Crankshaft Runout Question

[Northracing]

I have a couple of 250 widecase crankshaft cores and to pick the best one to rebuild, I set each of them in V blocks to measure runout. On both cranks, the runout on the main bearing journals was minimal, under 0.0005". But when I measured runout at the end of each shaft, it was 0.004" to 0.005". Runout is highest at the ends and is less as measurements approach the main bearing journals.

I have a 450 crank and did the same measurements and got the same results.

I have no idea if the end of crank runout is due to them being abused and banged around for decades or if this type of situation is common, although 0.005" is way too much. My main concern is on the timing side, don't want to ruin a bronze bushing and lose oil pressure to the big end.

Any observations appreciated. If I need to straighten out shafts, would be interested in the best approach.

Thanks in advance.

[Jordan]

It's good to get things right.
My experience tells me that a scored/worn timing side crankshaft bush is not a serious problem with Ducati singles.
They have a low pressure oil system.

[Duccout]

Hi,

I'm sure that Nigel has spoken about this in the past, so hopefully he will see your question and chime in.

Cheers,

Colin

[blethermaskite]

So when I had my 30 ton press I rebuilt a couple of widecase cranks, a 250 and a 350, as far as runout was concerned I would be happy with 0.001 at the primary case bearing journal (if it was unmolested) if not great I would want to see pretty much the same at the primary gear journal. On the timing end again I would like 0.001 on the bevel gear journal, I don't think there is much point measuring at the timing cover/bronze bush journal because nearly every one I have ever dealt with has been in pretty poor shape......either badly scored or battered. It goes almost without saying that poor crankshaft assembly accuracy will trash the lower bevel gears, won't be good for the primary gears, will ultimately cause premature failure of the main bearings and will of course make something of a mess of the timing cover oil control bush. I always checked an assembled unknown quantity engine by loosening the screws a little on the timing cover and the same on the primary cover (with gasket joints broken free) when the engine is spun over if either or both covers try to move around a bit I would say you could be reasonably sure the crank alignment tolerance is out. While not particularly Ducati I have worked on pressed up cranks whose excess run out was due to the shafts being 'bowed' relative to the crank pin (not bent) which I have brought back by careful 'squeezing' the wheels at the appropriate point to 'square' the assembly, If the wheels are 'squashed' a bit of work with a wedge will sometimes work
I am not suggesting what I have done is the 'best' way or even to the 'best' tolerance's but it has worked for me, I am sure some of the guys on here would work to closer figures (ideally so would I) but most of the time we are working with old, well used. worn, and abused parts ......so you do what you can (well I do ) Cheers George

[Northracing]

Appreciate the responses.
George, we may have similar backgrounds, I am relatively new to Ducati crankshafts but have been rebuilding Japanese two-stroke cranks for decades.

I have not ever before come across the situation where there is no appreciable runout on the main bearing journals, yet considerable runout on the shafts. My 'better' 250 crank has 0.004" runout on the bronze bearing journal and a bit under 0.002" on the surface the bevel gear sits - as well as I can measure with the woodruff key slot in the way. There is just under 0.002" runout on the outer surface of the primary gear journal.

No way I will run a crank with 0.002" on the bevel surface, thinking the crank was thrown about and damaged before I got hold of it, yet not sure...did some of these engines come with sloppy cranks or were the cranks that came into my possession damaged? I'm still on a learning curve.
Derek