Folding Bikes - Installing new BB

I've just removed the cup and cone BB from my Dahon Vitesse and am about to install a shimano BB 5500. I'm assuming the english thread type is correct. The drive side cup removal was a bit awkward, was very stiff, and from first tentative steps if feels as though I'm going to have to use a lot of force to get the new bottom bracket in so I'm getting paranoid that I've got the wrong thread type, or that the frame threads are a bit off and that I'll that they'll get damaged in the process.

How much force should I use? Is it just threadlock on the BB that needs breaking in?

Shouldn't need any force until it was time to snug it down.

Probably a good idea to take it to a bike shop and get them to face the BB and chase the threads to ensure parallel. (Needs an expensive tool)

Most inexpensive bikes have not had this procedure done to them before assembly, and it is well worth having it done if you intend to keep the bike.

Do you mean to detect whether there are any manufacturing defects in the bottom bracket shell?

It's mainly to prep the bottom bracket shell. The new bottom bracket should thread into the shell pretty easily. Did you grease the threads before installing it? Did you clean out the shell after removing the old one?

I replaced the bottom bracket on my Bike Friday Tikit and it was effortless, other than the final tightening. The Downtube, however, was a complete pain. It was way too tight, and the threads were not parallel. Ensuring the threads are parallel is probably the most important step; if they are not parallel, the spindle will not line up with the opposite side cup. It will also cause premature wear on the bearings.

Are you sure you were installing the correct cup on the correct side?

Use some anti-seize paste on the new threads after cleaning the threads out as well as possible.

Well, that was an ordeal. The original BB fit reasonably well though was stiff on the drive side. The shimano BB was OK on the drive side and very stiff on the non-drive side. Every time I encountered too much friction and thought I might damage the threads I took the BB back out, cleaned and re-greased. Amongst the grease there were some slithers of either metal or just whatever threadlock type stuff shimano had put on the BB; on close inspection I was pretty sure it wasn't metal, so I just kept tightening, removing, cleaning, examining the threads and re-greasing, and eventually the fit was OK. I've now got some Ultegra cranks. :)
What I didn't plan for was the difference in Q - the end of the crank was striking the kickstand, so that's had to go (I'd prefer to keep it really, as it's handy). All in all I've just shed 400 grams (kickstand was 150) and the bike is feeling amazingly light.

Still problems with the Sturmey Archer hub and I've got my eye on a Selle Italia Prolink saddle, but the bike is starting to feel like a really good fit.

Striking the kickstand... because of a difference in the BB length or the crank geometry? What chainwheel did you go with? Same number of teeth?

What was the purpose of the swap? Not being nasty - really curious!