Crank problems -250 Daytona.

[Haggis]

I have taken my crankshaft to an engineering shop to have it pressed apart for inspection. It was when Matt suggested that "It’s a good idea to at least remove the welch plugs from the crankpin and make sure there are no contaminants accumulated inside the big end pin" that I began to suspect that things might not be as simple as I hoped. See photo. There are no welch plugs. The pins in the centre appear to be 5 - 6 mm threaded rod. Both sides are the same.

I trust the guy in the shop. He has done some pretty heavy engineering on a Jota engine that used to belong to a friend of mine, but he is working to my instructions and was not happy that the crank is obviously different to the manual specs.

Does anyone have any advice that I should pass on before the crank is pressed. At this point the construction of the crank is speculative at best. I am not sure if I am looking at a solid pin with some sort of oil way drilled inside, or a conventional pin with improvised welch plugs.

The alternator has obviously spun. - Presuming that I am not looking at a complete pile of scrap, can anyone advise what I should instruct them to do with the tapered shaft in the second picture while they are working on the crank.

The history of the bike is slowly unravelling - I suspect that this bike has done a few miles. The piston is 75 mm so has obviously been replaced at least twice. - It is a 4 ring job. I am not sure this was standard on the Diana / Daytona. Can anyone confirm this ? All the literature I have refers to the Monza, or at least does not specify the Daytone.

Thanks for all you help to date.

Chris.

[graeme]

Hi Chris,
Your crank pin looks like a made one, not Ducati.
Usually the made ones I've seen have grub screws in each end, maybe the maker only had bolts and the heads were cut off?
The taper may be able to be lapped to the flywheel but you will have to use a bearing retaining compound to lock it as the taper looks sad.
Or you can have it built up and re ground, along with the flywheel.
See "crank pin oil holes" and you will see my failed made crank pin (hardening) and the grub screws in it.
Graeme

Ps, if you are going to reuse any of the rod and pin and bearing, be sure to examine each piece very carefully!

[Jordan]

Wow, that's the worst taper damage I've seen. Most Ducati singles I've seen suffer from that. I'm not sure if it happens on only rebuilt engines, but clearly it's essential to have scrupulous cleanliness when assembling the tapers. Petrol followed by alcohol works for me - no oil.
On some of my singles I have lightly lapped damaged tapers and used them without trouble. They had at least some undamaged surface, but this one looks to have none left alas.
I've never had to fix one, but I'm always ready with free advice, so:
- If you can't find a better replacement crankshaft, metal spraying or chrome plating the taper, followed by turning or grinding a new taper between centres should fix.
- It may be possible to lathe turn a new taper farther along, without building up the damaged shaft area, if a new flywheel hub were made to suit, also with altered taper position. I don't think there'd be a clearance issue, if a new standard flywheel/hub were used either, but of course you'd need to check.
- I don't see the non-standard crankpin as a problem, unless the holes have been modified and won't accept a stock pin.

Jordan

[Eldert]

Hi Chris

that crankpin looks like the ones Alpha Bearings use to make for Ducati singles .
they made conrods to . did you have a look at the rod ? has it Ducati 250 on it ?

Eldert

[joe46ho]

I think Eldert is correct, I think you have a Alpha crank pin, and if your rod does say "ducati 250" on it then it may be a reconditioned stock connecting rod. Here are some pics of a rod and pin I bought from the u.k. last year, this is an Alpha... you can see the rod has a pressed in race, and you can also see the pin looks just like yours. (the crusty coating is cosmoline, or some type of wax preservative)

Joe

[joe46ho]

I also forgot to mention, your crank may be fixable but that taper is in really bad shape... I probably have a spare crank in much better shape than that, p.m. me if you are interested in one. I dont have any good rods left (that I am not using myself) but I do have some spare crank halves.

Joe

[Haggis]

The crank turns out to be exactly as described by Joe and Eldert: Alpha pin and con rod with Ducati 250 on the side. It is as per the photos attached by Joe. The guy at the eng. shop was quite surprised that the thrust washers are built into the bearing.

The eng. shop are going to try to spiral weld the alternator taper. Apparently this involves spinning the crank slowly while welding something like MIG wire onto it, The taper will then be ground back to original. He is using the rotor to try to work out the angle. (I saw a thread in the forum somewhere related to finding the taper angle somewhere, but I don't think an actual value was ever stated). If I find our for sure I will post it here.

I know that these bikes are not power monsters by modern standards, but it seems a bit remiss not to have a woodruff key for the alternator. They seem almost designed to spin on the shaft.

This was going to be a quick clean, replace bearings and seals, then rebuild the bike. Foolish me!! Still now that the old girl is half a century old, I reckon she deserves a decent rebuild.

Thanks again guys.

Chris.

[graeme]

Crankshaft flywheel taper

Look here, this might help. (copy and paste above to search)
Eldert says he is almost sure it's 6 degrees

graeme

[Haggis]

Thanks.

If I had to guess I would have said the taper was more than 6 degrees. I suppose that is why we measure rather than guess. It will be interesting to see if the eng. shop comes up with the same answer.

Chris.

[Jordan]

When I made a tapered spindle for the magneto testing machine, to accept the Ducati flywheel, I wasn't concerned with the angle so much as getting a good fit. It's not so easy to measure the angle of a conical taper. But I do have a pristine flywheel taper, and that became my test gauge. On the lathe, the spindle was supported by the tailstock then roughed out. When the taper was near correct, marking ink was painted on it and the flywheel placed on, pushed up and twisted. The way the ink rubbed off told me which way to adjust the angle. Repeated until there was no discernible bias on the ink marking. When I was happy with the taper, I then machined the other dimensions so they would be correct to the final position of the finished taper. When repairing a crankshaft, a slightly different method is needed, to ensure the taper's position on the shaft is correct. The taper should be machined to the the exact correct angle but closer to the end of the crankshaft. Then it can be advanced along to the desired position. Finding that position is the trick, the only Ducati crankshaft drawing I could find is not clear on this.
There's nothing stopping someone from adding a location pin/slot to the crank/flywheel hub.

Jordan