which way do pistons go??

[mrcrw009]

I have a 1976 35 hp evinrude and i'm doing an overhaul on it. I put new rings and honed the cylinders. I torqued the connecting rods and main bearing bolts on the crankcase halves. When i tried to rotate the crankshaft through, when the pistons got straight up and down it jammed up and would not rotate any further in either way. I was wondering if these are rotational specific connecting rods or something and also wondering with way the pistons go referencing the spark plug. On the back of the pistons it says LOOSE on both of them, what does that mean? Any help would be great thank you.

 

[HighTrim]

Re: which way do pistons go??

Were the port edges filed down after honing?

The pistons need to be orientated so that the long taper is facing the exhaust side of the head.

 

[daselbee]

Re: which way do pistons go??

The word "loose" is stamped on them to indicate which side of the piston has the loose fit of the piston pin. Pressing a piston pin through, you will see that one side of the piston/pin has a loose fit, and the other side has a tight press fit of the pin.

The top of the piston fits into the combustion chamber of the head only one way. If the piston is in backwards, it will hit the cyl head.

 

[mrcrw009]

Re: which way do pistons go??

ok thanks. no i didn't file the edges down after honing guess but i just kinda shined them up i didnt really get agressive with it. i'm going to ge put it together and try it again. thanks guys.

 

[1946Zephyr]

Re: which way do pistons go??

If you had the loose side of the piston down when pressing on the wrist pins, then you could squash the piston out of round.