The Brave Little Magic Drill Press:Showa internals in Marzocchi forks

[Dietrich]

What follows is a photo journal of my most recent mad project. They said it couldn't be done.  Which of course meant I had to try.  (Also the fact that I'm cheap.)  

Long story short I bought a set of adjustable Showa forks off eBaY that were a little banged up in order to replace the non-adjustable Marzocchis on my Sport Classic GT1000.  I had been trying to improve the stock suspension on the cheap for some time.  Although the model they supposedly came off should have been a direct fit, and the ad said they had been thoroughly inspected for proper operation, they arrived with both legs too long to fit my GT and one leg bent causing binding and leaking oil.

After negotiating with the seller who was reluctant to refund, I eventually got half my money back (since half the forks were good). Still left me with a set of adjustable internals that were too long.  Only on thing to do to keep it under budget…..I set out to install the adjustable Showa parts into a set of stock Marzocchi forks.  All the research I could find online and people I talked to said it couldn't be done, people have tried, etc., etc…..  well, hmph.

Since my bushings are showing a fair bit of wear I was able to score an almost new set of Marzocchis from a friend to be sacrificed for this project.



I determined that I could make everything work, but would have to shorten the damping rod & spring spacer, machine the Zoch's fork bottoms to accept the compression adjustment valve, check the fork cap threads for fit, and even shorten the rebound adjuster parts to clear my low bars since they remain high no matter how the fork is adjusted.  To my surprise the Showa caps threaded right into the Marzocchi fork legs.  More on that later.







First step, shorten stuff.  I measured the difference between the Showas and my forks and shortened the internals by the same amount (but left the spring spacer a little long to add some preload).  I figured out the most cutting I could get away with for the rebound damping adjusters without compromising the oil seals, etc. and went for it.

[Dietrich]

(Later drilled and tapped for set screws for no-budge insurance.)



Home-brew machining arsenal:


I used a 1-1/16” drill bit to clear out the Marzocchi fork bottoms to accept the Showa damper bolt.  I used a same sized forstner woodworking bit to flatten out the hole and so the copper crush washer would seal.  Then drilled out the stock through hole to an appropriate size, 19/32”.

[Dietrich]

I had to file about 4mm of threads on the bottom of the Showa fork cap in order to get it to thread down all the way.  The thread pitch is the same as the Zoch's.





After a test fit I determined that the overall fork travel was compromised by the deeper Showa fork cap.  Just a little trimming of the inner for tubes was required after some careful measurements and comparisons between the stock and new caps.



Nothing like having the help of friends to get this kind of stuff together.



Adjustable fork madness!  If you haven't noticed I took the opportunity to have the upper fork tubes powder coated gloss black.  More on that later.



GT1000 under the knife:





Might as well throw in some Speedymoto tapered roller bearings while you're in there:

[Dietrich]

Install day!  Had a few friends over to wrench on bikes (secret ploy to make sure I had enough spare hands on deck to get these things on the bike…)



Well, I knew this would be a problem, but never expected the TOTAL HEADACHE in getting the powder coated legs to go back in the stock triples.  Ended up filing the top inch of paint back off and doing some…ahem….clearancing on the lower triple to get them in.















Got it!

[Dietrich]

Well, what can I say.  They work.  Was able to take a quick spin around the block, jumping off curbs, etc., and they definitely are much better than the stockers (understatement I know).  I used 5wt fork oil and now will set about fiddling with them until I like where they're at. I now have the option to install new valving and springs if deemed necessary.  I still had to remove the bars to adjust the rebound damping, might have to make a VERY low profile tool to do that with as long as I run these bars.  Love the look with the black uppers, but it was probably not worth the pain to re-install.  I did have an oil leak with one of my damper bolt crush washers that took a little RTV sealant to stop.  Obviously there were a few pitfalls and things to look out for with this mod, proceed at your own risk.   Me?  I'm happy…for now…. 

[koko64]

D. And they said it couldn't be done.

Well done!
Cheers

[GAAN]

wow

[rule62]

I absolutely love being part of the "Magic Drill Press" family.  Glad I could help out today.

[AdamX]

 

[hcomp]

Holy Crap! That is one of the strangest ways I have seen a drill press used! Nice Work!

[Langanobob]

Wow.  Outstanding!  A guy like you REALLY needs to buy a lathe and a mill.

[Michael]

Dietrich, we gotta get our new forks together and go riding!

[moto]

[pennyrobber]

Nice write up. Glad to see it all come together.

[hoyden]

It was much fun watching it all come together over the weeks and helping out!
And they said it couldn't be done. 'Feh' to them!
Great write up.
And what excellent photos!   

[triangleforge]

Breathtaking.