Modifying Marzocchi 35mm forks

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NewKidOnTheBlock
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Location: Oxfordshire, UK

Modifying Marzocchi 35mm forks

Postby NewKidOnTheBlock » Sat Jul 06, 2019 3:58 pm

Hi All,

It's been a while,i spent 2 years with my 250cc out of action but she rides again - someone forgot to gap the rings :oops:, ended up with a scored bore, no great problem, just took me a long time to get back onto it sadly.

Anyway, since I've been riding her again, my desire to improve the handling has once again become a priority. It's still on the Monza Jr 160cc forks and wheels, my intention was always to build some 18" alloy rimmed wheels, with a twin leading shoe front hub and some 35mm forks. Over a period of time I've acquired some 35mm Marzocchi forks, only to realise once I had them that they have no post to react the brake plate from, and that they're rather longer than the currently fitted set (about 745mm vs 650mm), this leads me to believe they were from a trials bike or similar?!? Has anyone modified forks to add a brake lug on, and is swapping out the stanchions and springs an option to make these usable or should I move them on and start again?

I also have collected some 18" Akront rims
1.85"-18" 36-TR-582-E Front
2.15"-18" 36-TC-189 Rear

Which I was hoping to fit to a new front hub with twin leading shoes, I had collected a twin leading shoe brake plate (I was led to believe it was from a Honda 175 (SL?? Perhaps), but I bought a Honda hub for it and it didn't match) but am struggling to find a suitable hub for it in the UK. Does anyone have any recommendations on how to ID the brake plate or where I might source a whole hub? I'm concerned about how to adapt the speedo drive to my original speedo too?

Cheers for the help

Keep the rubber side down!

Jordan
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Re: Modifying Marzocchi 35mm forks

Postby Jordan » Sun Jul 07, 2019 8:21 am

If you get some triple clamps that allow the fork tubes to slide upwards through the top one, you might get the effective length you want.
But it might depend on them not fouling handlebars. Clip-on bars could get around that.

The Honda 175 brake you have could be ideal. A TLS would probably be from CB175, SL usually having a single leading shoe.
Advantage is they used a torque arm like late model Ducati singles. No need for providing a lug on the fork slider.
Axle diameter OK?

blethermaskite
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Location: northern ireland

Re: Modifying Marzocchi 35mm forks

Postby blethermaskite » Sun Jul 07, 2019 8:48 am

I have very successfully used the front hub/wheel from a honda cb72/77,....... twin leading shoe, 200mm dia. wide shoes, torque arm fitting, 15 mm axle, and overall a quite narrow hub that fits easily in the forks needs to be set up well with decent race quality linings and will then stop you on a sixpence! the other brake to look for is the twin leader from the front of a Aermacchi road bike, (usually available pretty cheap on ebay in USA.)
Cheers,
George

NewKidOnTheBlock
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Re: Modifying Marzocchi 35mm forks

Postby NewKidOnTheBlock » Sun Jul 07, 2019 9:57 am

Thanks Both,

Jordan: The issue I have with these forks is that they're SO much longer than the stock ones, I know I could drop them through the triple trees/yokes but we're looking at about 100mm/4" which I think would look ridiculous! I already have clip-ons so that's not a problem though. Thanks for the information about torque arms rather than lugs, I hadn't considered this an option but there's no reason why not, perhaps that's how these forks were used before then?

George: Thanks for the information, so I've had a look at what I have and dug through some old invoices, it looks like my TLS brake plate is from a CL175 - the drum diameter is only about 160mm, the spindle diameter looks to be 15mm. I think I'll try to get hold of a larger brake rather than find a hub to suit that. Thanks for the tip on CB72/77 and Aermacchi, just annoying that the parts for these seem to be so cheap and plentiful over in the states but almost none available in the UK!

Cheers

Jamie

Edit: So I've now bought a complete hub+brake plate from a CB72/77 as well as another original Grimecia rear hub, this way I can build my Akront rims onto them and have some interchangable sets without having to modify one brake plate to another hub and/or strip down my old wheels for the hubs, keeping the bike on the road while I do these mods. Still leaves me looking at what to do with the forks though!

JimF
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Re: Modifying Marzocchi 35mm forks

Postby JimF » Sun Jul 07, 2019 5:37 pm

I put a 4LS hub on a 450 using a non-stock 35mm fork. The fork tubes were way too long and here in Evanston Illinois is (or was) a place called Forking by Frank. They cut the tubes down for me and threaded the ends so everything could go back together.

The springs were then way too long, but I found some dirt bike place that makes custom springs. I told him the length of the tubes, the style of riding and the weight of the bike and he make new springs to fit the tubes.

Jim

blethermaskite
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Re: Modifying Marzocchi 35mm forks

Postby blethermaskite » Sun Jul 07, 2019 6:46 pm

Same as Jim, just get them shortened, can't remember what the bottom end of Marzocchi 35 mm fork stanchions are like, some makes have a slug recessed in the bottom of the stanchion held in with a circlip so they are easy to shorten if you have a lathe or can get somebody to do it for you, its always more tricky if the damper retainers are held in with a threaded plug but again any good lathe guy should be able to sort it for you, most springs can be shortened too, and then just experiment with preload spacers to suit.
On your cb77/72 front hub to sort the speedo drive, remove the huge honda one (if you got it with the hub) and replace it with a simple 6mm thick allow disc screwed to the hub, bore a small offset hole in the disc to catch the tang of a standard old type ducati speedo drive gearbox......works a treat.
Cheers,
George

NewKidOnTheBlock
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Location: Oxfordshire, UK

Re: Modifying Marzocchi 35mm forks

Postby NewKidOnTheBlock » Sun Jul 14, 2019 8:18 am

George, could you please explain or show photos of what you mean for the Honda speedo adaptor? I can't get my head around that but it's something that I need to do. Thank you

Also I've come to the realisation that the forks I had were 32mm not 35mm :roll:. I now remember they were from a Benelli, after speaking to Nigel Lacey the other day I now realise that they aren't in fact that long, it's that the Monza Jr forks I was comparing against are very short.

The next question then is how long should my rear shocks be? Mine are 11" centre to centre and it rides level with the Monza Jr forks, presumably I need longer rear shocks to maintain my geometry. How long and what original or non original rear shocks would people recommend?

Many thanks

Jamie

blethermaskite
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Joined: Thu Mar 01, 2018 1:06 am
Location: northern ireland

Re: Modifying Marzocchi 35mm forks

Postby blethermaskite » Sun Jul 14, 2019 11:46 am

Jamie,
When you remove the honda speedo drive gearbox you are left with a fairly large dia. recess in the hub, so I made an alloy disc out of flat dural plate to fit into this recess held in by countersunk 6mm socket head screws, and bored a hole in the centre big enough to clear a suitable axle spacer. I had an old type ducati speedo drive gearbox which is driven by a bent flat steel tang which engages in an off centre hole in the standard ducati hub, so I simply bored the same dimension off centre hole in the dural disc plate to line up with this drive tang thus reproducing a similar driving system for the speedo gearbox as the standard ducati (but on the honda hub). You need to do some careful measuring to get the axle spacer dimensions correct to get just the right 'nip' to lock the ducati speedo drive gearbox on the axle, but still maintaining clearance for the tang to revolve freely.
Hope that is kinda clear, sorry but i don't have a photo of this mod.
Cheers,
George

joe46ho
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Re: Modifying Marzocchi 35mm forks

Postby joe46ho » Sat Jul 20, 2019 4:21 am

Yamaha xs650 fork tubes fit in the marzocchi lowers with very minor work, and they are plentiful, and cheap. you can get them new or used and in different lengths. I can dig up some pictures of when i did mine if you'd like
Too many projects to list...
12 Ducati singles currently

joe46ho
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Re: Modifying Marzocchi 35mm forks

Postby joe46ho » Sat Jul 20, 2019 5:04 am

i found a few pics, none of them assembled though, all you need is to make (or have someone make you) 2 adapters similar to this. Very simple piece made from scrap bar stock, this was a piece of 7075 aluminum i believe, but im sure you could use steel. this was a very cheap option for me, the xs650 forks (complete) in excellent condition where $65.00, im sure you could do better on the price.
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Too many projects to list...
12 Ducati singles currently


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