Hi!

I'm attempting to rebuild a 96 Specialized Hardrock. I decided to get a front suspension fork to replace the solid original. The bike had a 1" threaded steerer tube, so I ended up with some RST Omega forks with a replaceable tube, and I bought a 200mm, 1" threaded tube.

https://www.amazon.com/RST-Steerer-2.../dp/B001CJXD8O

I was hoping I could use the original headset, but it seems that the threads are a different size between my original threaded race and the new steerer tube. Also, the steerer tube is too long, and there aren't enough threads for the threaded race. Also, the original crown race is slightly loose on the new steerer tube.

What are my options? Do I have to get a short steerer tube? I was hoping to get the maximum handlebar height, but I see that was foolish. Also, what headset can I buy that would fit those threads, and not require me to replace the pressed frame races (I just painted the frame, and I don't have the tools to remove them anyway).

Sorry for the stupidity, this is my first time building a bike.

Steerer threads can be extended, and excess length cut off. It used to be standard stuff at bike shops, so just find an old shop, and they can probably help you out.
The loose crown race is probably a JIS/ISO issue. Your old fork was undoubtedly a JIS with a 27mm race seat, and the new one is likely ISO with 26.4mm seat.
I have corrected this with a knurling tool to emboss the race seat to make the effective diameter larger. The same thing can be accomplished with a centre punch. When doing this, it's also a good idea to use some kind of assembly compound such as Loctite 680 to keep the race firmly in place.

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...if you don't want to do this ^^^ (or cannot find a place to do it for you), if there is enough unthreaded length on the steerer remaining after you cut off the threaded part with a hacksaw, youi can find yourself a 1" threadless headset, and just go threadless. But you have to buy a new headset, and stem, and it looks very different. Plus 1" threadless headsets are difficult to find (but not impossible), as are 1" threadless stems (but you can use a shim and a 1 1/8" stem...those are more plentiful.)

Possibly your best option (once you find a headset that works with your fork), since you want some extra steerer tube length, is to use a bunch of 1" spacers under the locking top nut of your selected headset. They are readily available online. It looks kinda strange if you go to far in that direction, but it keeps your headset adjusted and youi can use the same stem you have.

Not certain why you decided to go with front suspension. If it is because you are gonna ride the hell out of this bike, a longer steerer length and spacers is probably a less good idea.

Thanks for the reply Dan!

If I bought a 26.4mm ISO headset to fit my new steerer tube, would I have to replace the JIS pressed frame races?

Also... I assume having a bike shop cut new threads in my steerer tube is going to cost more than 20 bucks (the cost of a correct-height tube)?

Edit: I noticed that the ISO standard cup outer diameter is 30.2, while the JIS is 30.0. So ISO cups won't fit my frame? Sheldon Brown's site claims that both JIS and ISO have the same threads per inch on the headtube- so why doesn't my threaded race thread on?

The same bike shop that would be equipped to thread the steerer would probably have a reamer to make the ISO cups fit.
As for the top cup not threading on, probably just a matter of having the thread chased with a die. This will be done in course of extending the threads.
Yeah, it will cost you a few bucks to have it done, but the alternatives are, buying the tools and doing it yourself, a heavy investment for a one time use, or paying somebody that has the tools and knows how to use them to do it for you.
Another option is to get a conversion headset. Tange and others, make headsets with ISO cups and JIS crown races and vice versa.

I went with front suspension because the roads in Cambridge are full of potholes, and I'm installing a 2-stoke 49cc engine on the frame, so I want to minimize road impact on the engine mounts.

I went ahead and bought a shorter steerer tube for 15 bucks, and an ISO headset. I might have to ream .2mm from the head tube, but that should be easy.

Need tall? a threadless conversion will work
the headset will slip over the unthreaded part of the fork.

spacers and BBB BHP 20 wiggle.com | BBB BHP-20/21 Stem Extender | Oversize Stems will give you the top of the steerer tube adjustment of that headset

Motorizing a bicycle (on the cheap) usually results in having poor braking capacity..

Why not just buy a MoPed and pay the road tax & licence fees?

You may be able to find an ISO diameter crown race separately for whatever make/model your current headset is.

JIS head tubes can be reamed to ISO spec.

They should be the same thread. You may want to chase the threads with a die, but extending the threaded portion will do this, if you decide to go that route.

I uses to have a moped. They are very heavy, and have poor construction quality.

I have a shimano slx disc in the front and v brakes in the back. I only weigh 155. I'll e fine for braking. I'm by really going for cheap, I've already put a grand into this bike.

Using a bike frame means I can keep it light, carry it into my house, avoid licensing/fees, and get maximum gas mileage.

What is wrong with pedaling? I hate noisy engines and 2 stroke exhaust fumes

Sorry, not sorry!

I like getting to work in half the time without being sweaty and having to change. I like being able to haul groceries easily from the store up a large hill.

light will break sooner than something with a More substantial tube wall,

You're on your own from here on out.

Don't get your knickers in a twist.

If you hate 2 stroke engines, it's probably because you're not riding one.

...I love it when these guys go by me in the bike lane here. Makes my day.

I dont need to , I'm right down town, in a small town. In No Big Hurry..

Nothing sounds as good or smells as good as a 2-stroke engine.

Close the Garage door and enjoy.