Split a crankshaft?

[blaat!]

Done with the tear-down, and my 250 NC is in pieces now. I've got boxes of bagged and labeled parts and hundreds of pictures on my digital camera to reference during reassembly. Feeling like I'm way down the rabbit hole now. I'm in the process of scrutinizing and measuring each part and checking to see if each one is within spec and fit for putting back into service. I have read in a couple places that you cannot check the bearing of the connecting rod big end by pushing/pulling/wiggling the connecting rod and assuming that if it is tight, then it is okay. I can feel some movement of the connecting rod axially, but not radially. I have the manual which specifies radial and axial wear limits for the big end, however I cannot find any info on how to split the crankshaft in the workshop manual or in the Mik Walker restoration book, just to do it. Mik Walker also says to inspect each roller bearing which assumes that it has been split and disassembled. From the wear limit "section view" it looks like a hollow pressed in pin with caps. I can easily see how each crankshaft flywheel side would be pressed onto the crank pin, but I'm not sure how to "un-press" it off. Has anyone been through this before? Are these reliable enough that I should just assume it is okay? I would hate to have to tear the motor down again.
Thanks!
-Jim

[Jordan]

There's some info here:

http://homepage.ntlworld.com/david.gibb ... ioning.pdf

[wcorey]

If it were me, I'd leave it be if there's no perceptible radial movement of the rod and feels perfectly smooth on rotation. Realigning cranks can be a real pain for us amateurs and is to be avoided if possible, be ready with a large lead hammer if you do it.
Micks restoration guide had me paranoid also but in talking to a few builders since, dis-assembly just for the sake of inspection is not a given. I had to do mine because I had a bit of radial 'click', turned out to be the rollers were about .001" undersize, though they looked to be in quite good shape even under strong magnification. If you decide to take it apart I may be able to assist, though the fixture I made for the 450 crank won't directly work on the 250 without a couple tweeks. Let me know if you get stuck...

Bill

[MotoMike]

Wow after reading that guide to crankshaft reconditioning, I'm a bit scared of that job myself.

[joe46ho]

Blaat...

Would I leave it be ? Not a chance, I would assume its junk until proven otherwise, trust me, you dont want to screw it up.
I have all the facilities to press apart/together, rebuild, and re-true the ducati single cranks. No one should attempt this unless they have everything to do it, and are comfortable doing it. If you want to send it to me, I can do it. Or send it to syds, or boretech (cincinnati. ohio)

Im sure ill catch hell 4 it, and no disrespect to mick walker, but I own that book, and find it pretty much useless, back when these motorcycles came out, and no one knew much about them it was probably great, but i have read it cover to cover, and while im not calling myself an "expert" as others on here might call themselves, I know one thing, that book had nothing in it i didnt already know, and left out a TON of info that people do need to know...

If your not ok doing it yourself I would definitely have someone else do it.
The thing everyone is forgetting is, even if all the "measurements" you take are ok you have no idea what the surface finish looks like (etching/rust/flaking)

If you dont want to take my word for it, ask nigel lacey, or malcome tunstell im sure they will tell you the same thing, ive pressed apart and inspected countless cranks that where sold on ebay as "good/tight/no slop" etc...and I have yet to press one single crank apart that didnt at least need a new set of 3.5mm rollers, side thrust washers and almost every one needed a crankpin, connecting rod, or both...

joe

p.s. the force required to press apart these cranks/ and the size of the arbor/bed needed to do it, i have found require a 400 ton press minimum , I use a 600 ton dake press (@ the shop of my regular 9-5 job)

[Jordan]

p.s. the force required to press apart these cranks/ and the size of the arbor/bed needed to do it, i have found require a 400 ton press minimum , I use a 600 ton dake press (@ the shop of my regular 9-5 job)

That's funny - I once used a 5 inch bench vice to split and reassemble a Matchless 500 single crankshaft, and it probably wasn't one ton capable, although it was a chunky cast iron vice. Not that I'm advocating such a bodge method, but 400 tons sounds extreme.

[blaat!]

Hmmmm... Well, I'm having the cylinder bored at a local machine shop. I have to take the crank/con-rod to them to refit the small end bush for the new piston anyhow, so maybe I can have them assess the big end. I'm sure they have a press, or at least a chunky bench vise

Either way I think I would most likely be okay, but it may be good insurance to have them split it and have a look. I can also have them check to see if the crank is out at all and look at all the surfaces with an experienced eye. I always try to do things myself, but this will probably be money well spent and I'm sure I'll learn something during the process.

Thanks for all your input.
-Jim

[joe46ho]

Good luck with the bench vise method, let us all know how that goes if you try it...

[wcorey]

Here's my little home brew rig, the pin on my 450 crank and many others before it came out with no drama at all...



I'm sure 600 tons works just fine but is overkill like making toothpicks with a hydraulic cordwood splitter...


Bill

[joe46ho]

Bill,

I like that rig, but it is definitely no "bench vise"

The point I was trying to make though (and i did mention it in there) was that the arbor plate "bed" if you will of my smaller press wont hold the crank. 100 ton- wont fit at all, 200 ton will fit just barely, cant align it properly, then its on to the 600 ton dake at work, which is actually our old retired "tire press" (for cushion tires on forklifts mainly)

I realize #1 its overkill...
#2 not many people (including me) have a 600 ton press at there house, that press is actually taller than my garage ceiling anyway...

Thanks for the charging system research by the way, been meaning to tell you that for a while...interesting reading.


Joe