atc 90 bigbore

[clown36]

i am building a 90 mini trike style mini hole shots 10" front rim suspention on the front after market frame my quest is big bore kits ive seen some that are 5mm over what cc would that be. these trikes have been neglected and forgotten

[Rustytinhorn]

bore x bore x stroke x .7854 =cc

[Vealmonkey]

Pictures my man, pictures. I have a big bore stroker, but I can't remember if 5mm over is 124 or 138. Stroke it on out to 183 or so. Also, vent the pressure from the crankcase and the head. You may want to look in to oil coolers to help extend the life of your engine. As long as the compression isn't too much, you should be good. With the higher compression engines, you are looking into the more exotic fuels, forget pump gas, it burns too hot, looks toward alcohol. Then you are starting to talk big carbs, jetted insanely, but it will help the engine live. If you use a pull starter you are looking into steel cable. Kick start wouldn't hurt either. But then you are talking using different engines than the atc90, but the options are there. You're getting into my territory now. Real crazy and you'll be resleeving your cylinder head, using stroker plates or shortening your connecting rods and modifying cb750 pistons! Expect to get someone to do your head cause the bored and stroked 90s like to breathe. I highly recommend a professional to do your head work too. Bigger intake valve and sometimes a bigger exhaust valve. Don't be surprised to find out how much you can wrap up in one of these engines. Not a Cheap build for a big bore stroker.

[clown36]

veilmonkey your just the guy i wanted to chat with the piston i found was big als. the cb 750 stroke and bore can you tell me about it your flat tracker was cool to see no one is building these i thought i was the only one. as far as pictures still collecting parts and info. oilcooler a definent head or case is better?

[Vealmonkey]

I don't know about the different cases or heads being better, but just different and all the heads were pretty much the same. The only difference with the cases is if you want a clutch or kickstart or no hi\lo gearbox. You could do some expensive machining or you could just use a cl90 engine case. Parts are pretty much interchangable and if you want to use a pull start, they can be converted with just bolt ons. My crank is a used crank with a poweroll stroker kit. I bought the stroker crank off ebay. I've managed to pick up another stroker kit with a piston and cylinder all ready to go so I've another to build. I can't remember, but the cb750 piston is like 7mm or bigger over and you definitely need to resleeve. Also, you will need to open up the throat in the cases that the cylinder sits down in. You might also have to clearance the sleeve for the crank. As far as cams, poweroll or webcam are 2 good sources. Try not to get a cam that is too crazy unless you are pretty much going to run WFO all the time. A bigger aftermarket intake and a bigger mikuni carb is a must. There were also some real interesting POSA flatslide that they used at one time, but they are pretty rare. If you want an already built trike, I can turn you on to a board member that has one for sale. I was interested in buying it, but it's been too slow cutting loose on some of my trikes to make room. It's a nice looking trike and pretty much has alot of the good stuff on it. So if you haven't started yet, you could pretty much have a pull start and go custom trike! You can pm me with questions if you like and I can send you the board members name with the trike for sale. Great price too for what the trike is. With a little detail work, it would be an awesome machine, cause it already is really nice and trick. Let me know. I don't want to tie up a bunch of stuff on this thread.

[clown36]

i am interested i dont have a frame yet i have clamps and fork tubes tire wheels oilcooler billet head oilcooler adapter custom built. cant seem to pm you

[Vealmonkey]

clown you will have to post pictures of what you have. The pieces may not work with an atc90. I have lots of parts though. I pm'ed the guy about you interested in a trike. Hope he contacts you. If not, we can get some things together for you. I've got aftermarket frames, suspension front ends and some other bits and pieces to get you started. Ebay is a good place to watch for stuff, you just have to know what to look for. With these old aftermarket frames, you pretty much want the rear axle assembly from a 75-82 atc 90\110. Any older and you get the multipiece rear which you don't want, and any newer than 82 and the brake assembly won't work with the frame. You can use either an atc90 or atc110 with the frames, you just have to use the correct front engine mount with the right front frame mounts.
Most aftermarket frames were 2 inches or so longer and a little lower or closer to the ground. The frame length is in the area between the fuel tank mounts and the steering neck. So all the tank mounts and frame mounts are in the correct place. You can pretty much put any tank and fenders on the frames. I even had 1985 tank, fenders and seat on one of the old aftermarket frames and it worked fine. The 83 and later tank and fenders and seat don't look very good on the older frames though, in my opinion anyway. You will need a stocker grab bar or an accessory grab bar rack. You can modify the fork tube on the aftermarket front suspension to take a front brake if you want, but it takes a little work. Most people usually don't run a front brake. Whatever handlebars you want and whatever lights you want to run. Some front brake lines are too short for these frames so you have to be careful, some throttle lines can be short too. Exhaust is up to you but a nice free breathing pipe is a major help. Some sort of aftermarket filter is a must and even an outwears cover is recommended. They are doable, trust me and the parts can still be found, it's just a little harder. And don't worry, there is a small die hard band of 90\110 trikers. They were racing and dune shooting atc90s' way before the 185 or 250r came out. I'm still looking for a suspension 90\110 frame myself. I have 3 suspension 185s's frames. 1 bolt on, and 2 weld on. You can do a search and find them. I have 2 suspension 70s and sold a third one. I even have most of a yt125 suspension and an rd350 powered suspension trike which needs alot of work. I like the older goofy stuff. I have a line or 2 on some older trike conversions which would be nice if they pan out, but rarely do many trike deals work out. I know of a member on here who is hooked up with a treasure trove of early stuff that he just hasn't cut loose on it yet. I mean real mind blowing trikes. A couple suspension 90 frames too. Wish he would open that up. There were pictures posted of these goodies too, so they definitely do exist. Sort of a dune trike grave yard, but the trikes are not all piled up on each other, but alot of side by sides. And there is also a building with even more treasures on the inside that hasn't been photographed. Just the stuff on the outside was making me flip out, I can hardly imagine what is stashed inside!!!

[clown36]

thanks for the info wanted to now more about the cb bore kit do you have info the clamps i have i bought at a salvage yard the came off a bandido frame the frame was spocken for. iam going to use a 1981 250r front spindle modified that way i can do stopys and nose wheels need more power to play with though and the cam i think web grind 3 but i also need bigger valves? can you point me in the right direction of those

[Vealmonkey]

As for valves a 30mm intake was not an uncommon mod. Usually the exhaust valve stayed the same, some changed them though. Usually alot of port work on the exhaust. Best left to a professional. The sleeve for the cb750 was an old custom made piece. The sleeves were so big, you can actually see some of the sleeve through a couple of the fins!! And the cb piston you used was up to you. If you did it right you started out with standard size cb piston and it left some for you to bore out if you needed. Compression was up to the builder and usually determined by the application. Real radical compression ratios are best left for racing bikes and not very playable at anything less than wide open throttle. You really need to figure out what you're going to do with the bike. If you're not racing, then compression ration shouldn't go above 10.5:1. It still lets you run high test pump gas or low grade racing like sunoco. Anything much higher and your looking at the exotic stuff. Camming the engine to the hilt won't help you for doing alot of slow speed goofing either. You have to keep the trike manageable with the aspect of how you are going to use it. There is really no such thing as an atc90 that will do alot of trail riding and then go drag race. The engines are just do not have that wide spread power. Think carefully what you want to do and go from there. And I hope you either have deep pockets or know a machinist with an extensive array of equipment that is very patient. This kind of stuff takes time and money.