Author Topic: 1975 Ducati 350 MKIII strip and rebuild.  (Read 1612 times)

themoudie

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1975 Ducati 350 MKIII strip and rebuild.
« on: June 12, 2023, 01:39:07 PM »
Just to keep you on your toes, I thought that I might post, perhaps infrequently, snippets and details of this rebuild of a 1975 Ducati 350 MKIII that I acquired in "big lumps" from a leaking shed, the roof of which it was holding up, having previously been rescued from a skip in Edinburgh as the then owner was emigrating! ???

First conundrum when stripping the engine is the removal of the alternator rotor. This is usualy achieved using a bell shaped extractor, with a 60mm OD x 1mm pitch thread that threads onto the hub of the rotor and then using a central screw against the end of the crankshaft, eases the rotor off the crankshaft taper. Not this one!  ::)

I had not seen a plain brass rotor afore and with my rotor extractor not fitting, resorted to making up my own puller, using bent M8 threaded rod and nuts, to hook behind the rotor; a piece of M10 threaded rod, with nuts to act as the central pressure screw and a piece of 65mm x 35mm x 3mm MS box section, drilled to keep all the threaded bits at the correct distances apart. I was able to "pop" the rotor off the taper on the crank, with relative ease.

What I found behind the rotor was that I was the pround owner of an early Spanish 'Motoplat' generator/ignition set up, with 4 rubber insulated wires, 2 x yellow for the regulator/rectifier charging the battery and a single red and single blue wires for the the ignition CDI/coil. The rubber coating is perished, exposing the tinned, multi-core cable beneath!  :(  Usually, Ducati used 'Ducati Electronica' components, but the fitment of this Spanish component would suggest that it is one of the last 350 MKIII engines built by Ducati and assembled in Spain in the MotoTrans factory, under license and where these engines continued to be manufactured until 1983 in the production of the MotoTrans 'Forza' and 'Vento' 350cc models. The latter being a stotter in it's later form. ;D

So, rather than re-using an unknown quantity 'Motoplat' generator, with dodgy insulation, I am going to have to resort to an 'Electrex' replacement set-up that'll not be cheap!  ::)

Good health, Bill

iansoady

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Re: 1975 Ducati 350 MKIII strip and rebuild.
« Reply #1 on: June 12, 2023, 02:46:35 PM »
Good luck! I actually think much of the interest in these projects is unravelling what a series of previous owners have misguideldly done. Better than Inspector Morse!
Ian.
1964 Norton Electra
1969 BSA-Suzuki
1992 Yamaha SRV250

themoudie

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Re: 1975 Ducati 350 MKIII strip and rebuild.
« Reply #2 on: June 12, 2023, 03:09:07 PM »
Aye Ian, that's why I like my family genealogy, it takes me to all sorts of places across the globe and all sorts of human situations!  ;)

Good health, Bill

Itsme

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Re: 1975 Ducati 350 MKIII strip and rebuild.
« Reply #3 on: June 12, 2023, 03:10:27 PM »
Crikey Bill that all sounds a bit complicated to me, but good luck in figuring it all out. As I age I realise more of my own limitations and rather than assuming I can tackle complicated jobs (be it bikes or buildings) I look at the bits I know I can do and then find some talented chap, or chapess, to do the other bits. This way I am finding less frustration at not being able to do a job and more pleasure at doing the bits I can do.

You sound to have taken on a big job there but I bet you will end up with a very lovely bike.

Ian

CrazyFrog

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Re: 1975 Ducati 350 MKIII strip and rebuild.
« Reply #4 on: June 12, 2023, 05:16:01 PM »
Interesting Bill, I look forward to seeing and reading more about it!
2023 Royal Enfield Meteor 350
2021 Honda CB125F

Moto63

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Re: 1975 Ducati 350 MKIII strip and rebuild.
« Reply #5 on: June 12, 2023, 06:14:33 PM »
Interesting Bill, I look forward to seeing and reading more about it!
Me too. Best of luck with it Bill 🤞

themoudie

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Re: 1975 Ducati 350 MKIII strip and rebuild.
« Reply #6 on: June 12, 2023, 07:46:01 PM »
Thank you for your interest. Wait until I start the re-assembly shimming of everything on it's shafts and then the shafts into the crankcases, that's when the "fun" really starts!  ::)

Good health, Bill
« Last Edit: June 12, 2023, 11:43:42 PM by themoudie »

themoudie

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Re: 1975 Ducati 350 MKIII strip and rebuild.
« Reply #7 on: June 12, 2023, 11:59:26 PM »
Stripped out the stator tonight that uses 4 x M5 x 15mm slotted cheesehead screws to hold it in place. They had been stud locked and spring washered in place!  :(

A ½" drive impact driver head was too big to fit in down the side of the stator. So, I had to resort to a ½" impact driver, with a ½" to ¼" converter, ¼" extension, 8mm ¼" socket and wide slot impact driver bit. Hit with a 2lb hammer!  ;D

The Motoplat Electronica encapsulated stator, from 1975, so 48 years old, showed cracking of the potting material due to stress from the wires and some of the wrap covering one of the generator coils is coming away.

Finally, the Motoplat stator wires, are showing perished insulation on the exposed ends of the stator feed cables that have been exposed to sunlight. Those wires exposed in the engine as they pass through the stator backing plate and within the outer cable sheath appear to still be in good condition.

However, as these Motoplat systems have a known short life expectancy, 30K miles, before going "PHUT",  :(  the whole lot are for re-cycling and replacement with modern Electrex components. The brass rotor when polished up will make someone a grand fridge magnet or paperweight!  ;)

Good health, Bill

Moto63

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Re: 1975 Ducati 350 MKIII strip and rebuild.
« Reply #8 on: June 13, 2023, 11:50:17 AM »
The brass rotor when polished up will make someone a grand fridge magnet or paperweight!  ;)

Good health, Bill
Err…. Last time I looked, I don’t think one can magnetise brass 🤦???
However with all the stress of impact drivers etc you’re having I think we can  all let your little slip go amiss Bill 😁
Cheers Michael NOT a magnet expert

Itsme

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Re: 1975 Ducati 350 MKIII strip and rebuild.
« Reply #9 on: June 13, 2023, 06:23:05 PM »


Don't they use brass tools in perfume factories to prevent accidental sparks from detonating the highly volatile base liquid that perfume is made from?

Ian

P.S. I'm not a magnet expert either Michael and I have no idea why I would possibly know anything about perfume!

Moto63

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Re: 1975 Ducati 350 MKIII strip and rebuild.
« Reply #10 on: June 13, 2023, 08:06:23 PM »




Michael I have no idea why I would possibly know anything about perfume!
Oh come on Ian. You gave the game away when you let it slip (see what I did there😉) about your blue alter top 😁

Itsme

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Re: 1975 Ducati 350 MKIII strip and rebuild.
« Reply #11 on: June 14, 2023, 05:30:19 AM »
I'd forgotten that my secret is out!

Delores the confused

Steve Lake

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Re: 1975 Ducati 350 MKIII strip and rebuild.
« Reply #12 on: June 15, 2023, 06:25:35 AM »
Ever the purist Bill ... this could get expensive!!!
if it's anything like my 'bargain' #10 then there are surely many more horrors yet to reveal themselves .... just saying ...

themoudie

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Re: 1975 Ducati 350 MKIII strip and rebuild.
« Reply #13 on: June 15, 2023, 08:27:12 AM »
Aye Steve,

Quote
Ever the purist Bill ... this could get expensive!!!
if it's anything like my 'bargain' #10 then there are surely many more horrors yet to reveal themselves .... just saying ...

Oh, don't I know it!  ;)  But, the SRX Mono cost £1,000 to rebuild the engine alone and another £1,000 for the rest of the chassis bits and pieces.  :'( :'( :'(  On the plus side we both use it and have been putting on 3K to 5K a year since it was back on the road. On a good day somebody might part with £2,500 for it, but I suspect ~£2,000 would be nearer the mark in the current climate.

As for the 350 MKIII, purchased about 20 years ago for £450 and sat in the dry, so no further deterioration. However, the engine could swallow £2,500 nae bother and the chassis another £1,500 and with clean 350 MKIII's now fetching £4,500 to £6,500, depending on how "original" or "BLING" the machine is. Being mine, the machine will be rideable, clean and modded to make it as easy to run as possible, not pimped to hang on a wall, or gawk over in a pub!  ;)

Having to use 10mm threaded rod to prise the crankcases apart, along with nylon felling wedges and a 2lb hammer!  ::) ;D ;D ;D

Bit hot for troshing, so take shelter and work "Como un español" or "Como una española", depending upon your gender in these PC times! ;)

Good health, Bill

Moto63

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Re: 1975 Ducati 350 MKIII strip and rebuild.
« Reply #14 on: June 15, 2023, 09:16:54 AM »
Being mine, the machine will be rideable, clean and modded to make it as easy to run as possible, not pimped to hang on a wall, or gawk over in a pub!  ;)



Good health, Bill
Well said 👍.. best of luck with it Bill. Looking forward to seeing, reading your progress with it over the coming weeks/months/years 😉🤦???
Cheers, Michael