So much depends on the bike's condition, your expectations, budget and resources. Can you afford to buy tools for this one project? Can you borrow them - or are you planning to do more bikes in the future? How bad is the bike's condition - is it simply the wrong color, or is it all crusty & rusty? By "used" do ya mean "cheap" or vintage... both? Do ya want a jaw-dropping show stopper and will do whatever it takes to make it - or just a nice lookin' daily driver? Are we talkin' a weekend here - or a full winter project or more?
heh - I'm not tryin' to be difficult, there's simply "tricks & shortcuts" that are different depending on whatcha want... for the best of the best there's little corner cutting that can be done, and it really outa be decided before
ya start. Still, I don't wanna give ya the wrong idea - fixin' up an old bike is not hard and can be lotsa fun
What Type of sand paper do i use to take off the old paint?
This depends on the bike's condition, if ya really want alla old paint off - then sandpaper isn't the way to do it. Striping the bike down completely
is far easier if ya remove ALL parts and beg, borrow, or buy a sandblaster. In less than half an hour you'll have a spotless raw steel frame. BUT caution must be used if it's aluminum (as well as a different blasting medium), older steel frames have brazed joints - gotta be careful with that too 'cause they're far softer than the surrounding steel.
No sandblaster? Bummer... ok, a 4" side handle grinder with a wire wheel will be a lil more labor intensive but outa still make short work of a bike's scruffy paint & rust. A low-cost muti-purpose tool that ya outa consider havin' anyway if yer gonna get into this game - it's just a bit dangerous tho so watch yer fingers and leave the guard on - ya bind up in a corner made by two pipes and it's gonna kick lol. Safety glasses are a must
have as it'll shed lil bits o'wire at about mach 10. Yer lookin' at about an hour or two plus some detail work with this method... longer if ya want "perfect" - the 4" wire wheel just can't reach into some of the corners. Speakin' of which, ya prolly want to get a Dremel for the detailing as well as about a zillion other projects that'll come up later.
IF the old paint isn't all that bad and there's not too much rust, then the above just isn't necessary. Not to mention using the original paint as a base coat can be far stronger than any rattlecan primer, this is when we get into sanding. Tryin' to get paint/rust off w/o power tools? I'm lazy and don't like it - but sometimes it's gotta be done. For the tough stuff I tend to use 80gt... it's tempting to use 60gt but that can often cause more labor later sanding out scratches. Try not to skip more than 20 "grits" or so with the rough stuff, the finer ya get - the more ya can skip till ya get to the really
fine stuff. The progression for cleaning & feathering old paint to clean steel usually goes somethin' like this: 60, 80, 120, 200, 280, 320 etc., the finer grits usually come later in the project to blend in imperfections. DON'T CHEAP OUT - with sandpaper the cheap stuff will cost ya more as you'll use a freakin' ton of it as it'll lose it's cut almost the first pass, particularly on metals - get the best wet/dry paper you can afford or you'll be filled w/a urge to smash things.
IF the paint is in really good shape and ya just don't like the color, all ya need to do is "frost" the surface to get the primer/paint to adhere. In this case it is far easier to use steel wool - not
the soapy things under the sink, check yer local hardware store for 000 and 0000 grade steel wool. That's not a typo - that's how they grade the fine "grits" of steel wool heh, three zeros is fine, four is super-fine. If yer doin' aluminum get stainless wool - if not, don't bother and get the regular stuff. This is true for aluminum and wire brushes as well BTW as non-stainless will contaminate aluminum.
Once that's all done and lookin' good - wipe it down with acetone or denatured alcohol (camp stove fuel) and a terry cloth rag (towel/washcloth). The terry's lil "fingers" pick up dust & grit where a cotton cloth will just smear it around - the soft cloth comes later for polishing an already clean surface - any grit with a "smooth" cloth will result in scratches. Oh right - obviously acetone & denatured alcohol are both crazy flammable so make sure to have good ventilation and DO NOT use power tools when there's a buncha fumes... I tend to do the wipe-downs outdoors because of that. If you don't have an air compressor, those cans of air for cleanin' yer 'puter work really well for those nooks & crannies... but that can get expensive and yer 'puter will get jealous lol
What type of filler do i use to fill in dents and what not?
This is one of the very few things JBweld is actually good for (ZOMG heresy heh), though it's a bit of a pain to work - it's really tough and sticks well. Still - I tend to prefer bondo's 'Plastic Metal' (No. 901), it comes in a 5oz tube and you'll prolly not need more than that. It's a fine enough consistency to "feather in" well to the surface and not leave an obvious ridge if sanded with 320gt or finer. If yer still havin' a problem with lil ridges and/or pits and the super-fine paper isn't helpin' - there's a ultra fine filler sold just for that purpose, but ya shouldn't need it for this.
What type of primer do i use?
I'm gonna assume yer gonna do this rattlecan style, that ya don't have a nice detail HVLC paint gun and compressor. There's almost endless options in spray paints, tho there's far better - I tend to use good old Rust-Oleum sandable primer, get a bunch of it as you will be sanding it lol, the more coats and the finer grit paper = the better the paint job. Three coats (not sanding the last) usually does the trick, but I tend to use it to see how bad/where my fill work needs be touched up. If yer bike had a lot of rust to start with - it couldn't hurt to use one of the rust blocking variants... tho I've noticed it doesn't "blend" quite as well. Oh right - you'll wanna get a complementary color to your top coat, if yer bike is gonna be dark blue - get black primer, red? Get brown or oxide etc. - the base coats can effect the top coat's tone... tho not a lot.
What paint do i use?
Again assuming the lack of a spray gun and keeping budget in mind - 'Dupli-Color Engine Enamel' is one of the best options as it's low-cost yet quite good, best yet as it's an engine paint it's fuel resistant. The catch is it comes in a limited color selection so if yer after somethin' different than the few different colors available - you may hafta sacrifice that fuel resistance... not a big deal - just try not to spill gas when yer filling it up lol or paint just the tank/engine with the fuel resistant stuff and the rest of the bike in w/e color ya want... I like the 'Dupli-Color' regular paints for that too.
Remember - a buncha light uniform coats with mebbe a lil super-fine sanding in between results in a FAR better job than tryin' to lay it on thick. I tend to hang the project upside down and start with all the tricky corners and stuff first - that way when ya flip the bike over for your final coats you can pay attention to makin' it look uniform and not hafta sweat the details or worry about gettin' runs as ya try to get that one missed corner.
Any Tools i have to use or buy?
Beyond the materials needed like the sandpaper, steel wool, and paints there's no tools ya really hafta
use or buy, but there's a buncha stuff that'll make yer life easier. If this is the only
bike ya plan on doing - then it's mostly just the Dremel multitool as there's so much other stuff that can be done beyond just this job. If ya wanna get a lil more - then it's the 4-5" side handle grinder. Again, it's a multi-purpose tool that can grind, cut, wirebrush etc. so it's an investment suitable for a buncha stuff other than just the paint job. Beyond that it's mostly labor-saving so it's up to you.
Time and patience and a clean
dry environment. For real - again I'm not messin' with ya heh, the more attention to detail, the more willing ya are to sand and recoat, even a touch of fine filler here and there to sand and recoat again - the better it'll look. Gotta let the paint/filler dry & cure FULLY before messin' with it - and even I have problems with that lol, primer ya can cheat with a lil as it really does dry quickly - but filler and paint really do need to set overnight for the best results... depending on temperature and humidity ofc. Your sandpaper will tell ya if you've been impatient - if it develops "gumballs", lil gobs/pellets of paint/filler on it - it's not fully cure and you've jumped the gun.
What type of paint do i use to paint the motor?
The 'Dupli-Color Engine Enamel' I mentioned before is the easiest and most economical paint to use. Painting as complex a surface as an engine can be... tricky, yet you'll still get a better job than one painted at the "factory" as those tend to be gawdawfull. Still, ya might wanna consider a pre-painted engine if ya haven't messed with one before as the best
way to paint an engine and have it look sweet is to disassemble it and paint the components separately. It's not tough really (ya do hafta remember to decontaminate the greasy with acetone) but it's something best reserved for when ya do a buncha internal engine mods anyway... which you most likely will get into at some point heh.