Piston question

[optmaxx]

So I just realized that KB makes a Hypereutectic piston for the Jeep stroker that you can use with the 4.0 rods that are much cheaper than the IC944s forged pistons...I imagine it's because of the materials used. I've bought one 944 piston in order to replace the damaged one, and there's been some upgrades compared to the original 944s, like they now have coated skirts and are about 18g lighter cause they have less material on some areas, so I've been thinking of replacing them all.

The other 5 pistons look ok, but there is some wear, like some vertical scratches that were most likely caused by having water in the oil from the cracked head, and they all show the same identical wear pattern but it didn't look too worrisome; but nothing beats new pistons.

UEM will sell me the rest of the 5 pistons in a way so that it'll be like I bought a set of six 944s, but even then a set of the Hypereutectic pistons still comes out cheaper.

So my question is, how much of a risk will it be if I put in a set of the Hypereutectic pistons since I had the forged 944s in the engine first? UEM said that I could make up some clearance with the Line2Line coating, but I'd have to tell them how much to add and I don't know what to tell them.

Is it too big of a risk to put in a set of Hypereutectic pistons after running forged pistons? How much Line2Line coating should I ask to be added if it's even necessary?

[optmaxx]

Here are examples of two pistons after some clean up of both sides. Pretty sure most of the wear is from the water mixing with the oil, and I've thought about reusing them but I might replace them all now.

[optmaxx]

Here's the new IC944 vs the older design. You can see where it has less material now.

[optmaxx]

So I might just stick with the forged pistons to avoid clearance issues. So before I bite the bullet and get the rest of the five pistons, do you guys think my other five need to bet changed?

I know pistons are always going to have wear marks, and the chances increase with DIY rebuilds and the quality of the machine work. So do the other pistons look too work out, and should be replaced? Or is changing the rest of the 5 over kill and still have a long life ahead of them? This was just a quick clean up too though, so they may look even better with a good cleaning and buffing.

Here's a pic with flash, and the rest of the 5 look very similar. Click or middle mouse click on the images to get the correct oriented view...not sure why the pics uploaded like that.

[Cheromaniac]

If the new pistons are indeed 18g lighter than the old ones, I'd change them all to maintain weight balance.

[optmaxx]

If the new pistons are indeed 18g lighter than the old ones, I'd change them all to maintain weight balance.

Yeah that's true. So to you, do the other pistons look too worn to reuse? Or are the wear marks barely anything?

[optmaxx]

Looks like some more space was machined out on the sides of the where the pin goes compared to the old one. Also some small ribs where there were none at the oil holes.

[75SV!]

My question is weather the KB Hyper has the proper quench. I read they have. I haven't seen a picture though. The pictures on Clegg's site, shows the open or round piston pocket. I also notice that on your picture of the IC944, new vs old.

[optmaxx]

There are two types of KB Hyper, one with a D quench pad, and one dished all the way around; these 944s have a D quench pad. I was wondering if anyone had issues, or if there would be any issues going from forged to hyper with cylinder wall clearance.

KB438C are the hypers I was looking at.

https://www.cleggengine.com/jeep-4-0-st ... b438c.html

[Cheromaniac]

Yeah that's true. So to you, do the other pistons look too worn to reuse? Or are the wear marks barely anything?

Those light scuff marks aren't anything to be concerned about.

[optmaxx]

Well I did a more thorough cleaning using hot soapy water and 1200 grit sand paper, and now the scuff marks are non existent. The skirts look pretty good now, like new so I'm not going to buy the rest of the 5, it'd be a waist of money.

I also asked my machine shop guy and he said that if it was his car, he'd reuse them cause they don't look done yet, and the wear didn't look bad enough to drop another $500+ on the rest of the 5.

He did say that if I was building a race engine then the new piston being 18g lighter would be a problem, but he wouldn't worry about it on my build. So I'm going to move forward and get this thing back together.

[optmaxx]

Some Clean up pics. Still need clean up the rest of the piston, but I wanted to see how the skirts looked with a better cleaning. Pics of 5 pistons of both sides, wish I had a buffer.

[optmaxx]

Pics of 5 pistons, of both sides.

[optmaxx]

Some more pics of my Piston cleaning journey . I mean I guess it could be used as a good reference if someone is on the fence about changing their pistons over some scuff marks, clean them up real good and see how they look after. I used oven cleaner and a drywall finishing sponge which worked good as a polisher while wet. All of these seem fine, and the rods still move freely on the pin.

[optmaxx]

More pics