My modded 66 build

[Street Ryderz]

A modded 66cc built from a varient not even sure who's I know I got it in 2014 ran it in my grocery getter for a few years with no issues so I took it out and decided to make some power with it and see how it goes!I would like to say that this is NOT a recommendation just information for those who like to play around with these engines!Once dissasembled and cleaned the bearings are pressed out and the transfers are opened in the case halfs just to match the cylinder witch has been opened slightly and the short angle closest to the exhaust is corrected by cutting into the wall and blending it back to the window edge!The first pic shows the cut and the next one shows the final angle blended in.The exhaust port was opened to 27mm across and 15mm in height witch is 25mm below the deck.The intake has been opened to 23mm across and 14mm in height the floor was dropped 1mm.The transfers window height is left stock as is the angle the ramps are smoothed and the sides are cut back a bit to meet the corrected angle of the wall and edge of port.The cylinder was decked so that the piston crown comes flush with the deck!The piston top was polished as was the head,stainless cap head hardware thru out case halfs and covers!I have yet to mount it and do a compression check and see how it runs but will update as I do!

 

[Bike_Builder]

I keep my squish at .020. That works well so far.

 

[Street Ryderz]

I keep my squish at .020. That works well so far.

My squish on this one is 3/4 of a mm any less and the upper dome hits the chamber radius!

 

[Bike_Builder]

That's tight!

 

[JerryAssburger]

Should be a Fire-Breather compared to before!

 

[gary55]

That's tight!

Yours is tighter 3/4mm is .030. If your getting away with .020" it's right on the edge of bouncing.

 

[Bike_Builder]

Yours is tighter 3/4mm is .030. If your getting away with .020" it's right on the edge of bouncing.

I'm pushing the limits! Lol, I had to divot a piston to allow the plug tip. He he he.

 

[gary55]

On some of my earlier builds I decked the jugs at .040. Some would work due to the inconsistent head configurations. On some I had to relieve some of the head material to keep the piston from hitting the head matting surface that extends into the cylinder. I'm still learning all the quirks of the differences in component designs.

 

[Street Ryderz]

This engine has been mounted in my bike now and has me confused a bit,I did a compression check and it only reads 140 p.s.i when the previous one read 180 p.s.i !?The only difference being I didn't trim the piston skirt on the intake side yet,And I had to raise the cylinder a little with a extra thin base gasket to get the head clearence needed!So I assume that I lost some compression there but am now currious if the piston skirt being cut to allow more duration has that much effect on the charge volume because I also found that with out the cut skirt my carb that had an 82 jet on the previous engine with the skirt cut,This one required an 8-10 jet size drop It has a 74 in it right now and it's still a little fat on top!The only other thing that I didnt do to this engine that was done to the previous is that I had filled the keyway for timming on the crank and re cut it 7 degrees retarded and I dont see that having any effect on the compression or charge volume,What I did notice from that is that the midrange power is not as strong and it fights the top end a bit!

 

[Bike_Builder]

Four stroking on the top is the fault of the C.D.I., the little black box that comes with the kit is a four stroke engine C.D.I.. They do that to cook the engine and get more parts money. Damn Chinese. Slightly different piston dome?