Reviving a 350 Mk3

[Boxprod]

Hello anyone and everyone,

I'm a very new member of the forum, but I've had my 350 for a long time - nearly 50 years. As a young student, I'd had a 450 Desmo (bought on the HP, so after a year I couldn't afford to keep it, sadly), and then with insurance from a stolen Triumph T120V, I eventually found my 350 Mk3 for £425 from Bridge Garage in Exeter. The engine number was 17811, which I understand made it a late 1974 Mototrans build. Judging from an engine plate fixed to the gearbox cover, it was originally intended for France, but we know that the UK importers "acquired" a lot of bikes which had been ordered by other markets. After a good number of miles, many of them in the USA, where I went as a postgrad for 18 months and took the 350 with me, I heard the noise of rumbling and determined the need for a new big end. Bernard Adey (Bernie's Spares and Repairs of Watford) provided a pattern one for a third of the Ducati cost, and a few thousand miles later the little end let go with predictable effect.

I did a deal with John Witt-Mann (Witty Ducati) to let him have my crankshaft plus £120, and he gave me a complete 350 engine, which is still with the bike. Its number is 18125, so an even later Mototrans build, possibly one of the last. I managed to buy a Green-and-White cam from Mick Walker, "relieved" the head to make it fit, added a 32mm PHF Dellorto and a Conti "silencer" plus a Vic Camp fairing which I cut down to half size, and with rearsets and a humped seat it was my daily rider for ten years. By then children and domestic bliss made me put it away in my father-in-law's garage, and it stayed there for years until we moved to Cornwall (family home) and it's now in my workshop being revived, if I can call it that.

The first thing I did was take the Motoplat ignition/alternator to Steve at Bradford Ignition (who's only 50 minutes away, very happily) and he has rebuilt the two stators I gave him, and confirmed that the "coils" are working, so with Jon Pegler's kind advice, I now will have a 12 volt Motoplat system when I get the bike up and running. I know people hate the Motoplat stuff, but I'm happy to keep it, and I've got enough spares to last me, I hope, especially now that LED bulbs and AGM batteries are available at sensible cost. And I'm afraid I'm on a tight budget, so the world of Electrex is a bit beyond me.

As I've started to strip the engine, I'm struck by several things. The first is that it turned over freely and kept compression after twenty years of inactivity. Indeed, everything still turned when moving the bike, so I'm astonished at the original quality of the engineering. And when I drained the oil - still with a slight green colour from Duckhams Q, and still clear, too - I saw the inside of the cases was still sparkling clean. Hooray.
Of course, the one bit that isn't is the combustion chamber, so that's about to be cleaned very carefully. The advantage of being quite old now, and largely retired, is that I can do things as slowly and carefully as I like.

But I have discovered a surprise. With a little too much end-float on the crankshaft and the gearbox shaft, I feared that the big end might be beyond use, and that's quite an expensive replacement. But as I took off the head, I discovered that there's no play up and down, just the expected side-to-side movement. And to my greater surprise, the rod is 18mm wide at the bottom end, meaning a 30mm crank pin, so not a very late Mototrans crank, it seems. And the conrod has the word DUCATI forged into it on one side.

Does anyone have an idea of the origin of the crank and rod? My guess is that John Witt-Mann rebuilt the late Mototrans engine with a proper Italian crank assembly, and simply didn't bother to mention it...

Otherwise, I'm planning to buy a new tank from India (with all the caveats, but my old one is so rusty I can't use it), repaint the fairing, reupholster the seat, and given new bearings, seals, chain, sprockets, brake shoes, etc., etc., at least my son will inherit it in roadworthy condition.
And to all members of the forum, I'm amazed and grateful for the accumulated knowledge and enthusiasm out there, and also at the politeness shown by everybody. That may be because we're all a little older than many forum-posters out there on the internet, but it's a breath of fresh air to read such well-informed and courteous discussions!

That's quite enough for the moment. If you have been, thanks for listening.

Peter.

[blethermaskite]

Welcome to the forum Peter I will have to say "snap" I also own a 350 mk3 which I bought new in 1974 and have owned for 50 years....as I often say to people who query my long time ownership....."when you find the perfect motorcycle why would you let it go", (maybe a little tongue in cheek there, but mostly true ) I am not really surprised your engine is still in good order.....they are a really nicely made bit of kit, my engine is 90% original with only rockers, clutch plates, and ignition/generator replaced. I have found the bicycle just about faultless (for me) except for the Marzocchi front forks which In my opinion were not up to the performance of the bike on fast country road work, I replaced them with a set of Ceriani GP racing forks (absolutely perfect!) Good luck with your rebuilt, there are plenty of people on here who will be happy to advise, (one note definitely replace your brake linings....don't ask me why I recommend this!!).
Cheers,
George

[themoudie]

Aye Peter, welcome to the forum.

Having purchased my '74 450 MKIII in 1976 (still wearing it out! ), John 'Witty' Wittman lived close by and as he had purchased Vic Camp's bikes and spares, I used to visit him for parts, advice and to 'assist'! John is still on the go, but not working on Ducati's any longer, I can ask him about you engine if you wish? John was sponsored by Duckhams and always used their 'Q' 20/50 multigrade in all his race bikes.

As for your '74 MotoTrans/Ducati 350 MKIII, it sounds as though you and George both landed lucky, compared to the one I acquired with only 1,400 miles on the clock in 2002, holding a shed roof up!

I started to renovate the 350 last year, the Motoplat/Italian wiring was goosed, the insulation falling off the verdigris wiring and the resin encapsulation on the stator cracked and flaking, it went in the re-cycling bin and I went the Electrex route. The barrel muff was bored off centre by MotoTrans, so when I replaced the cracked MotoTrans liner, there was a 0.006" gap beneath the liner shoulder and the top of the muff! The only way to resolve this was to partially put the new liner (after checking) into the muff, turn up two cones to hold the liner bore parallel to the lathe bed and then machine 0.007" from the top of the muff casting and 0.003" from the bottom so that it would sit parallel with the piston and conrod on top of the crankcases. Trying to shove the piston up a squint bore appears to have been the cause for the engines demise after 1,400 miles. When Nigel Lacey rebuilt the crankshaft for me, he identified the original grinding marks on the crankpin and suspected that it had done little work.

All the best and I hope that after rebuilding the machine you can start to wear it out again!

Good health, Bill

[Boxprod]

Thanks for the kind welcome, gentlemen.
I'm pressing on gently with the project, and I'm definitely intending it to be a sort of 'sports' version of a Mk3, especially as the half-faring looks almost the same as the original factory 750 Sports version (with a clear window for the headlamp to shine through, leaving the light mounted on the forks). I'll post some photos as it develops, but don't be surprised if it takes a very long time. Ho ho.
I mentioned the conrod, with DUCATI forged into it. Does that really mean that it's a factory rod? Or were Mototrans allowed to let us think they were using Italian factory components?
Any and all advice and knowledge will be very gratefully received!
Onwards and upwards,
Peter.

[themoudie]

Aye Peter,

My 1974 450's conrod has "DUCATI" on the forging and when I had the crankshaft assembly rebuilt, it was carefully measured and pronounced sound and within tolerance for more use. It sounds as though you have a Ducati conrod and providing you give the engine plenty of clean oil (change every 1,000 miles) and don't lug the engine, it should be fine.

Some copper plated "pattern" rods do not take well to being revved and a friend had a "pattern" rod in a 450 "let go" whilst racing! Grenading the front of the barrel and making a mess of the crankcases. Some creative welding and machining had the engine castings back in shape and with a new stronger conrod, racing again. As you do not appear to be intending racing your engine, I am sure that it will be fine.

The 1975 350 MKIII MotoTrans engine that I have had the crank rebuilt, has the original rod. Having only done 1,400 miles before the strip and rebuild to check the rollers, cage and crankpin, due to the conditions I found it in, it still remains wrapped up. I cannot remember if it has "Ducati" on the forging and as it is still all wrapped and sealed awaiting the engine rebuild, I am loathe to open it all up for a looksee, until I am ready to install it in the cases!

If you have any queries, initially use the "Search" window in the top right of the "Motoscrubs" site window, or have a read through the "Tech" information, via the homepage screen button. There is a mine of information available to you.

Good health, Bill

[blethermaskite]

Peter, My 350 is still running on its original rod/big end! after an estimated 50'000 odd miles! (I know even I can't believe it ) oil changes at 1000 mile intervals and lots and lots of revs, in fact I have revved the brains out of it for years running at a 8500 redline, it may be a Spanish built engine but its a good one. Ref the conrod in mine.....I think I last had the barrel off about twenty years ago! so I simply don't remember if it has 'Ducati' on the rod or not, I do remember it was copper plated.
Cheers,
George

[Boxprod]

Firstly, thanks to everyone's accumulated wisdom and experience, without which this forum surely couldn't exist!

I have applied it to my rebuilding of my 350 Mk3, and it's time to write about how I've got on. The past weeks have been proper spring in Cornwall, and I noticed the forum was a bit quiet, but now the weather has come back in and normal service can be resumed.

The rebuild has gone slowly but it's been very rewarding to get to know the intimate details of the bike again after all these years. As I have mentioned, I'm on the tightest possible budget (like many of us, a retirement income is a fixed income, so no chance to spend big money unless the savings take a turn for the better - which is unlikely with the present incumbent of the White House).

So I've stripped, cleaned and measured as carefully as I can, and decided to reassemble with new bearings, a new shim or two, new gaskets, O-rings etc., but no big-ticket items. I spoke to Nigel about the big end and conrod, and he suggested that if I felt reasonably confident, even though the assembly might be at the lmit of the factory-quoted tolerance, I could perhaps get away with it for gentle road use. That saved a bit, given the time it takes for a skilled builder to true a crankshaft, leaving aside the price of a good conrod. Fingers crossed. But I did give it a new gudgeon pin, and sorted out the end float at the little end.
As for the piston, which is a 76.4mm Asso (first oversize for them). Although the clearance from bore to piston was fine, it did need new rings, since the existing ones had quite large gaps at their ends. Asso don't exist any longer, so I resorted to the caliper and the internet. Which revealed that a particular model of Daewoo engine had exactly the right size or piston rings - at a very reasonable price. (By which I mean the prices that mass-market Asian manufacturers charge rather than rare European classic parts prices.)
Bearings from internet suppliers come at good prices, too, even in "quality" ranges, so that didn't hurt too much. And new stainless fasteners ditto, including nice domehead nuts for the engine mounting bolts, which are now also stainless.

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Ebay helped with things like good slightly-used sprockets, and EBC Brakes yielded brake shoes which could be machined to fit. On the subject of brakes, I recommend a book by Graham Blighe (website is https://improvingclassicmotorcycles.com), and with his advice I have worked on the shoes to make them fully floating. I did consider doing what many racers and even manufacturers did in the 50s and 60s, which is to reconfigure the brakes to have the activating arm facing forwards, which effectively increases the servo effect; look at Velocette, for example, and you'll see that there was a concern that ordinary road riders might find such brakes too powerful. But for the double-sided Grimeca it would be a bit of a mission what with the air-scoops and the stays, so I've gone for what I could achieve. And I've drilled air exit holes which look very 1960s.
The price of Borrani or Akront rims is eye-watering,so I've had to replace the old, and surprisingly bent, ones with steel - but it is Radaelli steel, so at least that fits the history of Ducati. It's rewarding to make your own wheel-truing jig and actually build the wheels. Spokes can be very expensive or quite cheap, and I'm happy to trim them to fit. Tyres ditto, but I read good things about Mitas, and they certainly look appropriate, almost TT100.

It may be useful for some to know what I did with the electrics. Since I couldn't manage the full Electrex transplant, and since Steve of Bradford Ignition is only 45 minutes away, I got him to fettle my quite large supply of Motoplat bits. He pointed out that they were designed to be robust, for snowmobiles and chainsaws and the like, and they're still used by those who race classic Yamaha two-strokes, so although the ignition coil on the stator isn't particularly strong, it's the one that isn't encased in potting compound - and he can rewind it with about 25% more wire. Result: stronger sparks. And he tested the CDI coils, one of which has a rev-counter signal (for a Yamaha), so that means an accurate rev-counter rather than the waving needle of a Smiths or Veglia dial.

IMG_20250412_173056.jpg

Match that with a cheap Chinese reg-rec, and it's now 12 volts all the way to the LED lamps, including a focussed LED headlight and even indicators. Total demand can't be more than about 20W at most, apart from the horn, and then system now charges at over 14 volts without load, 13.5 with headlight. All on a tiny 3Ah gel battery.
It's all rewired from scratch with modern materials, fuses and so on, and it all works, encouragingly. I've bought a Tri-clour LED charging light from improvingclassicmotorcycles.com and added a small digital voltmeter in the headlight, so I have belt and braces for the electrics.

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There's a slightly modfied chain oiler (the blue reservoir mounter where the horn was originally) which can be set to drip onto either side of the rear sprocket for a couple of minutes by a simple twist of the cap - Google Cobrra to see how it works, and then buy an eBay copy.

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Thanks to Dave354 on this forum, who also happens to live in Cornwall, I've found a great place to paint the bodywork, and I've now settled on a soft metallic sage green, like the 750 SS first run (the green frame bikes). But I may go back to the Desmo yellow, although the frame is now silver (Smoothrite plus lacquer), and I don't think that suits the yellow. Once the paint's done, I'll get my wife's sewing machine and stitch the upholstery for the replica Imola seat.
Using a cheap temporary fuel tank hanging on a stay bolted to the tank support, I wheeled the old bike out into the yard sunshine. I'd primed every oilway I could, and kicked it over a hundred times with the plug out. Checked the static ignition timing yet again (36º BTDC or thereabouts). Replace spark plug. Turn on fuel. Open choke. Clear clutch. One kick all through. Over TDC with the valve-lift. Ignition on, and kick. And it only went and started! As you can all understand, I was just bowled over that all the work actually breathed life into the old thing once again. As I said to my son (a modern Ducati enthusiast), it seems to be making all the right noises and none of the wrong ones.

Hooray, and I'll let you know how it goes when I've got it on the road.

Must buy a new helmet....

Pete.

[themoudie]

Bellissimo!

Looking good Peter, I hope that you are able to enjoy many miles on the weee beastie.

Good health, Bill

[Dave354]

Good skills Peter, she is looking great and I bet that the satisfaction and relief when she fired up again after so long dormant was overwhelming. I know it was for me!
I look forward to seeing it in the metal, maybe the Jennings run in September I’ll have mine properly on the road to ride with you?

Best regards

Dave

[Jordan]

Good to read about your mods, Pete.
My own home-baked ignition system came about after the Motoplat CDI system failed - the stator's coil that makes big volts for ignition had evidently over-heated and stopped working. Unfortunately it, along with all the other coils, was potted in resin and a challenge to access for repair. I started digging into it, but when I found a diode was buried in there too, I decided to give up on this garbage arrangement. What good reason would they have for putting it there?!
The Motoplat timing pulser on the right side of the engine is a good thing though, and I kept that in my planned modification.
Some research found that Indian-made motor scooters had electrical systems that are clearly copies of Vespa and Lambretta designs. I was delighted to find that the alternators were very similar to those on Ducati singles, and had parts that could be incorporated.
Apart from Motoplat, Ducati Elettrotecnica made their own CDI alternator versions, without the dreaded potting. I couldn't find an affordable one, so starting with a spare non-CDI stator, I removed one of the coils and installed an Indian CDI generator coil (available separately) in its place - fitted perfectly.
For the high tension coil under the tank (and associated CDI circuitry) I used an Indian scooter version.
This system has proven to be successful and reliable for some years now.
The Indian parts were far more affordable than Euro bits.