Thread: ORGS build up
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Old 10-08-2010, 10:34 PM   #78
x3300 OP
Joined: Mar 2005
Location: San Jose, CA
Oddometer: 170
Monolever Extension

I did some hunting around the Internet and took a few trips to local MC dealers with a tape measure in my pocket to collect some info on rear suspensions. I'm not sure of how wheelbase is measured, but I put down what I measured with the bike supported and the suspension topped out, plus an adjustment for the longer swingarm. Here's the tally; wheelbase, travel front and rear, swingarm length, final drive ratio:

bike       wbase   front  rear   salen  final

R80G/S     1465    200    170    410    3.36
CRF250R    1478    315    315    ?      -
R100GS     1514    225    180    455    3.09
R1200GS    1520    190    200    533    -
F800GS     1577    230    215    622    -
HP2        1610    270    250    575    -
HPN-Adv    1620    295    240    510    -
ORGS       1622    280    280    535    2.91
It seems 100mm is a common monolever swingarm extension. I wanted to get some more travel and figured I'd try 125mm, so 80mm more than the max of the R100GS paralever swingarm.

I marked the cut with a Sharpie pen, put the arm in the fixture, then went at it with a hacksaw. I put the cut where the swingarm tube runs exactly parallel to the centerline of the bike so that both swingarm tube and the extension tube ends would need 90 degree cuts.

Here's a view of the section.

The 2"x1/16" tube I mentioned in the previous post was intended for the cross brace. I bolted the back end of the arm at the 125mm index of the fixture then measured the angles the cross brace would need. I set the brace to give the maximum support and have just enough clearance to fit an 18" wheel.

I used this hole saw and a vertical mill to cut the tube ends. I set the head at the needed angle then made the cut.

The hole saw wasn't long enough to cut straight through the tube, so I needed to cut until the saw bottomed, remove the tube from the vise and cut off the scrap, and then remount the tube and continue with the cut.

I drilled this small hole in the bottom of the brace to vent the tube while welding.

Here's the arm and additions cleaned up and ready for welding.

I used masking tape to hold the extension in place for tack welding. I cut out small sections of tape and made the tack welds.

I used this big C-clamp to hold the brace in position for tacking.

There wasn't much room between the bottom of the arm and the fixture so I needed to use this short tungsten cap to get in there.

Welding in progress.

And the finished arm out of the fixture.

I measured the arm before and after welding with this height gage to check the alignment.

Here's the arm installed with a fender and shock mock-up.

I really like the look of the triangle the arm and big cross brace make just in front of the wheel.

I'll need to look into and decide on a shock before setting up the shock mounts.


x3300 screwed with this post 10-09-2010 at 08:13 AM Reason: Update URLs.
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