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KYB / SSS Fork Lug Measurement

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Fork Lug Measurements for SSS forks - There are some well known measurements for Honda's (33mm) and KTM's (35mm until 2016 when KTM changed to 33mm and a smaller axle).  But what about YZs?  I read 30mm, 32mm and 35mm depending on year and whether 2-stroke (YZ) or 4-stroke (YZF).  My crude attempts to measure with a plumb bob showed 30mm for my 2008 YZ250F forks (forks were off the bike and held vertical).  I have NO confidence in this measurement - it's just to imprecise.  Most data on the Web (yeah, I know!) gives this measurement as 32mm.  If you have made this measurement please post how you did it (if you did it mathematically I can follow that logic as well).  If you got the info from a tuner or manufacturer that is good to.  Any data for brand would also be welcome.

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Do it this way, measure the following carefully with a good caliper (example dimensions are from my KYBs):

Dim A = dia of the lower thin wall part of the foot, should be 33mm
Dim B = height of the small casting rib on the rear of same foot section, approx .25mm
Dim C = axel bore. easy at 25mm
Dim D = the distance from the inner ID surface of the axel bore to the top of the small rib on the rear of the foot, approx 36.5mm

The idea is to get good numbers on easy to measure surfaces and calculate the tough one to actually measure accurately.
Offset is the distance from fork tube center to axel center, so we use the dia of the foot and axel to calc them, and reference with D minus the rib height. The KYB is much easier due to the smooth casting, but same principle applies.
 

Offset = D-B-A/2+C/2
=36.5-.25-33/2+25/2 = 32.25mm

 

Older natural, heavier cast lugs will be 35mm offset, newer brown color thinner wall lugs will be 32mm offset.

There are different lengths as well
 

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The older 35mm lugs are 06/07 in the SSS I believe the AOS fork on the 05 is as well. 08/09 are 32mm but are natural aluminium in colour the brown 32mm lug was not around til 2010. Not sure on any of the older oc forks was only interested in SSS. 

MM 

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The year of lug offset change varies with displacement, as does length, and upper tube dia. All this info is on Betarider somewhere in a conversion thread.

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I just measured a '07 YZ250 fork leg by 2 different methods:  one using a plumb bob and the other using a 1" dowel in the axle hole with a centered mark formed on my lathe.  One measurement was 32.5 mm and the other was 32.4 mm.  Close enough to the measurements provided above.  Even SHARP pencil marks will cause more error than than the difference found in my 2 measurements.  The only problem is that it was stated that the earlier SSS forks has a lug offset of 35 mm; that doesn't seem to be the case with the '07 YZ250 2-stroke forks.

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I made a template to make this measurement on SSS forks.  This 'L' shape template allows a measurement to be made in the same plane - 32mm is correct for these '07 YZ250 forks.

 

IMG_0003.JPG

IMG_0004.JPG

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Hi Glenn, I found the center of the lug by running a string from the top compression screw to the bottom rebound screw. I found that the non-brake fork has a grub screw on the center-line as well as a cast-in mark on the lug itself - this is the mark that you see in my measurements. Note that my template has an offset (it is "L" shaped) so I can keep the measurement in the same plane. Armed with my own measurements I went back and made the measurements according to your directions (included below for everyone else). I never did figure out Dim B (you list as = height of the small casting rib on the rear of same foot section, approx .25mm) but the other measurements were the same as yours so I agree that your method works wonderful - pictures would be nice to help get the correct measuring points. Your original directions follow:
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Do it this way, measure the following carefully with a good caliper (example dimensions are from my KYBs):

Dim A = dia of the lower thin wall part of the foot, should be 33mm
Dim B = height of the small casting rib on the rear of same foot section, approx .25mm
Dim C = axel bore. easy at 25mm
Dim D = the distance from the inner ID surface of the axel bore to the top of the small rib on the rear of the foot, approx 36.5mm

The idea is to get good numbers on easy to measure surfaces and calculate the tough one to actually measure accurately.
Offset is the distance from fork tube center to axel center, so we use the dia of the foot and axel to calc them, and reference with D minus the rib height. The KYB is much easier due to the smooth casting, but same principle applies.

Offset = D-B-A/2+C/2
=36.5-.25-33/2+25/2 = 32.25mm

Older natural, heavier cast lugs will be 35mm offset, newer brown color thinner wall lugs will be 32mm offset.
There are different lengths as well.
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Edited by kenpowell

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