Modern Vespa

When replacing I know it's best to replace both races.

But concerned about the difficulty of shoving the race back into the frame (the race on the fork I think will be fine). I've seen a couple of different methods but until it's apart I am a bit concerned how I'll go.

So is it likely that the race in the frame will be healthy enough to leave it in place?

IMPORTANT: I can't leave the bike in pieces for ages as I fight this - it's my only vehicle.

(Yes I probably have lefts some balls scattered along some 4wd trail)

PS, my top set look perfect as they were replaced about 2 years ago and I inspected them a few days ago

It's usually the lower race that causes notching, rather than the upper race. After all, it's the lower race that takes all the impact going over bumps - the upper race just holds everything in place with no wobble.

I use a piece of rebar suitably ground and bent to gradually knock the lower bearing free - a specialist bearing puller might do an easier job though.

To replace, I use an impact socket that matches the race's outer diameter, and *very carefully* start it off dead straight in the fork. What size I forget, but one of my collection was 'perfick'.

saw that method. It's more likely to be my first choice rather than using a long threaded shaft that needs a perfectly sized bit at the bottom anyway.

but do you reckon that race in the frame is going to be damaged or just the bearing cage (the bit which holds the balls) or just the race on the fork?

I did this job (a long time ago now) and if I remember it was just the one on the lower fork that required the most patience and finesse. It was also the troublemaker causing the notch.

Be a good time to replace that front fender to a reflector-less one!

Freezing the new bearing and heating up where you wanna put it with a heat gun or similar helps immensely as well.

sure. freezing is easy. not sure how much my heat gun (one of those ones with a battery that's swappable across a range of tools) will be able to heat the tube/frame though - it's a big mass of steel.

I would expect the bearing cage to be OK - but both races (frame and fork) are suspect, as they both get an equal hammering.

When the top ones died the cage was mashed and balls had fallen out (could see this when i peeked under the plastic cover). I had my mechanic replace them so i don't know the condition of the races; plausibility also f'd.

GTS steering bearings (Post 2596221)

The top ones get buggered by rust, lack of grease etc, and sometimes by over-zealous tightening - they should have almost no pre-load.

They need to be sealed cartridge, like on my rollerblades.

Or conical rollers instead of ball bearings.

Discussion and some photos of lower bearing installations on Scarabeo scooters, which I believe are constructed similarly to your scoot.

https://www.apriliaforum.com/forums/showthread.php?333976-Beo-500-ie-Steering-Head-Bearings

Drawing the lower bearing's upper race into the tube so that it's straight requires some finesse - freeze spray, and a set of steel bearing presser plates, manipulated by nut tension along a long length of threaded rod. Crude yet effective for the ambitious DIY home mechanic.