Rebuilding Marzocchi Strada Shocks

  • Thread starter Thread starter Grant
  • Start date Start date
So, back to the Stradas if I may please?


Paddy said:
You need to cut it, usually i do a cut at about 45 degrees

strangely i took this picture for a customer in south Africa today asking the same question.
The rubber o ring behind the nylon ring acts as a sort of spring to keep the piston seal (nylon ring) expanded in the shock cylinder


Click to expand...
Seems counter productive to cut a slit into a seal - kinda stops it sealing IMHO. But, I can see that's how I have to do it!

Also, anybody know where I might find less stiff springs please? My Stradas are going on a 1973 Yamaha DT250!!!
 
M6NTL said:
S
Seems counter productive to cut a slit into a seal - kinda stops it sealing IMHO.
Click to expand...

Not if the seal is too small and it relies on the o ring behind it to expand it to fit the tube. In that case it doesn't seal "until" you split it. a piston ring in the engine is split for the same reason  ;)
 
Cheers Tom you can just see the o ring behind/showing through the sleeve/ring on my picture above, it doesn't do a lot but it does allow the ring to expand and contract a small amount. ;)
 
Paddy said:
Not if the seal is too small and it relies on the o ring behind it to expand it to fit the tube. In that case it doesn't seal "until" you split it. a piston ring in the engine is split for the same reason  ;)
Click to expand...

Hmmm. But a piston ring has a 'correct' end gap, so that when it is up to operating temparature it closes this gap, without nipping up in the bore. Exact same way a turbocharger seal works...

Is this what controls compression damping? My shocks, when I took off the springs, had great rebound damping, but practically zero compression damping - as I understand it this is common...
 
If the seal has not stretched then it too will have the correct gap once fitted and in the tube. Any fluid passing the seal because of the split would be negligible especially if you have the split at 45' as i have. The seal prevents metal to metal contact  between the piston and damper tube, Fluid that did pass would be constant in both compresion and rebound and allowed for in the  strength of the one way valves spring i expect.
These are just basic 40 year old shocks but if set up properly work well. I have no doubt a modern set will work a lot better but only if the rear shocks are your weakest link :D
 
Paddy said:
If the seal has not stretched then it too will have the correct gap once fitted and in the tube. Any fluid passing the seal because of the split would be negligible especially if you have the split at 45' as i have. The seal prevents metal to metal contact  between the piston and damper tube, Fluid that did pass would be constant in both compresion and rebound and allowed for in the  strength of the one way valves spring i expect.
These are just basic 40 year old shocks but if set up properly work well. I have no doubt a modern set will work a lot better but only if the rear shocks are your weakest link :D
Click to expand...

They're going on my 42 year old DT250 - they'll be Sh1tloads better than the stockers!!!
Just need softer springs for this little lightweight bike...
 
Bit more info. According to the Marzocchi rebuild instructions, lack of compression damping is due to a sticking foot valve.
So, I removed both my foot valves and sure enough both were stuck open and offered zero resistance to being blown through. They free off easy enough with a bit of a wiggle, but I'm guessing they'll only get stuck again...
Here's a picture showing the left one freed up, and the right one stuck open...


 
M6NTL said:
Bit more info. According to the Marzocchi rebuild instructions, lack of compression damping is due to a sticking foot valve.
So, I removed both my foot valves and sure enough both were stuck open and offered zero resistance to being blown through. They free off easy enough with a bit of a wiggle, but I'm guessing they'll only get stuck again...
Here's a picture showing the left one freed up, and the right one stuck open...

Click to expand...

the set of Marzocchi's I took apart had exactly the same issue with the "foot valve". Freed them up, fiddled with them, and they stuck open again before they were even put back in. I have not put the shocks back together as I have not come up with a solution, not much point putting them back together if they are not going to have any compression damping. What are your thoughts on how to cure this issue?

Paul LeClair

ps great technical thread, although skipping past the idiot posts is a bit of a pain in the ass! Really, guys? Keep in mind this forum is open to be read by anyone anywhere in the world at any time. Some of these inane, ridiculous, and just plain fucking stupid posts are starting to get under my skin........ Imagine your employer (or a potential employer) or your spouse or your mother or your children reading some of this ludicrous crap, I know I don't want to read this off topic stupidity in what is otherwise a really useful technical thread.
 
Its interesting reading back that Craig was saying the AG2's are not strada's because i have always called them Strada's and AG2 Strada's ?Certainly the rebuild kit is the same. Always learning something new  ;)


I also didnt know the black number was spring strength, in this case 3.
 
Paul LeClair said:
the set of Marzocchi's I took apart had exactly the same issue with the "foot valve". Freed them up, fiddled with them, and they stuck open again before they were even put back in. I have not put the shocks back together as I have not come up with a solution, not much point putting them back together if they are not going to have any compression damping. What are your thoughts on how to cure this issue?

Paul LeClair
Click to expand...

Well, what I plan to do is to dismantle the valves, stick the tophat part in my lathe and turn a chamfer on the face that goes into the hole on the valve plate, thereby giving them a way to go back down and seat correctly even if they are slightly misaligned - I believe that this is the sticking issue.
 
Paddy said:
Its interesting reading back that Craig was saying the AG2's are not strada's because i have always called them Strada's and AG2 Strada's ?Certainly the rebuild kit is the same. Always learning something new  ;)


I also didnt know the black number was spring strength, in this case 3.
Click to expand...

Still looking for lighter springs for my Stradas, anybody got any for sale???
:-)
 
M6NTL said:
Well, what I plan to do is to dismantle the valves, stick the tophat part in my lathe and turn a chamfer on the face that goes into the hole on the valve plate, thereby giving them a way to go back down and seat correctly even if they are slightly misaligned - I believe that this is the sticking issue.
Click to expand...

well, I have been looking for a reason to buy a lathe and then attempt to acquire at least some of the skills to use one......... ;) There would be a niche market, modifying Marzocchi shock "foot valves" to ensure that the shock will actually have some compression damping.

anyway, sounds like a great idea.

Paul LeClair

 
Paul LeClair said:
well, I have been looking for a reason to buy a lathe and then attempt to acquire at least some of the skills to use one......... ;) There would be a niche market, modifying Marzocchi shock "foot valves" to ensure that the shock will actually have some compression damping.

anyway, sounds like a great idea.

Paul LeClair
Click to expand...

That's exactly what I did - bought a lathe and milling machine, having never worked in Engineering or had training or experience, and taught myself as I went along.
This project has all been done by me on my old Brit machines;

 

Attachments

  • image.jpg
    image.jpg
    141.8 KB · Views: 54
  • image.jpg
    image.jpg
    103.4 KB · Views: 43
  • image.jpg
    image.jpg
    151.9 KB · Views: 49
M6NTL said:
Still looking for lighter springs for my Stradas, anybody got any for sale???
:-)
Click to expand...

What spring strength do you have, and what do you want?
Also, knowing the length would help.
I have some spare Strada springs shorter than for the Laverdas but not sure of the weight.
When I get back to base I will look to see if he spring weight sticker is still in place.
 
M6NTL said:
That's exactly what I did - bought a lathe and milling machine, having never worked in Engineering or had training or experience, and taught myself as I went along.
This project has all been done by me on my old Brit machines;
Click to expand...

Cool thing that.


  Keith
 
In my opinion the secret of any good machine be it lathe or mill  is weight and that's where the old Brit stuff scores. Before i started messing about with spare parts i spent 36 years as a tool maker in the same engineering shop. We worked on prototype medical research equip but the workshops always came alive at lunch time as the bike parts came out and what was called "home office" jobs were worked on :). Although i left nearly 3 years ago they still let me back in to the machine shop to do my projects  :D
 
Grant said:
What spring strength do you have, and what do you want?
Also, knowing the length would help.
I have some spare Strada springs shorter than for the Laverdas but not sure of the weight.
When I get back to base I will look to see if he spring weight sticker is still in place.
Click to expand...

The sticker says 4, and the spring free length is 210mm. The wire thickness is 7.35mm. I truthfully don't know what I want, just lighter than these for the little DT.
Thanks, much appreciated..!!..
 
You must log in or register to reply here.
Back
Top