Ducati.ms - The Ultimate Ducati Forum banner

1 - 20 of 22 Posts

·
Registered
Joined
·
19 Posts
Discussion Starter #1 (Edited)
Ducati 250 owner in Edinburgh Scotland.
Just had the crank fitted with a new conrod kit (Lacey Ducati) the crank cases fit together perfectly with just the crank but discovered the cases wont fit cleanly together if I use even the thinnest shim.
Looks like the LH main bearing journal is the problem with the radius to the shim thrust face not being correct, if I fit the original main onto the journal I can see about 1mm clearance between bearing and thrust face on the crank.
If the crank rebuilder (and myself) had known of these issues he could have cleaned up the journal radius and thrust face whilst the crank was split but we were unaware.
I have had advice from Lacey Ducati to say that these journals can be an issue and that chamfering the inside lip of the shim can help, I tried that but I think I would need to remove a lot of material before the shim could sit flush.
A machine shop friend thinks he can fit the assembled crank in a lathe then turn by hand to clean up the journal and thrust face
If this doesn't work, any other suggestions on the best way to sort this would be appreciated.

Regards
 

·
Registered
Joined
·
19 Posts
Discussion Starter #4 (Edited)
Apologies, I made a mistake in the first post, the crank cases go together perfectly with just the crank. it is when a shim goes on I get the problem.
Will check the crank pin clearance tonight but it certainly feels good, very little side movement.
The new crank pin is the Samarin make, Nigel Lacey is happy with the brand and it looks great, come with the thrust washers etc which have all been fitted.
The old main bearing will not sit flush on the thrust face so must be some issue preventing seating.
With the crank installed with no shims I get at least 1mm end float, as soon as any shim goes in, the crank cases will not close, showing a gap about 1mm.
It appears to be an issue with the LH journal not allowing proper seating of bearings or shims.
I marked the journal and spun the old mains on it to see the contact area but I will be rocking it as I turn it so making little contact all the way but if held up to the light there is a gap between bearing and shim face.
Con rod alignment looks like I need to shim lots on LH side
second pic shows case gap with an original .32mm shim installed
 

Attachments

·
Registered
Joined
·
214 Posts
looks like your bigendpin is protruding and preventing the shim to seat .

i was gonne answer your question on motoscrubs but i have problems logging in

Eldert
 

·
Registered
Joined
·
19 Posts
Discussion Starter #6
Hi Eldert,

I think the motoscrubs forum has died so I joined here today.
That is an optical illusion thanks to my photography skills, the crankpin is flush or just a fraction below....I just checked again.
The shim is stopped before getting to the thrust face.
Just checked the worn original shims, ID is 32mm ! so they have been ovaling around with the crank over time. If positioned in a certain way they can be made to sit on the thrust surface but when in the engine it is impossible to get them to be central around the journal so if one part sits on the journal radius it won't sit flush.
Either I have to machine the journal radius perfect or have the shims machined to fit exactly which may be very difficult.
What would the perfect radius be? I guess machining the journal to the thrust face at 90 deg is not good practice? but looks like that would sort it.

Regards,

Alex
 

·
Registered
Joined
·
214 Posts
Hi Alex

the bearing has a large radius on the inside . the shims are flat . what i do sometimes is get a old bearing and
a shim . put the shim on the crankshaft ( when the crank is on the bench ) put the old bearing over the crankshaft journal
and give it a good whack with a large hammer . that way you have a shim with the correct radius .
you might give that a try

Good luck Eldert
 

·
Registered
Joined
·
19 Posts
Discussion Starter #8
Hi Eldert,

That is a great idea, I can try that if I can't square it up on a lathe tomorrow, one worry would be, sticking the old bearing on the journal radius.
Similar to your idea I thought about a quick tack weld on an old main bearing to lock it up then apply coarse grinding paste and grind the journal to shape that way.
I will give my machine shop pal a go tomorrow to try clean it up by hand turning on his lathe, what do you think about a 90 deg zero radius?
No idea what happened to this crank in the past, bike only done 7000 miles, no idea if the crank pin was original but if so, poor Ducati machining.

Regards,

Alex
 

·
Registered
Joined
·
2,124 Posts
Hi Alex. The slight radius where the shaft meets the flywheel is good engineering practice; a sharp 90 deg can lead to cracking when forces are applied to it. The problem is that the shims do not have a large enough I. D. to clear the shaft radius? I think that the best bet is to file the shims out so that they clear the shaft. You can do this with a large half-round file or with emery wrapped around a former, a piece of round wood, say, or for an easier route, a grinder on a Dremel. I would not start turning down the crank as you are risking all sorts of issues.
 

·
Registered
Joined
·
19 Posts
Discussion Starter #12
Thanks to all for advice and help.
I had my machinist friend (by hand) remove the worst of the overly large radius and this has already made a difference, I just need to modify the shims very little by Eldert's method or a file, I hope to have shims and bearings fitting flush on the thrust face this eve.
I found that even with the original worn shims with an ID of 32 mm it could still cause issues as you could not always locate them centrally, so the worn shim could still sit on the radius and not be flush, this is what was happening before.
I am probably over thinking/worrying about this as I think once running the shims would center themselves?
This is my first Ducati single build so likely being too cautious.
Appreciate all the advice
 

·
Registered
Joined
·
19 Posts
Discussion Starter #13
Well, still not fitting.
My friend had machined off a small amount off the radius and a shim or bearing sat closer to the face but still not flush, I did not want to use too much of his work time to took it home.
First tried a 1mm shim, cases did not close, 0.5, same. Chamfered the 1 and 0.5 mm shim, case would still not fit, with the 0.5 I tried to bolt the case but the crank stopped turning so I stopped.
Put in a 0.3mm shim, not chamfered, case closes better, carefully bolted it up and found crank needs a little pressure to turn, no free fall of the crank but not much extra pressure needed either.
Measured end float about 0.02mm. That is as far as I got.
I expect I have not chamfered the shims enough and will try again, the 0.3mm is likely not sitting on the thrust face but how to measure. Could try some blue tac with oil under the shim to see compression.
Would have tried Eldert's auto taper method but had no tube with a 30mm id to hit on the bearing with, will find some today and use Eldert's method on the 1 and 0.5mm shims.
I begun the search for another crank last night :frown2:
Pic is the shims after filing, there is more chamfer than it looks.
 

Attachments

·
Registered
Joined
·
1,234 Posts
In the first pic, is the raised part you are talking about outlined with black marker? That appears to be the thrust face that should seat against the bearing. The end float between that face and the inner race of the bearing is what the shim should take up. The shim doesn't need to fit flush against the full face of the crank wheel. As long as the shim fits over the OD of the shaft that enters the bearing it is OK. Likely the overall width of the rebuilt crank is a bit wider and you will need to use a thinner shim to eliminate the end float. The best way to determine the shim thickness is to assemble the shaft into the cases without shims, torque the cases to spec. and measure the end float with a dial gauge. Lever the crank fully to one side, zero the indicator and pry the crank to the other side to determine the float. I'm not that familiar with the singles and don't know if they call for any preload on the crank like the twins do, but if so add that figure to to your measurement.
 

·
Registered
Joined
·
19 Posts
Discussion Starter #15 (Edited)
Thanks,

I had the crank in without shims and got 1.5mm end float, put in any shim above 0.2mm and the crank becomes tight.
I think I figured out the problem...when measuring the crank end float with no shims, (engine lying on LHS) I was getting too much end float...then I noticed that the RH main bearing inner was moving together with the crank.(outer is solid against the casing)
I have been lightly using a screwdriver against the crank wheel from the cylinder mouth but this must be too much force.
I have been measuring bearing movement and not crank end float!, bearings are all SKF C3, (properly fitted in by heating the case and cooling the bearings in freezer, they practically dropped in)
It was too difficult to measure the crank end float separately from the bearing movement but I remembered a 0.3 shim made the crank too tight so I decided to rely on crank freefall as my guide thinking that the end float of the crank must be very small. I tried a 0.25mm shim it was turning with moderate pressure but no free fall so tried a 2.0 shim, much better with just a bit free fall with the case tightened.
So all I needed was a 0.2mm shim.
There is some end float if I force the crank against the case but this just moves the bearing inner a little.
The RH bearing does not appear to have as much axial movement but still has some.
I will call the bearing supplier but I am happy enough with the setup for now, I expect the supplier will say this is normal axial movement, there should be a little.
 

·
Registered
Joined
·
2,124 Posts
There will always be a little play in a ballrace bearing. BTW, are you tapping around the inner race once the cases are bolted up to snug the inner race up to the crank shoulder?
 

·
Registered
Joined
·
19 Posts
Discussion Starter #18 (Edited)
Hi,

Yes I have had the gasket in when doing most of this crank/shim work, I think that pic was taken with no gasket to show the gap.
I never thought to tap the bearings onto the crank once bolted up, will check for that later today. There was so much axial load from the over shimming, it should not have be an issue?

Regards
 

·
Registered
Joined
·
2,124 Posts
Yes, the tapping around the inner races that the bearing is tight up against the crank face will ensure that there is no settling in later and give you more accurate shimming measurements. That goes for the gearshafts too.
 

·
Registered
Joined
·
19 Posts
Discussion Starter #20 (Edited)
A quick measure this morning with the crank and 0.2mm shim in showed very little movement, the crank has some free fall but not for 100% of rotation only from 50% so just a fraction off but better that than no shim and a bit too much end float. I split the cases, removed the shim put in the crank and closed all up again, RH mains has about 0.8mm axial movement, very little on the LHS.
I tried tapping the inner bearing race onto the crank journal but no difference.
I will be picking up a new bearing Sat morn
 
1 - 20 of 22 Posts
Top