Motorized Bike Project.

[willardnigma]

From my experience (I've owned the phantom 85 and all of the little 2 strokes.)
for 2 years my main mode of transportation was a motorized bike. It's what I was riding when I got the call about my dad, motivating me to rush over to the next county on hilly backroads.

All of those engines are from the same factory. The phantom 85 I bought was horrible. The head, piston and crankshaft replacement to go from the 66cc to the 85cc creates a ton of problems that ruin any longevity of the bike.

REPLACE ALL BOLTS for mounting the engine and for the intake and exhaust with good ones bought locally. as much as these vibrate I've seen the exhaust and intake bolts shear right off. I've heard of the rear sprocket bolts doing the same, but haven't experienced that myself. You know the typical chinesium quality doesn't pair well with a high vibration 2 stroke.

All of the quality from any of the sellers is hit or miss. The biggest way to get the best performance from my opinion is shorten the intake, get a high compression head. Polish your ports (lots of deburring from the casting on the jug) Windowed piston and reed valve attachment.

Being a china bike rider you know all to well about jetting the carb (hard to find jets for the stock carbs, best finding an aftermarket that fits)

As far as exhaust upgrade go, they're hit or miss. It's all about the rpm range you're running at. The stock one does well if you know how to enlarge the opening just a smidge. The ones referred to as "banana pipes" are just snake oil and sound a bit louder, but aren't truly tuned to give any performance.

All of these kits are way too overpriced vs buying the cheapo kit and finding the aftermarket parts to slap on yourself.


If you want I can link everything that was on my bike that's still in use today since 2018
(the new owner has only had to replace the chain and air filter)



And just like any other china bike
LOTS OF LOC TITE is a must.



Base motor kit

I recommend this High compression head, as the other design are lacking in cooling. You will notice a difference compared to the stock one

Windowed Piston. DO NOT get this upgrade if you don't get the reed valve, or you will lose a lot of performance

Reed Valve (wont get much out of this without having a windowed piston



And the final part, bike wheels with the mounts for brake rotors tend to fit the rear sprocket just fine. This is a must if you want any longevity as pushing the engine harder than stock can rip right through your spokes. Hell even a stock engine can do it if you get one thing out of alignment.

[Megadan]

Originally Posted by willardnigma

From my experience (I've owned the phantom 85 and all of the little 2 strokes.)
for 2 years my main mode of transportation was a motorized bike. It's what I was riding when I got the call about my dad, motivating me to rush over to the next county on hilly backroads.

All of those engines are from the same factory. The phantom 85 I bought was horrible. The head, piston and crankshaft replacement to go from the 66cc to the 85cc creates a ton of problems that ruin any longevity of the bike.

REPLACE ALL BOLTS for mounting the engine and for the intake and exhaust with good ones bought locally. as much as these vibrate I've seen the exhaust and intake bolts shear right off. I've heard of the rear sprocket bolts doing the same, but haven't experienced that myself. You know the typical chinesium quality doesn't pair well with a high vibration 2 stroke.

All of the quality from any of the sellers is hit or miss. The biggest way to get the best performance from my opinion is shorten the intake, get a high compression head. Polish your ports (lots of deburring from the casting on the jug) Windowed piston and reed valve attachment.

Being a china bike rider you know all to well about jetting the carb (hard to find jets for the stock carbs, best finding an aftermarket that fits)

As far as exhaust upgrade go, they're hit or miss. It's all about the rpm range you're running at. The stock one does well if you know how to enlarge the opening just a smidge. The ones referred to as "banana pipes" are just snake oil and sound a bit louder, but aren't truly tuned to give any performance.

All of these kits are way too overpriced vs buying the cheapo kit and finding the aftermarket parts to slap on yourself.


If you want I can link everything that was on my bike that's still in use today since 2018
(the new owner has only had to replace the chain and air filter)



And just like any other china bike
LOTS OF LOC TITE is a must.



Base motor kit

I recommend this High compression head, as the other design are lacking in cooling. You will notice a difference compared to the stock one

Windowed Piston. DO NOT get this upgrade if you don't get the reed valve, or you will lose a lot of performance

Reed Valve (wont get much out of this without having a windowed piston



And the final part, bike wheels with the mounts for brake rotors tend to fit the rear sprocket just fine. This is a must if you want any longevity as pushing the engine harder than stock can rip right through your spokes. Hell even a stock engine can do it if you get one thing out of alignment.

Oh, believe me I am well aware of all of this information. I don't go into anything without doing epic levels of research. I do thank you for taking the time to say all of that though as it may help others.

Believe me, I planned on doing a LOT to this engine, and replacing most of the hardware, anyway.

As far as the Phantom 85 reliability, it's actually improved some now that they stopped using those stupid bushings. They now use the same connecting rod as the new "110cc" YD100 engines, which use a 12mm needle bearing. In fact, it uses the same needle bearing as the MS460 chainsaw the jug and piston are based off of.

The only real reliability issue they have now is the pistons are breaking apart, and part of that is due to the casing quality, the other part is due to the ring gaps being a bit on the tight side as far as I can tell. One ring was ok at .012" but the other was on the tight side at .006mm. Ideally for the bore size I wouldn't want a gap smaller than .011" when considering they run fairly hot.

I actually purchased a high quality MS460 piston with caber rings for it and gapped them myself. I take no chances. I am also splitting the case and replacing all of the bearings. The crank bearings were damaged during assembly. The crank itself also needs to be trued badly as I can see the runout visibly and it causes binding with the bevel gear. Since I am going to have it apart I am going to balance the crankshaft and try to get my balance factor to 65-70%.

As far as the rear sprocket mount. My idea was actually as you described with the rear hub. Of all the options, that seems the best one in my opinion. I can then run a set of spacers and a 200mm rear disc for clearance.

[Megadan]

Ready for comical levels of bad, even by Chinabike standards this thing is so bad it makes our bikes look like a Rolls Royce.

So, let's start with the 3 dimensionally warped exhaust flange. They got this sucker so hot, even if I wanted to try and straighten it, I don't think it would hold a seal without grinding half of the flange away. Then it would be super thin. Thankfully, they did open a warranty claim for it so I should get a new one.





THEN! To skip forward, I noticed the engine would get tight and loose as I turned it over. The crank is so out of true the bevel gear (small drive grear on the crank) is visibly moving in an eccentric manner. I had planned to pull the crank and true it anyway because I always planned to balance it. Not only that, but everything has a gritty feel to it like it was rolled in sand. Even the crank and lower rod bearing sound SUPER gritty.

Imagine my surprise when I split the case and THIS fell out. (picture is linked, larger image for better detail if clicked ) This isn't even all of it lol. Everything is coated in aluminum flakes too. I have some work ahead of me



So, yeah.... New breaings going in for sure.

[Megadan]

So, second part of my now build/rebuild is not using the stock piston. In the week I have been on just a Facebook group for this engine, 3 piston failures. All of the breaking apart at the ring lands and crown. A couple on the skirt.

I am not yet decided on what route I want to take with the piston yet. One thing I do know, I am NOT using the stock piston. The casting quality and ring quality aside, the piston wall clearance is grand canyon levels of huge.

My first option is an MS460 piston, which is .12mm taller in crown height over the stock piston, so I still have a ton of room with the squish gap before it becomes an issue. It also uses the same exact type of rings at 1.2mm, and the one I ordered is a pop up piston and it came with Caber brand rings. One slight upgrade, besides a small bump in compression, would be the fact that the piston ports for the transfers are a good amount larger than the Phantom ports.

This is the stock vs. MS046 piston transfer ports. If I had to guess, they are about 30-35% larger.



The second is an MS380 piston. This piston could work, and in terms of performance has the greatest potential. It's 1.2 mm taller in crown than the stock piston. As it stands, this means my squish gap is negative. On the plus side, this does mean that I could mill the top of the piston down and precisely set my squish gap to whatever I want. If there was any real drawback to it over the 046 piston, it would be the thicker 1.5mm rings. It's not a big difference, but extra drag does mean lost power.

On the plus side, the piston transfer ports are flipping enormous in comparison to the other two pistons. I would hazard a geuess of close to 60-70% larger when compared to the original Phantom piston. This means at higher RPM there is greater potential airflow, which makes up for the thicker rings a bit.



The other issue is that it uses a 13mm width needle bearing over the 15mm of the 460 and stock piston. On the plus side there are needle bearings that work, and the rod end at the wrist pin is a hair over 11mm wide, so there is plenty of room to work with.



I am still up in the air about windowing whatever piston I choose or not. A part of me thinks this engine could be a little softer in the low end power and make up for it with higher RPM power. A non-windowed 038 piston with some careful port work could change this motor into something a bit more reliable without sacrificing the upper RPM power. We shall see.

[Megadan]

To wrap up the piston side of things, after waiting a rather long time for the bearing to get here I can now confirm all I need to do is mill the top of the 038 piston to set the squish gap to exactly what I need and window the piston. The 038 bearing is exactly the perfect size for the rod end. It does loose a little bit of bearing surface area as the rollers are a tiny bit smaller than the wider 046 bearing, but I don't thing this will be an issue.

[Megadan]

I am about to wrap up the bottom end today or tomorrow. First I took my housings, removed the bearings, and cleaned them in the parts washer at work. I then replaced both clutch shaft bearings and both crank bearings with FAG high speed rated (14k rpm) 6202 C3 spec bearings.

Since I had the crankshaft out I decided to do the balance drilling. I set my balance factor on the factory piston and achieved a 68% balance factor.





The last step in this process is that I need to true the crankshaft. I have the dial gauge and stand needed to do the job, but I lack the stand to do it. There are stands out there one could buy, but they are quite expensive and I would have to wait a coulpe of weeks for it to arrive. Instead, I decided to make my own using some scrap bits from work.

It isn't pretty, but it's level and will do the job just fine. Cost. Free.