An update on the Twin,
Are they all like this? Of course the crank didn't fit properly.... with only the top center main bearing (CMB) shell fitted it won't budge. I pulled the crank, removed the new bearing, popped the old one in and re-assembled. Spins freely. Ok so what's the difference?
So on closer inspection both ends of new top CMB sit proud of the carrier even though its properly seated, and also the profile is quite different. The taper of the old and new bearing is completely different. If you haven't seen the CMB for a Twin, it tapers as it gets close to where the 2 shells join.
So this difference in taper and with being a bit longer, when the CMB is seated into the carrier the radius of the shell is too narrow.
I don't have another bearing, and seeing I've got all Saturday to work on this I'm going to modify the bearing to fit. Worst case I buy a new set.
I put the top shell into the lower carrier and filed it flat. Took it out and rubbed it on 600 grade sandpaper sitting on a flat surface. Checked it in the top carrier and it's flush. Installed the crank but as soon as I fit the crank ends fully it won't turn. I put the crank handle on a turned it twice. Pulled it all down again and checked the bearing. Shiny spots where the taper is wrong.
I don't have the equipment or desire to work on the bearing surface, but I can change the amount of "squish" by reducing material from the back of the bearing. With the bearing in wood blocks in the vice, I filed the outside of the bearing, then sanded both shells smooth again using the sand paper on a flat surface. This takes a lot of time.... Checked the thickness with my calipers and sanded it again a couple of times until it was flat. Installed the bearing, crank and... hey it's not good but definitely better.
Rinse and repeat...... 3 hours later I've finally got a smooth spinning crank, with only the Top CMB shell installed. Looking on the bright side, I'm now a master at getting the crank in and out. Plus it's a massive arm workout, I'll be looking like Arnie in a few days.
Installed the bottom CMB carrier and pulled it tight. Crank won't spin. So I backed off the nuts a turn and it's nice and free again.
I cut some shims out of thin (0.3mm) aluminium sheet and tried again. With 1 it's better, with two it spins smoothly.
So I've spent all day to get to this point and the question is - is there some clearance tests I can make to see if it's OK or do I look for new bearings?
Comments appreciated.
Samo