Knurled Pistons??

['66 Fury I]

If I remember well, back in the '60's, I read about a process where piston skirts were knurled to reduce piston to cylinder wall clearance and retain oil to assist in engine break-in. Does anyone remember this? Was it successful? Any input would be appreciated. I'm just curious. Lindsay

 

[Big_John]

As I understand it, it was really a temporary fix. It raises the material on the skirts to take up the clearance, but the raised areas won't wear as well as the skirt.

I had some pistons done way back in the early 70's by a reputable shop, where a good friend worked.... and I took one look and decided against using them.

Actually, I would be really surprised if any shops were still doing it.

 

[Trace 300 Hurst]

I did that for my very first engine rebuild on a 273 back in 1974, because this teenager hadn't the money for pistons. Worked "okay" for a teenager's car, and would probably work "okay" for a low load and low annual mileage weekend car. As Big John said, the knurling will wear away faster than a new skirt surface, and yeah, I'd be surprised if you can find a shop to do it. But pistons aren't expensive anymore, and I certainly wouldn't do it now. Hell, new pistons might be cheaper than shop hours, AND they're delivered to your door.

 

['66 Fury I]

Thanks! Wasn't planning on doing this, just curious. Lindsay

 

[CBODY67]

If I remember well, back in the '60's, I read about a process where piston skirts were knurled to reduce piston to cylinder wall clearance and retain oil to assist in engine break-in. Does anyone remember this? Was it successful? Any input would be appreciated. I'm just curious. Lindsay

The "knurling" of the piston skirt was more about getting a few more miles out of a set of worn/used pistons than not. Not to forget the financial savings for those who were of more modest financial means, at the time. Not unlike knurling valve guides rather than replacing, for example.

Knurling the piston skirts also meant the cylinders did not have to be bored, in a time when boring a cyl was a major operation to get done.

It IS possible that some racers did have their new piston skirts knurled for added oil in that area of the motor. Usually, though there were some very shallow circumferential grooves/lines in the piston skirt, for possible oil retention and wear gauges, as I recall.

Enjoy!
CBODY67

 

[70bigblockdodge]

Would say it is more about noise. A piston can have a pretty large clearance and still be stable enough for the rings to seal. Especially the super tall Chrysler pistons.

 

[1970FuryConv]

Factory Pistons are made of cast aluminum. Since they take full force of combustion, I would not think knurling would last against cast iron cylinder walls.

 

[65sporty]

Like everyone else said no one does it anymore, but if I can find it there is one floating around at the shop. Old tool from days gone by for engine overhauls, not unlike knurling valve guides like CBODY67 mentioned

 

[Trace 300 Hurst]

Factory Pistons are made of cast aluminum. Since they take full force of combustion, I would not think knurling would last against cast iron cylinder walls.

It lasted "long enuff".

 

[1970FuryConv]

It lasted "long enuff".

Then I guess that's enuff.