Ducati 450 Desmo rebuild

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I've owned this machine since 1978. It was three years old and bog standard. As well as using it for transport because I couldn't afford a second road bike, I entered it in the annual local hill climb in road trim and then began to enter it in races from 1983 onwards, looking outwardly standard. I won the Irish Road Race Championship 500 cc title on it in 1985. Over the years, it gradually became more of a dedicated racer and I thought I would never bring it back to road trim. It had the usual tuning mods but it was nearly always uncompetitive unless it was wet or the course was twisty. I had to ride the wheels off it to get anywhere. In short, it has had a very hard life. When the opportunity to buy a Seeley G50 came along, the little Duke was retired from racing duty. I delayed bringing it back to road trim because I knew there was so much work (and expense) involved. It has been a slow and painstaking build, when I could afford the time.

Here is the old girl in 1985 at a CRMC event in Cadwell Park, England, more or less outwardly stock but with a tuned engine.



Here it is in September 2010.



I am getting close to making some noise, and I am waiting impatiently for the yellow bits to come back from the painter - tank, seat, side panels and front mudguard. I am aiming to get it ready to run in a local non-competitive event at the end of this month.
 
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This is really a special, not a back-to-original restoration, so my apologies to the purists. I well remember the bike in standard trim. The engine and rolling chassis were grand, but the ancillaries were often very poor quality. The tank rusted through in 1981, the original electronic ignition failed in 1978, the 6 volt lighting was dangerously bad and the suspension was so hard that it would rattle the fillings out of your teeth. The chrome wasn't great, the paint on the front forks became blasted with road chippings and vibration cracked the rear mudguard and chainguard. The Smiths instruments were the same as fitted to the BSA B25 unit singles and they were really more like toys than proper meters. But ... the bike was beautiful, a styling coup as striking as the 916 or the Supermono. And it was light and agile and allowed you to extract the best from the modestly powered engine.

The chassis is mostly standard but with some modifications. The front forks have had the paint stripped and professionally polished. The rear shocks are Falcon, made for the bike. The swinging arm has been braced at the wheel spindle mounts like the Aermacchi racers. Years ago, I hacksawed the centre stands lugs off and bent and shortened the rear subframe - butchery! It took ages to re-make and weld the lugs back on so that the stand was straight in all planes and the right height. You can't see the welds now. The same with the rear subframe. The wheels and brakes are standard, apart from the Lockeed master cylinder. I replaced the original disc years ago because it was worn beyond service limits.





I have seen many Ducati specials over the years, with different tanks, seats, mudguards, etc., and none come close to matching the beauty of the standard yellow Desmos - not even with the "mini-900SS" body work. The tank, seat, mudguard and side panels will be original and in Desmo yellow (or orange, as some would say), with the stock transfers. I prefer the black painted forks and triple clamps but my excuse is that polished alloy is easier to keep looking nice.

I hope to have the paintwork back by end of this coming week. Engine and chassis details to follow.
 
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They are a nice looking bike. I have a friend that has a 450 and a 250 he prefers the 250. Says the 450 is a rougher motor to run. I only have a 250 narrow case so couldn't verify if it is true. Please post pictures of the finished bike.
 
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Hello Dave, I note the must have steering damper. The larger carb and manifold, braced swing arm, and a wider rear rim?
I see a coil so assume points?
Are you using the bear trap valve springs, or no springs?
I assume big valve?
Bored?

It looks very nice. They are my favorite up the hills bike and other larger bike riders are shocked that it was only an old 450 that kept with them.
But you have to be very smooth or they bend themself in knots. (flexy bike) And the smoother the road the better.

I've had 3 yellow disc brake 450's and all had GT 250 frames without the bracing along the back bone and down the battery area. The factory must have made up some late ones from spares and sent them to Australia. I have had 1 that was a 450 frame and I couldn't pick the difference in frame flex. (and fork flex, and swing arm flex)

I raced one for several years in F3 and that ended up with a 900SS swing arm and triangulated frame, etc,etc,etc. The one I have now was spare parts for the race one. I'll dig out some pics and scan them for your interest./ amusement

graeme

graeme
 
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GRM 450 said:
Hello Dave, I note the must have steering damper. The larger carb and manifold, braced swing arm, and a wider rear rim?
I see a coil so assume points?
Are you using the bear trap valve springs, or no springs?
I assume big valve?
Bored?
Graeme — the carb is a 40 mm pumper that was recommended to me many years ago by Ducati race specialist John Witt Mann in England. In hindsight, it was probably no better than say a 36 or 34 mm but it's all I have at the moment. The swinging arm is only braced at the fork ends. Standard front rim and WM3 rear. I use the Imola camshaft, standard hairpin springs. 42 mm inlet valve, standard 36 mm exhaust valve. Inlet port has been shaped. The piston is an Omega 86.6 mm (see pic). Factory crank, con rod (I would not trust the pattern ones), gearbox and clutch but aftermarket straight cut primary gears.



GRM 450 said:
It looks very nice. They are my favorite up the hills bike and other larger bike riders are shocked that it was only an old 450 that kept with them.
But you have to be very smooth or they bend themself in knots. (flexy bike) And the smoother the road the better.

I've had 3 yellow disc brake 450's and all had GT 250 frames without the bracing along the back bone and down the battery area. The factory must have made up some late ones from spares and sent them to Australia. I have had 1 that was a 450 frame and I couldn't pick the difference in frame flex. (and fork flex, and swing arm flex)

I raced one for several years in F3 and that ended up with a 900SS swing arm and triangulated frame, etc,etc,etc. The one I have now was spare parts for the race one. I'll dig out some pics and scan them for your interest./ amusement
graeme
Yes, the swinging arm is a little flexible, but frame flex was common on many bikes of the day. The gusseting on the frame makes no difference. I found that the harsh suspension would tend to magnify flexing, and I have fitted softer springs front and rear. I also found from experience that softening the springing eliminated handlebar shake. This was a real problem on bumpy Irish roads not just with the singles but also the 900SS, and that had quite a stiff chassis by the standards of the day. I found that it would go wide on tight corners and back in the 80s I fitted longer rear shocks (by I think 1/2 in) which allowed it to track a line precisely and gave it a quicker turn-in.

Look forward to seeing those pics of your race bike. Never heard of fitting a 900 swinging arm — interesting!

Dave
 
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Love what you're doing Dave, and I really don't think anyone is going to be offended.
Looking forward to more pics!
daveh said:
... straight cut primary gears
To reduce losses from helical-cut gears or is it a cure for clutch slip (like the Pantah has) by changing the primary ratio?
 
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britbike220 said:
They are a nice looking bike. I have a friend that has a 450 and a 250 he prefers the 250. Says the 450 is a rougher motor to run. I only have a 250 narrow case so couldn't verify if it is true. Please post pictures of the finished bike.
I think you are right, the 250 is probably the best of this family of singles. I had a 250 narrow case Mark 3 (like the Mach 1) in 1980 and it was a quick little bike. Head to head against a 74 250 Desmo, it would romp away. The 450 is a bit rougher, but I never found it unpleasant.
 
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pictures may take a day or 2.
road bike,
I used 650 Pantah Marzocchi legs with 40mm off the tops, mated to Ceriani sliders with Marzocchi insides, and longer Koni rears. That lifted the bike up about 20mm, gives a better ride.
42 inlet and 36 ex. 87mm wiesco, std road cam lapped so it doesn't bind, 4kg springs like SS or Pantah, 36mm Dellorto, bathtub head and flowed, 500SL honda rod and crank pin, steering damper, master cylinder sleeved smaller, RT head with decompression so it's easy to kick without waiting for it to get TDC.

old race bike,
I cut 6mm off each end of the SS swing arm to fit in between the 450 frame on the race bike and made a disc carrier for the SS wheel with a small RG 250 rear disc. Chrome moly bracing from steering head to the swing arm pivot area.
88mm, Imola cam, no springs, flowed, 36mm Dellorto, total loss, no flywheel, electronic ignition, money, money, etc,etc Lots of fun though.

I can remember my SS running wide on bumpy corners, over sprung and under damped as I remember. But lovely on a good winding road.
 

grandpaul

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Beautiful project Dave, well done and a fine machine.

I transported a friend's Duc 250 to the state capital years ago to a buyer; if i would have known back then what i know now, that bike would be in my collection getting a bit of track time every now and then.
 
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Hi Dave,

Nice to see the old girl getting back on the road, that brings back memories! Still gt the 350 at home, but I wish I'd kept the desmo too!!
 
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Hi Paul — thanks for your comments. I usually learn something new each time I read your build threads. The last one I read was the Norton N15CS Hybrid restoration, which looked like a difficult project.

Hi John — good to hear from you again! Didn't know you had a Desmo. :eek:
 

grandpaul

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Dave, the N15 isn't quite done! I just timed the mag a few minutes ago, I still need Monobloc carb rebuild bits before I can attempt a startup.
 
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Hi Dave,

Yes I had a 250 Desmo....you might remember it , the one with the nickel plated frame, I know it was raced again after I sold it!!
 
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A few photos of modifications from standard.



The original damper internals are in a box and were replaced some years ago with Maxton internals. They did an excellent job. The domed screw conceals a slotted adjuster rod for compression and rebound, and softer springs. You can just see the tachometer, which is an electronic replacement 60 mm instrument.



New points cover made in house from scrap dural, concealing a Lucas RITA stator and rotor. The original cover was tin and secured by what look like the hands of a clock, held by external pillar bolts (see Graeme's bike). This will not fit over the Lucas unit, which is bulkier. I copied the design of the Commando, with two internal pillar bolts and countersunk 4mm allen screws.



Second spark plug, which normally uses a 10mm short reach plug from a Honda 50. Usually, the oil drain has to be extended and curved round the plug and cap and looks like the one on Graeme's 450. Problem is that the oil has to travel a little uphill to reach the middle banjo. I got a shorter 10 mm chainsaw plug and stripped the insulation from a NGK racing spark plug cap so that the original oil drain pipes could be used. Time will tell if this works or not.



Exact copies of the original headlight brackets made from scrap stainless plate, mounted on the lathe faceplate and holes bored to size. I have temporarily lost the chromed strips that surround the rubber mounts on the forks. The tube protruding from the headstock was for a half-fairing mount. I decided to keep this just in case I fit the fairing in the future. The headlight lens is from a scrapyard and cost €5. The original headlight rim and bowl had some gravel rash and bad dents but were repaired by Marque Restore Chrome Platers, who did an excellent job. http://www.marquerestore.co.uk/
 
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Don't laugh too loud about the leathers, remember it was a long time ago







graeme
 
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How could I laugh about your leathers when you see the duct tape on mine :mrgreen:

Lots of interesting things to see! There is a lot of engineering on that bike, and it must have taken many man-hours to execute. The extra bracing tubes look like the best way to stiffen the frame. How did the bike feel after you did this? Interesting that the factory didn't do this with their works racers, though. I notice you kept the kickstart! I see the modded 900SS swinging arm and the rear disc — nice work. Old Racing Spare Parts in Italy now sell a Seeley-style swinger for the singles (http://www.oldracingspareparts.com/parts_s/01r0083.htm).

Thanks for posting those :)
 
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This thread is about a present tense 450 and the red bike is very past tense. And I can't wait to see the end reult of this one.

I read a book by Tony Foale (sorry if I got his name wrong) and another fellow who I don't remember, about frame design. A very good book that made sense.
Some Chrome Moly and a welder, access to SS bits, and a wrecker.
I remember it went over the bumps in the top gear dog leg without backing off after the bracing, but it started the front forks pattering braking at the hair pin at Lakeside.
So it put more stress on the front end.
The kick start was easier than bump starting in 1st gear on flat ground.

What forks or internals are in yours? You have caught my interest with yours.
 
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GRM 450 said:
What forks or internals are in yours?
The fork alloys and stanchions are the original Cerianis. The damping internals were made by Maxton, UK suspension specialists (http://www.maxtonsuspension.co.uk/) and see first photo of previous post. The internals are similar to an early 2000s R6 Yamaha. The dust shrouds a major source of fork stiction because they grip the stanchions too tightly. I mounted mine on a mandrel on a lathe and used a sharp engineer's scraper to gently widen the ID so they are a looser fit on the stanchions. The operation is now silky smooth.
 

xbacksideslider

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Great thread. I have to chime in.

I had two Desmo singles, 350 and 450, both 1967 MK III D models. I also had a 250, a 1965 Diana with the endurance racer package - bigger 5 gallon tank, the big headlight and of course the rearsets. WM 1 and WM 2 Borranis. All three of those bikes did thousands of miles in Sunday morning and mid-week street racing in Griffith Park in Los Angeles, CA. They also took me to UCLA on a daily basis. The bigger Marzocchi forks off of an RT450 bolted right up to the 450 Desmo; I stroked it 5mm when the big end went out, and welded a tab onto those forks to mount an RD350 caliper/hub/disc on it.

I don't know what the specs or the name of the cam was but it was sold to me by the US West coast distributor - ZDS - in the mid to late 70s; I had to have slots milled in the the cam bearing bore to get the cam into the head. I milled both heads and tried it in both the 350 and the 450. They were both wide case, long rod, engines, of course. That cam worked!

My brother had a 350 Monza/Diana clone. That thing ripped! High compression was the key. Diana head/cam, high compression piston. A good friend also had one that was even faster.

IMO the best combination amongst the singles is a 350 narrow case - because of the short rod, Diana head, with lots of compression; JB Weld the floor of the spring box and the floor of the intake port, raise that port. That's the combination.
 
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