I do not know about CycleX 890 12.1:1 kit.
I have Dynoman DP890 12.5:1.
CycleX stepped sleeves that were really cheap a year or 2 ago.
Sleeve-cylinder sealed with Wurth Super RTV silicone that hopefully will keep oil on the right side. I do not think that it was needed to bore wider in the bottom for sealer on that cylinder. My 970 cylinder got it.
Cylinder has holes in air vents 1-2, 3-4 as usual when boring.
Good thing with these flat JE pistons is that they can be milled to adapt to the head and cylinder height and get needed compression.
Pistons not milled here:
I have done a test ride last year. I had to use double washers under sparkplugs for clearance. Compression too high for Shell V-power fuel. Tested different cams. Pinging despite DP315 cam set with less than half lash making lots of duration.
The pistons are now milled 2mm off which I guess will be in correct range for the used head with ~24.5cc chambers.
Need to verify which base gasket and head gasket to use. Maybe thin RCS base, thick MLS head gasket.
I had to widen chambers a little bit more due to contact. Chambers were opened before.
Not wide enough here, contact. Made the squish angle deeper.
My 970 kit (70mm) my bike has now was also JE 12.5:1 flat pistons. Also CycleX sleeves, their thicker 74.5/69 mm, also very cheap a year or 2 ago
Milled them around 3mm to match other heads with 23.7cc chambers.
Piston crown thickness was around 7mm so no problem to shave. The 890cc (67mm) pistons about same thickness.
Cylinder had to be milled too, 1mm off since the very pistons outer top area were lower. Needed to be closer to head for better squish. Work fine with 125-75 cam.
My billet block 71.25mm piston setup used as a master for correct volumes and comparisons to land in same compression area which it did. The guy in the shop has tuned bikes since the 70's.
