Am I crazy?!

[Ranger4581]

Ok everyone first time posting here. I have an issue....so I decided it would be a good idea to buy a stihl ms170. 40 bucks I said what the hell...yes it had a busted piston no idea why. So I replaced the piston I get it together and it won't start...at all. Pull the carb back off and look into the cylinder I see the dam piston doesn't come past the intake port....so it doesn't let in any fuel or air. Saw spins over fine but the piston doesn't extend past the intake port...am I missing something here or am I just stupid. Leaning towards the latter but what the hell. Both pistons old and new were the same height..pin height and skirt height...it was an identical piston from stihl. Someone have any input trust me it would be very appreciated.

 

[1Alpha1]

First and foremost, hello & welcome to the forum. Hope you like it here.

Are you saying the piston doesn't go up or down at all? Or......just that the piston doesn't rise above the intake port? If both pistons are exactly the same as you say, there shouldn't be a problem. But yet there is.

I'm going to assume that you connected the connecting rod to the piston pin. If you did, then I'm not going to be much of any help to you, as I'm stymied.

 

[rngrchad]

Make sure you put the ring gap towards the intake side. The skirt of the piston may be different on the exhaust and intake. Is it in there backwards? There is an arrow on most pistons. This arrow faces the exhaust port.

 

[Thommo]

The piston should not go down below the intake port. The incoming air and fuel is sucked in below the piston as the piston goes up and then the fuel and air is pushed up through the transfer ports to the top of the piston as the piston goes down. Did you use a good oil resistant sealer when you bolted the bottom cap back onto the cylinder. If there is a vacuum leak the saw wont run.

 

[dougand3]

If the piston skirt doesn't go above & clear the intake port at TDC....
1. Con rod broken - they are cheap stamped steel in these saws.
2. Piston wrist pin and bearing are not inserted properly thru piston & con rod.

 

[s sidewall]

If the piston skirt doesn't go above & clear the intake port at TDC....
1. Con rod broken - they are cheap stamped steel in these saws.
2. Piston wrist pin and bearing are not inserted properly thru piston & con rod.

Same, possible a bent connecting rod.

Steve