Most frames will work it just depends on how much fabrication your willing to do.
Id say do a little research on this site and look at some of the other bikes. I just finished mounting an engine and there was a bit of tinkering to be done to fit it in the frame. I think( CORRCT ME IF IM WRONG GUYS ) you will have the same issues with a rack mounted engine as well.
Hmm. This is the third reply to this question that missed the mark. Fabricating mounts, is absolutely not a problem for me.
Fabricating a new frame, when I find out that the motor won't physically fit between the tubes, that is out of my realm of ability.
What size frame did you mount your motor in? 14, 15, 17, 19, 21" frame? Or some number of centimeters? Frames are measured from the center of the bottom bracket to the top of the top tube. so if you don't Know what size your frame is, it's fairly quick to measure.
The three bikes this motor could find a potential home in are a 46cm, and 52 cm road frames, or a 17.5" mountain frame.
A 26" frame would be HUGE. I think you're talking about a frame that handles 26" wheels. My road bikes both take 700c wheels, which are really 29". A 26" frame would be a 66cm frame. The largest frames made are 68cm. They quite seriously look like skyscrapers.
If you have done this conversion, go look at your bicycle. On the seat tube, there is usualy a decal that says what size the frame is, and what material it's made of.
for the HT engines, the carb limits how far they can be pushed back towards the seat tube, and the spark plug limits the vertical space needs. Unless you have an atypical cruiser bike, basically it should fit.
I got a 65cc into this bike http://bikepedia.com/QuickBike/BikeSpecs.aspx?Year=2006&Brand=Norco&Model=Wolverine&Type=bike
it has NO room to spare, so i guess it's as small as you can go. On the other hand, there is a guy on here fitting a lawnmower engine into a BMX via flexible jackshaft, so it all sort of depends on your desires/perseverance.
edit: Oh your planning on throwing them into road bikes, i see now. In that case, i would say it looks like they would fit, but some kind of mount will need to be fabricated i think, because that looks like a flattened aluminum downtube? If it is, drilling the frame is out as is the stock attachment methods. If you need to fab a mount it's difficult to say if the engine will fit or not. I would still say yes for the 52, but the 46's top tube looks like it slopes towards the seat. Your spark plug might have some issues there.
Sorry i cant measure mine, it's in the garage due to snow, and is slightly inaccesable.
i'll do it asap, but i'm pretty sure my frame was a 22". I spent a couple mins googling it, but i couldn't find the specific 22" measurement. I'll try and dig my shed out over the next few days, as well as pics this spring.