Piston/Cylinder Problem

GoldenMotor.com

kdaddy1980

New Member
May 22, 2013
117
2
0
Ohio
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
 

2door

Moderator
Staff member
Sep 15, 2008
16,302
175
63
Littleton, Colorado
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
 

fatdaddy

New Member
May 4, 2011
1,516
4
0
San Jose, Ca.
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.
 

mew905

New Member
Sep 24, 2012
647
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Moose Jaw
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.
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 :confused: 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.
 

kdaddy1980

New Member
May 22, 2013
117
2
0
Ohio
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
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..
 

Jumpa

New Member
Aug 12, 2011
607
2
0
Cape Cod
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 :confused: 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.
Mew... thank you for this valuable bit of information