Jeep Strokers

If you are using forged, .016" should be ok. If you are using Hypereutectic .024" is right
Towing with forged, .018" is good. Towing with hypereutectic .026" is right.

What you got in it? and how hard you gunna lean on it?

It has the icon ic945-030 forged pistons. So the ring gap should be OK? I haven't had the time to pull it apart yet. Maybe I will get a chance tonight.

Given you issues with overheat maybe Forged Towing factor of.018, for a margin of safety.

This rebuild had no overheating issue. and with the forged piston at 0.018 gap I am still unsure as to why this thing keeps failing. 4 of the pistons ended up being ruined and the other 2 would have been shortly. The whole side of the pistons ,top to bottom, on the thrust side are scarred up. The oil pressure seemed good, temps were good , bearings look pretty good. I measured the piston to cylinder wall clearance. At first I thought it was a little tight but after double checking them they seem to be okay. 0.003 best I can measure. I can't seem to find any issues with the oil flow. except maybe the lack of holes on the clevite rod bearings, but from what I read that shouldn't be an issue.

I'm stumped and about ready to give up on this and just put the old 4.0 back in it

It's possible the pistons are binding on the small ends of the connecting rods thus not allowing them to rock completely from side to side once the engine warms up.

Other things to consider:

What alloy is the ic945-030 piston made from?
2618 alloy is strongest, but expands more.
4032 is not quite as strong, but has lower expansion.

Forged pistons usually come in these two alloys, and will require different piston-to-cylinder wall clearance. (In addition to proper ring gap clearance as already discussed) Piston manufacturers can provide all of these recommended clearances. I'd check that out.

I think these are pressed in pins, but have you checked your pin-to-rod small end bore clearance; could be binding up affecting piston alignment.

The ICON 944 and 945 pistons are T-6 2618 alloy.

Cheromaniac wrote: ↑October 28th, 2021, 4:33 am The ICON 944 and 945 pistons are T-6 2618 alloy.

I'm seeing them advertised on different sites in both alloys. Are they being miss-advertised? I thought they were 2618 originally, and then later on offered in the 4032(?).

I6FAN wrote: ↑October 26th, 2021, 11:34 pm I think these are pressed in pins, but have you checked your pin-to-rod small end bore clearance; could be binding up affecting piston alignment.

Edit: I meant piston pin bore-to-pin clearance.

X2 on the clearance Cheromaniac was referring to. There was also an issue with the balance pad on the top of the rod interfering with the bottom of the piston. Should see witness marks on the bottom of pistons if this is happening.

I used SpeedPro Hypereutectic in mine, but yes forged expand more, and have different boring requirements. Did your machinist bore for Hypers and then you installed forged, cuz that would do it, big time.

I6FAN wrote: ↑October 28th, 2021, 11:44 pm X2 on the clearance Cheromaniac was referring to. There was also an issue with the balance pad on the top of the rod interfering with the bottom of the piston. Should see witness marks on the bottom of pistons if this is happening.

The balance pad on the rod small ends needs to be ground away and rounded off before pressing in the ICON pistons. Otherwise the pistons WILL bind in the bores once the engine warms up.

The literature I have from Icon says the IC945 are 4032 alloy. The machine shop said he bored the cylinders .003" wall clearance over the pistons. I measure 3.902" bores, but I am just using a set of mitutoyo calipers and a cheap telescoping gauge.

I had not heard about grinding the rod small end for clearance while using ICON pistons. Never seen or heard that from anyone and I didn't tell my machine shop to do that. I will go over and look to see if there are marks on the underside of the pistons.

Thanks Guys

I don't see any marks on the bottom of the pistons.

It's hard to get pictures with the rods still on tho.

Actually there may be a very very faint marking on the rear piston pin boss face where it radius to the bottom.
It's really hard to tell. Does anyone have an example as to what I'm looking for?

It looks like there may be something there, but hard to tell from the photo. I've seen pictures of it on here before (or some Jeep forum), but my limited search failed to yield anything. There is a lot of conversation about it on here you just need time to search it.

viewtopic.php?p=42015&hilit=grinding+ro ... pad#p42015

At any rate, you need to get some good measurements of your clearances. I "get it" that your instruments might not be up to par, but if those are correct, or close, that could be your issue. Your shop probably did good work, but there's always a chance something got missed.

Since you have it apart, do the rods swing freely from skirt to skirt? I did not use Icons, and I removed a lot of my balance pads to make up for .060" over pistons. But even if they swing free they may touch when hot. Can you get a USB borescope, or a dental mirror?