250 Strada Strip Down

[Duccout]

Hi Nigel,

Thanks for the pictures, very interesting, I wonder why Ducati never did a similar thing on the production line? Although AFAIK the modern Scrambler models still use the same angular thrust bearings that started way back with the first 750's, so maybe Ducati could say that they got it right.

I was lucky to get my 750 bottom-end back from Anthony's workshop, I left it with him and he told me to telephone in two week's time, but every time I called he never answered the phone; this went on for a few weeks and eventually I got an answer and he asked me to come over on Sunday and assist while he rebuilt the engine. I learned a lot! When the time came to leave he said that he could not help me carry the engine down the rickety old wooden staircase outside his workshop because he had recently had an operation; how I managed to carry it down without dropping it and breaking my neck was a miracle. Shortly after that Anthony experienced personal issues and disappeared and apparently some customers never saw their engines or parts again!

Cheers,

Colin

[Jordan]

Like this....

Nigel

That looks nice Nigel, but necessary?
I won't say there should be no problem with bearing inner races spinning on shafts, just because it never happened to this mild-mannered rider.
I'm wondering if a higher strength grade of Loctite than the one you tried could have succeeded.

[LaceyDucati]

Jordan

Not for road use and you would struggle to install the nut with an alternator.

This was for race use and my aim has always been to try and prolong the life of what are rare components. Wear on the journal of an already used crank is inevitable in race use and it's only a matter of seasons before it becomes unservicable. In the past that just meant the sacrifice of another cheap unwanted road bike, which is not an option nowadays. Metal spraying and hard chroming are viable options for repair, however it's not as easy to successfully repair as many think and also not cheap. That is if you want a true running crank afterwards! Making new cranks is also an option (as the one in the picture) but for many the price would cause serious distress

The issue with Loctite for me is the wear is not even (mostly on one side) and gluing it in the centre of the wear will make the crank run out ( further than it probably does anyway!). This can also be a problem if the crank is worn and you try and tighten it into the main, but that's another story. It's all about perspective and I fully appreciate that sometimes "needs must" leads to all sorts of fixes and wishful thinking. Certainly for most road use the requirements are far less critical. The loctite I used was a fairly strong engineering adhesive, however I think the gap (wear) was too small and it was just beaten out under load, heat and vibration from misalignment.

There is sometimes a lot of misalignment in the crank main bearing area and this is maybe part of the issue with wear in this area. Being inquisitive...."why is that like that" and trying to specify tolerances for the manufacture of parts has meant I've had to look further. All I can say is that over the years the more I discover the more I wish I hadn't! I'm sure Ducati wasn't the worst but Ignorance of some of the finer detail is bliss!

Regarding the later bikes like the modern scrambler, my guess is the cranks are harder on the journals and being one piece cranks align better, when compared to the old bevels,

Nigel

[Harvey]

Thanks Nigel for that interesting bit information.

[Duccout]

I mentioned that the timing side main bearing outer race was polished where it faces the flywheel where had been rubbing against something, and on closer inspection it has been running against the sealing plug in the crank-pin.

Cheers,

Colin

[Jordan]

it has been running against the sealing plug in the crank-pin.

Mystery solved. Thanks for the info.

[Duccout]

Quick update:

The crank is on its way back from Wales where Nigel has fitted a new big-end and I am in the process of checking the bottom end and gearbox parts prior to shimming everything. I have checked the oil pump drive alignment and that is OK.

The head is all checked over and wrapped up ready to go back on, and I found something really weird when I stripped it - the inlet port was coated in a layer of sticky gum. I don't know what it was, but it wiped off easily with petrol and a rag, so I am puzzled why it built up in the first place when it was petrol soluble? I can only guess that the gum is ethanol that is left behind by contact with the hot inlet port.

Old men in sheds......

Cheers,

Colin

[Bevel bob]

Tank liner disolving?.

[Duccout]

No, the tank is not lined.

[Duccout]

I have an early Christmas present - a crankshaft from Nigel with a new big-end! I've also found that the kick start shaft bush in the crank case is loose and has been turning with the shaft...... You never know what you will find.


Colin