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Old 04-11-2012, 02:23 PM   #52
FJ_Kevin OP
Gnarly Adventurer
Joined: Dec 2010
Location: Maryland ==> originally from Long Island
Oddometer: 365
Well, I am finally back to the 465 project after taking a break to finish this years taxes ... and yes I had to pay even more, and yes it was very very painful!!!

On to to more pleasant topics, I ran across this nice fold out brochure for the 1980 YZ lineup. It has some great illustrations, especially of the rear monoshock suspension where I have been focused the last few days...

Next are some photos of various shock absorbers I have in my possession. The 1st photos shows (top to bottom),

-1980 YZ465 shock with standard spring and short reservior
-1981 YZ465 shock with stiff (marked with blue paint) spring and long reservior
-1981 YZ465 shock with standard spring and long reservior
-1982 YZ490 shock with Eibach spring and long reservior

All the shocks have adjustable rebound damping via the adjuster knob on the left. The 490 shock also has adjustable compression damping via a knob on the right (not shown in this photo). In addition, the 490 shock has a greater number of rebound damping settings from which to choose.

My first task was to take the springs off in order to determine overall condition of these units. I found the shafts were good on all of them, however, it was evident that two of the 465 shocks needed a nitrogen charge and all but the 490 shock needed new rubber bumpers.

There were a few pleasant surprises too. First, the 490 shock (with Race Tech decal) was in great condition. I also found the springs for the 465 shock fit the '82 490 as well. This is important because of the difference in the 465 and 490 suspension design. The 465 uses a spring made from a tapered wire to get a progressive spring rate. The '82 490 uses a link to give a rising (progressive) rate suspension with a constant rate spring.

I found too that the Eibach spring was much, much stiffer than the 465 springs. My guess is that it is much stiffer than a stock 490 spring. Fortunately, there was the firmer (blue) progressive 465 spring (no longer available from Yamaha) also in the bunch. The standard 465 spring felt soft and pretty well sacked out whereas this firm one seems just about right for me @180lbs.

Here is a photo of the springs. Left=Eibach 490, Middle=Firm YZ465, Right=Stock YZ465

And here is a photo of a nice looking '82 490 showing the rear suspension link (the '83 on is even more different).

It is unclear to me is if the differences in the 490 shock damping action as a result of the '82 link setup are enough to hinder performance when used in the YZ465. In any case, given the very wide and noticeable adjustment range and great condition of the 490 shock, I decided to give it a try.

Note that the 490 shock requires some reduction in the front shock bushing width for it to fit in the 465 frame. I also had to insert 0.5 inch spacers in the front tank mount to give some additional clearence for the compression damping knob under the tank. And finally, the 490 shock is about 0.5 inches longer than those in the 465 and gives a wee bit more suspension travel.

Here are some photos of the 465 shock setup compared to the 490 shock as they are mounted in the bike. Notice the compression damping knob on the 490 shock.

- The 465 shock...

- The 490 shock...

The tank mount spacers before final machining...

At some point I would like to take a crack at rebuilding the 465 shocks. Please send me a note if any of you have instructions on how to do this.

More to come...

My '81 YZ465 Factory Race Replica

My Vintage Husqvarna/Motocross Restoration Extravaganza Thread
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