About to deck my cylinder a millimeter for more compression and noticed this...

[DollarStoreMotorcyclist]

So some time ago, I made my first post here and got help with fixing the main jetting on my carb and now with my 32t sprocket I'm cruising shy of 30mph with this 50cc kit.

I'm still power hungry so I checked my squish gap with solder wire and I had to fold it 3 times before it squished the wire at all, which I measured to be about 4.5mm.

Now I got the cylinder block and the cylinder head off and looking at it I can't tell if there's any squish band at all but there's still enough clearance to still sand the cylinder down a millimeter for more compression anyways.

I start looking at the cylinder and piston for any wear and I see this wide but shallow streak on the piston and cylinder on the exhaust side. Not sure if it's a cause for concern but I don't think it looks good. Obviously, there's also a lot of carbon buildup on the piston and cylinder head which is probably from my engine always running too rich until recently and the fact I accidentally ran 8:1 fuel/oil mix for the first 40 miles I have ridden this engine.

So what I'm asking is: 1) Is there a squish band at all? 2) Should I still go ahead with sanding a millimeter off the cylinder? 3) Is that streak on the exhaust side of things a cause for concern? 4) What should I do about cleaning that carbon buildup?

Any comments about what you guys think the condition of this engine so far is also appreciated. This engine currently has 500 miles on it. The shiny particles in the cylinder is from paper towel cleaning not metal.

 

[Nickt919]

If I’m seeing correct, the engine had a head and base gasket leak on the exhaust side.
You can see oil buildup and oil tracking on the engine outside between the head and cylinder and cylinder and case.
Hard to tell but it appears the case halves are not aligned on the front.
I’d take the 2 remaining studs out, stuff a rag in to cover the crank area, and use a long piece of block with #400 grit to even the surface where the cylinder sits.

Then when you go back together, clean all surfaces well, new gaskets, and torque it down.

The carbon isn’t too bad. The type oil used can do this as well as the leaks. I use mineral spirits and/or acetone to clean. The piston top can be wire brushed a bit to loosen the the carbon and scuff pad to get inside the head dome. Careful not to take any aluminum off.

 

[DollarStoreMotorcyclist]

That head gasket leak you see was from when I broke one of the head studs and still ran the engine before fixing it when I originally built this lol. Engine was super rich as I hadn't jetted it at all yet (wouldn't get hotter than 215F) so as far as I know it didn't do much damage if any.

I didn't notice the case halves not being aligned until now but that might actually correct a port match issue I have with transfer ports.

I'm not sure if the oil all over the exhaust side of the cylinder cooling fins is from a leak in the exhaust pipe fitting or from the base gasket but it might be a combination of both.

This is what the exhaust side of the cylinder looks like after some cleaning with acetone and a paper towel

 

[GW's Motorized]

The bore doesn't look too bad. Optimal squish is between 1mm and .8mm. Mine is set at .86mm on my Phantom 85.

 

[Wyvern]

2strokes get greasy no matter what, even totally sealed you will get a film with time.

Exhaust gaskets are notorious for leaks, so you probably had a small one.

Personally I wet sand/lap sealing surfaces, but it's usually unnecessary.

Also, unless you are very lightweight and short and have a very torquy engine, 32t seems too "tall" of gearing and you will likely gain top end and torque going to a 36 or 38.

 

[DieselTech]

To me that cylinder head dont look to have a squish band area in the cylinder head, to even set the squish gap.

 

[DollarStoreMotorcyclist]

The bore doesn't look too bad. Optimal squish is between 1mm and .8mm. Mine is set at .86mm on my Phantom 85. -GW's Motorized

Thanks for quelling my fears of the worst. Yea I figured ideal squish gap is about 1mm but shaving off 3.5mm from the cylinder seems pretty excessive to me so I'm just gonna sand off 1mm and go from there.

2strokes get greasy no matter what, even totally sealed you will get a film with time.

Exhaust gaskets are notorious for leaks, so you probably had a small one.

Personally I wet sand/lap sealing surfaces, but it's usually unnecessary.

Also, unless you are very lightweight and short and have a very torquy engine, 32t seems too "tall" of gearing and you will likely gain top end and torque going to a 36 or 38. - Wyvern

Yea, I'm thinking some rtv will do the trick if I ever bother to buy some for when I have to work on my car.
It is likely true that 32t is too long of a gear ratio for that engine especially given I live in an area where 4-8% grade hills are common. I weigh 140 lbs though and shy of average height but wearing a big coat and dirt bike helmet is not doing me any favors in the aerodynamics. I do have a 36t sprocket lying around to compare to the 32t when I get the courage to spend an hour to true another sprocket on my wheel.

To me that cylinder head dont look to have a squish band area in the cylinder head, to even set the squish gap. - DieselTech

I'm aware that the squish band when present is typically around 40-55% of the total combustion area on the cylinder head but in this case, it looks like a thin flat ring that only covers 10%. Maybe that's cause this cylinder head wasn't made for 50cc?

 

[Chainlube]

I totally missed the 50cc part and was a little puzzled by the squish area on that head. But now that I see that, it makes sense. 48cc engines never really came with much of a squish band. The one I put on the Auto-Mini was the same as you have, I knew I saw that someplace else.

Does the piston come up flush with the top of the deck?

 

[ImpulseRocket]

That head doesn't really have a squish band. That tiny little bit of it that could be considered squish isn't going to really make a difference at the end of the day. It's a low compression chamber design to begin with.

 

[DollarStoreMotorcyclist]

Does the piston come up flush with the top of the deck? - Chainlube

Probably not. At TDC, the edges of the piston is about 2-3mm below the top of the cylinder without the head gasket on but it's a dome shape so the center of the piston is above the cylinder

That head doesn't really have a squish band. That tiny little bit of it that could be considered squish isn't going to really make a difference at the end of the day. It's a low compression chamber design to begin with. - ImpulseRocket

I figured the effectiveness of this squish band is pretty minimal if that's what it's supposed to be. Does anyone know of a higher compression head out there for these 50cc engines? The cylinder bore diameter is 40mm.