Mk3 fork questions

[yoper1987]

Hii, everybody
For earlier forgive me for my English)) I'm from Russia)

I have a frame from ducati mk3 about 1968-1972 of release..... I want to put not an original fork under disk forward brakes.....
Maybe somebody faced the matter? ? The fork from what motorcycle can be put on this frame.... without special changes of a frame! ? From what to take a forward wheel? ... etc.

Can be better to use original yoke with fork feathers from other motorcycle?

For earlier thanks)))))

[Jordan]

Hello
Many fork assemblies can be made to fit a motorbike.
But, the details of the fork's steering tube need to suit it.
It must be able to go through the frame steering head, with the bike's bearings fitted. And it must be long enough.
Adapting pieces need to be fitted at top and bottom - made with a lathe.

An easier way is to use fork tubes of the same diameter, keeping the bike's triple clamps.
The easiest to modify in this way are the later 35mm forks, because the tubes on these are simply clamped at the top as well as the bottom. You would need to have the 35mm triple clamps, which also can fit earlier Ducati models.
35mm is a common fork tube diameter on many different bikes.

I once used Yamaha RD fork tubes on a Ducati SCR (35mm), and found I could use the Ducati bottom sliding legs with no further modification needed.
This SCR was with 35mm clamps at the bottom, but did not have a clamp at the top. It was more like the earlier, smaller forks. But with the Yamaha hex bolts at the top it worked OK.

[JimF]

Hi Max,

I am reading into the question that you want to put a disc brake on the front end.

The early Ducatis had 31.5mm fork tubes, and the later Ducatis had larger stronger fork tubes which I recall were 35mm. Given the date range you have given us, your bike could have either the smaller or the larger fork tubes.

I think Jordan might is saying that your task would be easier if you find a disc-equipped set of forks of the same size so that they will fit in the existing triple trees, and that will be easier if your bike has the larger 35mm fork tubes. i hope I got that right.

I am extrapolating that the front wheel will have to change so as to have a rotor grafted to it, and the hub and rotor will have to fit in the distance between the fork tubes.

Otherwise the entire front end of a disc-equipped bike including the triple trees will have to be grafted to the front end of the Ducati. This means the steering column would have to fit the steering head, the steering head bearings would have to fit, the steering column might need to be shortened or lengthened...

Owing to a new fork's length and weight, the handling characteristics of the motorcycle would likely change. I am not sure if the handling would get worse or get better, but it would likely change one way or the other.

Hopefully I got this right. Best wait until you get more replies to make your decision. Also, attach a photo of your bike's front end so that we might be able to tell you what size your existing forks are.

Jim

[yoper1987]

I once used Yamaha RD fork tubes on a Ducati SCR (35mm), and found I could use the Ducati bottom sliding legs with no further modification needed.
This SCR was with 35mm clamps at the bottom, but did not have a clamp at the top. It was more like the earlier, smaller forks. But with the Yamaha hex bolts at the top it worked OK.

The distance between fork pipes at Rd same as well as at ducati turns out that or you thought out any adapter? ? ? Wheel used from Rd? ?

[yoper1987]

Hi Max,

I am reading into the question that you want to put a disc brake on the front end.

The early Ducatis had 31.5mm fork tubes, and the later Ducatis had larger stronger fork tubes which I recall were 35mm. Given the date range you have given us, your bike could have either the smaller or the larger fork tubes.

I think Jordan might is saying that your task would be easier if you find a disc-equipped set of forks of the same size so that they will fit in the existing triple trees, and that will be easier if your bike has the larger 35mm fork tubes. i hope I got that right.

Jim

Fork from a ducati not yet at me..... so I can't tell it the sizes yet... But how I understand ..it is 31,5mm

[LaceyDucati]

Many racers in the UK used Honda CB400 four (70's vintage) front ends, forks wheel etc. Not sure what's necessary in the way of mods/bearings etc., but I'm sure it's not difficult. There were no frame mods necessary and I think the legs were 33mm if I remember right.

Nigel

[Jordan]

I once used Yamaha RD fork tubes on a Ducati SCR (35mm), and found I could use the Ducati bottom sliding legs with no further modification needed.
This SCR was with 35mm clamps at the bottom, but did not have a clamp at the top. It was more like the earlier, smaller forks. But with the Yamaha hex bolts at the top it worked OK.

The distance between fork pipes at Rd same as well as at ducati turns out that or you thought out any adapter? ? ? Wheel used from Rd? ?

On mine, I used from Ducati SCR (35mm) :
Complete triple clamp assembly
Bottom aluminium fork legs.
Wheel, brake, mudguard
and from Yamaha RD:
2 fork tube assemblies.

The whole RD fork legs including the bottom aluminium sliding parts could have been fitted. But, I don't know if brake would fit OK - different tube spacing?

Thinking again, I think it would be easiest to find a complete disc brake front end to modify for your bike.
Then you will have no trouble with different distance between fork tubes.

But the easiest non-standard disc brake to fit to a Ducati single is from a parallel twin. A complete front end from a Ducati 350 or 500 GTL fits singles perfectly.
There are 1 disc and 2 disc versions.

[JimF]

Max (a.k.a. yoper 1987) asks the questions:

"Help me to understand from what type (from which ducati) this frame... and whether correctly I understand that this fork 31,5mm?
Whether and $860 for all these spare parts are expensive?"

image.jpeg

2image.jpeg

I get first crack at the answers but I may miss somethings so please let's all try to help Max. If I miss something please speak up.

The frame is a wide case. It looks to be a Ducati frame to me. If you have no frame now but have an engine you should measure the width of the engine case where the rear engine mounting bolt passes though so as to determine if your engine is a wide case or a narrow case.

The forks are 31.5mm.

The frame is a street frame but it has no stiffeners for a 450 engine. That's not to say it wouldn't hold a 450 engine. But let's not get into that unless you do.

The good:

The steering head bearing races are in place, that's one less thing you'll need to find.
The battery tray looks solid.
The swing arm and its pivot pin are in place, again you won't have to find those.

The bad:

Most frightening is that the frame appears to have been lengthened or repaired. That welded in tube in the frame's main top tube should not be there. Can anyone on the list tell if this is a repair or if it is stretching the frame? If it's stretching the frame then your wide-case engine won't fit right. It it's a repair then the frame mush have been seriously damaged at some point and any misalignment between the steering head in front and the engine/swing-arm in the back could be hard to detect now but potentially dangerous later.

The back end of the frame has been cut off. Normally you would see the two tubes at the rear end curve inward and connect forming a loop. The loop helps to mount the rear fender and taillight assembly.


The front fork:


The good:

It appears that this bike had been fitted with clip-ons from the factory. The headlight mounting stanchions are the short ones needed with clip-ons.

The steering crown is a rare and and valuable one that was used on the bikes with clip-ons.

The center stand is included. This is important because the motorcycles had no side stand.


The bad:

I don't see the other half of the steering head bearing races and front fender has a dent in it.

These forks are known for being a bit spindly and it's rare that at least one fork tube is not bent. Considering the frame tube repair/modification and the chopped rear frame I would imagine this frame and fork saw a lot of hard riding. I would expect that one or both tubes will need to straightened on a hydraulic press.

As for its value, that's too hard to call. For me I would think it too expensive particularly because of the frame modifications. Here in the USA I once put a 450 street bike frame, with the stiffeners, up for sale and the most anyone would pay for it was about $500 USD. It did not have a front fork but the 31.5mm forks are not too hard to come by.

The steering crown on its own is probably worth $200 to $300 in my estimation, but that price could have come down now that some reproductions are being made.

You may have an availability issue too. How often do Ducati parts come up for sale there and how likely are you to find another frame and how long will that take? Are there any importation taxes placed against parts sourced from outside your country?

Jim

[amartina75]

I would not use that frame as it is without having someone
With experience making or modifying frames fixing it.
It looks poorly done to me. It's a bad picture but the weld looks
rough to me.
To me the value there isn't in the frame anyway
it's with everything else. The fender looks like a widecase
Mk3 fender very hard to find trust me I've been looking for one
For a few years! The top fork clamp is valuable the headlight ears also
The swing arm is hard to find for sale. The centerstand is kind of
hard to locate when you need one.
I could see those forks selling complete, on eBay for
up to $400-$500 because of the top clamp and headlight ears.
A standard set of forks sells for $200 or so.
I've seen fenders sell for $300 to $500 if they are hard to find ones
Like that one.
Now, Would I pay that much...NO absolutely NOT
But, I'm relatively poor and can't buy stuff unless it's a
Good deal.

[Bevel bob]

I think the frame has been lengthened to fit a non ducati engine .