6 Pack Pistons with textured sides?

[JLM-90]

Hello everyone, Anyone know why these pistons have this texture on the sides and what they were for? They are on new 440 source forged rods and I was told they'd be fine to put in my engine but I've never seen pistons with this. I've always thought they were suppose to be smooth, all 8 have this. Thanks for any insight

 

[toolmanmike]

Those have been knurled by a machine shop. It is to tighten them up in the bores. Like knurling valve guides. A temporary fix.

 

[yella71]

Measure them and your bores then you will know your clearance. if its good use them.

 

[1 Wild R/T]

As Mike said knurling is very much a temporary fix... If you are building a show poodle go ahead & use them... If you plan to put any serious miles on the car I would rather do it right & only have to do it once.... Knurling was a patch type repair from the 40's & 50's when people only expected an engine to last 20-30K miles..

 

[Sahara]

Yeah, I always associated this sort of repair with flat head fords and that kind of stuff.

 

[JLM-90]

Thank you I didn't think I should use them. I'm building a mild street 440 that I'd like to enjoy on the road but it's got the .130 in the hole pistons which made me curious about these. The extra point on compression isn't worth the risk. From these at least. Thank you again for the insight and advice!

 

[66Satellite47]

Those are knurled, which can work for while, not he best plan, but... If you are .130 down the hole, that's a really mild deal. I'd find some pistons to get you up .020 or .030.
Edit: If they are 6Pak pistons they should not be down .130. with a stock 6.76 rod. They seem like late '70's pistons.

 

[JLM-90]

These are 6 pack pistons, they've got the same specs as the l2355's and the valve reliefs. Reading up on knurling I'd assume they're also older pistons that someone put on some new rods too. I was curious/directed to them because the pistons in my 440 are the low com .130 in the hole motorhome ones.

 

[66Satellite47]

OK, That knurled 6pak piston will not be .130 down the hole. A knurled piston will perform fine for a while. How long don't know. That was a common deal well into the '70's. Mopars don't wear the pistons very badly because of their L/R ratio. So a knurled piston could last a long time. Just say'in.

 

[BSB67]

Have the pistons mic-ed. You should be able to get a measurement on both the upset (knurl) and not upset part of the skirt. My guess is they are probably fine if your starting with a different motor. The pistons were knurled because of the cylinder bore. If there is some knurl left, its probably not much. Have the new block final finish bore to 0.0025" to the knurl and when the rest of the knurl wears, you'll probably still be in tolerance. That piston will be fine to 0.005" but will have a little slap.

Or maybe just dress the skirts

 

[Challenger340]

I'm confused here....
are you planning on using the 6-pack pistons on new freshly Bored & Honed Cylinders....
or,
simply removing your .130" in the Hole Pistons and using these "standard" Bore 6-Pack Pistons in your current Bores if that's what they are ?

I guess what I'm asking is
What size are the 6-Pack Pistons Versus your current Bores ?

"Ring Travel' will NOT be the same ?

 

[JLM-90]

A fellow I know offered to sell them to me for my engine. My engine is a std bore with perfect cylinder bores no rig rim no nothing. it was a less then 5g miles motorhome engine. Those are std pistons so they would/should go in without any problems. Just balancing the Crank to them. I was cautious about them due to the texture on them which I now know is from knurling (Thank you again everyone for all the info). I've decided to pass on them and just stick with what it's got and do a freshen up on the engine.

 

[BSB67]

45 year old motor with 5K miles no rust and perfect bores. Wow.

 

[joe smith]

I remember knurling back in the early 70's... I remember having an engine bored and new pistons was more money than we paid for alot of cars back then.. It was a band aid for us young people working for $1.50 an hour.....

 

[1 Wild R/T]

I just bought lightweight forged pistons for a 440... $650... Seems like allot, then I went & filled my gas tank $65.. Pistons seem like a bargain...

 

[Sahara]

Yeah, filled my Jeep last week. The pump stopped at CAN$100.00, so about US$70.00 and it still wasn’t full.

 

[Challenger340]

IMO...
Strange how people can't 'afford' to FIX anything anymore.... Boring/Honing/Rebuilding properly is waaay too expensive for most ?
yet most of the same guys complaining ?
have NO PROBLEM going out on an 7-8 year never-never DEBT payment plan for a Truck that's basically JUNK the day they finish paying for it ?

 

[overbore]

Challenger 340 made a good point about Ring Travel.
At piston TDC and BDC piston rings come to a dead stop and change direction. As they do this they flex up and down producing heat and also transferring more heat to the cylinder wall in that spot because they're stopped. This wears a little 'dip' in the cylinder. In a high mileage engine you can actually see these dips. Dips are there even at 5K. Don't believe me run a ridge hone with 400 grit stones down it 1 or 2 light passes and you will see them. They may only be .001 - .002 inch deep but they be there.Now, if you don't hone that dip out and put in a piston with higher ring position in relationship to piston pin when the rings hit that dip they will bounce and flutter. Which equals more heat and blow by. If you hone the dips out a .002 dip will equal .004 more bore. (.002 to a side = .004) Which messes up the new piston to cylinder wall clearance.JLM-90 could use the low compression pistons he has with new rings and a lite de-glaze on the cylinder walls. Go with smaller chambered heads and a cam with the earliest intake closing time and most duration he can find that will bring the dynamic ( not static ) compression up to 8.0 -8.1 for pump gas. My 2 cents.

 

[moperformance]

I remember knurling back in the early 70's... I remember having an engine bored and new pistons was more money than we paid for alot of cars back then.. It was a band aid for us young people working for $1.50 an hour.....

WOW! My first job paid $1.25 hr. Busboy at a local rest. It took a year to pay the local speed/machine shop off for my first 383. Brought back a flood of memories on that on. THX!