Manco Thundercat/ GX200 project almost ready, need suggestions please!

Last weekend my dad turned 54 and i bought him an old manco thundercat (may be called thunderbird im not sure). When i was young he bought me my first minibike and i have never fallen out of love with them. My brother and sister (11 and 13) both have doodlebugs and my popps has been really wanting to get something with a little suspension that he can putt around on with the kids.... that being said
I have a gx200 clone with all of the basic/easy mods done and of course all of the free ones as well. As the engine sits it has
-exhaust -air filter (with stock intake andifold) -governor removal -re jetted- index spark plug- 18 LB valve springs -advanced timing and smaller cooling fan. The only thing left on the engine i would like to do is aluminum flywheel.
So the engine is far more than he will ever need/use.
I dont know what you guys think about the thundercat but i have always liked it, a friend had one when we were younger and i liked them then and still do.

What are your expert opinions about these frames. Iv already ordered new seat shocks but something MUST be done with the front end.
Is there a common thing people do to either replace the forks or make them function. I would like to just get new forks and be done with it.

Please let me know what you think about this setup and what my options are concerning the forks. They are un-salvageable at this point. I would like to put factory forks back on it but i just cant seem to find them. Is there something else i need to know about the front end? and does anyone have one of these bikes with a gx200 in it?

btw this engine IS going in THIS frame and it WILL run, my heart is set on this setup. I respect if anyone is in disagreement with pairing the two but please dont try and convince me otherwise. I just need to be pointed in the right direction as far as locating aftermarket/origional forks. or is there a more common fork that will fit this bike. Thank you in advance for your time. This project means very much to me.

i am sorry if i did not put this in the correct place. new to the site but not to minibikes :)


New Member
I just sold a Manco Thunderbird. I'm guessing it's what you have. Manco is still in business, but they are now American Sportworks American SportWorks formerly Brister's and Manco ATVs, Scooters, Go Karts & UTVs | Lots of parts are still available. I had a clone on mine, so I know it will fit. Are the forks completely bent up or something? Mine were all rusted up when I got it, but I kept soaking it with PB Blaster and they finall came apart. I was able to clean them, paint them, lube them up and put it all back together. Post a picture so we can see what you're working on.
ill get a pic later on this evening. what happened is, the person who owned it before ran steel rods inside both tubes of the forks. Im guessing one of two things happened: there was a crash and completely sheered both tubes at the same place and they ran steel rods in there just to make it rideable
or ,what i think happened, is that the front springs became so worn that they just cut the tubes in half and ran the rods in, thus making it a fixed front end. Ill have the pics later.

that info that you gave me really helped. I apreciate it very much.
Welcome to OldMiniBikes. There is a minibike shop located in Taylor, MI. Located at 12950 Beech Daly Road. Their phone # is 734-992-3648. Give them a call and maybe they can help you with a set of forks that would work for you. Just measure the neck before hand. Good Luck P.S. Check my photos I have a Thunderbird too.
i like that tcat bill

Bill, that is pretty much the look i am going for. i like it allot. here are a few pics of the engine. I have to file the timing key and put they flywheel, fan, and shroud back on so right now its naked. Im fixing to tear out the old snowmobile engine that came with the thunderbird and fix some welds/ mount the gx200. This is going to be a sweet build. pics of the bike will be on later

the first two pics are of its current state, the last pic is when i first got it.
One thing you'll need to do is beef up the motor plate. It flexes to much with the stronger motors. I put a brace at the front of the motor plate made from a scrap piece of 3/16 plate-notched to go around the down tube and then to the plate. Doesn't flex hardly at all and made a big difference.
the plate that is on there now has been welded on and modified. I was just going to clean the welds and beef it up a bit but hearing what you posted, i think it will bw easier to just build a solid one right from the get go.

thanks for the advise.

Also: tips on improving scrub brake? My friends worked well and this one is hardly able to stop the bike. everyting looks good on the scrub brake beside the part that makes contact with the wheel. It is worn and exactly what you would expect out of an old used minibike. I was going to weld another steel plate directly onto the existing one.

Is there a better way?

No that will do nicely. The one on my bike was so worn it looked like someone blew a hole through it. They replaced it with a curved piece of metal that fit the tire better(more contact surface).


Active Member
Hey Bill, I took your advice and welded two braces on my Mancompany build. Seems to help. I think I'm going to put a disc brake on the sprocket as soon as I have time to research sizes etc.

Mw, You might consider that too. There is a thread where I asked about how to put disk brakes on, and members sent some good pictures of their set ups.
for some reason I really just like that scrub brake. The bike i used to ride with worked well, in fact it worked better than my clutch band ( which also seems to eat those clutches pretty quickly). The disk brakes on the doodlebugs aren't worth two dead sure they make better ones but those sucked.
If the brakes become insufficient i'll have to look into a different setup.

I appreciate all of the input. Not only does it help with the technical parts but it makes me want to get to work.!

These pics should help. the forks pretty true and there i no realistic way of getting them separated. Im going to grind and weld those forks the best i can, maybe fix the spring retaining rings and just see what happens. The engine plate needs complete removal/replacement. I was going to re-in force it anyway so building a new one may even be easier. I have all of the dimensions of the stem and ID of the mounting holes....ill post them tomorrow. If i can get a fork cheep enough ill just that.he wants shocks no matter what i tell him.
I have more pics and appreciate the feedback. thx
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Active Member
Hey MW, any progress on the T Bird? I think you could find something to use for a new set of forks, but it would probably take some cutting and welding. If your dad is just going to use it in the yard, front shocks are not that important. They don't really work that well anyway. Do you have any colors in mind for it, or are you going to paint it?