MXR Stock AER48 Valve Stack

TCMB371

The Silent Assassin
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Location
Temecula, CA
#1
Just for reference, here are the stock valve stacks for the AER48 on the MXR's.
(In my opinion, it was way under-damped for anything more than easy vet style motocross tracks).

All shims are 6mm ID.
Synthax is [ShimDiameter(mm)].[ShimThickness(mm)]
Topmost number is the piston facing shim.

Base Valve - Compression

30.10 (x6)
22.15
30.15
28.15
26.15
24.15
22.15
20.25 (x2)
baseplate (25mm x 1.5mm)

Base Valve - "Rebound"

31.4 (slotted bleed shim)
10.05
18.40 (x3)
7mm nut

Mid Valve - Compression

30.10 (x6)
28.15
26.15
24.15
22.15
20.15
18.15
16.15
14.15
16.10
18.20
20.20
22.20
24.20
plate (25mm x 1.5mm)

Mid Valve - Rebound

28.10 (x4)
26.10
24.10
22.10
20.10
18.10
16.10
14.10
12.30 (x2)
baseplate (18mm x 3.0mm)
7mm nut
 

TCMB371

The Silent Assassin
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Location
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#3
One immediate mod i did... the fork needs more low speed compression damping, and ultimately more compression damping overall.

As a quick and easy modification, i suggest changing the 6x 30.10 face shims on the base valve over to 5x 30.15 shims, and soak up the extra .15mm of total stack height by removing the last 20.25 shim and replacing it with a .10 shim of equal or greater diameter. This will increase the low speed a bit, but also add high speed damping as well.

Given the same diameter,.15mm thick shims are 3.375x stiffer than .10 shims.

5x .15mm thick shims = .75mm tall lowspeed stack
6x .10mm thick shims = .60mm tall lowspeed stack

(.75/.6)^3 = 1.95x stiffer. In reality its a little less because the 6x .10mm shims will have a little extra deflection friction than the 5x .15 shims due to more surface area contact, so we're probably looking at around 1.5x stiffer or so.
 

Don Thuren

Well-known member
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62
Location
Bend, Oregon
#4
I have a different definition technique regarding damping terms compared to most.. Again, just my way of tuning/thinking.

Low speed damping = Free bleed
Low-mid X-over damping = Any staged valving/transfer shims/flutter
Mid speed damping = Larger face shims and/or the middle of the pack
High speed damping = High shaft speed flow restrictions(Ports/Large OD fulcrum shims/very thick shims)

Anyway, this makes me curious about that base valve rebound bleed shim... That thing could be making the fork feel very loose and wallowy!

EDIT: To add, me personally if that bleed shim flows both ways(not checked) I would call what you did adding more mid-speed support.....
 

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