crank drive conversion - motor spindle case too tight in bb shell

[sandyman44]

finally decided on a tongsheng tsdz2 to convert my dahon.
ran into an unexpected issue after removing the bottom bracket. The motor spindle won't push through the hole - it stops once the threads are in, after only a few cm. I've tried moderate percussive force (gentle tap with hammer), don't want to try anything harder as I'm pretty sure it'll jam.
the insides of the bb shell are clean, shiny and well greased (its a new bike) as is the face of the spindle of the motor (by me, after I unboxed it).

my calipers' prongs are too short to reach the centre of the bike's BB shell so I can't get an accurate measure on it yet, but by feel with a finger it seems to be slightly smaller diameter once beyond the threads. not sure if this is normal or not as I am not in the habit of removing my other bikes cranks and BB's.
by my reading of the standards if its ISO it could be 33.6 mm shell diameter and the motor is 33.5mm... not a lot of tolerance! but not sure if that diameter is applicable across the whole of the shell.

is this something people have seen before? should I try and make the motor spindle case a wee bit thinner (sanding the paint and an outer tiny bit of metal off?) or is it feasible to file a tiny bit off the inside of the BB shell (not sure how to attempt it though).

or do you have to hit the damn things really hard to get them in the hole?

or am I stuffed?

 

[Woosh]

The motor spindle won't push through the hole - it stops once the threads are in, after only a few cm.

this is typical result when there are small defects in the welding inside the bottom bracket shell.
I woud put a bit of shoe polish or black grease on the motor's BB, push it through until it stops, then use a torch to find out where too much metal is left inside the bike's bb shell. Use a dremel to get rid of the imperfections.

 

[sandyman44]

hi whoosh.
thanks. I tried grease but didn't gain much. however I bought some burr and grinding bits for my dremel and slowly shaved tiny bits of the inside of the BB shell away in the central unthreaded section, and was able to get it fitted.

and it rocks. reference our previous discussion on another thread - much nicer to ride than BBS01, and its entirely happy fitted with the motor tilted forward of the BB (leaving the space under for seat post to drop out the bottom which you need on folder). the angle makes no difference to the torque sensor behaviour. I'll post some pics another time.