Crank Binding

[Slackdabber]

199A Rebuild progressed smoothly....until, the slightest tightening of the engine bolts and the ignition side crank flywheel is binding on the LH Crankcase.   Main bearings are where they should be and the crank belongs to this motor.  Any thoughts/suggestions please?  

Also the crank pin isn't flush with the crank halves, on the LH side which is fouling, it is recessed, on the other half it is very slightly proud.   Should it not be flush on both sides?

Edited Thursday at 03:58 PM by Slackdabber
Additional info

[konrad]

I think this relates to your prior post about huge side-clearance on connecting rod.  I have read about the washers on the piston pin, but have never seen a motor that used the technique.

What struck me as odd, is that the big-end bearing itself seems to have a lot of clearance to the crank wheels and could walk from one side to the other.   

So, even though that motor may use washers on the piston pin for rod centering, it may still be that the crank wheels are too far apart.  But this is all speculation on my part. I don't work on "antique" motors. 

[lineaway]

So I looked at your pictures. Show us how the pin sits in the crank from a side view. Most rods only needed 18 thousands clearance. Granted I have luckily not done a bul. 

Edited yesterday at 12:49 AM by lineaway

[Slackdabber]

Crank pin position

[lineaway]

There you go, it is not pressed all the on the one side

[konrad]

Is that a crack?

[Slackdabber]

11 minutes ago, konrad said:

Is that a crack?

No, doesn't appear to be looking through a magnifier.

[konrad]

1 hour ago, Slackdabber said:

No, doesn't appear to be looking through a magnifier.

Can you feel anything with a sharp-tipped scribe?  A crack could explain the problem you are having.

Another thing to consider is the history of the crankshaft.  After repeated pressings, the pin/crankwheel interference fit can become too loose.  

If you have a dial indicator and a means of supporting the crankshaft, measuring the runout could tell if the crank wheels have shifted position,  

[Slackdabber]

Thanks for all your help guys.   I think I will have the crank overhauled as a result of this discussion.

[stevem75]

Often, when assembling Bultaco engines the crankshaft will bind on one crank case half after the case halves have been torqued to specification. Generally speaking the crank can be given a quick swat with a dead blow hammer to “center” it in the cases.  It will spin freely once centered. 
Your crank does need to be repaired.  The pin isn’t sitting flush on the one side and it isn’t pressed fully on the other.  As well there does appear to be a crack in the one crank half.  Good used cranks are easy to find and can be rebuilt with a new rod kit to bring back to oem standard. On the inside of all Bultaco crank wheels are balance factor numbers.  Be sure you do not have more than a two number spread between the halves.  You had also asked about the rod moving side to side excessively. In the mid 70’s Bultaco was having trouble with Sherpa cranks seizing. Most times this would occur during higher speed applications such as riding a road section for several miles.  The crank thrust washers were seizing and causing catastrophic damage.  The fix was to remove the washers and use small end spacers at the gudgeon pin between the rod and piston to align the rod on the crank pin.  Your crank is this design.  It’s normal and desirable.  It still is pressed together using 22 thou clearance on the crank bearing, and gives a much more reliable running crank at higher rpm.  
Steve