What oil in the forks will produce a smooth ride ?

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slimslowslider said:
Some years ago I made these cross sectional sketches of the fork.
Fully compressed on the left, fully extended in the middle, fully extended with damper cap removed on the right.

What oil in the forks will produce a smooth ride ?


What oil in the forks will produce a smooth ride ?
Click to expand...
These are of course, the best I've seen of the roadholder!
I have not tried to do anything to the compression damping on my forks but I did do some work on the rebound. I made sure that the rod fit snugly in the damper cap. Then I expanded the damper piston (pictured nicely in the left hand drawing attached to the damper rod.) by pounding the correct socket into it. I then finished off the fit by spinning it up against my grinder. Since the damper tubes were worn differently I did not achieve an exactly equal fit of the piston in the left and right fork. I adjusted the rebound damping by adjusting the viscosity of the oil in the two sides. In the tighter of the two sides I put straight Ford type ATF. In the other side I mixed in a bit of non detergent 30w oil. To my satisfaction they both have the same amount of resistance to being pulled upward. The bike rides great and the topping out clunk is non existent.
 
slimslowslider said:
Some years ago I made these cross sectional sketches of the fork.
Fully compressed on the left, fully extended in the middle, fully extended with damper cap removed on the right.

What oil in the forks will produce a smooth ride ?


What oil in the forks will produce a smooth ride ?
Click to expand...
Make a pdf and put them up in resources section. They will live on forever. ;-)
 
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"The King's English once again."

Sadly! :(

Re the forks/parallel, etc. My Norton forks were stiff/not very effective back when I bought the bike in '06.. I rebuilt them and, in doing the re-assembly, discovered that the problem was not the forks themselves. It was the Hyde fork brace that the previous owner had installed. Despite the fact that the Hyde was adjustable, it was not adjustable enough to actually allow the forks to be parallel - which they WERE without the Hyde. IOW, the Hyde forced the forks to NOT be parallel. Whether this was an inherent problem with the Hyde, or whether this particular one was not properly machined/cast from the factory, I don't know. I removed/adjusted/reinstalled the Hyde multiple times with no improvement; I tossed the thing in the trash.
 
I've added fork braces to a couple of bikes and the improvement was noticeable even before I got out of the parking lot. One was a /7BMW and the other a GL1500 Goldwing. Why the factory did not include this is a mystery to me, as the stability prior to fitting the brace was questionable at best. I've never felt the need for a brace on either my Commando or my Atlas. I added a fork damper to the Commando but it was unnecessary. I've heard that the Hyde units were hard to fit.
 
The fork damper that the PO installed was another Commando "upgrade" that I tossed in the trash. Bike handled better without it. It seems that any change to anything OEM is referred to as an "upgrade"...even if it's actually a "downgrade." Go figure. :rolleyes:
 
Expanding the damper piston (AKA damper valve) as motorson explained in post #61 is one way to get more rebound damping. You can also get more rebound damping by cranking up aftermarket cartridge adjustment. But cranking up rebound damping to prevent top out clunk is not a good idea. You don't want too much rebound damping because when you hit a series of bumps your forks won't rebound fast enough for the next bump and then you hit the next bump with the forks already compressed. Better to have a top out hydraulic bump stop for rebound to prevent top out clunck. Fancy cartriges are nice and trick and adjustable but they don't actually work any better than the stock setup with an expanded or oversize damper piston (damper pistons are easy to make). When both types are set to have the same rebound damping - you can't tell the difference.

.680" is the damper valve (damper piston) diameter you want along with 15 wt oil. 20 wt may be too thick.
 
Good posting ^^^ and nice to have the opportunity to experiment at such a modest price too !
 
Why wouldn't just changing the fork oil to a different viscosity achieve the same thing without taking anything apart except the drain plug and top nut? What am I not understanding about this?
 
Thomasa said:
Why wouldn't just changing the fork oil to a different viscosity achieve the same thing without taking anything apart except the drain plug and top nut? What am I not understanding about this?
Click to expand...
Depends on which thing you're asking about, Heavier/Lighter oil has a noticeable effect in rebound damping. There is effectively no compression damping with stock forks so a little more or less is negligible.
 
Thomasa said:
Why wouldn't just changing the fork oil to a different viscosity achieve the same thing without taking anything apart except the drain plug and top nut?
Click to expand...
With the excessive clearances and large holes as standard the viscosity needed to get into the right range may end up being too viscous and no longer a fork oil. So better to get the clearances and hole sizes into the right range for a 20wt fork oil to work well and then you have a good choice of fork oils in the 5wt to 30wt range to adjust to your requirements.
 
Thomasa said:
I've added fork braces to a couple of bikes and the improvement was noticeable even before I got out of the parking lot. One was a /7BMW and the other a GL1500 Goldwing. Why the factory did not include this is a mystery to me, as the stability prior to fitting the brace was questionable at best. I've never felt the need for a brace on either my Commando or my Atlas. I added a fork damper to the Commando but it was unnecessary. I've heard that the Hyde units were hard to fit.
Click to expand...
Fork braces are engineered IN to most bikes. Most people think of it as merely a "fender bracket", not understanding it's rotational twist that needs resisting.
When the OEM fender is binned, and a fiberglass thong is hose clamped on, the original fork brace is gone too.
 
Along with a tighter fitting damper piston you should replace the alum damper cap if its worn. Decent cycles used to sell bronze caps that lasted longer. You can also drill and sleeve the alum caps with K&S 3/8" ID brass tubing (perfect fit) fastened with loctite.

What oil in the forks will produce a smooth ride ?
 
jseng1 said:
o





Got a photo?
Click to expand...
DU Bush

What oil in the forks will produce a smooth ride ?


Recommended tolerances:
- Housing - min/max: 0.3747/0.3753inch
- Shaft - min/max: 0.3106/0.3115inch
Bearing size when fitted:
- Bore - min/max: 0.3117/0.3143inch
Length tolerance +/- 0.010inch

Best to drill and ream to 3/8" before pressing bush in, drilling alone can cause issues with clearances as a 3/8 drill creates a slightly undersize hole for reaming.

I use RGM alloy damper caps, the DU bush removes the issue of galling on alloy so the damper rod can be alloy too. Right is one unconverted, left has the DU bush. You need to check the length of the bush, I just took the first 5/16" DU bush at 3/8 OD and 3/8 Length so 3/8 length could be wrong.

What oil in the forks will produce a smooth ride ?
 
kommando said:
DU Bush

What oil in the forks will produce a smooth ride ?


Recommended tolerances:
- Housing - min/max: 0.3747/0.3753inch
- Shaft - min/max: 0.3106/0.3115inch
Bearing size when fitted:
- Bore - min/max: 0.3117/0.3143inch
Length tolerance +/- 0.010inch

Best to drill and ream to 3/8" before pressing bush in, drilling alone can cause issues with clearances as a 3/8 drill creates a slightly undersize hole for reaming.

I use RGM alloy damper caps, the DU bush removes the issue of galling on alloy so the damper rod can be alloy too. Right is one unconverted, left has the DU bush. You need to check the length of the bush, I just took the first 5/16" DU bush at 3/8 OD and 3/8 Length so 3/8 length could be wrong.

What oil in the forks will produce a smooth ride ?
Click to expand...
So you are downsizing the damper rod from 3/8" to 5/16"?
 
jseng1 said:
So you are downsizing the damper rod from 3/8" to 5/16"?
Click to expand...
No got a bit mixed up with the BSA which are 5/16, so just go for 3/8" ID and 15/32 OD

  • Recommended tolerances:
    - Housing - min/max: 0.4684/0.4691inch
    - Shaft - min/max: 0.3731/0.3740inch
  • Bearing size when fitted:
    - Bore - min/max: 0.3742/0.3769inch
 
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