I'm kind of late in posting this but being a bit anal.....here it goes....I'm a newb here, just on my first build but I can't resist and have to mention a few things and make a couple of observations. I'm not trying to step on any toes, hurt anyone's ego and mean no disrespect whatsoever. The point is that there is almost never a black or white scenario. The truth and reality is almost always in the grey.
First, the title of the thread when first posted mentioned trying to achieve 60mph but the real emphasis in the title seemed to be on blueprinting. Yet so many got hung up on the 60mph part and that it couldn't be done before even hearing what 'mods' CreativeEngineering had planned. Reminds me of all those engineers/physicists/scientists saying that an object heavier than air can never fly. Then came the Wright brothers and the rest is history. If his aim was 120mph+ then the negatives would have been more warranted and even then you could say that sure 120mph is possible from the HT engine if you threw it off a high enough cliff to achieve terminal velocity.
I guess it all depends how scientific you want to be about this challenge.
Originally Posted by BarelyAWake
Armchair engineers abound, the speed claims have always been a touchy issue, newbs whom think a sprocket swap will achieve mach 2.567 exactly 'cause "they did the math"...
Let's not even get started on those that think a $10 wallyworld speedometer is even vaguely calibrated - even if they know enough to switch it from KPH to MPH lol, so many obsessed with speed alone - they have no idea what it takes to get there, one-upmanship the primary interest they'll happily tack on another 2-5-10 even 20mph to impress. Yet so terribly few will provide any substantiation, posting all sorts of pics of their shiny bike, even vids on youtube - yet somehow they jus' can't seem to find the time to hand the cam to a buddy, to film the car's speedometer whilst they ride...
I agree here that selective censorship is necessary on here to keep the quality of the information accurate and free of the 'oh yeah, well my dad can beat up your dad' immaturity, especially for the newer members such as myself. While quite familiar with 4 strokers I must say I'm a relative newb when it comes to 2 strokers and my only real 2 stroke experience is with 2 stroke model glow engines.
Coincidentally can these HT spark ignition 2 strokers benefit from exhaust throttling in addition to the carb throttling as is often done on glow engines which increases the throttle response?
As to the car speedometer, I hope you weren't being entirely serious.
I know I may be splitting hairs here but I don't think that that particular method of measuring speed is entirely precise either. Sure, it can give a rough hobby level idea of the speed but it is not at all uncommon for car speedos to have an error margin of +/- 5mph or more. Then there's other factors too on top of that. Heck, just changing from bald worn tires to brand new ones will change your speed at a given engine rpm by the difference in the circumference between the bald and new tires. I do agree with you on the wallyworld speedo thing however. Heck even the most expensive speedo you can get from the "house of Spandex" with spot on calibration is no good since all the ones I've seen you yourself enter the diameter of your wheels/tires but without taking into consideration the weight of the rider and how much that rider will compress the tires reducing their circumference and so skewing the actual speed reading. So the only accurate and precise way of measuring speed would be through the traps like CreativeEng wants to do. IMO anyways.
Originally Posted by Creative Engineering
What about the crank bearings & the seals?
They must be bad...right?
Not so fast there skippy...let's have a look at reality for a moment.
There are very few bearing manufacturers on the the planet. In order to stay competitive in a global market certain ISO, (Interntional Standards Organization), standards must be adhered to. The fact that this is a cheap Chinese Bicycle engine does not mean that there is a cheap Chinese bicycle engine bearing manufacturer. Given the capital outlay for a bearing plant, and the fact that a high volume is critical to success...there's not even the slightest chance that the crank bearings in these engines are sub-par!
I do have a bit of an engineering background let's just say but I am not a machinist per se yet I can appreciate the quality of your work and believe your project is not only feasable but very doable indeed. However I must disagree on the bearing issue. There are bearings and then there are bearings. ISO provides certain, essentially minimum standards, that manufacturers in a particular sector should adhere to. Some meet these standards while others exceed them. Others fall somewhat short yet their goods are in circulation nevertheless. I haven't enough experience with the HT engines to pass judgement on bearings in them but quality-wise these engines leave much to be desired and if bearing failures in these engines are common I seriously doubt the bearings are top of the line. To illustrate, install the same quality bearings in a properly machined engine (like the one you're working on for instance) versus an off-the-shelf HT engine with misaligned cases and guess where the bearings will last longer? It's a combination of soundness of original design and final execution.
ANYWAYS, thank you all for listening to my rant. And please I'll give you my milk money just don't give me a wedgie.