340 pistons

[wrenchturner]

Do the skirts on 340 pistons need to knurled??The new set are not but the ones that came out are.I'm not sure of the brand of new pistons,as this engine and the new components were not purchased by me.
I do know that both old and new are marked .040 on the top.so I have to assume this engine has been rebuilt before.?
Thanx in advance.

[rumblefish360]

You assume right on the rebuild. As far as the pistons go, I never heard of knurled piston skirts.

[Darn Dart]

I've seen knurled piston skirts in a couple of engine I tore down. All that is done by the machine shop is the piston skirts have a grid stamped into the skirts to make them fit tighter in the bore for a el chepo rebuild, so you wouldn't have to bore it. I wouldn't recommond it if you have the proper piston fitment.

[DAVE JONES]

These guys are right......Throw them away. This knurling trick is used for repair or rework in the machine industry. If done properly and in the right application, it works fine. I dont know if they were done properly but this is THE wrong application. What they do is to knurl (displace) material usually in some sort of a diamond pattern and it is very rough. This makes the diameter larger on a piston. Then they have to go back and turn the knurled area back to the dia. that they want. Only problem is, the knurled area only has 50% of the material left and on a rotating assy with friction...... IT WILL WEAR INCREDIBLY FAST..... dj