How to get this out?

[Jordan]

This is a detail from a drawing of a single crankshaft, showing end dimensions.
It's just legible.
It looks to say diameter 12 f8 -0.016 -0.043

Not sure what the f8 refers to - maybe it defines the smoothness of the finish - but the rest is clear enough.
12mm diameter nominal, but actually slightly smaller, within the range of 0.016mm and 0.043mm under 12mm.

I've owned a few Ducati singles, all of them have some wear at this place. I don't worry about it, and haven't suffered any breakages due to oil starvation. It's just one of the imperfect design points, luckily not critical.
My take on it is, as well as oil being pumped to the bush, centrifugal effect of the flywheels tends to suck oil from the end of the crankshaft. As long as there is oil there, it will get to the big end.
Note that several British motorcycles used a non-contact method of feeding oil to the crankshaft. A steel tube, mounted in the sidecover, went into the end of the crank a short distance, from where it squirted oil in. It had positive clearance such that metal parts didn't touch.

Jordan


> by blaat!
> I'm up against the same problem. The workshop manual specifies the bushing ID tolerance as 12mm to 12.027mm, but gives no info on the crank end. I'm
> thinking that it would be 12mm, but I don't have my crank here to check.

[blaat!]

The cumulative Motoscrubs knowledge base is impressive!

F8 refers to ISA/ISO standard diameter tolerance limits: +.016mm to +.043mm

The numbers are restated below the 12F8 as negative for clarity.

Therefore the max shaft (11.984mm) with the min bushing (12mm) would leave a clearance of.016mm, or less than .001"

The min shaft (11.957mm) with the max bushing (12.027mm) would leave a clearance of .070mm, or just under .003"

Mystery solved, I think.

[Bevel bob]

Sounds very much that a new bush is needed in my case. after spending so much time getting my timing right i am reluctant to loose it, i'm thinking it should be possible to remove the timing case without moving the points plate,and not disturb the gear meshing if i tap the shaft back after removing the cam retaining screw , --or am i missing something?.

[LaceyDucati]

Hi all
You've stumbled into one of the mysteries/ myths of the the Ducati single engine. The original Ducati tolerance provides a clearance as 0.016 to 0.070 which in the perfect world would be lovely. BUT add the facts that:
Seldom do the cranks run absolutely true and a lot are worn out of true to the bevel gear shoulder, this is largely due to cranks going out of true when run.
The bush has an interference of 0.04mm in the casing which when installed in the unequally supported casing will go out of true by around 0.025mm.
And the real bad one is that not all the holes for the bushes line up with the main bearings, the worst I have found so far was about 0.175mm off centre.

This is why you find badly worn cranks and bushes. If you have just put a tight bush in there to the original Ducati spec, you will probably find you will struggle to turn the engine over if you have not got the head and barrel on. If you don't believe me, put a new bush in and try and turn the engine over with the rod. All this will achieve is more wear, more metallic particles floating around the engine and a within a few hundred miles, a return back to the state it was in before you replaced the bush.

Having measured many used engines which have come in running, clearances of up to 0.25mm are really not that uncommon! So thats all very well, what is the answer? ....

If you can get a clearance of 4 thou (0.10mm) or less and turn the engine over freely without any rubbing, then thats probably as good as it's going to get. I would have no qualms about running with 4 thou (0.10mm) clearance. What I actually do is aim for about 3 thou clearance and try it, if the crank rubs then I will put engineers blue on the end of the crank and see if I can hand scrape the bush slightly wherever its rubbing in order to get the crank spinning freely. Should that not work then I just go for plan B and line bore the cover in line with the main bearings. Then I fit an oversize bush with about 3 thou clearance and pretty much without fail the crank will spin as free as can be. This all assumes you have the engine apart; this checking and aligning of the bush is something I always sort out well before I think about assembling gearboxes and final builds. (Sorry if I started talking "thous" halfway through the posting but engineering all just works better in thous and tenths rather than decimals of mm).

Great as these engine designs are, unfortunately some of the tolerancing in the manufacturing was far from the drawings. From my experience its a case of the more questions you ask, and the more you investigate, the more you wish you hadn't started looking. Despite all this it is possible to engineer out the worst of the problems and a lot of the time our fears and worries come to nothing!

If you don't want sleepless nights, don't ask me what else doesn't always line up

Best Wishes
Nigel Lacey

P.S Bob , yes it's perfectly possible to remove the timing casing without disturbing the points. Put the engine on TDC and roughly mark the points cam relative to the cover. When you install the cover ensure the shim stays on the end of the timing gear and make sure your temporary line marks line up and all will be well. You only need to mark it with a marker pen as one whole tooth out is easy to see and you would be about 15 degrees out (if my memory serves me right). This assumes you don't turn the engine over in the meantime, but even then if your marks line up the worse you can be is 180 degrees out and that should be pretty obvious!

[Bevel bob]

Thanks Nigel, from the sound of it , I need to stop fretting, although i' think mine would be free with 2 thou clearance, the crank was doing skipping rope impressions before trueing and was not tight in the bush ,now true there must be room to spare.What do you use to measure bush ID's? , awkward with a caliper.

[LaceyDucati]

Bob
I use a small bore gauge, they usually come in sets going from 1/8" to 1/2". Mine are Moore & Wright with a central screw operating a taper acting on two balls that expand out. You rock it in the hole and set the gauge till you can just feel resistance, you then measure the gauge with a normal micrometer. With practice you will find that you can feel & measure to a lot less than a thou. They can be expensive but, there are cheap versions available, see Ebay link below. Never tried these cheaper versions, but I expect they will be accurate enough for this job. Wouldn't use a vernier for this job, trouble is with Digital verniers is they show a resolution/accuracy well beyond there feel (known by engineers mockingly as "very nears"!!)

http://www.ebay.co.uk/itm/SET-4-SMALL-H ... 4cef5aa4e3

Best Wishes Nigel

[Bevel bob]

Thanks again Nigel, your answers always hit the bulls eye.

[Octane]

I've heard of another method but not tried it.

You need a shaft that's a very close fit inside the bush. Pour some oil into the blind hole where the bush fits, then press the shaft into the bush.
As the shaft goes in, the oil will be pressurized and will theoretically push the bush out. Again, I've not tried it, so dont complain to me when you get oil all over your shirt

[Jordan]

The oil line holes would let the pressure out.

[blaat!]

I got all the bushings out of the timing cover with no issues. These are the pictures of the timing cover mounted on the mill to bore the timing cover crank bushing in line with the crank.

A.jpg

I used a standard mill bed anchor through the points hole to mount the timing cover to the bed. I also circled the edge finder I used to locate center.

B.jpg

I placed the side cover on top of the timing cover and located the center of the crank bearing recess.

C.jpg

Looking inside the crank bearing recess at the timing cover bushing. Once you find center of the crank bearing recess, remove the side cover and bore the timing cover bushing recess to be oversized (just under 16mm).