"cartridge emulator" front suspension damper notes

ccolwell said:

Hope this helps.

https://forums.bmwmoa.org/showthread.php?42105-Gold-Valve-Emulator&highlight=gold+valve+emulator

It made a huge difference on my bike. Well worth the cost in money and time.

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gtgt_bangbang said:

Read enough good to great things about Race Tech's Cartridge Emulators to add to Must-Have list.

Emulator is a spring-controlled check valve / flow controller which is inserted between the original (modified) damper rod and (stiffer, shorter) main suspension spring.

A cartridge kit "specific" for 36mm BMW tubes is ~ $220 from racetech direct , which seems a heck of a lot for what it is but I didn't spot any cheaper sources.

The PN is basically an indicator of diameter , the "33xx" being correct series for 36mm OD tubes,
and there is a less-specific kit that can be had for ~ $140 (genuine. ) which still seems a hecka lot , but enough less to take the leap.

I talked to MFG's tech rep who said the less-specific kit will work fine in the beemer (oi, have to make your own 1" spacer / bushing; easy do)

Will know more today but the "BMW" kit I think just added some short tube spacers to the box.

note - the RT springs came with a short length of stout plastic pipe, a little more sturdy than the usual hack of sched 40 3/4" PVC,
which should be long enough for the required distance pieces plus pre-loaders

Seems to be sufficient info on the MFG's site, and tuning/adjusting the cartridge is a very normal thing to do, (valve spring rate & settings, check valve port size/count),
to make the cheaper kit work jess fine

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Visian said:

where this spacer is suppose to sit. Just wanted to make sure. Ian

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The emulator needs to sit 'sufficiently clear ' of the top tip of the damper rod,
to eliminate any interference between damper rod & lock nut protruding from bottom of emulator.
Iinterference there could create a leak path around emulator's valving.
Also need enough gap to assure no throttle / choke-points against oil flow , up from rod tip through the emulator.

Only a wee bit of clearance is sufficient ( rod ID / 3 )

While many bikes have CUP seats on the rod top ( which allows for non-interference & emulator seating w/out additional parts)
the top tip of the BMW rod will still be a raised stub, , ~1" high , even after "decapitating" the tip for flow purposes.

Thus a spacer required where shown, between damper & emulator

I think the "kit" / BMW specific version (3308) mainly adds a pair of aluminum tube spacers to the box, and while I'm sure its a very nice spacer,
for 80 bucks extra and me being too lathe-poor to make my own, I was going to have MetalSupermarket rough cut some AL tubing ( there is a perfect size stock tube for this) , to be finished @ home by flat sanding,

However the RTech springs came with a heavy wall PVC tube for preload spacer,
which ought to be long enough to take make a couple of these spacers AND for preload spacers.

I figure light wall (sched 40) 3/4 PVC worked well for decades , and there being zero mechanical / duty difference whether a spacer is placed above or below the main spring. (spacer of course usually sits atop of main springs, just to simplify measurements & access )

The OD of the spacer just has to allow sitting free movement inside the fork tube ID,
and the spacer ID has to be large enough to accept the little shoulder on the emulator.

Any spacer requird will ALSO add to the overall spring " height " , as far as preload measurements ( as does the emulator body itself) ,
so that the upper limit to new spacer length, assuming you still want a gap on top, to adjust preload above main spring as usual.

You could easily just make a lower spacer do both the as BMW-specific solution AND the preload spacer, but I think I'll use top and bottom pieces.

Im still presuming the RT springs are short enough to allow for any lower spacer + emulator + and a bit more short for preload tuning (as opposed to your springs that stood out of fork tubes unloaded)


The adaptor needs to seat well enough on the damper rod shoulder to avoid significant leaks between the two pieces
( a leak there could ,again , short-circuit around the emulator / valved path),

so I'm going to grind the plastic spacer & steel damper seat together with a little valve seating compound to assure a well conforming joint.
The main spring presses the emulator & any spacer down tight on the damper tube, so no need to get too too carried away with seating,
as long as the valved path flow is >> than any leak flow, the emulator will do its job

Visian said:

...pre load spacers...

Ian

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OldCamper said:

: why mess with the valving at all?

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