Knurling pistons

[Schurkey]

Once upon a time, thousands and thousands of years ago, I worked for a school-bus company. They had a '70's Ford small-block in a van which was treated to a .020 overbore, .020 rings, and the original "standard" pistons which were knurled-up to + .020.

Damned think knocked like a diesel. That rebuild was a year old when I got there, and was still running when I left.

Yes, knurling pistons can work. For awhile.

Yes, knurl them big, then file/sand down to size. I'm kind of thinking this was NOT done with the above 302. I think they knurled to .020, and the high-points of the knurl soon wore-out, causing the knock.

Yes, this was high-tech in the '20s and '30's, and was losing favor by the '60s.

[Bob Hollinshead]

I've also heard of people spreading the skirts

[kirkwoodken]

I've done knurling in a lathe with standard lathe knurling tools, but only knurled the non thrust side, figuring it would keep the rings aligned where they belonged. Worked for me. Light knurls, minimal filing. I also made some little jacks to put between the skirts to add some stiffness to the side I knurled. Have also known people who beat the pistons in with a hammer and didn't have any problems. They said when you beat them in, they size themselves. I never tried that.

[Leftcoaster]

Way back in the '60's a friend's late 1950's 948cc Morris Minor had piston slap and a burned valve at 38,000miles

Being hairy a##ed boys without micrometers and bore guages, we pulled the head and pistons and took them to our small town engine rebuilder, who "ground the valves", with a shrug knurled the pistons, lent us a cylinder bore ridge remover and three legged hone, supplied gaskets, a ring compressor, "chord rings" and several warnings, then guided us out the back door

Those damned pistons were so tight we had to bash them into the bores with the wooden handle of a sledge hammer, and this after gapping the rings

The pistons didn't seize, didn't knock, and oil consumption was zero - - my friend eventually sold the car after thrashing it for a good 30,000 miles

Mind you, at 2.480" x 3.000" those things had the bore and stroke of a transport truck air compressor and topped out at ~5,000rpm - - extrapolate at your peril

Many years later I saw a device which had a finger shaped rocker pivoting on a shaft 2/3rd from the rocker tip, said " finger" then vibrating rapidly and "peening" the inside of a piston skirt so the o.d. was increased - -

[pdq67]

IMHO you will be fine!

My old junk301 had probably .0075" on the no knurl pistons, sure it knocked and such, but it ran like "Jack the Bear"..

W/JCW Badger/Triplex/Simplex cast 1/8" over, 1/8" tall, 1/2 round 290hp/283 pistons in a worn out stock bore small journal 327 block.

My Machinist set it up by having me put the pistons in backwards so that the pin offset helped the thrust, but it slapped until it warmed up. And he told me so, it's an old roundy-round motor trick....

pdq67

[redsmokin57]

For those of us to not have seen a Knurled piston, does anyone have any photos?
Cheers Steve

[lorax]

For those of us to not have seen a Knurled piston, does anyone have any photos?
Cheers Steve

[rfoll]

I assembled a 350 a few years ago using a set of standard 2256 pistons in a clean 4" bore block. After cleanup, a couple of clearances came out to .003". These pistons don't grow like the old ones did, but I never heard a sound out of them in a car with a quiet exhaust. I just can't see this motor being significantly noisier with an additional .0005" clearance. Run it on the test stand if you are worried.

[lorax]

I assembled a 350 a few years ago using a set of standard 2256 pistons in a clean 4" bore block. After cleanup, a couple of clearances came out to .003". These pistons don't grow like the old ones did, but I never heard a sound out of them in a car with a quiet exhaust. I just can't see this motor being significantly noisier with an additional .0005" clearance. Run it on the test stand if you are worried.

I think some of you are missing the point here. It appears the bores are .003 larger than stock oem clearnances, not .003. Nobody would be looking to knurl a set of OEM forged pistons with .003 bore clearance.

[BigBlocksOnTop2]

I have knurled many yrs. ago. I left the knurl loose in the quick change tool post (may help to follow the cam shape of the piston). Afterwards I used a fine file to get it to size. Sure it was a bandaid but it worked very well. I would do it again and if that happens I would take advantage of the Napier second ring. It will work, believe me.

[Schurkey]

For those of us to not have seen a Knurled piston, does anyone have any photos?
Cheers Steve

I'm thinking that Perfect Circle sold a knurling tool that embossed PCPCPCPCPCPCPC onto the piston.

[lorax]

Funny, Darin Morgan started a thread on this subject back in 2008.

viewtopic.php?p=132972

[CREngines]

I have a knurler i picked up for a rainy day. Never used it though but i know the process works to a degree. The trick is to knurl them up big and put them in tight so they clearance themselves. The coating may be a little more kosher these days. If you decide to pursue it i could probably loan it to you.

Maybe I can just run out to your place one day and we can knock them out?

That shouldnt be a problem. Im sure we can figure it out and do a nice job. I had another shop do an antique continental piston for me one time when new ones were out of the question and it worked perfectly.

I just dug it out and looked at it, you are going to have to separate the pistons from the rods, which as im sure you know is no big deal.

The knurler is pretty simple. Its a Lisle the same as in this thread that was referenced earlier, only they seemed to think it was for doing rings.

viewtopic.php?p=132972

Its adjustable for the depth of knurl. the piston sits skirt down on that little table and you move the crank back and forth and it progressively works the knurl wheel deeper into the skirt.

[DCal]

The PC knurler is the one I used and the rods stayed on. Hand filed them for approx .001 clr and that motor was rode hard for five years before it started using excessive oil. These were cast pistons.

[CREngines]

was thinking about this a little more. if those forgings have any internal ribs on them then my knurler may not work because that back up roller has to ride on something relatively smooth. Something to check.

Your a good distance from me, if you can use it may be easier for if i just ups it to ya and you can send it back when done.