Ducati 250 mk3 1974, fitting a timing wheel

[Scottish888]

About to change over to a points set up from the Ducati Electronic ign.
I bought a timing disc on ebay, meant for motorcycles but it is quite large, 190mm diameter so I will have to mount it further out.
After removing the brass hex plug I can see the screw inside the crank, I think that screw is for holding a timing disc but outside that is thread that takes an 8mm bolt, (screws in 10mm deep) I would prefer to use that thread to mount the timing disc, is that ok to use that thread?


Regards,

[ducwiz]

Yes of course, it is. The user and workshop manual show, that a timing wheel or a pointer tool can be mounted, to enable ignition timing adjustment manually or using a strobe light.
The "screw" - or it's slit - you see, is a grub screw with a conical head, which seals off the oil passage to the primary gears. The oil flows from the crank pin through the hollow LH shaft.

cheers Hans

[Jordan]

I think a disc of 190mm diameter may be too large to use with a strobe, engine running.
But it's very good for static timing!

[Scottish888]

Thanks folks,

I did not want to remove that grub screw as I tightened up in the rebuild and rather not disturb it, dont like slot heads. I should replace it with an Allen screw in the future.
The Haynes manual suggested to remove and use the grub screw thread but i'd rather use the 8mm thread.
Thanks again.

[themoudie]

Aye Alex,

I hope that you have better luck than I did. The root cause of all my woes was a faulty AAU. Since lashing the cash on an Electrex ignition set up 'STK 169D', the difference has been night and day. If I had recognised the problem from the initial backfire and carb blow-off on the third kick in September 2019, I could have saved myself 20 months and the best part of £500 of expenditure!

If you require dimensions from the timing disc holder that I use I will see what can be done. With the Electrex ignition, the set up and timing marks are all on the right-hand side of the engine, so no hopping about from one side of the engine to the other and requiring an assistant to provide the remaining "octopus arms and eyes" when timing, with the strobe!

Good health, Bill

[Jordan]

But there is only one threaded hole in the end of the crankshaft - 8mm.
Where is the other referred to?

[themoudie]

Aye Jordan,

As you say, there is only the one 8mm diameter threaded hole in the end of the crankshaft.

I never removed

".....the screw inside the crank,..."

quote from Alex.

Quote from Alex

"I think that screw is for holding a timing disc but outside that is thread that takes an 8mm bolt, (screws in 10mm deep)...."

No, that tapered head grub screw is to block the flow of oil through the end of the crankshaft and the exposed 8mm ID thread, with a depth of 10mm is what is used to secure the timing disc/pointer to the end of the crankshaft. You could of course remove the grub screw and give yourself more thread in which to thread the timing indicator 8mm mounting bolt. BUT! If you drop it inside the case, there is going to be a lot of fishing with a magnet or claw flexi-grab and you will have the alternator magnets to compete with, as well!

There needs to be a tang in the end of the timing tool that is used to mount the timing disc, so that it engages in the end of the Woodruff keyway in the end of the crankshaft. If you do not have this you are relying on a friction fit between the timing indicator/disc mount and the end of the crankshaft, with the intention that you are going to spin this up to at least 4,000rpm to check that the AAU is working correctly. If you do not physically lock the tool to the end of the crankshaft, you potentially end up incorrectly timing the ignition spark. Alternatively, remove the cover that may require another gasket!

Quote from Alex

"I would prefer to use that thread to mount the timing disc, is that ok to use that thread?"

As Hans suggests

"Yes of course, it is. The user and workshop manual show, that a timing wheel or a pointer tool can be mounted, to enable ignition timing adjustment manually or using a strobe light.
The "screw" - or it's slit - you see, is a grub screw with a conical head, which seals off the oil passage to the primary gears. The oil flows from the crank pin through the hollow LH shaft. "

Good health, Bill

[Scottish888]

Thanks for all the information,
I had thought that the grub screw was a smaller thread, I built the motor a while ago and have forgotten what thread the grub screw is.
I'll just leave it in place.
When/if it starts how much oil will come out of the timing plug hole?
Bill, thanks for the offer on holder dimensions, I'll have a go today and let you know how I get on.
Regards

[Duccout]

As Bill say's, it is a lot easier to fit a new Electrex World kit, then you won't have to worry about strobing.

Colin