installation tools for the new bearings by cutting a slot in one old inner race and one old outer race (the KDX175 has the same bearing size for top and bottom). The slotted race can be use to drive the new race and then be removed - the slot makes the removal easier.


Slotting the races
kdx175_01_steering_stem2.jpg
kdx175_01_steering_stem2.jpg (134.75 KiB) Viewed 10972 times


After a little deburring, the slots were ready. The bottom bearing was slid down the stem as far as it would go followed by the slotted race. Then a handy pipe/tube was slid over the stem to drive the new bearing into place. Worked like a charm :-)


Driving the lower stem bearing
kdx175_02_steering_stem2.jpg
kdx175_02_steering_stem2.jpg (216.08 KiB) Viewed 10972 times


Next up: the outer races. I seemed to recall reading the the outer races are countersunk, that they go in farther than the lip of the tube. I neglected to notice on disassembly hence the slotted race to be used as a driver.


Driving in the steering stem outer races
kdx175_03_steering_stem2.jpg
kdx175_03_steering_stem2.jpg (145.29 KiB) Viewed 10972 times


Well, it turns out that on the kdx175, the outer races are flush - no slotted race required. No problem, you can't have too many slotted races in your slotted race box :grin:

I will do final adjustment after the forks are back on.


Stem - greased, installed and ready
kdx175_04_steering_stem2.jpg
kdx175_04_steering_stem2.jpg (275.77 KiB) Viewed 10972 times


Now, back to the forks. They are already apart so, hopefully, it will be straight forward.
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Re: HopFrog's 1980 KDX175 Build Log

Post by KDXGarage »

Good work!

Cool to see one without a VIN
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Re: HopFrog's 1980 KDX175 Build Log

Post by HopFrog175 »


I jumped back to the forks, had them all cleaned up and ready to put together but ran into a stopper - no fork oil :doh:

I will pick some up first chance. In the meantime, I can document a small side job - beating some metal back into shape :lol:

I had two pieces needing attention, the front brake cable guide ring and the aforementioned spring spacer:


Some bent parts
_click image to zoom_
kdx175_00_straightening_parts.jpg
kdx175_00_straightening_parts.jpg (171.75 KiB) Viewed 10958 times


The cable guide came bent from the previous owner and the spring spacer had been so solidly stuck inside the fork tube that I had to bend it to remove it.

I hunted around for a bit, found that steel bar with a taper on the end that I had been saving and figured starting with the hard one made the most sense.


Straightening started
kdx175_01_straightening_parts.jpg
kdx175_01_straightening_parts.jpg (205.58 KiB) Viewed 10958 times


Hammer was applied (and ear plugs) until a cylindrical shape was achieved. The slot is wider because, not really being a metal worker, I inadvertently stretched the metal and the diameter was too large to fit into the fork tube. Cutting a new slot, and the hammering a little more, fixed the problem.


Spring spacers compared
kdx175_02_straightening_parts.jpg
kdx175_02_straightening_parts.jpg (172.02 KiB) Viewed 10958 times


I used the same technique to get the cable guide back into shape. Managed to get just the plastic insert off of ebay - it fit :-)


Cable guide
kdx175_03_straightening_parts.jpg
kdx175_03_straightening_parts.jpg (211.65 KiB) Viewed 10958 times


Mounted on the top triple clamp (I think this is the right spot) and it looks ready. Another item crossed off the list.


Mounted
kdx175_04_straightening_parts.jpg
kdx175_04_straightening_parts.jpg (169.93 KiB) Viewed 10958 times


Now, I really am ready to get back to the forks!
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Re: HopFrog's 1980 KDX175 Build Log

Post by KDXGarage »

Great job on the spacer. That's going all out.

Some used to suggest a safety wire to keep the ring in place.
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Re: HopFrog's 1980 KDX175 Build Log

Post by HopFrog175 »


Safety wire, yes! I do have a safety wire day planned. I typically overwire and do more than really needed (a habit I picked up after the bolts came loose on a Muncie front bearing retainer - had to pull the 4-speed in a parking lot :-)

So, I picked up with the forks. "Might as well measure the springs," I thought. Hah - mental note: always measure the springs as soon as you pull them out :whistle: Both springs measured below the specified 592mm minimum. Ok, time to round up some new springs.

While figuring springs out, might as well finish the rear brakes. The first round of business was to replace the rear brake torque rod needle bearing that is fitted to the backing plate. The old one was worn and rusted. They are unavailable from the dealer so that left ebay or a bearing supplier. The size is 12x18x16mm. I ended up buying one through Amazon:

Code: Select all

Size:               12x18x16mm (id x od x width)
General part no.    SKF HK 1216
Alternate pat no.   SKF HK 1216.2RS
Alternate pat no.   HK 1216-2RS-L271

Rear brake torque rod bearing
_click image to zoom_
kdx175_00_rear_hub_brakes.jpg
kdx175_00_rear_hub_brakes.jpg (188.98 KiB) Viewed 10945 times


Tapped the bearing in to get it started and then used the press.


Bearing installed
kdx175_01_rear_hub_brakes.jpg
kdx175_01_rear_hub_brakes.jpg (284.73 KiB) Viewed 10945 times
kdx175_02_rear_hub_brakes.jpg
kdx175_02_rear_hub_brakes.jpg (162.17 KiB) Viewed 10945 times


New o-rings for the hardware: one on each side of the needle bearing and one for the brake pivot shaft. The needle bearing o-rings go in the two end caps. I did not know they existed until I cleaned off 40-yrs of crud and found the old ones. They definitely needed replacement although, amazingly, the were still a little bit stretchy.


New o-rings
kdx175_03_rear_hub_brakes.jpg
kdx175_03_rear_hub_brakes.jpg (217.37 KiB) Viewed 10945 times


New brakes all cleaned and pivots greased, this part is ready to install!


Rear brakes ready
kdx175_04_rear_hub_brakes.jpg
kdx175_04_rear_hub_brakes.jpg (387.3 KiB) Viewed 10945 times
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Re: HopFrog's 1980 KDX175 Build Log

Post by KDXGarage »

Good job! Don't forget to grease the pivots and spring ends.

Thanks as before for taking us along on the rebuild ride.
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Re: HopFrog's 1980 KDX175 Build Log

Post by HopFrog175 »


Progress on the forks, I left off after discovering springs sagged out of tolerance. Some of the older KDX's are listed as having 30mm dia fork springs so when mine measured a little under 30mm I figured I was set. Still, I wanted to talk to someone to make sure I was on the right path so I called RaceTech and ended up talking to Matt.

I told him that I thought the springs were 30mm even though they measured a little under. Nope, he said, they are 29's which nobody uses. He put me on hold to "dig around" and came up with some 28mm springs with an acceptable rate of 0.40 kg/mm and a length of 490mm. It turns out that they have similar travel as the old springs even though they are shorter - evidentially, newer springs are made from metal with superior properties when compared to springs from 40-years ago. The wire is thinner so you get more travel per unit length. You just have to replace the original preload tube with a longer one,

The springs came in a day and looked fine.


RaceTech FRSP 284340
_click image to zoom_
kdx175_00_racetech_FRSP-284340_springs.jpg
kdx175_00_racetech_FRSP-284340_springs.jpg (369.83 KiB) Viewed 10888 times


I also got the fork oil (5wt) and was ready to go but then looked at the new spring preload spacers: a couple of pieces of 3/4" PVC. My immediate task was to figure out what length to cut them to. This led to checking around and sifting through stuff to get a grasp on which way to go. Everyone reports that the KDX front is too soft for anyone over 120lbs. I am 155 but am in the novice category for dirt so I figure to start softish and build up as needed. To this end, I am thinking using the 0.4 springs with light preload (4mm) and 5wt fork oil. When I get to the point of checking fork sag, hopefully, I can adjust the preload to get it close. And, if damping is to little, I can always move up to a heavier fork oil.

I will do a write up on all of the details of the springs and setting the preload.

The forks - they are half way assembled, hoping to have the front end back together in a day or two.

hf175w.jpg
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Last edited by HopFrog175 on 01:42 am Mar 29 2021, edited 1 time in total.
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Re: HopFrog's 1980 KDX175 Build Log

Post by HopFrog175 »

KDX175 Front Fork Spring Details

Mar 28, 2021

KDX175 - New Fork Springs
RaceTech FRSP 284340
                                                      My              My
                                    New            original         KDX175
                                   KDX175           KDX175      with new springs
--------------------------------------------------------------------------------

Fork tubes ......................   36mm              36mm           36mm   

Fork Spring condition ...........   spec       41 yrs-old - sagged   new
Fork spring length .............. 600-625mm          573mm          430mm
Fork springs minimum length .....  597mm            under min      unknown
Fork springs outer diameter .....   29mm              29mm           28mm
Spring rate ..................... .35-.38 kg/mm      sagged       .40 kg/mm

Spring spacer length ............   80mm              80mm          214mm
                  OD ............  27.5mm            27.5mm     28.7mm (3/4" PVC)
                  ID ............  20.3mm            20.3mm           ---
Fork cap protrusion into tube ...  27.8mm            27.8mm         27.8mm
Preload .........................  unknown           unknown         4mm

Fork oil ........................    10wt            unknown        7.5wt
Fork oil height (forks extended).   531mm             531mm         531mm


Notes:

 - the manual states: forks extended with springs removed when measuring fork oil height
 - the original fork springs have a 29mm diameter (unusual, hard to find)
 - replacement fork springs can be 28mm
 - original springs were much longer than today's replacements - 600mm vs 430mm
 - KDX175 fork bushings are integral with the lower fork casting (not replaceable short of machine work)



For the spring preload, I settled on starting with 4mm and then moving up later if/when needed. The fork cap protruded into the fork tube a little over 27mm so the top of the spacer needed to be 4mm higher.


Preload calculations
_click image to zoom_
kdx175_preload_calc.jpg
kdx175_preload_calc.jpg (231.41 KiB) Viewed 10888 times


The steps were to insert the spring, washer and the overly-long PVC. Then, mark the PVC at the top of the fork tube. Remove the PVC and measure down from the mark by the calculated amount (23.8mm in my case) plus the thickness of the top washer and make a second mark. This is where to cut. I forgot to add in the thickness of the top washer but it still came in close enough and it is easy to add additional washers for fine tuning.

hf175w.jpg
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Last edited by HopFrog175 on 02:15 am Apr 02 2021, edited 1 time in total.
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Re: HopFrog's 1980 KDX175 Build Log

Post by KDXGarage »

While reading about the springs, my burst out loud comment was, "Please tell me you bought them!" :-)

Good going.

A couple of considerations, I would suggest 7.5 weight (mix of 10 and 5).

Also, the original oil quantity is based on those springs and a different spacer. You have less spring metal taking up space, but more spacer volume, so it may be OK with the stock oil quantity. You might have to play around with that.

You are going to be world's better than what was stock. A source for KDX175 new fork springs, AWESOME!

Some of the KDX's had stiffer springs than other models and years. A 1995+ is 0.35 Kg / mm rate, but 1989 - 1992 is just 0.30 Kg / mm. Ridiculous!

Are you 155 in full gear or is that 155 plus the weight of gear, water backpack, tools, spare partss, etc. ?

As always, thank you very much for posting all this. It could help people for years to come.
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