Installing a new piston in my 199B and it feels like there is some friction with the top end bearing, all new parts, maybe it needs to break in ? feels like it is rubbing on the spacer on the ends of the bearing?

There should be clearance there. Having new parts does not mean that you are guaranteed the correct clearance. It would be risking damage to run it without clearance.

If you need to, make the spacers a bit thinner. Aim for about 0.5mm total clearance.

Jep the con rod ends should definitely run free of any friction, neither piston pin nor lower crank pin should feel any kind of rough in iny direction.

You have chamfered the two holes in the piston? 

Did not know about any kind of clearance spec, pain to take apart but want it to last. Not sure on piston hole chamfer will have to check that. many thanks for the ideas!

Took it apart and it was not the spacers that was the binding issue, it was the bearing in the rod. did not realize the bearing was a press fit as well as the pin into the piston, keep thinking it should work like the Japanese bikes but it is different. checked the old bearing and pin and it was press in also. Seems tight but it is a new bearing piston and pin. going to put it back together and cross fingers it works ok. So what's with chamfering the holes, is it an issue?

It isn't a press fit into the rod, it should push in easily by hand and the piston pin should pass thorugh the bearing freely by hand. 

Would normally agree with that but that is not the case with this one? on the jap bikes it works that way, maybe bultacos are different? the bearing pushes in by hand till the pin is put in then it needs to be pressed in.

It is normal practice to warm the piston a little bit to allow the pin to slide into the piston. But as far as “press fit” I’ve never seen that on a Bultaco.  The gudgeon or ( wrist pin) should slide through the bearing easily.  

14 hours ago, slowrider said:

Would normally agree with that but that is not the case with this one? on the jap bikes it works that way, maybe bultacos are different? the bearing pushes in by hand till the pin is put in then it needs to be pressed in.

Definitely nothing to do with it being a Bultaco, they're like any other bike, Jap or otherwise. If you can't freely slide the pin through the bearing when it is in the rod then something is wrong

Maybe someone has built the crank by sourcing individual parts instead of buying a Bultaco rod kit and the ID of the rod for the small end is undersize. I bought a Sherpa project a couple of years ago with a rebuilt engine (by a ''mechanic'' supposedly) and the conrod wouldn't freely spin in the crank, it was stiff. Splitting the crank revealed it wasn't a proper rod kit and the bearing used was incorrect. Rebuilt with a proper kit and problem solved

Definitely a neat fit, but should slide together with minimal force by hand, not 'pressed' in.

Well this is disappointing, since the old bearing and pin have the same clearance issue as the new one it must be the rod that is the wrong size. can it be reamed or time to buy another rod?

17 hours ago, slowrider said:

Well this is disappointing, since the old bearing and pin have the same clearance issue as the new one it must be the rod that is the wrong size. can it be reamed or time to buy another rod?

Is it possible that the eye of your conrod has had some mechanical damage that has deformed the little end of the rod, causing the hole to no longer be perfectly round?

To answer your question, if the hole is still round, the hole can be honed larger. If the little end has been deformed then it is time for a new rod.

Was thinking the same thing, gave it a quick feel for damage and found nothing, thinking its time to see if I can get a micrometer in there and find out what the actual ID should be? 

Talked to Hugh's bultaco and he recommended a brake hone till it fit right, thinking that is a great idea.