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Discussion Starter · #1 ·
I see DRATV listing this 51mm crank on ebay;

51mm Stroker Crankshaft with Mods Fits XR CRF 50 CRF50 CRF70 51MMCRANK Read | eBay

I see I will need to run a 69mm tall cylinder;

TB 721 54mm bore x 69mm tall cylinder - Pit Bike Engine Parts - CYLINDERS - TBW0721 - TBolt USA, LLC

or a trx90 cylinder, from what ive researched. Could also use shorter cylinder but need a spacer plate...?

The TB kit should bring it upto 113cc and the trx90 on a stock bore 86cc.

Will the TB cylinder require my original 70 cases to be bored? the trx90 wont require boring?

on the DRATV website I read that this will only work with the crf50/70 cases, I thought it would work with a ATC70 aslong as I modified the ignition? the trans and clutch should bolt up and it'll fit the cases?
 

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Discussion Starter · #2 ·
so im still on the hunt for info with this, im seeing alot of 52.4 and 69mm 110 chinese cylinder kits. But there is variants in stud spacing, im right in thinking and saying I need;

  • Diagonal distance between head-barrel fixing holes (centre of eye to centre of eye): 69 mm (2.7 inches)
  • Smallest distance between head-barrel fixing holes (centre of eye to centre of eye): 50 mm (2 inches)
this thread has provided me with alot of information;

http://planetminis.com/forums/z50-ct70-jdm-monkeybikes/162286-updating-z50a-engine.html

so my next question following on from stud spacing would be, is there anyone on here who could bore my honda cases, or whats the chances of me being able to do it with a dremel :O (I did see a thread where someone had done it with a dremel, thats why I'm asking).
 

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I bored my cases with a dremel and it turned out ok. As long as you dont cut into the stud holes/thread I dont really see how you could mess it up. I have a chinese crank in my atc70 cases and its fine except you do have to notch the ignition side to allow the pickup coil to fit. The 12v side covers also dont line up perfectly with 6v cases but not a big deal unless you are a perfectionist. Dratv also has a 54mm cylinder buts its 63mm tall. If you found a spacer for cheap it could save you a buck. 54mmx63mm Cylinder Lifan Zongshen Jialing 50 and 70 CC | eBay
 

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Discussion Starter · #4 ·
I can get cylinders cheap enough. I want to run the original atc cases so they match the frame numbers. I think il order the cylinder and crank and use the base gasket as a rough template to cut.
 
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