Fork damper teardown

Rebuilding the front forks on a ‘73 750, and would like disassemble the dampers to clean out the silt.

Nothing in my manual about it, and I recall reading somewhere to be really careful…the damper tubes are pretty delicate.

It appears that a rod inserted through the holes at the far end while an open end wrench on the aluminum cap would work.

Any thoughts here?

Thanks,
Marc

I am a bit new at this myself, but just finished rebuilding my front forks with new parts including a Landsdowne kit. If you just want to clean the aluminum sliders out, and replace the oil, get the bike in a secure position where you can remove the front wheel. Drain the oil by removing the small screws towards the bottom of the sliders. Or, you can wait for the oil to drain out when you remove the bolts (one on each slider) that are in the recesses at the bottom of each slider that you eill find, after you remove the front axle to remove the front wheel. At the top of each slider there is a retainer under the rubber gaiter. Once you loosen that completely, the slider should come off. You will need to remove the large caps at the top to refill the tubes once the sliders have been reinstalled.

Thanks for the quick response; I’ve got the forks out of the yokes/off the bike and taken apart. Cleaned out the sliders and replacing the stanchions (originals were pitted), bushings and seals.

What left is the spring/damper assemblies. I’ve got one spring off, and paused at the point of removing the aluminum cap to gain access to the inside of the dampers.

I REALLY don’t want to damage these things, but won’t consider the job done without getting the crud out of there.

Check how sloppy the rod to aluminum cap is. If it rattles then replace.
Check the rods for pitting, (Water got in). If they are then they wear out the caps. Then replace.

there is quite a lot of detailed info on clearances : both of the top cap to the rod and the damping cup at bottom of rod compared to internal diameter of damper tube. See JS Norton website and RGM damper components on their website. If these aren’t right, damping will be seriously compromised.

jan nelder said:

there is quite a lot of detailed info on clearances : both of the top cap to the rod and the damping cup at bottom of rod compared to internal diameter of damper tube. See JS Norton website and RGM damper components on their website. If these aren’t right, damping will be seriously compromised.

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Replace the top cap. The clearance is crucial and sadly the aluminium caps quickly wear out of speck. I would recommend you replace them with the RGM cast iron version they last for ever. I fitted a pair roughly 20years ago with no issues so far.

MarcD said:

I recall reading somewhere to be really careful…the damper tubes are pretty delicate.

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The only "delicate" parts would be the alloy cap threads as the steel damper tubes should not be delicate and as already mentioned, the caps are often in need of replacement, possibly also the damper rods and valves.

some damper tubes( go faster versions ) are aluminium.... very obvious!

I bought some new stanchions, and plan to rebuild nothing fancy but improved , I found on JS motorsports https://jsmotorsport.com/product/damper-upgrade-kit-for-roadholder-forks/ , which might last longer .

MarcD said:

Thanks for the quick response; I’ve got the forks out of the yokes/off the bike and taken apart. Cleaned out the sliders and replacing the stanchions (originals were pitted), bushings and seals.

What left is the spring/damper assemblies. I’ve got one spring off, and paused at the point of removing the aluminum cap to gain access to the inside of the dampers.

I REALLY don’t want to damage these things, but won’t consider the job done without getting the crud out of there.

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If your using all the stock parts , you can swell up the size of the piston with a taper ,this helps the rebound I think , also you need a good cap and damper rod . There is technical info on JS Motorsports website.

To get the alloy damper cap off, grip the bottom of the damper assembly (the solid bit) with soft jaws in a vice. Gently heat the alloy damper cap with a blowlamp and using a good fitting spanner undo it. Never had one fail to undo doing it this way.
I close up the clearance of the piston using a short tapered punch to make the piston slightly bigger (as shelby right has said) Enables you to use thinner fork oil than the 20w50 that was std.
If the damper rod has suffered corrosion, clean and emery it back to bright metal. Even if the alloy caps clearance to the rod is slack, the resized piston will try to force a lot more oil through the cap to rod gap so using 20w50 will still have good fork action.
As a test, assemble the (clean but unmodified) damper and rod, and put the end of the damper in a cup of 20w50 oil so the oil is at least halfway up the damper. move the damper rod up and down to pump oil through the damper tube till it comes out of the alloy cap.
Dissemble and modify the piston (make it bigger so it just slides up and down the damper tube) Repeat the test. you will be amazed at the difference. So much so you will be using thinner fork oil.

JS says aim for 3-4 seconds to pull rod upwards, while assembled damper immersed in 20W fork oil