Why is piston knurling all the rage on YouTube?

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StreetSleeper

StreetSleeper

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Even if it did benefit performance versus a smooth surface riding on oil against a honed surface-how much power could it possibly add?
1/4 of 1 horsepower?

2horsepower on a big, high rpm build?

It doesn’t seem like it would be that much of a gain.

Why is this a hot topic? What’s next? Nitriding and polishing rocker shafts? Axle gears? Soaking our air filter in rocket fuel-where does it end?

I bet Dan the Man started this mess.

It would be interesting if there was an exhaustive list of priority to focus on but that would literally be in the performance books.
 

It's click bait started by Uncle Tony...but seriously...a short answer and to stay on topic apparently it was once used as a cheap overhaul fix to get another year or so out of an engine. It cleaned up piston to bore clearance without an overbore but keep in mind this was prob back in the 30s and 40s when cars smoked and nobody cared etc. so Uncle Tony read it somewhere ran his mouth and his loyal followers lapped it up like dropped ice cream off a sidewalk.
 
Apparently while talking piston UTG brought up in passing that he read Smokey use too knurl pistons and Smokey said he gained hp, now people are debating if it would, Brain said he gained like 8 hp but lasted only one 250 lap race.
 
273 said:
Apparently while talking piston UTG brought up in passing that he read Smokey use too knurl pistons and Smokey said he gained hp, now people are debating if it would, Brain said he gained like 8 hp but lasted only one 250 lap race.
Click to expand...
this has been hotly debated in the 2T world for years...

the "theory" runs that old song of a loose motor is a fast motor, but when piston to wall clearance gets too big they get noisy at best, and toward the other end start wearing the bore from slamming into it or just breaking off piston skirts. so the tinfoil ball cappers think: if i knurl the piston, it'll hold more oil and that'll cushion the piston and provide more lubricity to the interface of the skirt/wall while also sealing the bore.

i'm sure somebody thought of this while taking a break from their perpetual motion machine project.

could it be worth a few ponies? yes, absolutely. under the right circumstances. but with the trade off in longevity.

remember, smokey was the ultimate master of subterfuge. sometimes he'd do **** just to throw people off his trail of what he was *actually* doing. i wouldn't put it past him that he would let that "speed secret" out knowing that the motor would make more power but eat itself up in short order, which would be just about perfect in a 300 lap race. cuz ya can't win a race if you can't finish that race.
 
I'm heading out to the shop to knurl some pistons for the Allis Chalmer.

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1MeanA said:
How long do the rings last with eff'd up bores?
Click to expand...
very good question I think with a race motor it prob didn't matter they were tearing it down anyway after a race or two. That was the thing, Uncle Tony mentioned "Smokey Yunick" I think in his banter about it.
 
fishmens67 said:
That was standard practice on the first valve job on cast iron heads.
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Yup and now If I see it I know they need gone over ... I usually disassemble and feel the play though as soon as I find 1 loose one I call it done "they need sent out" etc. especially now that the X and Js are 55 or 58 years old etc.
 
knurling pistons is similar to taking out half the windshield to reduce frontal surface area of the car, with the rest of the windows still in the car.

It's a hack move to reuse a worn out piece. Powell does a good job of WHY it's a poor choice and the actual contact patch a properly sized bore has with the piston, if any.

More nonsense from Phony.
 
StreetSleeper said:
Even if it did benefit performance versus a smooth surface riding on oil against a honed surface-how much power could it possibly add?
1/4 of 1 horsepower?

2horsepower on a big, high rpm build?

It doesn’t seem like it would be that much of a gain.

Why is this a hot topic? What’s next? Nitriding and polishing rocker shafts? Axle gears? Soaking our air filter in rocket fuel-where does it end?

I bet Dan the Man started this mess.

It would be interesting if there was an exhaustive list of priority to focus on but that would literally be in the performance books.
Click to expand...
You would've lost the bet, as per usual.
 
If I recall Tony yacked about the skirt rubbing the cylinder wall and the guy from Powell was like "eeeeent wrong..." isn't the first time Tony stuck his foot in his mouth... :lol:
 
Knurled pistons can work very well ,, in the right situation .
It is an excellent fix to save money and not have to bore, or buy new pistons .
To be really effective for a long time,,,it should be concentrated on the minor thrust side of a piston .
That way ,it doesn’t see the full load against the cylinder wall and won’t wear off easily .
It basically just acts to take up clearance in the cylinders,,,and keeps the piston from rocking in the bore .
Usually you are only talking about 5-6 thousandths knurl height at the most ,,depending on the condition of the pistons,,and bores .
As long as the bore taper is not excessive,,,it will work for quite a while .
Using oversized, file fit rings goes a long way in helping oil consumption as well .

Of course,,,we are only talking about an everyday street engine,,,mostly a daily that needs to help keep food on the table .
This is not for a performance application .

I’m sure Smokey was pulling someone’s chain .
He was the Master of deception,,,,,fooled NASCAR many times,,,,and only told his secrets later towards his death .
What a Great engine man !

Tommy
 
Desoto291hemi said:
Knurled pistons can work very well ,, in the right situation .
It is an excellent fix to save money and not have to bore, or buy new pistons .
To be really effective for a long time,,,it should be concentrated on the minor thrust side of a piston .
That way ,it doesn’t see the full load against the cylinder wall and won’t wear off easily .
It basically just acts to take up clearance in the cylinders,,,and keeps the piston from rocking in the bore .
Usually you are only talking about 5-6 thousandths knurl height at the most ,,depending on the condition of the pistons,,and bores .
As long as the bore taper is not excessive,,,it will work for quite a while .
Using oversized, file fit rings goes a long way in helping oil consumption as well .

Of course,,,we are only talking about an everyday street engine,,,mostly a daily that needs to help keep food on the table .
This is not for a performance application .

I’m sure Smokey was pulling someone’s chain .
He was the Master of deception,,,,,fooled NASCAR many times,,,,and only told his secrets later towards his death .
What a Great engine man !

Tommy
Click to expand...

back a long time ago , I bought a basket case street hemi, 66 belvedere , the block had been bored .030 over before he bought the pistons , was way too loose , I knurled the hell out of the pistons myself at a friends machine shop , way over did it (read heavy) .
Then did my best to sand the hi spots off from the tips of the knurl , ( to make it last) ,while trying measure them , measuring the knurl was time consuming and a ***** but I got it done .
It worked very good to great , ran good , lasted till I sold the car due to hard times , I beat on it every time I drove , and drove it to work every day till gas got too expensive for it ....
 
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