Georgieboy - Marzzochi fork mods

Joined
Nov 8, 2003
Messages
200
Likes
0
#1
The current crop of 45mm USD forks are very similar to an early showa example.The reason you have a lot of play in the bushings as you have already pointed out is to try and overcome some of the binding that is prevelant in this model. The bushing lan on the chrome tube has not been relieved to allow the bush to flex as it passes through the triple clamp area. If you can take the chrome tubes to a competent machinist and have the bushing area machined the same as a modern KYB you will have a remarkable improvement in the responsiveness and feel of the fork. If you have explored the valving on these forks you will notice that the compression valve is extremely soft while the midvalve is really firm. It would appear that the midvalve provides a great deal of the damping within the fork. This can be a compromised situation. With such a soft comp valve and such a firm midvalve I would be concerned at the possibility of cavitaion within the cartridge. The rebound damping on these forks can also be improved. If you wish to record the valving and present it I would be happy to make some recommendations for you. Also I find the Marzzochi forks work best with a relatively low oil height 130 - 135mm 5wt.
Regards
Terry Hay
 
Joined
Jan 2, 2001
Messages
416
Likes
0
#2
Terry, i appreciate your assitance.
I own a '98 wr250 huskie that came stock with a conventional 50mm marzocchi. I did some fiddling with it and became more happy with them every time i did something in shimming dept.
But last month i purchased a wrecked huskie cr125 from '99, and they come with 45mm usd marzocchies, the ones yr talking about.
After cleaning inside outside and replaced a few o-rings, I did some work to the midvalve. It came with a very strange midvalve config and i reworked that to a midvalve with 0.5mm float and a very light stack. I immediatly lightend up the rebound stack as the rebound comes with tiny holes, which i feel are a damping obstruction itself.
The latest version of work i did is this. Changed the midvalve back to a checkvalve using the smallest shim that covers the comp holes. Rebound i left alone, but i feel i have to lighten that up even more(or drill out the holes a little) The basevalve has got 5x 23.10 shims and furter a light hspeed stack.
I feel i can go firmer on the lowspeed shims and lighter one rebound.
Springs are ok(static sag with half full tank 35mm) no binding in the legs cause if i pull up the legs they sack back easily.
I use high oil levels 80mm,to fight the bottoming, and i am 65kgs with gear. Woodsrider, and moderate enduro rider(B rider?)
I am learning a lot lately and i take every opportunity to feel other bikes suspension. What i notice is that other bikes feel very death when you push them, and mine feels plush. Maybe too plush, and i have to frim it up a little when i become faster. However i am happy with the way it is acting now but like to hear yr comments as i find them very interressthing. It is becoming cold overhere so maybe i see the time to make some stack changes while waiting for wether improvements.
 
Joined
Jan 2, 2001
Messages
416
Likes
0
#3
Terry, do you see the time to elaborate a little further on these marzocchies.
Maybe i am on the right track but certainly can use some info, thx in adv.
george
 
Joined
Nov 8, 2003
Messages
200
Likes
0
#5
George
I'm sorry I must have overlooked your last post. Is there something specific you would like help with, or are you simply after general information?
Regards
Terry
 
Joined
Jan 2, 2001
Messages
416
Likes
0
#6
Terry, thnks for replying.
No i just need general information. A few pointers, or maybe telling me i am on the wrong track. Something like that.
I have noticed the play between the innerleg and outer, on the bushing. You can really see the freeplay when you look inside the tubes.
But i can live with that.
I widened the rebound holes to 4mm, and smoothend the comp holes on all the pistons.
I use a checkvalve right now, but with g-loads bottom out easy. That is why i use high oil levels(up to 80mm) but maybe i am wrong there and i have to crank up the lowspeed on shimstack. I like the performance over roots etc, but braking bumps i am not sure yet. Maybe i need some more performance there.
At the moment i ride endurance, but when i go to the track i might need that midvalve back in.
Can you point me a midvalve freelift for this fork type. I assume lowlift are in the picture with these forks, as they use small cartridges(26mm).
What do you know about the rebound. I use a light stack, 22.10, 18.15 & 16.15, nut.
thnks george
 
Joined
Nov 8, 2003
Messages
200
Likes
0
#7
George
The biggest effect cartridge diameter has is on your rebound damping. The smaller your cartridge the heavier you valving needs to be. Try this stack on your rebound.
4x22x0.1
13x.01
21x0.1
18x0.1
16x0.1
14x0.1
13x0.1
12xo.1
I believe the nut on those forks provides the final pivot diameter.
Just continue to run a check valve for now. We'll take it one step at a time.
Post me your comp stack and we'll see what we can do with that.
Regards
Terry
 
Joined
Jan 2, 2001
Messages
416
Likes
0
#8
Thx Terry, i will need to order the shims.
Can you explain to me why the need for more cq heavier rebound with smaller cartridges? And this piston comes with tiny rebound holes. 4 x 3mm. Is that also a factor?
 
Joined
Nov 8, 2003
Messages
200
Likes
0
#9
George
Unlike the comp valve which only sees an oil volume equivalent to that being displaced by the damper rod, the rebound valve sees the entire cartridge oil volume(minus the damper rod of course). So if you alter the cartridge diameter you should also alter the rebound valving. With a smaller cartridge you have less volume to achieve the same amount of damping. So naturally you will require stiffer valving.
Regards
Terry