STOCK UPPER FORK TREE MOD.  -  Observation - comment - caution!

When doing the "famous Gary from NJ" fork mod.,  my upper triple clamp will be a modified stock lower.  I'm in the process of doing that right now.   Again, this is for a modified STOCK LOWER that to become an upper.  This is necesary since you need to have pinch bolts, as the new tube position will be through the upper clamp  (see Garys' picts).  RYCA now offers a upper clamp too.  Gerry made an entirely new upper....way cool looking piece!

Anyway - back to the mod I'm doing on the donor stock lower:

1) Stem removed, cut flush with the top surface of the clamp.  check
2) Steering stops removed and smoothed.  check
3) Stem hole opened to .875, that is SLIGHTLY larger than the stock hole in the upper clamp.  I'm fine with that as it will give a small amount of room for misalignment.   The upper bearing will actually hold the stem in alignment with the frame along with the lower bearing - as by design.  The upper tree will then be sandwiched between the crown nut and the bearing retaining nut. CHANGE:  

I check the thickness of both trees - they are the same at ~ 26.7mm.  I noticed that the stock tree upper, has a spot face relief on the underside where the stem comes through of a depth of 4.86mm.  The purpose of that spot face is to allow the larger OD threads (where the upper stem bearing nut engages) to enter into the underside of the upper tree.  

I checked my new tree then and added a spot relief with a 1" drill.  I had to drill a little deeper to accomodate the angled cutting face of the drill.  I went down ~5 mm.   A little deeper is not a problem, too shallow is.

WITH the spot relief, the top chrome nut will now tighten the upper tree down directly onto the top face of the bearing nut.

WITHOUT the spot relief, the top chrome nut MAY  (will in my case)tighten the upper tree down onto the ramped transistion area or even the top threads of the larger OD threaded portion of the stem where the bearing nut engages.  If so, the upper tree will not bear up against the retaining nut.  This could result in the top threads being damaged; the bearing nut backing off - causing loss of bearing preload and loose head bearings.

FIX:  spot relief - takes more time and effort...but easy to do initally.  If the mod is already done?  Machine a ~1/8"  (3mm)  flat washer that goes between the bearing retainer nut and upper tree.

Reminder of what the stem dimensions are (sorry..no camera today to take a pict.)   From the top down with a vernier on the ODs.:

Chrome crown nut 21.75 mm dia. - 12.5 mm height
Smooth section for upper tree:  22 mm - 22 mm height
Small transistion:  2mm in height
Bearing Ret. Nut: 24.75 mm dia. - 15mm height

As you can see by the dimensions listed, the smooth area for the top tree is smaller than the top tree.

Gary ; comments?    You may have added the relief - I'm not sure, but its something to look for....

Mike


One HISTORICAL note:  "old" style bikes used to have a pinch bolt at the crown nut.  BUT, those crown nuts had sleeves that went through the upper and locked against the bearing retaining nut.  The savage doesn't have this design.  The upper tree just slides over the stem and as the crown nut is tightened, it loads the upper tree down onto the bearing retainer nut, locking it into position.

Hi Gary.

I'm 100% in agreement, that is set up is better than original.

Maybe I wasn't clear in my explanation:

The bottom relief will allow the taper /  larger OD section of the stem to intrude into the top tree "as much as needed".   Its not a matter of the top crown nut having a reduced thead count.  there are plenty of threads available.  The issue is on the bottom of the tree.

The safety issue is IF:  the top tree contacts the little "ramp" section or the bearing retainer threads BEFORE it contacts the bearing retaining nut.

As you said; the top tree is the effectively the "jamb nut" for the upper retaining bearing nut.

I'll have to post a pict.....

here are some picts.  I used a stem and the OEM top.

Picts 1 and 2 are the top and bottom WITH the bottom relief in place, as stock.  You can see that the flat washer under the crown nut is needed due to running out of useable threads!  Relief covers some of the bearing retainer nut threads.

Picts 3 and 4, I flipped to top tree to simulate a "no relief" condition. You can see the "ramp" section prevents the top clamp from going any lower, which many result in the top clamp not jambing the bearing retaining nut.

My camera was dropped, so the picts with the shaded left edge distort the image....   nothing is bent!  lol  

I've got a 1" drill you can use...   OR come on down with the tree and we'll drill it real quick....

OR:  yes, use a 3mm washer / spacer above the bearing retainer nut / below the upper tree to close the gap.  The only down side is you'll have less threads at the crown nut.

.

Here are some photos of the actual assembly. I don't think it's worth shimming.

The adjusting nut is torqued to spec, so there is no movement at the nut nor is there any wiggle. The distance between the bottom of the upper triple clamp and the top of the adjusting nut is 0.039" or 5/128 of an inch.

swing69 wrote on 03/31/15 at 17:07:08:

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Answer 1: I think that the final spacer was 127mm. My length isn't important. You just need to cut the spacer so you are 7mm below the top of the fork tube (fully extended).

Answer 2: The 130mm is measured with the GVE installed, the spring out, and the fork tube at the bottom of its stroke. It's a distance (in mm), not a volume or liquid measurement. I find it helpful to use a syringe with a piece of hose attached so the total length from the bottom side of the top handle to the bottom of the hose is 130mm.



Just rest the syringe on the top of the fork tube and pull up on the plunger until you're sucking air.

As I mentioned a few posts ago, 140mm might be a better value. I don't think I'm getting 90% use of my stroke and the extra 10mm will make a big difference.