Motoscrubs.com

So I've been putting some mileage into my recently bought 1975 350 Mk3 and have been fixing a few minor faults.... worn carb slide, breather pipe, dodgy cables. And it's come to my attention that the bike didn't really have the full PDI check that the bike shop promised, less than tight chassis fixings and cylinder head bolts and.....although the engine oil was clear when it was delivered, after 100 miles, the dipstick said it was missing about a litre of oil (although it could be the dipstick lying as I've read they come in different lengths). I received almost no history about what work has been done to the bike, beyond some receipts and MOTs from the 1980s. They show the mileage being only a thousand miles less than what it's showing now, so I'm not sure what's happened there...
The engine appears to be a bitza, as the head looks Italian (short fins etc) but the engine number (starting with a "1") suggests Mototrans.
This being the case, I'm going to do an oil change and check the oil pump idler gear for plastic.
Some questions for people out there, if you don't mind......
It has Electrex World ignition fitted, Can I remove the oil pump cover without disturbing the timing?
Is there a way of telling if a high capacity oil pump is fitted (once the cover is off) markings of some sort?.
The bike runs well, pulls nicely at low revs but runs into some heavy vibration between 4000 and 5000 RPM (mostly felt through the left hand footrest) but then seems to smooth out above 5k, is this fairly normal? Because of my nervousness about the engine's history, I'm reluctant to keep the revs high for too long until I've checked the pump. It's running an Amal Concentric 930/301 and the plug was quite sooty until I replaced the slide, possibly the needle might be worn as well?

Hi,

Lots of questions in your post! Your engine may well be a Mototrans, as Italy fitted their engines into their bikes towards the end of production (see '1975 Ducati 350 MK111 strip and rebuild' by themoodie) which covers just this subject.

It is easy to tell if your oil pump is a standard Ducati one as the aftermarket ones look completely different. The ignition rotor can only be fitted in two positions, so if you align the timing dots on the timing gears and mark the rotor position with a marker pen you should be OK. You will probably have to turn the engine a few times to realign the bottom timing dots, but the ignition rotor should still go back in its original position.

Vibration is normal on the 350, just keep an eye on the tightness of the engine mounting bolts. As for the shop's PDI, we read so many things about dodgy dealers, that it seems good policy to take anything that a seller say's with a pinch of salt.

Cheers,

Colin

I have exactly the same machine, so mine has a Mototrans engine which has been running faultlessly now for nearly 50 years (yes really) and I would estimate has about 45 maybe 47/48 thousand miles on it, (don't know lots of failed speedometers!) my engine does not have a fibre timing gear has been steel from new, just post us a photo here of your oil pump when you get in there, mark the timing unit position and just don't move anything while you have the timing cover off and it should be an easy refit. Re vibration ....thorny question I would say my engine is remarkably free from vibration right through the rev range (I rev mine consistently to 8500) ,however I am on rearset footrests and I have a vague memory that the standard rests were a bit more vibration prone......probably because they are bolted to the engine crankcases rather than the frame, frankly in my experience no two similar used Ducati's ever seem to run exactly the same on the vibration front, very much down to who has been into the engine and what they have done in there? mine has never had the engine split from new (yes really) so is as originally built. Hope this helps.
Cheers,
George

blethermaskite wrote: mine has never had the engine split from new (yes really) so is as originally built.
George

At nearly 50 years, that is impressive. You must be the gentlest gear-changer ever.
And you may have had the luck to buy a particularly well-shimmed and assembled engine.
I know of brand new Ducati bevels (twins) that were disassembled by enthusiastic owners and rebuilt, before any riding was done.
Nice to work on new clean engine internals!

A bit off topic here (apologies to the OP) but regarding gear changing: many years ago I took my Ducati 750 bottom end to Anthony Ainslie's workshop for him to look at the main bearing bosses on the crank and for reassembly. He got me busy washing off all of the parts while he examined everything through an eye glass. He then exclaimed:"You know how to ride your bike don't you?" Asking what he meant, he told me that there was no wear in any of the gearbox components, because I was careful in my treatment of the gearbox, unlike a lot of riders who are brutal.

Quite an eye-opener to me. Clever man Anthony.

Cheers,

Colin

I'm the same as you Colin and I suspect it comes from being the person who rebuilt multiple gearboxes in an earlier career (albeit mainly cars, trucks and earth moving equipment). It always amazes me how some people change gears with little appreciation on what's going on inside the box to make it happen.

Ian

I have always found the gearbox on my 350 particularly sweet in operation, however it did get a bit notchy a while back before I took it of the road for the last couple of years, so while I was fitting my new 12v alternator I of course had to dismantle the clutch....and therin is another tale and lesson to be learnt......I replaced the full set of friction and steel plates about six years ago with a nearly new used set that came from a blown up race engine, they were cleaned carefully and fitted.....all worked fine....so when I stripped it last week the steel plates were severely rusted and the friction plates were covered with 'goo', the reason? the plates I had fitted had been running in Castrol R which had absorbed condensation in the engine and had rusted the plates plus had reacted with my mineral oil and produced the 'goo', all cleaned up another set of SH plates and back to normal nice gear action
Cheers,
George

Check that the primary gears have a little backlash at all positions. Mine had a tight spot caused by the crank being out of line and doing an impersination of a skipping rope .

OOOer Bob!

Mine had a tight spot caused by the crank being out of line and doing an impersination of a skipping rope .

That sounds a bit iffy, but no doubt you are living with it, with no ill effects to date.

I have yet to measure my '75 350 MKIII cases to see if MotoTrans managed to bore them parallel to the crankcase mouth and at 90°to the central case faces. All has gone quiet, with regard to the liner and muff, so I can only hope for a premium bond payout this month to pay for the remedial work. Maybe have to punt it on, rather than complete the rebuild?

Good health, Bill

Timing: If it's not kicking back when you start it (not too far advanced), and if it's running well (not too far retarded), the timing is probably pretty close.
Oil: Dump out the old — lean the bike over to get it all out — then pour in the proper amount. Dip sticks on the singles are....iffy.
Transmission: I upshift both my 350 and 250 without the clutch and they shift very nicely that way in the lower rpm ranges.
Vibration: Nothing out of the ordinary, both run smoothly.
My Sebring has been impressively reliable, no problems whatsoever; after two years of daily riding had to put a rod in the 250, which was poorly maintained before I got it.