1975 Ducati 350 MKIII strip and rebuild. MotoTrans?

[themoudie]

HELP PLEASE: JON PEGLER

Aye Jon, at present I am in the process of rebuilding a late 1975 Ducati 350 MKIII widecase engine. I am the 3rd owner from new.

George (blethermaskite) also has one of these late 350's that apparently the MotoTrans factory built for Ducati and they have 32mm OD crankpin crankshafts.

My engine number: #18013 This, I am told is not an Italian Ducati engine number?
The machine was first registered in London, UK, on 8th, October 1975, the last road tax renewal disc was purchased on 16th, September 1977 and expired on 1st, October 1978. The bike has not been taxed since then and has never been subjected to a UK MoT test (DVLA online records).

Nigel Lacey is checking over the crankshaft for me and has found some oddities:-
1. The crankpin is 30mm OD, not the expected 32mm OD.
2. The conrod shims are 0.90mm in thickness, when 1.00mm thickness is the "standard" usually fitted.
3. The original honing marks on the crankpin are still visible, indicating a low mileage; as do the bright rollers, showing no dulling/wear.

I can confirm the latter, as I have found at the bottom of the box of "bits" the original Smiths speedo head, displaying 01405.4 miles. I was sceptical of this mileage, at the time of purchase, having experience of these instruments on my 1974 450 MKIII, owned since 1976! But, Nigel's experienced eye and engine knowledge would tend to indicate that this mileage might be accurate?

The engine was fitted with screw adjuster rockers and an apparently "soft" cam.

The clutch adjusting plate on the nearside outer case does not have the wording "Made in Italy" cast below the "DUCATI" cast lettering. Also all of the polished alloy casings on Italian built machines appear to be made from a different die-cast alloy, as these "Spanish ?" casings do not take the same degree of polish. I know that this machine has been neglected and kept either outside by the original owner, until sold in 1989, or holding up a leaking shed roof belonging to the previous owner, from whom I purchased it in 2000. Since my acquisition the boxes etc have been sitting in my dry, workshop, awaiting the time I would release the moths from the boxes and my wallet!

I do not have the "original" cylinder head, so cannot check the tell tale increase in height of the fins above the exhaust port that I believe is a diagnostic feature of MotoTrans built engines.

I attach images of the clutch case, cam and cam with the rockers.

Do you have any factory information that might confirm that this oddball engine came from Mototrans?

Thank you for your time.

Good health, Bill

[Bevel bob]

My knowlege of this model is miniscule , the cam does not look too soft for practical road use . The primary cover could have come from another bike as it exhibits more damage than mine that has had a hard and long life.

[Jon Pegler]

Hi Bill,

Your engine number is the indication of a Mototrans build. An Italian built 350 motor would start with 0----.
I've come across a number of these motors over the years with their unique Mototrans characteristics.
I'm not certain of the exact numbers but I think almost 1000 of these motors were built and fitted into Italian 350 Mark 3 rolling chassis, certainly over 900.

The camshaft fitted is probably a mild Scrambler ( white ) cam. The rockers look to be Mototrans items.
The crank is probably an early type widecase crank, Mototrans not fitting the later rod/crankpin until after 1976. It may well have a date stamped onto the flywheel. I would guess a 1973 date. ( I know engine number 18900 is stamped 12/73)
I would also guess that it has the Motoplat flywheel with the odd size thread for the extractor 62 x 1.25mm rather than the Italian 62 x 1 mm threaad.
It would have had the plastic oil pump gear fitted originally.
Once Bologna stopped producing Ducati singles Mototrans upped their game for a few years and started using all the later Italian developments, like the larger crankpins. They then went on to produce the 350 Vento/Forza range from 1977 and the Strada 250 from 1978.

By the mid-late 1970s quite a few 350 Mark 3s were being sold by West London Motorcycles in Acton, one of the last suppliers of Ducati singles in London. It may well have come from them. They were still selling new, old stock bikes until 1978.

Jon

[blethermaskite]

Bill, My 74 350 mk3 350, is as far as I can determine a Spanish constructed engine, tall exhaust port fins, long head fin round to the inlet port, no made in Italy on the clutch inspection cover, motoplat electronic ignition, ........but.....a green and white cam, solid rockers, and a steel oil pump gear, I have never had the bottom end of this motor stripped from new so I don't know if it has the Spanish alternator, and I don't know what dia. the crankpin is. My engine number is DM 350 17824 I think the dealer here in Northern Ireland I bought from got all his Ducati machine stock from Coburn and Hugh's ???? Hope this info is useful......if only to add more confusion
Cheers,
George

[blethermaskite]

One other possible bit of ID info, my 350 was one of the ones that came with the impossible set up of clip on bars and forward footrests don't know if that was a Spanish or Italian eccentricity
Cheers,
George

[themoudie]

Thank you Bob, Jon and George, for all the info.

So, Mototrans engine!

I think that a 173 cam might be a useful addition to replace the white(?) cam, there's one in the spares stock!

Not sure about the date stamp on the crank, as that is with Nigel at present.

Yes, the Motoplat flywheel, with the odd size thread 1.25mm, rather than 1.00mm pitch was fitted. However, the perished cable covering emerging from the totally encapsulated stator guaranteed that the whole assembly was heading for the recycling bin, along with the accompanying rat's nest of degrading multi-coloured spaghetti and green verdigris terminals. Electrex and Vehicle Wiring Products products are going to replace them.

A plastic idler gear was fitted and melted when I applied some heat to ease the seized lower bevel woodruff key etc, a 2nd hand steel replacement is on the list.

The West London Motorcycles, Acton, dealership sounds a plausable supplier, even though Coburn & Hughes were the sole concessionaires at the time, especially as the leading three letters of the registration number are "LLU". Now you know what it is going to be named, especially as it has been up here in Scotland all it's days.

The Ducati concessionaires were Coburn & Hughes, Luton, in the mid 1970's, after Vic Camp gave up the business and John Wittman, "Witty Ducati", had bought the Vic Camp business. After I had bought my '74 450 MKIII from The London Motorcycle Centre, Wandsworth, they had 6 x 250 MKIII, 1 x 350 MKIII and 4 x 450 MKIII, plus a couple of 250 Desmo and a single 450 Desmo, all seconhand that I could choose from in July 1976. I obtained my spares from John Wittman. I did visit Coburn & Hughes, as they were within 20 miles of where I was living, but the place was in uproar, with the amount of warranty work coming back in the door, including the "Scrambler" singles, 750S and 750 GT twins. There were lines of 250 and 450 MKIII's, a few 350 MKIII's and all that I saw had the "chiropracters dream" set up of dinky clip-ons and the forward set footrests, as did my 450. I think that this was the "standard" set up and can be seen going back to the 250 models of the early to mid 1960's. The top yoke mounted, raised bars, being very "unfashionable" in Italy. Only the Desmo's had the rearsets, along with the same clip-ons as the MKIII's. The 350's and 450's having the de-compressor lever mounted on the left-hand clip on, beneath the clutch lever. It wasn't until the early 2000's rebuild that I put home made rearsets on mine and the swan necked clip-ons in 2020. I have still to decide what setup I am going build this 350 with, but it won't be the "chiropractors dream"!

Good health, Bill

[themoudie]

UPDATE!

Received a new cylinder liner, piston and other bits from Nigel and went and spoke to a local engineer, who has years of experience and runs a very nice BSA Rocket Gold Star himself and asked if he would tackle the cracked liner replacement, to which he agreed. I don't have the engineering skills or tools required to machine the cylinder head bolt cutouts in the liner flange, or to relieve the skirt sufficiently to allow clearance for the flywheels and the con rod.

Today, after being away for a short break, I was captured on the telephone. The old liner came out after baking, no problem, but the cylinder muff was oval, interference between the muff ID and new liner OD was 0.005" and when machined at the factory the muff bore was scored from top to bottom, as the tool had not been retracted, before withdrawing it from the bore! "¡AH! ¡No lo verán!"

After adjusting the interference between the muff and new liner, it was popped into the re-heated muff and held in place using a threaded bar and plates to hold it fully seated, until the assembly cooled. Upon checking, the liner flange was fully seated on one side and had a 0.0055" gap at 180° opposite from the top of the muff!

Nothing for it but to put the assembly back in the oven, remove the liner and check that the liner flange was indeed at 90° to the liner cylinder, also that there were no burrs or protrusions from the upper surfaces of the muff to prevent seating. All seemed well, so back in the oven, slide in liner and clamp. Yet again, the liner flange was fully seated onto the top of the muff on one side and had a 0.0055" gap at 180° on the opposite side, from the top of the muff!

It would appear that the upper and possibly the lower faces of the muff are not machined at 90° to the bore of the muff and consequently the liner cannot seat correctly on the upper surface of the muff. If the lower face of the muff is also not horizontal to the bore, or the crankcase mouth, then I have further misalignment.

This may be the reason for the heavy black oiling/ blow by that was stuck to the inside of the whole of the crancases and their contents and why the piston had been attacked with wet and dry by the previous owners. The side thrust forces on the piston rings, would have prevented them from sealing and the old liner is certainly oval in the bore and cracked from both of the 90° nibbles made in the liner skirt to allow for the con rod clearance.

So, instead of being a relatively straightforward liner replacement, this is going to cost as much as I paid for the whole bike 23 years ago!

The liner is going to be moved in the muff so that ~10mm protuds from the bottom of the muff, rather than the flange being fully seated. Then two aluminium mandrels are going to be machined up so that the liner can be used as the mandrel through the whole assembly and the upper and lower faces of the muff machined, so that they are horizontal to the bore of the liner. The barrel assembly will then have to go back in the oven, heated and then be clamped, so that the liner flange sits tightly to the upper surface of the muff when cool.

A whole lot of faffing and I can see the engine alone costing £2,000 in bits and engineering labour, before I let myself loose on it to assemble it. Squish clearance, valve clearance, bevel drive shimming, ........

It would appear that the older less developed narrow case engines, might have been better made than widecase engines and any late widecase engines, still running, are probably the best of the bunch. Any engine, with a low mileage and having lain for any length of time, with mechanical problems, has probably self destructed from bad production techniques, lack of quality control and possibly within the original warranty period.

"Así es la vida!"

I'll keep you posted.

Good health, Bill