Boygofast 47mm sleeved cylinder info

Spare_Parts

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Nov 29, 2017
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Thought I would share some info on the Boygofast 47mm steel sleeve cylinder. First off it is a steel sleeve. Did a super scientific test on it, touched it with a flap wheel and it threw yellow sparks. Red would be iron. Took some pictures, port mapped it and measured the height which is 70.6mm. The thing that stands out the most to me is the tapered transfer ports. It is not just the sleeve, the casting have the same shape. Next oddity is the intake port. It is a different shape than the casting. The sleeve hangs down past the top off the casting about 1mm. The "V" at the bottom is just random. The exhaust port seems close to the casting. This casting has open transfers with bridge and the exhaust port is also bridged. The transfers are no longer open because of the sleeve. Non of the bridging serves a purpose any longer so it should be removed. We are currently searching for chrome faced rings https://motoredbikes.com/threads/47mm-steel-sleeve-cylinder-ring-help.54285/

I'll keep this thread updated with any new info. I have some ideas to keep the sleeve from dropping or rotating.

Post 47 for updated ring info.
Ring set update!
https://motoredbikes.com/threads/boygofast-47mm-sleeved-cylinder-info.54304/page-6#post-480567
Picture time!!

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Street Ryderz

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Oct 14, 2016
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You got lucky with that one imo,those transfers are the preferred ones and known as eyebrowed, they serve a useful purpose in that they create a swirl in the chamber as they first open at the high point and the pressure is at max.The intake could have the top flushed with no adverse affect and depending on induction type you may want to enlarge it yet anyway.The exhaust top of port at 29 is odd 27 or even 26 will be much better and go great with those transfers again deep at 33(high side) that gives 23 degrees blow down duration and retains your torque!
 

JerboaJohn

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Jul 29, 2018
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interesting, looks well thought out and all ya do is finesse it. hope you find the rings! it'd be great if someone wanted to bore it couple mm's :) looks thick,,
 

Will'smotobikes19

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Apr 9, 2018
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1,653
Not really going to weld to the al just to the steel and fill the rest with jb weld. You have a point it may not be very strong. I've never seen a dropped sleeve before but he was talking about ideas on how to lock the sleeve in place.
 
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