marzocchi shocks

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Anthony B
Cucciolo - the Lil Pup
Posts: 8
Joined: Fri Jan 27, 2012 10:10 pm

marzocchi shocks

Post by Anthony B » Thu Aug 15, 2013 4:09 am

Hi the marzocchi shocks on my 750ss needed rebuilding and I have taken them apart put new seals etc in them but they dont recoil by them selves. Took them to a place recommended to me and they have told me that they need to drill a hole in the side and fit a valve to refill with gas ,is this right ? _?_

GeoffW
Mariana
Posts: 43
Joined: Sat May 19, 2012 2:01 am

Re: marzocchi shocks

Post by GeoffW » Fri Aug 16, 2013 3:00 am

Hi Anthony, that advice you got doesn't sound at all right. Gas doesn't sound like a relevant factor at all when you understand how these forks work. If you want to restore the bike accurately then the only gas in them should be air and that's at atmospheric pressure as best I remember them. A second opinion would be worth seeking out, you might simply have holes gummed up inside your forks through years of neglect and a simple clean out with new seals and the right fork oil might get them working OK. As it happens I'm currently in the process of cleaning out my Marzocchi forks (1974 750GT based SS replica).

I might be doing a conversion to more modern performance using gold valve emulators to improve the original damping design. I believe Steve sells them and I'm sure he can provide advice on the kind of improvement you'd get from the gold valve emulators, considering the rather crude behaviour of the 70s Marzocchis on anything but smooth surfaces. Steve also has a link on that product page to installation in Marzocchi forks of that era, which explains how they work.

According to the manufacturer's (Race Tech) website list, your bike would require the FEGV S3501 gold valve emulator kit and the FPEV AD3507 P adapters. You could be lucky and not have to make your own adapters if their list is correct, but you'd be wise to get them apart and take some measurements of the damping rod, piston etc. to confirm which version of the emulator kit would be right for yours. I suspect mine would require the 3801 rather than the 3501 and probably custom made adapters - fortunately I have access to a lathe and experience with minor fabrication if I decide to go down that track.

Perhaps Steve could chime in at this point 'cause I'm talking from pretty limited experience as I've only rebuilt standard Marzocchis in the past and it could be a case of something very worn inside yours or maybe just something sticking or gummed up. I won't be so rude as to suggest they are wrongly assembled but were they behaving that badly (no rebound) before you rebuilt them?

Vince
750 GT
Posts: 191
Joined: Tue Nov 09, 2004 12:28 am

Re: marzocchi shocks

Post by Vince » Fri Aug 16, 2013 6:03 pm

Emualtors are a good thing,but a bit hard to fit to rear shocks.Your at the wroung end of the bike mate.

Anthony B
Cucciolo - the Lil Pup
Posts: 8
Joined: Fri Jan 27, 2012 10:10 pm

Re: marzocchi shocks

Post by Anthony B » Fri Aug 16, 2013 10:27 pm

Thanks for the reply, I took them to a ducati shop here in Adelaide and he has sorted it out for me .They were working fine in the first place just was told the wrong info to start with :-D

GeoffW
Mariana
Posts: 43
Joined: Sat May 19, 2012 2:01 am

Re: marzocchi shocks

Post by GeoffW » Sat Aug 17, 2013 3:34 am

Sorry I misunderstood Anthony, what a dill! I was thinking front forks because they are so fresh in my mind from pulling them apart - which should be called forks I realise now of course. So did your shockers in fact need gas? I remember some of those Marzocchi shocks had air reservoirs in the late 70s, but don't remember seeing them on the SS models.

Anthony B
Cucciolo - the Lil Pup
Posts: 8
Joined: Fri Jan 27, 2012 10:10 pm

Re: marzocchi shocks

Post by Anthony B » Sat Aug 17, 2013 4:19 pm

no gas needed the spring act as the recoil ,so a quick poilsh and ready to go back on the bike and move on to the next part of my rebuild

Spagjet
Mach 3
Posts: 79
Joined: Wed Jan 08, 2014 9:07 pm

Re: marzocchi shocks

Post by Spagjet » Sun Jan 12, 2014 11:19 pm

the "gas" in Marzocchi shocks (in the bit that hangs off them with the valve on it) is just air. Me and my cousin rebuilt a few sets years ago and did some experiments with getting the right amount of air back in. All they are are "bump stops", if you really hit a big pothole and fully compress your shocks it can really throw the bike if it is a sudden stop so those shocks have got a rubber bladder inside the bit that hangs off with a little bit of air in it. Air is compressible so the shock oil rushes into the "bit on the back with the bladder" and compresses the air in it (which is a hell of a lot more gentle than a rubber stop), then goes back in the shock when it recoveres from the "bottom out". If you try and put too much air in the bladder it either pops it straight away (they say you can't even hear it pop) or pops it when you hit the next pothole as there's nowhere for the oil to go. I can't remember the exact numbers but it's something like 2 and a half psi of pressure or something tiny like that. You're supposed to have a special tool that can deal with such small pressures to get the right amount of air in them but we lived a long way from anything like that so figured out through careful trial and error that if you put the air gun you fill the tyres with air with on the valve on the shock and give the trigger a VERY quick smack with the palm of your hand it's all good. I know that because I made a pressure tester with a very sensitive air pressure gauge on it which you could put on the valve and read that it had the 2 1/2 psi but when you pulled the tester off you heard a little hiss as the valve shut which was the 2 1/2 psi escaping (hmmmmm). So the trick was giving the air gun a slap and leaving it at that, if you tried to check it you lost it. Everyone we asked said it couldn't and shouldn't be done yourself and it was VERY easy to pop the bladder so not to try but we both had Marzocchi Stradas on our bikes back then (my GTS and his LeMans MKIII) and no money so gave it the pills and got away with it. I bet there is a lot of Stradas out there with popped bags though that the owners don't know about. It's a very bad thing if the bladders are popped as the oil has got nothing to push it back into the shock if the bladder has got no pressure in it. In it's normal (not compressed) state there should be no oil in with the bladder, if the bladders popped and some of the oils in there all the time there's not enough oil in the actual shock for it to work properly. It's a very specific amount of oil in there that it needs every bit of to work properly. In other words if the bladders popped the shocks are rooted.....

If you want to do it yourself, stick your thumbnail on the valve pin, you will hear a little hiss and then nothing. This will tell you the bladder wasn't popped and you can give it the "palm slap" with the air gun. If you don't hear a little hiss that either means the bladder is popped or that there is simply no air in there. Give it the "Palm slap" and then the thumbnail again. If still no hiss, bad news, if there is a little hiss the bladder is fine and just needs one more palm slap. Who said you need expensive tools???

dukabmw
Cucciolo - the Lil Pup
Posts: 5
Joined: Tue May 31, 2011 4:07 am

Re: marzocchi shocks

Post by dukabmw » Sun Mar 26, 2017 3:25 am

Spagjet wrote:
Sun Jan 12, 2014 11:19 pm
I can't remember the exact numbers but it's something like 2 and a half psi of pressure or something tiny like that. You're supposed to have a special tool that can deal with such small pressures to get the right amount of air in them but we lived a long way from anything like that so figured out through careful trial and error that if you put the air gun you fill the tyres with air with on the valve on the shock and give the trigger a VERY quick smack with the palm of your hand it's all good. I know that because I made a pressure tester with a very sensitive air pressure gauge on it which you could put on the valve and read that it had the 2 1/2 psi but when you pulled the tester off you heard a little hiss as the valve shut which was the 2 1/2 psi escaping (hmmmmm).
From the manual
The reason for pressurising the bellows is to keep the oil under pressure which will minimize aeration giving more consistent damping.
It should be remembered that the bellows contain a very small amount of air and therefore widely fluctuating pressure readings will be obtained if normal tyre pressure gauges are used. The best results are obtained by using an in-line pressure gauge which will exactly register the pressure of the contents in the bladder (ref.93.58).
Bellows should be inflated to a pressure of 28 - 42 psi (2 - 3 Kg/cm2) and a pressure reading taken.
Recheck the reading and ascertain the amount which was lost when taking the first reading. Inflate the bladder again to a reading which allows for the amount of air which was lost in removing the inflation apparatus.
PLEASE NOTE excessive pressure may damage the bladder and force the damper oil past the seals. Retighten the valve cap.

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