so the crankcases seemed to go together smoothlyl but now the crank dosent revolve readily (it was alright with with the ign side only) Is there anything i can try before re-separattion?

cheers steve

The crank is likely sitting proud on one side of the case.  Bultaco had a special tool to help center the crank.  To fix this first look down at the crank from above and see which side the crank is sitting closest to.  Likely the magneto side case.  Give the crankshaft a good quick wrap with a hammer (deadblow hammer ) and this will "center it " in the cases.   Immediately it should turn freely.  Don't hit the crank too much as it can throw the alignment.   You just need to swat  it hard enough to push slightly.  All cranks will do this.   Modern bikes included need centering too 

 

steve 

The crank is located by the seal housings. If the housings aren't fitted the crank can slide up against one side. Once you fit the housings the crank should be centered.

the seals are on oj, now looking for a hammer s 75

Oldjohn is right.  The seal holders should be in place while installing the crankshaft.  It does help to locate the crank in the right spot.  However it is still likely that the crank will sit to one side and will need a quick smack to center it.  

 

Steve

your were  right steve the crank is about 3mm to the ign side I tapped it with a hammer but no movement , i do have a sledge hammer but...

There's something wrong if the seal housings are fully seated yet the crank is still off-centre. There should be very little crank end-float with the housings fitted and a standard case gasket fitted. With a cold engine 0.5mm is plenty and you wouldn't want much more than 1mm. You certainly shouldn't need to be tapping it with a hammer and it shouldn't even be getting close to rubbing on one side. If it's that far off centre there's something very wrong - incorrect seal housings perhaps, or gaskets behind the seal housing instead of just the o-ring, or maybe the housings simply aren't seated fully. You can check this with a thin feeler gauge (say .002") but be careful jacking things around with the seal housing bolts - the housings are a bit fragile. If the crank end float is excessive or it's off-centre you may have to shim or machine the housings but unless you have some oddball or mismatched parts it shouldn't be necessary.

as you can tell im a bit of an amateur so im thinking of professionals. I ve heard theirs a guy in surrey nr gatwick uk whose good any thoughts?

Hi Scbond, apologies, I am a bit behind with things, only just read about your problem. Here’s what I do— I find 2 spanner’s that are a tight but easy fit in the crankwheels opposite the crankpin if it is necessary to give a bit of a tap on the crankshaft with a copper hammer to nudge it over a bit. This stops all of the pressure being put on the big end a bit sideways. Just to mention, I now assemble my motors always using a SKF NJ 205 ECP /C3. On the ignition side. It makes assembling the lower end so much easier, also a lot easier to undo if something is not quite right. When the mains do go it is usually this side. The roller bearing is much more sturdy than the usual ball bearing of the same size. Hope this helps one —- or more of you guys out there ! John.