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Motorized Bicycle Crankshafts 50/80cc & 100cc Side by Side Compared & Measured!

Motorized bicycle community has so much bad information floating around on how parts work. How things function and basic facts are somehow lost over basic logical mechanics of how things work in real world. Whole bunch of people seem to think the cranks are identical with just different rods or stroke lengths. You see people dremial, Drill and hack apart 80cc cranks the same way you would a 100cc crank. There is no 100cc Crank with 3 holes in it that would balance with any piston that is 47 mm like in minarelli or 80cc build. Or the person drilling hell out of a 80cc crank for 47mm piston when already balanced near 65% with 2 stock holes already drilled lol! You see people all the time making concrete vibrators pretty much lol. So try explain that to people that 100cc crank is bigger in mass and the reason you drill 3 holes vs the ones with 1 hole in 80cc cranks and they get all weird and crazy cause they can’t understand balancing basics of a crank that drilling 3 holes in for there 47mm piston just trashed it! Or the ones that use ball bearings as balancing point LOL nothing whole fruit loop crew that does not understand the topic of balancing a crank, you know the science that has not changed in 112 years of doing it has to be wrong…. with that aside! Here is the actual dimensions and why there used for what they are! 100cc cranks have more counter balancing mass for bigger piston. You could drive a 50 to 64mm piston with one ideally. Smaller crank for 50/80cc is ideal for 40 to 48mm piston. If you want to learn more about Crank parts and their weights. check out this video I already did on some parts most people use in builds they make!

All right guys we’re going to talk about basic crank design and how these work okay this is a 38 millimeter crank this is a 40 millimeter crank and i’ll show you how to find that really easy uh you’ll find these in 50 cc’s 80cc builds you’ll find this in like the ld 100 bt 100 yd100 and phantoms this is a long connecting rod this is a short you will find these

Like an af 80 on this crank which is the same length as the yd100 rod and those are found in the 80cc builds uh the only ones that use these short ones are usually the cylinders that have no head like the flying horse builds and stuff like that or the 50cc builds so we’ll talk about that later though but for now i’m going to show you side by side um zero so

Usually about 15.5 yep usually about 17.2 clues so 17.10 i was in there all right we’ll do the whole width which is 42.5 and this is 45 millimeter the entire length is about 106.64 and the entire length is about the same on that one what is not the same is the shaft coming out of these so well we gotta get that off that bevel there we go so we got 20.4

It should be 18. glow 17.8 it’s usually about 18 somewhere’s in there 32.12 31.45 we got 24 22.76 all right so there’s that rim on this is 15.9 the rim on this is 16.4 point five all right so this crank is a lot heavier than this crank and this offsets the heavier piston a little bit because of all that extra weight so when you see somebody drilling out

Holes in these there’s usually three and the smaller ones for the bigger pistons and usually just one drilled up here let’s see there’s usually just one drilled up here in the heavier cranks for the same size piston now this one here would take three holes that same size so to balance it anyways there’s not as much mass over here to balance it i guess would

Be the logic to it there’s more throwing around on this side so anyways where do you went over that in another video all right so this connecting rod if we can do this the total length is 11716.5 all right and then on a short one it’s 110.3 so you got 116 and 110 on the short so this is a js 50 which is a 50 cc rod um the af 80 is the same length as

This except lighter than the yd to go on this and the thickness of these are all the same instead of like this ends 11.2 11.2 we got 10.7 and 11.3 so the uh 80cc one’s actually whiter that’s kind of funny didn’t know that well anyways i just figured i would do it side by side and then if anyone else wants to know this is eight millimeter and these are

One millimeter thread pitch length sure yes one millimeter oops i just killed it let’s go one two one yeah close the other one millimeter thread pitch eight millimeter same thing with the hole here yeah well it’s reading the inside of the threads with the hole itself we can get it 8ml smaller key it could be that that keyway is because this is a used

One no i’m at 2 mil these are slightly bigger no 2.2 maybe this one’s this one no i must have had it crooked so we’re looking at 2.2 millimeter and olives which is probably three thirty second keys let me go get a key and we’ll find out all right guys so let’s see we got 332 second 2.4 millimeter so that’s what the keys are for these let’s double check

Make sure they fit nice and snug there’s another one nice and snug all right the opening on this 13 14 millimeter almost 14. i mean we’re not doing a hole right here yeah that’s about 14 now both of these so i just figured i would show a close-up of them side-by-side and kind of what you get you know oh my god i almost forgot so here’s the other thing too

This is 38 millimeter this is 40. all right all that means is that a space that pin is about from the edge it is two millimeter from the edge of that to where the pin starts and this one would just be one millimeter close enough one millimeter so basically all it is is this pin is moved one millimeter closer to this shaft center so from the center point of

This pin to the center point of that pin this would be one millimeter closer than the center point of this pin to the center point of that pin so i hope that explains it but from here to the center point of that one would be 20 millimeter and for this one the center point would be 19 millimeter from this one to the center point of that the two holes so i

Hope that explains it one’s just 19 center to center and the other one is 20. that much of a difference you

Transcribed from video
Motorized Bicycle Crankshafts 50/80cc & 100cc Side by Side Compared & Measured! By Build-Break-Fix