Engine Trouble help lol

[Wyvern]

Am I supposed to sand them down?

I just wet sanded mine (lapping) a little bit to remove imperfections.

Theoretically you'll gain a tiny bit more compression and squish if you sand it down flat, bit probably not enough to notice.

Personally I woud lap it a bit and call it a day.

 

[Chainlube]

I just wet sanded mine (lapping) a little bit to remove imperfections.

Theoretically you'll gain a tiny bit more compression and squish if you sand it down flat, bit probably not enough to notice.

Personally I woud lap it a bit and call it a day.

The squish has to be measured, .7 to .9, if it's made too tight you run the risk of the piston contacting the head when the engine warms up.

Take it off, sand it, put it on and measure, take it off, sand it, repeat as necessary kind of thing. This is where modeling clay comes in handy.

 

[Chainlube]

Am I supposed to sand them down?

You don't "have to", it's beneficial if you do. The top of the cylinder and the bottom of the head, so they are both smooth and flat. That way you get two flat mating surfaces.

This one I'm working on, the whole head was like the outer area at one time.

You'll need a piece of glass and a couple sheets of sandpaper, 120 and 220 grits (economy sanding). You can go finer, but 220 will get you a good seal.

 

[Chainlube]

The squish has to be measured, .7 to .9, if it's made too tight you run the risk of the piston contacting the head when the engine warms up.

Take it off, sand it, put it on and measure, take it off, sand it, repeat as necessary kind of thing. This is where modeling clay comes in handy.

That measurement is in mm.

 

[robe]

Sanding a bit off does make quite a difference. Subjective observation here but I'd guess 10 or 15% more power and easier starting.