Cylinder not inline with crankcase

[MonkeyBiker]

I bought a triple 40 style PK80 kit from Gomax Industries.

When I installed it I thought that it looked a little off keel looking at it from the top but the crankcase was inline with the down tube on my frame and the chain wasn't riding up on the teeth of the drive sprocket so i figured it was cool.

After a couple of months of riding I figured I'd pull the cylinder off and check out the piston and maybe do a little port cleanup if needed.

Upon doing so I noticed that the cylinder stud holes are rotated a few degrees off of what would be square to the crankshaft.

I'm guessing they're still centered on the cylinder/piston bore because there wasn't any indication of any wear in the cylinder due to piston offset or binding, and it runs pretty well.

Maybe not as fast as I have heard these are capable of going. So it looks like my transfer ports are maybe overlapping a bit? Intake and exhaust ports don't seem to be affected. This is my 3rd new motor and I've had a handful of used ones, but have never seen this issue before.

Anybody have experience with this? Is it just typical of these motors or is it out of the norm enough to be considered a factory defect? Could it catastrophically fail?

 

[Wrench]

Chinese Specification Tolerances "Close Enough is Good Enough"

 

[DAMIEN1307]

Chinese Specification Tolerances "Close Enough is Good Enough"

That's what their 12 year old "senior" techs and so-called QC people will tell ya anyways...lol.

 

[ImpulseRocket]

Not unusual to see. My Phantom 85 was this way. Basically the 2 random case halves they slapped together were drilled differently. Sometimes you can correct this a bit by loosening all of the case bolts and twist the halves into a slightly better alignment, but it's rare to get them perfectly even. It alsonoften requires decking the case halves to get the sealing surface even. For the most part it shouldn't cause too many issues as long as the jug seals to the case. It does make installing the cylinder and head a pain though.

In your engines case (pun intended) I would say there probably isn't much chance of correction as it appears to be way off. I would say to either just let it be, or order a new set of case halves and swap them out.

 

[MonkeyBiker]

Thanks guys for your input. Like I said, it's been running fine and I didn't see any real alarming signs when I pulled the jug off. I've got it back together with fel-pro lower and copper head gasket. While I had I apart I took a little off the head with sandpaper on granite to hopefully have brought the squish clearance down and trimmed a wee bit off the intake side of the piston skirt. All port openings on the inside of the cylinder wall were already chamfered. I saw a thread about sharpening the bottom edge of the transfer port divider so I did that. Also found a shimming washer for the spark plug so the spark is facing the center of the combustion chamber now. I

suppose some of these things are trivial, but I'm hoping all together they'll add up to enough to push me over the 30 mph threshold that, even with a 36 tooth rear sprocket, I've been stuck at. Oh yeah, I also cut the flange and header pipe off a stock muffler and bronze brazed it to a banana pipe that I cut the flange off of. The banana pipe worked well in the higher rpm's, I'm hoping it gives me a little more in the mid range till I can get a proper moped expansion chamber to adapt to this motor. Thanks again for the input, y'all!

 

[ImpulseRocket]

Thanks guys for your input. Like I said, it's been running fine and I didn't see any real alarming signs when I pulled the jug off. I've got it back together with fel-pro lower and copper head gasket. While I had I apart I took a little off the head with sandpaper on granite to hopefully have brought the squish clearance down and trimmed a wee bit off the intake side of the piston skirt. All port openings on the inside of the cylinder wall were already chamfered. I saw a thread about sharpening the bottom edge of the transfer port divider so I did that. Also found a shimming washer for the spark plug so the spark is facing the center of the combustion chamber now. IView attachment 201980View attachment 201979 suppose some of these things are trivial, but I'm hoping all together they'll add up to enough to push me over the 30 mph threshold that, even with a 36 tooth rear sprocket, I've been stuck at. Oh yeah, I also cut the flange and header pipe off a stock muffler and bronze brazed it to a banana pipe that I cut the flange off of. The banana pipe worked well in the higher rpm's, I'm hoping it gives me a little more in the mid range till I can get a proper moped expansion chamber to adapt to this motor. Thanks again for the input, y'all!

I've never really noticed much change from the Banana.pipe. I tried one a long time ago. I found a modified stock muffler better in terms of power and noise.

 

[GW's Motorized]

I suggest cutting the gasket a bit that is covering part of your transfer. Recently a member here put the gasket on wrong and it greatly affected his performance.

 

[MonkeyBiker]

I've never really noticed much change from the Banana.pipe. I tried one a long time ago. I found a modified stock muffler better in terms of power and noise.

I usually take the cap off the stock muffler and cut the stinger down to about 2 inches. That produces a noticable difference but is there anything else that can be done to the stock muffler?

 

[GW's Motorized]

I usually take the cap off the stock muffler and cut the stinger down to about 2 inches. That produces a noticable difference but is there anything else that can be done to the stock muffler?

It can be gutted and made into a decent glass pack

 

[robe]

You can replace the tube that is welded to the cap with a larger one, open up the baffles and drill larger holes in the pipe with the threaded bit welded to it. You need to cut it to do that but goes back together easy with a strip of sheet metal and pipe clamps.