I got my bottom end back together and was able to check the squish gaps with the pistons I have on hand. I measured the chamber CC as best as I could and came up with a 6 cc chamber. Not exact since it is a fixed head cylinder, but fairly close.

Surprisingly, with both base gaskets in place the MS380 piston actually clears. It has a fairly tight squish gap of .6mm and would give a compression ratio of nearly 12:1, which is a tad high lol. The bigger issue is it blocks the transfer ports and closes off the exhaust port, so it definitely needs to be milled down to work.

The stock piston with both base gaskets has a 1.72mm squish gap and has an incredibly low compression ratio, 8.9-9:1. Possibly a design choice to keep heat down and allow it to run on cheap gas. With one base gasket it drops the squish gap closer to something more acceptable of 1.12mm, and bumps the compression up to 10:1 With no base gasket it's right on the edge of squish gap tolerance at .52mm, but like the 038 piston the compression is near 12:1

Unsurprisingly, the MS460 piston ends up with the best overall figures. With 2 base gaskets its still nothing special with 1.6mm squish and 9.1:1 compression, but with one it has a squish gap of exactly 1mm and a compression ratio of 10.45:1. A pop up piston with 2 base gaskets lands somewhere in the middle with a 9.6:1 compression ratio while also maintaining the port timing of the 2 gaskets.

I am going to run a flat top 460 piston with 1 base gasket as I view it as the best combination overall. and then likely port the exhaust side to restore some of the lost timing and increase duration.

Dangit Dan! Stop it! I don't need any more projects. :lmao: Building these motorized bikes are so much fun. I got too many irons in the fire. I promise I'm not going to do another motorized bike. Not right away anyway. :hehe:

LOL. Jerry, this is keeping me from having too many irons in the fire. I keep wanting to buy another motorcycle, but it's the last thing I need. This gives me something to fill the time and scratch the itch.


The funny thing is, this engine is considered one of the most powerful out of the box engines and here I am trying to improve it.

You and I know there's no such thing as being the most powerful already. :lmao:

Or that anything made in China isn't going to need some help to actually make it good or reliable.

So I decided on running a standard 460 piston with one base gasket. With that in mind I splurged and bought the highest quality piston I could and got a Meteor brand piston.

The quality difference compared to the others is tangible and visible. It's also .02mm taller than the Hyway pop up piston, which means my squish gap should be .96mm, and a compression ratio of 10.5:1. I am quite happy with that.

I took my rather pricey piston and then proceeded to ruin it and put two windows in it lol. Not too bad considering the old beat up lathe I had to work with.

https://i.ibb.co/d48qm6M/20220430-162602.jpg

Now I just need to finish cleaning up the ports and get if running.

Better than what I did back in the day with a dremel.

I kind of want to start a 2 stroke motorized bike racing league now.

They have a racing league in California, but it is dominated by bigger four stroke mills.

They do have 2 stroke races, though I know little about them. I do know that there are guys out there doing hybrids with cylinders from Minarelli scooters pushing stupid amounts of power though. 10-15hp from a 70cc engine. :wtf:

Then you have the speed demons who are just obsessed with going 60+mph on a bicycle. Heck, there is even a gentlemen who builds custom wheelsets just for motorized bikes with 11mm thick spokes, sealed roller bearing hubs with extra thick axles, and really beefy double walled rims.

The last time I looked into doing this for the fun of it, none of this stuff was even a thought. It blows my mind lol

Heck, even this phantom engine I bought has to make about 5-6hp and is very torquey. Watched a video of a guy that took a stock phantom, had an expansion chamber modified to fit it installed, put a 32 tooth sprocket on his bike and hit 52mph.

anything over 40 on a bike feels, well "fun".

Saying from experience when I got mine to top out at 55 with just the right gearing (took a full mile to hit that speed).

Then the drain screw vibrated out and I lost my gas.

I am more concerned with pulling power than top speed. With a 40 tooth rear my max speed at 9000rpm will be around 40 to 45. That puts my cruising speed around 20 to 35, which is all I desire.

Well you have the high compression setup. If you want more pulling power I'd lengthen the intake a bit, remove the baffle from the exhaust (if using the standard chinese 2 stroke one) and open it very slightly using a step bit.

and by slightly, I'd make it just 4-5mm larger than it's current opening diameter



Shorter intake and more open exhaust is higher rpm but less pulling power and vise versa.

The intake expansion chambers (boost bottles) have felt like snake oil to me. I haven't seen any improvement from them, just a change in sound that some perceive to be an improvement.


If you're feeling brave you can run nitro to the intake. I will say it is fun, as long as you don't have to turn and there are no potholes.

They do work, but only for a short stent and it's risky

The Phantom 85 standard exhaust is actually already a lot bigger than the normal.china doll engines. 28mm inside diameter with a straight 19mm exit pipe. The exhaust port matches the pipe and is pretty darn big. The intake side has very aggressive port timing and a steep slope just like the saw it is based off of. With a Reed and windowed piston combined with the exhaust and really good exhaust timing and blowdown right out of the box this engine is pretty torquey as it is. All I have done is bump the compression a bit and port matched the intake to the Reed block. I will actually play with more aggressive stuff later.

Boost bottles aren't worth the time. I have no desire to run nitro or nitrous or any other silly stuff. Premium unleaded is fine by me.

Made a video somewhat covering the bike and build.

https://www.youtube.com/watch?v=t6zs0fmf1vI&t=14s

My slightly bigger disc brakes came in today. 160mm vs 203mm discs.

https://i.ibb.co/d70LWq5/280043885-1...14047318-n.jpg

Not to worry, the front is getting the exact same brakes. The main reason for the huge rotors is for sprocket, chain, and caliper clearance. The chain on the 40 tooth is going to create a potential contact point with the calipers, but it will hopefully be just close enough.

https://i.ibb.co/CBymrZ5/279950451-1...34835582-n.jpg

I am still going to have to space the rotor out, but with the new style of dual pull calipers I have, that has to be done anyway since the new caliper positions the pads further out than the original unit. Thankfully, I have a lot of room to work with on the brake side, so I actually think this will work out rather well.

https://i.ibb.co/LSq8Khf/279913206-1...47166523-n.jpg

You can also see in that last picture how far the caliper sticks in toward the hub. The new calipers I bought are a dual pull style instead of the single that the original units are, and as I mentioned previous the pad centerline is moved outward as well, but on top of that, they also stick inward less than the original units too.

https://i.ibb.co/BLCXK6N/279856331-1...62079229-n.jpg


So, my plan to to setup the bike and just start with the rear wheel and work my way forward. I plan to pull the rear wheel anyway to actually check the wheel bearings and make sure they have proper lubrication, it will be a good time to work on the rest of the setup. I just don't trust whomever assembled it.

The "OCC" sized sprocket hub adapter is sized perfectly for this bikes rear hub. My plan to hopefully prevent issues with slipping is to to key the surface of both the adapter and hub with a little sanding and then utilize some Loctite 638 retaining compound which has a shear strength over 4000psi and is also decently high temp and oil resistant. Thankfully this adapter is also machined properly and a nice snug fit with the hub, which will really help.

If you are thinking that the retaining compound won't be enough, I have watched that stuff hold a bearing race in place when the breaing locked on up an enormous 480V motor and ended up spinning the shaft on the inner race and wrecking it. It's some impressively strong stuff.

One nice thing about buying a cheap bike like this is my entire lack of guilt in buying cheap ebay parts to upgrade it. The parts on the bike are just as cheap and shitty :hehe: