Author Topic: 1975 Ducati 350 MKIII strip and rebuild.  (Read 1613 times)

themoudie

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Re: 1975 Ducati 350 MKIII strip and rebuild.
« Reply #15 on: July 12, 2023, 10:57:21 PM »
Making steady progress working through the disassembly and cleaning of engine components.

I have attached an image below that I hope is self explanatory, showing the components attached to the upper bevel camshaft drive shaft. You don't see that many shims in a Jap or British motor, let alone on a single shaft and a single bearing!  ::) Ducati at its best.

When I pressed the Self Aligning bearing out from it's bushing, the two large diameter shims appearred from between the bearing outer race and the bushing! :? The inner shim against the bearing is quite dished across its width and I wasn't expecting to find shims between the Self Aligning bearing and it's housing.

I may, MAY, use an alternative 350 cylinder head to the one that originally came in the tea chest, with other parts. So, questions asked of more learned souls than I on a Ducati singles forum!  :-\

When re-assembling a new bearing into this bushing should I insert these two shims before inserting the bearing, or should I omit them from the assembly?

And, what do I need to measure to ascertain the correct shimming, if required?

N.B. this is probably a late 350 engine assembled by MotoTrans, or using MotoTrans components, assembled by Ducati!  ::)

There is no indication of these shims that I can see in either the Clymer, or Haynes manuals.

I may be some time at this one!  ::) ;)

Good health, Bill

iansoady

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Re: 1975 Ducati 350 MKIII strip and rebuild.
« Reply #16 on: July 13, 2023, 09:02:41 AM »
And there I am struggling with a simple Triumph engine! Good luck Bill.....
Ian.
1964 Norton Electra
1969 BSA-Suzuki
1992 Yamaha SRV250

xbally

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Re: 1975 Ducati 350 MKIII strip and rebuild.
« Reply #17 on: July 13, 2023, 07:29:47 PM »
Have just come back from a Shelsley Walsh evening meet-there was a 70's Ducati single and a Laverda Jota there-very nice too!
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themoudie

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Re: 1975 Ducati 350 MKIII strip and rebuild.
« Reply #18 on: July 13, 2023, 11:20:36 PM »
Thank you Ian, I'm no sure about the "simple" bit, you appear to have cracked the holding pushrods, compressing piston rings whilst lowering barrels conundrum succesfully. ;)

Just been out for a canter on the 450 afore watching tonights "Who do you think you are?", plenty of urge left at half throttle (60mph) and getting 20 miles to the litre (89mpg) consistently, E5 or E10, with Millers Oil VSPe Power Plus added, so far so good.

All the best with the Grumph build.

Thank you xbally for the compliment. Like all machinery getting on for 50 years of age, they require "attention" and can be cantankerous, but give me a lot of pleasure.

Good health, Bill

Steve Lake

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Re: 1975 Ducati 350 MKIII strip and rebuild.
« Reply #19 on: July 14, 2023, 06:45:11 AM »
Like all machinery getting on for 50 years of age, they require "attention" and can be cantankerous, but give me a lot of pleasure.

funny that.... i said that about SWMBO ..   i'm currently living in my workshop ..  might get repatriated in a week or so  ;D

themoudie

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Re: 1975 Ducati 350 MKIII strip and rebuild.
« Reply #20 on: July 14, 2023, 09:11:32 AM »
You asking for a skelp round the lug there! ;D  Lucky, you wus allowed to stay in the dry workshop and not put out to grass, like that old dicker!  ;)

Cauli's and broccili coming out our ears and the rasps/blackcurrants as well.

Good health, Bill

xbally

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Re: 1975 Ducati 350 MKIII strip and rebuild.
« Reply #21 on: July 14, 2023, 02:00:26 PM »
Yes my1996 Ducati Monster 750 has turned into something of a cantankerous money pit.....last 2 years on and off the road with one problem after another.......Spent last Friday trying to cure fuel starvation problems to no avail. Now have to fit another fuel pump and correctly moulded OE fuel hoses in an effort to get it running something like again. Like the older singles its a great visceral experience to ride...when it's going well.
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themoudie

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Re: 1975 Ducati 350 MKIII strip and rebuild.
« Reply #22 on: July 15, 2023, 04:18:20 PM »
Thought that I should check clearances in the cam drive upper bevel, after finding extra shims, not mentioned in workshop manuals i.e. the ones at the back of the upper bearing, inside the bushing. (See image attached to July 12, 2023, 10:57:21 PM posting)

I mic'd up the components and they measure as follows:
Depth of bushing (internal) = 11.20mm
Depth of bearing (overall) = 11.00mm
Shims = 0.23mm and 0.21mm
Raised inner rim of tower = 0.10mm
Gasket = 0.10mm

So, no wonder the second shim was being squeezed from between the bearing and the back of the bushing. Trying to squeeze 11.44mm of bearing/shims into 11.20mm of bushing + say half the depth of the gasket after torqueing = 0.05mm, means 0.29mm of pre-load on the outer bearing track!

The gasket surrounds the rim of the tower and is of the same depth, so when the tower is torqued to the cylinder head I would have thought that would provide sufficient load to the outer bearing race to hold everything snug, with only the 0.21mm shim in place behind the bearing in the bushing.

Engineer's comments welcome.

Suspect worn tooling, mismatching Spanish/Italian components and clumsy assembly at the factory! :(  Sounds familiar to those who have studied the UK motorcycle industry debacle and actual Italian "engineering", rather than the "rose tinted" gloss! :(

More micrometer work at the assembly stage. ;)

Good health, Bill
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Steve Lake

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Re: 1975 Ducati 350 MKIII strip and rebuild.
« Reply #23 on: July 16, 2023, 06:57:30 AM »
come on Bill, you know you love the challenge  ;D , all i can say is ... i won't be getting myself a ducati any time soon, or any italian bike for that matter  ;D , ok, my Son's 350 morini is a lovely bike, both to look at and ride, but ye gods did we have a game sorting out a missfire  ... which only happened once the bike was warmed up ... yours truly was called up as Son figured it was an electrical issue, i had it here for 2 weeks, went through everything, timing, quality of HT, etc etc, even got my oscilloscope out to watch the advance/retard curve on both cylinders, so it wasn't electrical, while i had it i went through the fuel system with a fine toothed comb and found no problem there, but ... i did find, that after a 30 min bimble around the lanes that the front pot was a lot hotter than the rear (unusual, as you would, if anything expect the opposite) so out of interest i got out my trusty 'colourtune' and found that the rear cylinder was not firing consistently, we'd changed the plugs, so i changed them again ... to no avail. not having ever checked compression 'on the fly' (nor know how to) we took off the rear rocker cover and found that the exhaust valve rocker was nipping up when hot ... seems Son had over tightened something or mixed up some shimming ...  funny old world .... (well, the world of old italian bikes may not be quite so funny )

themoudie

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Re: 1975 Ducati 350 MKIII strip and rebuild.
« Reply #24 on: July 16, 2023, 08:30:57 AM »
Morning Steve,

Thank you for the info, I too have been through that rigmarole with the Morini and although it is clear what steps are required to make adjustments in the Morini manual, it can all get a bit shoogly as you tighten the rocker pillows (support blocks) and if you don't give them enough room they nip up. Old BMW 5, 6, and 7 series have a similar set-up and most people give them a bit of slack, "just in case", hence the castenet symphony!  ;)

Mine is definitely lack of electrically induced advance, caused by an incorrect voltage coming from the trigger coil to the CDI circuitry and the advance, which is switch like and not a smooth curve, not being triggered. The advance is not extreme for an "old school" 125 4 stroke single, with 11:1 compression, of 36° BTDC @6,000rpm, it just won't rev above 2,500 - 3,000rpm, coughs and splutters and then dies! :(

Out for a canter today sometime, after doing some chores about the place.

Cheers, Bill