Outside the box build

[moofus02]

Taking inspiration from 190mech, 2strokd and Ryan I've been rounding up parts and researching to sort out what might work. I like the 125 mx build that broke in halfand I've road soon 80cc mx bikes that were lots of fun when on the pipe so I got to thinking that a 80cc mx build might make a good Street motor. Was looking at yz 85 at 47.5x47.8. I thought a 48mm crank would work but then I found a 47mm full circle crank on eBay so now I'm thinking a yz 80 at 47x47. Now I need to find a junk yz 80 top end to do mock up with. Open to thoughts on this idea. The mx top ends look so nice compared to the scooter stuff. Should be interesting if I can make it work

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[90GTVert]

Sounds like a great idea. John's the man with all the experience here so I'm sure he'll have some thoughts for you.

Did you buy the full circle crank just very recently? If so, I may have bid you up. I thought I was gonna get a steal on one at $60 last week and then someone else bid with me right at the end. If that was you, wish I knew. I was just gonna pick it up to keep on the shelf since they are not easy to get.

[moofus02]

Yes bought it last week strangest auction I've been in. Complained to eBay about it. I hit it once with a max bid of 150 20 minutes before it ended kept refreshing my browser. The auction ended showing 1 bid with me winning at 60 pay now. I finished supper and went to pay and I owed 113.must of been you that hit it at the last couple seconds but those bids didn't show until I went to pay. Computers suck sometimes. Was going to get a 48mm crank like Ryan had because it was close to a yz 85 stroke when I found this one. Ryan was nice enough to send me a link to this but I was already watching it begging the wife for permission to bid lol. This crank is nice same size as the 90 stuff so no extra work required. If it doesn't work for this crazy idea I can use it with one of my 54mm top ends. If it does work it should make a strong runner with the cvt tranny keeping the rpms in the sweet spot. God I love scooters

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[90GTVert]

I watched it from just after it was posted, crossing my fingers then I bid 110ish 30 seconds before it ended. I guess we gotta see if other 49cc members are bidding on all the cool stuff like this now. lol

Worst case scenario you stick it with a 52-54mm bore and have a lot of torque or resell it and prob make a profit.

[moofus02]

Yes it's nice just found a yz 80 Cylinder and head for 25 that's scared up needs a sleeve but would be a cheep way to do the mock up before I spend money on a good Cylinder. Just need a piston then to finish mockup. I'm going to look some more maybe I'll find a trashed topend with piston cheep. I can always buy good stuff if it looks like it will work

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[190mech]

Here is my 2cents worth..I have a large pile of core cylinders for prototype use..The Mina case has a deep mouthed cylinder flange,short rod,paper thin cases,restrictive reed pointed in the wrong direction(Ive said this before!!).,,OK,the late style YZ80/85 jug is a nice design,its fitted into a strong case,big diameter crank wheel,long rod,14mm piston pin,piston pin is at 19.5 from the piston top..Mina 90+ has a 26mm piston pin to piston top..We need a stout/thick adapter to join the fragile Mina case to the YZ80 jug,,that jacks the jug up,then the rod length needs to go waaay up even with the Mina long top crap pistons!
Doing all the calculations(I already have),we'll need a 98mm rod(RD125 twin) grafted to a Mina crank,using a Mina long top 47.5-49mm piston(good luck finding them!),which will give us an 8mm adapter plate,not enough to make a smooth transition to the huge well designed YZ transfers!
I really hope you can create a better mouse trap,but feel without hours of attempting to weld on the thin cases its a project destined for the "dud" pile(mine is huge!!)
By far the best way is to graft MX cases to a scoot CVT setup,but then we gotta find something with a right hand ignition...

PS,If a man could cast some crankcases that would house a BWS 100 crank,and copy the upper case of a YZ 80 all in one mold,then we'd have something!!

Regards, John

[ryan]

i have the bws aerox 100 engine, tell me more what would i have to do to make that bad boy into a mx top end!!

[moofus02]

I used to have a rd 125 twin. Don't know where it is now. The stock cases are limited by design but I didn't have enough measurements to know what I was looking at. Right side ignition motors are hard to find but grafting an entire 80 motor to a scooter tranny would be the best option of course. I was hoping yamaha cases had better metal in them for welding but by your observations my biggest problem other than the case restrictions would be finding a rod that would work that is longer than what I have. The earlier yz 80 motors had 12 pins from what I can tell but finding internal dimensions piston pin height rod specs etc is proving difficult unless you have stuff on hand to measure. Google hasn't been kind to me. Worst case I'll use this with a 52mm or 54mm mina top end

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[190mech]

Here is a good reference site,doesnt list every piston or rod,but has lots!
www.mitaka.co.uk/catalogue_index.htm

Ive been trying to open up the YZ80 can of worms for months,but trying to splice the jug to Mina cases is a tough one!!If I come up with a plan,I'll be sure to let y'all know..

[ryan]

im not 100 percent sure but couldnt you use the small gy6 studs for the exhaust and tap the cases for them? and even if they go through the other side you could grind them down and maybe lightly weld over them for safety? idk but ive been thinking of doing a 2001 cr125 lc build on my aerox/bws 100 engine

[moofus02]

Thanks for the link John I have searched and found nothing like that before. Did find some rd125 rod kits on eBay time to measure and see what is possible. The longer the better from what I understand

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[190mech]

I do it on paper,,Draw a center line and put a crank c/l mark a few inches from the bottom,then measure up 62.5mm for the cylinder flange,draw a deck line there,,now figure your stroke and mark that above and below the crank c/l(45mm stroke is 22.5 above and below crank c/l),from there you can add the rod length to the stroke points,then check the donor jug deck height from the cyl base and the bottom of the transfers from the cyl base,,Now choose a piston pin to top height from possible pistons and mark where they will be at TDC and BDC..Next find where the jug will line up with the ports at BDC,all this mess should give you the spacer/adapter thickness needed..

Ryan,Wish it was as easy as relocating studs!This is a MAJOR undertaking that'll take many hours in the machine shop..I do remember a short thread on ScooterInvasion of a BWS100 grafting a KX85 jug on,the dude was in South Africa the best I remember,,I looked and couldnt find the thread..It had a large adapter plate nicely welded to a severly decked case..

Here are a few pics of a 90cc case and YZ80 interface puzzle;

[ryan]

forgive me if im wrong isnt the am6 top ends available and will fit the minarellis? if you go to scootertuning.ca kevin showed me some real nice bbk that are mx top ends for scoots. i believe its under l/c conversion.

[190mech]

I never had an AM6 jug in my hands,but heard the cyl stud spacing is different.The AM6 would be a much easier graft,but their transfer tunnels are very small compared to a modern MX jug of the same size..Can you find any stud spacing dimensions for an AM6 Jug??

[ryan]

i actually have a friend who has a am6 50mm cylinder, i will get the spacing probably tomorrow