250 Crank Work

Ducati single cylinder motorcycle questions and discussions, all models. Ducati single cylinder motorcycle-related content only! Email subscription available.
Moderator: Morpheus

Moderator: ajleone

Stan Lipert
Posts: 52
Joined: Wed Nov 28, 2012 4:40 pm
Location: Cleveland, Ohio

250 Crank Work

Postby Stan Lipert » Wed Jan 27, 2016 8:57 pm

Just sharing some photos of a recent crank refurbish. 1965 Mk3 250.
I machine the oil journal a fresh face, disassemble to clean and inspect, found all of the rollers and bearing surfaces good, press together and true.

I faced the oil journal before disassembly, since the crank was true from the factory:
Image

After pressing apart, I welded a slide hammer bar to pull the pin cap. Plenty of sludge. I can then cut off the weld tack, a little sanding, and then reuse the cap:
Image

Rod has little wear, no pitting. Wire wheel to clean:
Image

Pressed together, I use a 1.5 pound brass hammer to true, easiest done is for me to use a straight edge to get the outside faces of the wheels parallel.
Checking was done by spinning the crank in the cased, with an indicator on the oil journal:
Image

Total runout of 0.001" is good for me!
The timing case will get a custom oil feed bush to match the new smaller O.D. of the journal. I go for 0.003" clearance.

Stan

flanker
Posts: 104
Joined: Mon Apr 06, 2015 1:22 pm

Re: 250 Crank Work

Postby flanker » Thu Jan 28, 2016 4:57 am

That's clean work Stan! Impressive!,,

flanker
Posts: 104
Joined: Mon Apr 06, 2015 1:22 pm

Re: 250 Crank Work

Postby flanker » Thu Jan 28, 2016 4:58 am

My sump was filled with what looked like petrified oil

Nick
Posts: 243
Joined: Sat Jun 01, 2013 4:57 pm
Location: Paradise

Re: 250 Crank Work

Postby Nick » Thu Jan 28, 2016 5:01 am

Thanks for that. Great info, and nice work.

I've trued many cranks using a brass/led hammer and then measuring runout on a crank truing stand, but I didn't know you could also check the trueness with the crank installed in the cases.
Have you confirmed that you get the same readings with the crank in the cases as with the crank on a truing stand?
Put a Mikuni on it!

Stan Lipert
Posts: 52
Joined: Wed Nov 28, 2012 4:40 pm
Location: Cleveland, Ohio

Re: 250 Crank Work

Postby Stan Lipert » Thu Jan 28, 2016 4:26 pm

Nick, I would probably use a truing stand if I had one, to save time. Since the final destination of the crank is bolted into the cases, isn't this more accurate?

Rick
Posts: 340
Joined: Thu Nov 11, 2010 1:12 am
Location: Northern Plains, USA

Re: 250 Crank Work

Postby Rick » Thu Jan 28, 2016 5:41 pm

When I saw your photo of the bungee cords through the connecting rod I remembered having seen that done maybe 40 years ago, but I forgot about it probably 39 years ago- glad you sparked my memory.
I think you'd get more accurate truing using a stand rather than the crankcases- looseness in the bearings, dowel pins,etc, would accumulate to make the readings better than they really were. If you could borrow a stand you could take the crankshaft out of the cases and see if you get the same reading on the stand- I doubt if they'd be the same. The best stands I've seen are made for balancing grinding wheels for surface grinders- with your shop and experience making a copy wouldn't take long. Plus, with a stand, you wouldn't need to take the crankshaft out of the cases to make adjustments.
I have some bench centers, but I don't trust that the crankshaft ends haven't been buggered up, so I've never used them.
Rick

Stan Lipert
Posts: 52
Joined: Wed Nov 28, 2012 4:40 pm
Location: Cleveland, Ohio

Re: 250 Crank Work

Postby Stan Lipert » Thu Jan 28, 2016 7:03 pm

Okay, next time I get a chance, I'll compare with a truing stand.
I don't trust bench centers either- that beveled hole at the end of each crank is where a hammer may have been used for disassembly.

This got me thinking about crank flex and vibration. I know that the bearings are loose when cold, and the cases expand when hot, and the bearings get looser when the cases get hotter, and the crank bends and flexes at each rotation. It would be interesting to see how much the oil journal wobbles around.
I can tell with authority, that every engine that I've tuned on a dyno, the engine will make the most power when it is HOT. The looser the better?
I think so.....

double diamond
Posts: 555
Joined: Thu Apr 28, 2011 1:20 am

Re: 250 Crank Work

Postby double diamond » Thu Jan 28, 2016 8:49 pm

Tony Foale describes a very simple and effective crank truing stand at: http://www.tonyfoale.com/AermacchiEngin ... ntTool.pdf
I agree with Tony that this tool is better than supporting the crank between centers or supporting the left and right journals in a stand.

Matt

Rick
Posts: 340
Joined: Thu Nov 11, 2010 1:12 am
Location: Northern Plains, USA

Re: 250 Crank Work

Postby Rick » Thu Jan 28, 2016 8:59 pm

Stan,
I didn't want to drive the bearings all the way onto the crankshaft, and couldn't find my test indicator, but these photos show a simple rig that will probably be better than using the cases:
true 1.jpg

true 2.jpg

You probably have v blocks and parallels in the shop.
And anything Tony Foale does is well thought out.
Rick
You do not have the required permissions to view the files attached to this post.

Stan Lipert
Posts: 52
Joined: Wed Nov 28, 2012 4:40 pm
Location: Cleveland, Ohio

Re: 250 Crank Work

Postby Stan Lipert » Thu Jan 28, 2016 9:23 pm

Double,
Tony's jig/fixture is cool, but this was in response to him not knowing where his crank was bent. I probably have trued more cranks than Tony, having worked as a mechanic for years. I have not had a problem crank yet that I could not true, including bent rod big end pins.

Rick, I have a surface plate, machinist v-blocks and machinist parallels, but I think the cases are more accurate. Is it a problem not knowing where to press/wedge/hit?

Stan


Return to “Ducati Singles Main Discussions (& How to Join)”

Who is online

Users browsing this forum: Bevel bob and 52 guests