My Phantom Experience.

ImpulseRocket as a new person in the hobby that was a enjoyable and impressive story also I think inspiring.
Thanks. I try to include as much information as I can when I do posts like this because I often find that most people don't, and it can be frustrating when you are looking for information.

Ex. People do port work, show pictures of the work, and share the results. No information on the port changes, or often very little or confusingly laid out.
Howdy folks. I joined several years ago when I first got into motorized bikes. Built myself a basic "80cc" Walmart Schwinn cruiser that I rode for a while until I had other life priorities come up and get in the way. Upgraded to motorcycles, but I still kind of missed the very cheap fun of a motorized bike, so I decided to build another one.

*Warning: Long post! Enter at your own risk! lol

So, me being who I am I decided the engine kit with the worst reputation for reliability sounded like a good idea to me. What can I say, I am weird. I pulled the trigger when I learned that they now come with a needle bearing wrist pin instead of the bushing. I also went into it knowing that the issues were likely cased by more than just that, so I did some measuring and investigating. The following pictures I am going to post are going to be kept small, so if you want larger just click on them for greater detail.

To start with, when I received my Phantom engine I noticed 2 things immediately. First, everything, and I mean everything, was covered in metal particles. Second, the crank would not turn over by hand for more than 3/4 of a revolution without binding up.

The first issue, well... let's just say their "quality control" measures are total junk. I decided to tear the motor down completely to clean everything up. This is some of the metal shavings that fell out of the crankcase side. (quarter for scale). I mean some too, the rest of it went everywhere else.

The second issue, which I thought was the bearings, ended up being my crankshaft was so out of true that the bevel gear was visibly moving in an eccentric manner and binding with the clutch gear. I first decided to balance the crank before doing any other work. Long story short I ended up with a 54% balance factor with my chosen piston.

Next I built myself a truing stand to try and straighten the crank out. My truing stand was a bit crude, but it ended up working rather well once I used 4 rare earth magnets to hold it to my steel work table. The crank had 7 thousandths of vertical runout from being pinched, and 5 thousandths of lateral (perpendicular?) runout. I got both down to about 1 1/2 thousandths and decided to leave well enough alone. The bevel gear now turns like it should and no longer binds with the clutch gear.
My caveman level truing stand.

Since I had already come this far I just decided to replace all of the case bearings anyway. I am sure I could have cleaned them out and saved them, but bearings are cheap enough and I felt like it was a good idea to start fresh. I also decided to replace all of the case hardware with much higher quality stuff from the local hardware store. In for a penny, in for a pound.

So now that the bottom end was mostly sorted and re-assembled, I moved on to the piston. Even with the new wrist pin bearing there are several people that have had pistons break from what appears to be ring snags or just plain poor casting quality and tolerances on the pistons themselves. I personally test fit the stock piston and rings and turned the motor over by hand and could feel one of my rings snagging on what I assume is the intake port on the right side. Having talked with a couple other people on a facebook group for this engine I decided to check out some of the aftermarket piston options. I ordered a Meteor brand MS460, a Hyway Pop-up MS460, and a Hyway MS380 piston.

To start with, the stock piston cylinder wall gap is enormous, which I believe partially contributes to the skirt failures that I have seen a couple people have on the intake side. I measured my OEM piston at 51.88mm and cylinder at 52.02mm at the loosest point (52.00 tightest). That is a cylinder wall clearance of .12-.14mm, or over 5 thousandths. Some people may find that ok, but I don't. I can physically rock the piston ever so slighty in the bore.

The Hyway piston measured in at 51.93mm, and the Meteor at 51.95mm. Giving clearances of 35 thousands and 27 thousandths respectively. Neither of these pistons can be rocked in the bore. Both of these pistons also have taller crown heights than the stock piston. The Hyway being .12mm taller, and the Meteor being .16mm taller.

Other benefits of the aftermarket pistons has to do with the transfer port windows on the side of the pistons, both the meteor and hyway pistons have larger windows than the stock phantom, meaning a potential for better flow at higher rpm.

The MS380 Piston functionally will work. Piston diameter was much like that of the other two aftermarket units, the transfer windows are the largest of the group, and crown height is even taller still. Over 1mm taller than the standard piston in fact. The one catch is that it also uses a smaller width wrist pin bearing. Luckily, the MS380 saw bearing works perfectly, so it is still an option. The downside to this piston is that the crown is so tall that it starts blocking the transfer ports and exhaust port. The upside is, that with 2 base gaskets your squish is really nice and tight (.52mm measured on mine).

Transfer windows. First picture Stock left, Hyway MS460 right. Second Picture. MS380 Left, Stock right.

One other thing that all of the aftermarket Stihl pistons share when compared to the OEM Phantom piston that I also find incredibly important? The ring pins are ever so slightly further apart. They don't catch the ports. Minor detail, but a big one.

At the end of the day I chose the MS460 Meteor piston for the following reasons. With 1 base gasket in place the Meteor has a squish gap of .96mm. While not super tight, it is within the realm of "good" without making the compression too insanely high. Compare that to the stock squish gap of 1.72mm. The quality of the material, casting, and machining alone are superior. The piston to wall clearance is the tightest of the bunch while still being acceptable. The only catch was I had to window it myself. Not my greatest work ever, but I figure if it does fail I can try again. The bridge between the two windows ended up a bit narrow, but we shall see how it holds up. I installed it with the set of caber rings that it came with.

My window job.

The last bit of detail on the Phantom engine and their potential reliability issues has to do with the cylinder itself. More specifically the finishing of the port edges. They are rough, and sharp, and not chamfered at all. If you decide to get one of these engines it is well worth taking the time to at least clean those port edges up with a round diamond burr or grinding stone.

The actual ports themselves in terms of casting flaws are actually pretty decent. There wasn't a lot of flash or metal bits hanging around to get sucked in, though I still cleaned it thoroughly. The only work I did to mine was to port match the intake flange to the reed and I did raise my exhaust port .5mm to help compensate for the loss of 1 base gasket. Probably not necessary, but what the heck.

At this point I have only test ran it on the frame while I am still putting my bike together. It runs very strong. Hopefully I fought off all of the potential failure points, but only time will tell. The carburetor that it comes with is jetted rather lean for this motor now, likely a change from the previous generations which seemed to be rich. I have mine jetted up with an 80 main jet (stock is a 72 or 75) using Keihin 99101-124 jets. May be a bit rich, but I didn't want to risk a lean issue on a new motor.

A couple of shots of my bike in progress.

My personal opinion on these engines is that for the quality you get, they are horribly overpriced. The quality control is terrible on several items, especially the exhaust, which I am now on number 3. The welds are terrible, and the flanges are always warped badly, or have pin holes. I could go on, but even with the supposed "upgraded" parts, I don't find myself all that impressed for the money I spent.

That being said, if you are willing to put in the time to go through and correct the issues, I do believe this motor has the potential to be pretty darn good. I have even seen one person use an MS460 piston with no window and a standard intake and he said the power is still impressive, so that is also an option.

That's my story so far, sorry for such a long winded post! Hopefully some of this information can help others in the future.
I have enjoyed every letter of your article on your experience with the phantom 85 engine kit. In fact, I'm going to make a Chuck's bill hilly crank stand motorized based on yours. Love the simplicity. It's like my truing stand. Mounted on a 2×12 by 16" long. And the clarity and confirmation that it is a mock of the Stihl Ms 460 cylinder with a 380 piston.

I'm thinking the best way to maximize this hobby, for me, is to buy a lot of 10 kits directly from the supplier.
I'll go thru each engine, cylinder and time the piston and sell them for the same 350 each kit. $200 for mild porting, maybe 3 hours each but I'll end up with 3 kits for free. It actually make a profit?? Lol