On Nov 30, 5:18 pm, John Martin wrote:
Your fit will depend also on how you machine the bores - i.e. the
finish. Bored, reamed, honed, burnished? A roughly bored finish with
little interference might give you a light press fit, whereas a bore
burnished to the same size might be a heavy press or shrink fit.

There's always Loctite.....

John Martin

Loctite is almost certain to migrate into the needle bearings. When I
wrote 'Whack it with a hammer' I meant swage the exit hole down a
little and let the pin expand it back to a very snug press fit but
that might score the needle bearing journal and it wouldn't stay tight
for long under a load.

I've had some success adjusting a press fit without precise diameter
control by not reaming full depth, so the interference fit section is
short. If it's too tight I just ream a little deeper and try again.
This is the prior-planning version.

Move the needle bearings into the housing, if there's room.

Change to a drillable pin, install a roll pin in the shaft and
matching slot on one side of the housing and a snap ring on the other,
assuming you have enough room between the assembled 4140 housing and
the bearing cup to push in the roll pin and install the snap ring.
Lots of low-end equipment uses mild steel for roller and needle
bearings.

Press the needle bearing cups in last. Then you could clean Loctite
off the dowel pin. If you can tolerate heavy grease it will keep the
needles in place pretty well, otherwise put in a temporary plug.