Finally got the last of my parts in to hopefully finish my bike this weekend. In the meantime I have started working on a backup engine. I purchased it for 50 bucks less than this one on ebay, but it's basically the same engine. The "110cc" engine that is actually 85cc.
https://www.amazon.com/DONSP1986-CDH...ps%2C95&sr=8-3
Funny enough it's the same bore and stroke as my Phantom motor, but if there could be a polar opposite, this would be it.
For starters, the port timing numbers are pathetic. As delivered the squish gap is 2.77mm. Some of that is thanks to the .95mm thick head gasket it comes with. If the squish gap wasn't hilarious enough, that head gasket has a bore hole of 58mm, so it leaves a large open area for combustion to get into. All of this on a head with a pretty large combustion chamber too. I am dead serious when I say this engine probably wouldn't even make 90psi on a compression check with the ports wide open.
The intake, exhaust, and transfer port timing and durations are also pretty miniscule thanks to the way the iron cylinder liner is installed/machined. Blocking a lot of the ports, not that it is a great design to begin with. Thankfully, a lot of that can be corrected. These are the timing numbers I got with one base gasket.
Intake - Opens 62 BTDC/118 ATDC and 124 Duration. Exhaust - Opens 68 BBDC/112 ATDC and 136 Duration. Transfers - Right Side 53 BBDC/127 ATDC, 106 duration. Left Side 51 BBDC/ 129 ATDC, 102 duration.
Blowdown - Right side 15 degrees. Left Side 17 degrees.
One thing I have decided to do is run 2 base gaskets. This will help add a little more to the desperately needed transfer port and exhaust duration numbers. It harms the intake timing a little, but I have a lot more room to work with on the intake port in terms of timing than I do with the transfers, so it is a fair trade.
This is how the ports look with 2 base gaskets.
Intake TDC and BDC:
Exhaust BDC:
As you can see, the iron sleeve protrudes down from the roof of both ports quite a lot. On the intake side it's actually perfect as it is. I plan on using some epoxy to ramp up to that lip to try and eliminate turbulence and cut back the bottom of the skirt flush with the lip. On the exhaust side it needs to be ground away fully, and that will really open up the port.
The issue is, it increases that already enormous squish gap to 3.12mm. As you can see here with the head gasket and a 3mm allen key in place just how far down the piston sits in the bore now.
The plan is to take 2mm off the top of the jug, and then about half a mm from the surface of the cylinder head. That should set the squish gap to about zero with no head gasket, and about .8mm with it.
I already got a little bored and decided to polish the hell out of the combustion chamber. The top of the piston is getting the same treatment.
Before.
After.
The rest of the lost power is going to come from port matching the cylinder and crankcase transfers. As you can see from the gasket and cylinder, there is quite a bit of misalignment on the intake side of the transfers on both sides, as well as a bit of mismatch from the iron sleeve cutaway. All easily fixed.
Yes, I am building a motor for the same bike that my Phantom is on. Partly as a backup, mostly as a side project. Kind of an interesting exercise in opposites. I want this engine to be a tractor like a CG engine. Less RPM, more grunt down low. Paired with a longer header tube "clone" expansion chamber like this one
https://www.amazon.com/dp/B07RR6Z7D8...roduct_details It should be exactly that.