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New Rear Shocks - CM450E

tomeben

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Joined
Mar 30, 2021
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Location
Cobden IL USA
Since the rear shocks will go on as soon as I have the swingarm back in place, I thought I should solicit (can we do that here?) suggestions for dialing them in before I get that far. All comments and suggestions are welcome, and appreciated, and thank you. Here's what I got... old shock for ref.
https://4into1.com/adjustable-black-chrome-performance-cnc-shocks-eye-clevis-320-330mm/

shock oldnew.jpgShock top.jpgShock bot.JPG

Adjustments are Preload via the top, similar to the original lower spanner adjustment. And Rebound via the lower knob labeled Fast/Slow. I cannot turn the upper adjustment by hand without the included tool, but I can turn the bottom knob very easily with my fingers.
So aside from go ride it and see what I like, what are the basics; too little or too much of what will put me in the weeds?! I won't be scraping pegs, I want to be safely confident the rear end is going to stay where it's supposed to. I've been riding on what I'm sure are the original shocks, I couldn't compress them against the floor by hand, so likely I have no idea what I'm in for... as in how well the bike could ride. Cheers.
 
For the preload you set it up for what's called sag. You'll need 2 helpers for this, 1 to hold the bike upright and one to measure.
Bike upright w/o rider you measure from the ground to a fixed point on the rear of the bike. Now sit on the bike and have the 3rd person make the same measurement as before. Adjust until you get either 1" of sag or 25% of total shock travel, whichever is less.
Rebound is a bit trickier. It's more done be feel or seat of the pants engineering. Fast rebound means the shock allows the spring to bounce back to full length quickly while slow means it is slower to react. The faster it's set the squishier the rear feels on bumps while set slower can make it feel like a rigid frame. I would set it where it "feels" good and then take a couple hard fast corners. If it feels squishy or unstable thru the turns then slow the action of the shock a little and try again.
 
Note of CAUTION:
If you purchase these shocks, or any similar, with an aluminum lower clevis attachment, be very, very sure you have your lower mounting bolt and the clevis threads perfectly aligned before you torque them to spec… all of 22-29ft lbs on a CM450.
Here’s what happens if you don’t:
92243b7323d48129c92228f826032f48.jpg

The threads strip right out.
I haven’t decided whether to re-install the old shocks for now, and hoping I can easily get replacement ends - I’ve emailed 4-1, and have also seen them on eBay and Amazon.

Tom - 1982 CM450E
 
Tom....
First you'll need to use a correct length bolt (NOT the original) Its active length MUST be as long as the outside to outside measurement of the clevis....
Plus, the torque specs for steel into aluminum are far less than steel into steel......
 
Last edited:
Tom....
First you'll need to use a correct length bolt (NOT the original) Its active length MUST be as long as the outside to outside measurement of the clevis....
Plus, the torque specs for steel into aluminum are far less than steel into steel......

Thanks, Steve… that’s a big help, and though obviously I didn’t know, it makes complete sense when you explain it. As noted, I’m still learning, and I certainly appreciate the guidance.


Tom - 1982 CM450E
 
I found this…
https://www.futek.com/bolttorque/metric
Using a M8x1.25 (grade 5) bolt in this calculator, I’m getting 13.5 ft lbs with a base (thread) material of either steel or aluminum. Confusing, since the FSM clearly states 22-29 ft lbs for original steel/steel(?) lower shock mount. Am I reading something incorrectly? Ideas, suggestions?
Snug the bolts tight, and call it good?

(EDIT: The lower shock bolt is M10-1.25x30, not an M8. Ran it through the calculator again, with 5mm thread engagement in aluminum, and got 13.3 ft lbs.)

Tom - 1982 CM450E
 
I've never used shocks with aluminum lower mounts, but this is one of those examples of why I use a good "feel" when tightening most components other than engine parts, and ignore most torque values for general/frame-related fasteners like this. If you've turned enough wrenches in your life (and you certainly are no stranger to tools), you usually develop physical "experience" with certain size bolts and nuts in most, and many times even some specific, situations and you can usually feel when it's tight and time to stop tightening more. Torque values can sometimes cause you to overthink a situation IMHO.
 
Torque values can sometimes cause you to overthink a situation IMHO.

I agree, and I’m good for a bit (maybe a lot…Lol) of overthinking. My brain says it’s a shock mount so it should be secured appropriately, and I completely missed the “oh, it’s aluminum, be careful”. Another clue should have been the FSM giving no value for the top mount other than “securely”. And they stripped well before 20 ft lbs, so the 13 may be accurate.
No worries, it’s why I’m here… and still learning. I always appreciate the feedback, thank you!


Tom - 1982 CM450E
 
Add the depth/spacing/additional length for a split lock-washer and a flat washer under the head, to the bolt length....

Snug only until the lock-washer gets even/flat/closed.....
 
Add the depth/spacing/additional length for a split lock-washer and a flat washer under the head, to the bolt length....

Snug only until the lock-washer gets even/flat/closed.....

That’s it… perfect! Thank you.
(I had considered not using the threads in the clevis, and going with a longer bolt and lock nut, but neither the bolt head nor nut will clear the sprocket on the left side.)


Tom - 1982 CM450E
 
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