Piston/Cylinder Problem

kdaddy1980

kdaddy1980

New Member
I tore down an old engine to replace the wrist pin bearing and crank assembly .when i tried to start it, it locked up, i pulled the jug off and the crank moved fine but the piston only goes about halfway up into the cylinder it has some marks on the skirt where it looks like the skirt has curled out on the edge of it. i thought i might have the piston in backwards but i tired it the other way and still the same thing. can pistons skirts warp after you take them out. any help with this problem will be appreciated
 
Sounds like a parts mis-match. The piston is hitting the crank. That's what damaged the skirt. You said you replaced the crankshaft. Did you compare the stroke with the one you replaced? Same piston and connecting rod?
Why did replace the crankshaft? And no, pistons don't warp from being removed from the cylinder, unless it was dropped or otherwise damaged while it was out.

Tom
 
Order a piston and rings from the same vender you got the crank from. You will have a better chance of the parts matching up. Sounds like ya need a new piston anyway. Worse case you might have to also buy a cylinder to match.
fatdaddy.
 
fatdaddy said:
Order a piston and rings from the same vender you got the crank from. You will have a better chance of the parts matching up. Sounds like ya need a new piston anyway. Worse case you might have to also buy a cylinder to match.
fatdaddy.
Click to expand...

Agreed, I bought a new piston with a lower wrist pin, so the new one ended up hitting the head unless I used 3 base gaskets and 2 head gaskets. Compression was insane, but power left........ a lot... like.... everything to be desired.

there are 2 known cranks in existence: 85mm length (eye to eye) and 80mm length (these are referred to as 110mm, but that is their total length, eye to eye is 80). The 80mm are the newer ones (?) from the "Type D" motors that Dax, speeddemon and others sell. the 85mm are older, and usually found in Skyhawk motors.
a shorter crank arm would have solved my problem, sounds like you got a piston for my crank.
 
2door said:
Sounds like a parts mis-match. The piston is hitting the crank. That's what damaged the skirt. You said you replaced the crankshaft. Did you compare the stroke with the one you replaced? Same piston and connecting rod?
Why did replace the crankshaft? And no, pistons don't warp from being removed from the cylinder, unless it was dropped or otherwise damaged while it was out.

Tom
Click to expand...
wow, i didnt even think about that but youre right .because i got the engine from zone 8, and then got the crank from gasbike.net and it would only take one revolution or less for the skirts to be bent up an cause it to sieze in the cylinder. i compared the stroke with the old one and its different. the piston bottoms out just slightly enough to bend up the edges of the piston skirts out.
i replaced the whole crankshaft because my connecting rod was just flopping around in there loose as a goose and i wanted to replaced the crank bearing and couldnt press out the crank pin myself so i bought it all as one piece, and it was cheaper.. but that didnt help..
 
mew905 I don't know if I am understanding you right but is the 85 a little longer stroke or the other way around?
 
mew905 said:
There are 2 known cranks in existence: 85mm length (eye to eye) and 80mm length (these are referred to as 110mm, but that is their total length, eye to eye is 80). The 80mm are the newer ones (?) from the "Type D" motors that Dax, speeddemon and others sell. the 85mm are older, and usually found in Skyhawk motors.
a shorter crank arm would have solved my problem, sounds like you got a piston for my crank.
Click to expand...

Mew... thank you for this valuable bit of information
 
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