250 Strada Strip Down

[Duccout]

It's apart! Had another go this morning, but there was no movement whatsoever, it was not budging..... Then I remembered Nigel's advice to tap a round bar through the selector drum, and after a few taps the seal broke at the bottom; once that happened it was just a case of plenty of Plus Gas around the joint and keep working between the oil filler, gear selector drum and breather outlet until the cases were apart. Now for the big clean up and inspection.

This engine definitely looks like it has never been apart before, and it is still on a standard, original piston, so I think that the mileage is low; unfortunately it was previously owned by a gorilla. Sometime in its life the top bevel bearing has broken up and whoever tried to fix it almost wrecked the engine as they had left the shims out of the bottom bevels, which broke most of the teeth, and had bolted the timing cover on without aligning the oil pump tang, as the evidence is still there.

Cheers,

Colin

[Duccout]

Not good, the drive side mainshaft is worn as I suspected, and one of the gearbox bearings is horrible. I can't find any play in the big-end, which is a plus. Thinking time.....

I have Loctited crankshafts into the mains before (on vee twins)but it makes future strip downs 'interesting', and in view of the difficulty in splitting the cases anyway, I'm not keen. Steve Wynne always used Loctite on the main bearing journals of his engines, and advised me to do so years ago, but I remember that during a subsequent strip down, the only way that I was able to get the crank out of the bearing was to hold the entire crankcase assembly over a block of wood and bring the crank down sharply against it.

Colin

[themoudie]

Aye Colin,

Pleased to read that the cases parted. Less so the resulting debacle revealed.

Whilst the big end may appear sound, with all the surrounding mayhem you describe, I would be having the crank stripped and inspected as a matter of course. It may not require a new rod, pin or cage, but a set of rollers could suffice and you would have peace of mind knowing that it was sorted.

As for Loctite on your crankshaft main bearing journals that might be fine for racing V-twins, but sounds a bit OTT for a road going 250 single. If necessary, metal spray and re-machine the journal to size, but that doesn't appear to be a problem from your decsription.

As for the gearbox mainshaft (input from crank), a good secondhand one should be available, either from Nigel, one of the Continental/US secondhand dealers, or FleaBay.

Sorting out some useable pairs of bevel gears for the cam drive would appear to be a much bigger problem/expense in my eyes than the worn mainshaft.

Hope you don't find more nasties, as I have with the 350.

Good health, Bill

[Duccout]

Hi Bill,

It is the main bearing journal on the crankshaft that is worn; I am just about to take some measurements with my micrometer to see how much wear there is, but there is enough to give up and down play.


Cheers,

Colin

[blethermaskite]

If the shaft has worn then the corresponding bearing inner race will be worn a little too the combined wear giving a little movement, it may well be that a new bearing will bring your wear tolerance down enough to use a smear of loctite to take up the slack........as an aside you can break a loctite bond with heat from an oxy/acetylene flame .
Cheers,
George

[themoudie]

Aye Colin, my misunderstanding!

Have to say I would measure up the journal and look for amount of interference, with the inner race of a new main bearing. If it were at all suspect, being a non-engineer, I don't know what the interference tolerances should be, I would opt for some metal spraying/machining, whilst the crank is apart to inspect the big end.

BUT! That could just be "Old worry guts!" I understand that a wee drop of Loctite (unknown grade), but stronger than nut lock might do the trick if the wear/interference fit is minimal and I would have to use MAPX, as I don't have oxy/acetylene to hand.

All the best, Bill

[Duccout]

Measuring the bearing journal with a micrometer, I am getting 29.997 mm, and measuring the bearing inner race with a bore gauge, I am getting 29.972 mm (remember I am not an engineer, but I took several measurements and they were all very close to this) so it appears that the main bearing has worn more than the shaft (which tends to happen when soft material rubs against hard).

Here is a poser for any Sherlock Holmes out there: upon inspecting the timing side main bearing, I found that the outer race vertical surface, which faces the flywheel, is polished and has obviously been rubbing against something, but there is no corresponding mark on the flywheel, and this should not be possible anyway because the boss on the flywheel does not allow it. So what has it been rubbing against?

I pulled this engine apart to sort out the damaged bevel gears, thinking it would only take a day, but I am getting in deeper and deeper with every part that I look at.

Colin

[LaceyDucati]

Colin

I would consider the measurement of 29.972mm of the main bearing journal perfectly acceptable used with a new bearing. A new crank would be around 29.995 to 29.9985 from my experience so nothing really to worry about.... less than 29.960mm and I'd be looking to build it up. Wear on the timing side crank face is not a rare occurrence! Normally either a raised area of casting or worse still the end of the timing idler gear shaft, more careful assembly at the factory

My experience of loctite on crankshaft journals is it doesn't work and I would never recommend it. The few times I tried it on race bikes in my early years, I found at the end of the season it had disappeared. This wear issue is the reason many racers (including myself) clamp the crank into the main bearing using a bobbin between the main and primary gear. If it did work (as has been said) it could make disassembly very difficult. Also remember the wear on the crankshaft will all be on one side, so gluing it central to the wear will fix the crank out of true. and probably give the mains (and there housings) more of a hard time than if it was just left to float. Just my thoughts on the matter.

Nigel

[Duccout]

Thanks Nigel,

I have often wondered why Ducati did not clamp the drive side crankshaft into the main bearing, as the shaft always seems to spin in the bearing and wear the shaft. I had a problem with my old 750 with a lot of wear on the shaft and had it metal sprayed and reground, so that the new bearings were a really good fit, and thought that was the end of it, but no, after a few thousand miles the shaft had spun in the bearings again and worn the shaft. I took the bottom end to Anthony Ainslie who explained what was happening - bearing housings wrongly sized and misaligned. He showed me what he did to vee twin main bearing housings, turning new ones to the correct sizes from bronze, etc.

AFAIK, most British bikes with roller bearing mains used a ball-race one side and the crank was located onto it to prevent end-float. Still, they had their own problems I suppose.

Cheers,

Colin

[LaceyDucati]

Colin

Like this....

Crank 1.jpg

Crank 2.jpg

The first is a crank from my first race bike (350 Sebring) which I modified to allow the use of the flywheel (via the taper) and still allow me to lock the crank into the bearing. I did quite a few 450's like this. The second is one of a batch of new cranks which included a thread above the taper to enable the same. Doing this eliminates the wear on the journal. The thread needs to be larger than the existing shoulder to avoid reducing the taper length....that's where I had to get inventive with the modified cranks

Never understood the logic of using bearing sleeves, it weakens the cases and just adds another dimension for inaccuracies and problems. Probably some work around inadequate design/manufacturing ability. I spent a few evenings at Anthony's workshop in Surbiton when I first started racing...although I think as much time was spent in the pub next door as in the workshop!

Good luck with your rebuild.

Nigel