More piston pin wear in 4.0 than 4.2 motors

Performance mods and Advanced Stroker discussion.
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GoatBoy4570
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Where's the "any" key?
Posts: 25
Joined: June 25th, 2016, 7:05 pm
Stroker Displacement: 4.2
Vehicle Year: 1983
Vehicle Make: AMC Jeep
Vehicle Model: CJ-7

More piston pin wear in 4.0 than 4.2 motors

Post by GoatBoy4570 »

I just recently stripped down a collection of five 4.0 and 4.2 engines and noticed the piston pins in the 4.0 motors had more wear, at first i assumed that pins in the 4.2 where harder or where getting better lubrication but on further thought i was thinking it maybe due to the 4.0 having a higher silicon content (harder) hypereutectic piston. one of the 4.0's was relatively low miles and still had a bit of pin wear compared to the much higher miles 4.2, maybe the 4.0's were working harder but the bi-metal rod bearing weren't showing that ? not enough ZDDP in the synth oil ?

I was wondering if anybody else had encountered this pin wear on motors they have torn down ?
KarmaKannon1
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Posts: 63
Joined: May 21st, 2020, 10:13 am
Stroker Displacement: 4.7
Vehicle Year: 2000
Vehicle Make: Jeep
Vehicle Model: Cherokee
Location: Utah

Re: More piston pin wear in 4.0 than 4.2 motors

Post by KarmaKannon1 »

I have a set of both used pistons and rods. You have me wondering now. I might have to check that out when I get a second. I didn't really inspect either very well because I wasn't planning on using them.
GoatBoy4570
Where's the "any" key?
Where's the "any" key?
Posts: 25
Joined: June 25th, 2016, 7:05 pm
Stroker Displacement: 4.2
Vehicle Year: 1983
Vehicle Make: AMC Jeep
Vehicle Model: CJ-7

Re: More piston pin wear in 4.0 than 4.2 motors

Post by GoatBoy4570 »

I was thinking if i'm gonna reuse these 4.0 pistons of my build i will have to rotate the pins 180*

Probley gonna run 15w40 in this build so that may help, def gonna shim the spring on the oil pump and run more oil pressure, try and sling a little more up there !
jsawduste
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Posts: 1032
Joined: February 28th, 2008, 3:13 am
Stroker Displacement: 4.9
Location: Michigan

Re: More piston pin wear in 4.0 than 4.2 motors

Post by jsawduste »

From the posts thus far it seems your making observations and forming opinions about things that are not significant in the grand scheme.

These engines have a reputation for running hundreds of thousands of miles. Only if abused or not maintained will you have any problems. Yes the later models do have cylinder head cracking and there is a few breaking piston skirts. These are the exceptions but even then could be considered rare.

The camshaft theory is just that a theory. There are a number of parameters you're not taking into account.

Hi pressure doesn't do anything but wear the cam/dist. drive gear faster.

Done right you'll use floating pins with an aftermarket rod.

15w-40 was never a factory spec oil. Run what the factory recommends. They are smarter than all of us and the design of the engine has been around long enough to prove it. The extra ZDDP is a good thought but after the cam is broken in even that need is diminished.

Key factors are a tight quench. Something you're not going to get with 4.0 pistons. The commonly available stroker pistons from the parts houses are full dish leaving you with a sub par combustion chamber and limited means of achieving a desired compression ratio.

Several folks have made comment of Russ. Russ Pottenger is one of the pioneers in developing a user friendly assortment of parts that play nice together. He can furnish you with everything you need to build a stout long lasting stroker from mild to wild

Focus on static and dynamic compression ratios. A tight quench and a cam that matches the desired HP/TQ rpm ranges.

IMHO the heavier crank is superior. I tend to disagree with the cost saving opinion. Since you have both talk to Russ and decide which crank you want based off the parts you choose.

If you do a cursory search here you will find his contact info.
GoatBoy4570
Where's the "any" key?
Where's the "any" key?
Posts: 25
Joined: June 25th, 2016, 7:05 pm
Stroker Displacement: 4.2
Vehicle Year: 1983
Vehicle Make: AMC Jeep
Vehicle Model: CJ-7

Re: More piston pin wear in 4.0 than 4.2 motors

Post by GoatBoy4570 »

Yeah i once had a XJ with close to 400k on it and i never heard any top end pin noise , i guess this motor is okay with the pins gettin loose.

The oil that is spec'd for the motor is more to meet EPA mpg requirements, im not a fan of running oil that pours like water, i like to see pressure so i know more is getting to where its needed, and i like knowing there is a proper wedge separating moving metal parts.

guess i'm gonna have to look at making sure that oil pump drive gear gets some lub, any suggestions ?
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