Cherojakee

Thanks. Yea I'm going to use a flex hone and inspect the other pistons. Already have the ridges reamed.

I was going to replace all pistons. But now needing the head, I will probably trade off and just re-ring the others.

Cherojakee

You can see where the crack starts at the bottom of backside and it makes it way towards the skirt and ends about halfway up where the side skirt starts at.

texastaz38

Just going to throw this out there. I worked in an automotive machine shop in high school, graduated in 1977 so...been a few years but....your on the right track for a low budget rebuild. You have already ridge reamed the cylinders, now ball hone the block to achieve a good cross-hatch pattern, then, re-micrometer the cylinders for size.

Now you know the finished cylinder size, compare to the actual current piston size in the state they are in. If your outside of the tolerance you want on the piston skirts, take the pistons to a competent old school automotive machine shop with your cylinder bore sizes for each cylinder. The shop can actually "knurl" the piston skirts to get them within tolerance.

This process is fairly simple with the correct equipment and should be far cheaper than pistons. You can expect about 1/2 to 2/3 life out of the "knurled" piston skirts. So, 50k-75k miles depending on your maintenance and use.

I know this thought process will get blasted but, a country boy will survive.

Happy Jeepin'

Cherojakee

Pretty interesting, I hadn't heard of that.

Cherojakee

Ordered a new head from Clearwater. Not much more than a remanufactured.

BlueRidgeMark

Yeah, that's something an old-timer recommended to me once. Knurled, then hand-lapped to fit. I did that, and that engine ran fine until it got run with NO coolant in it. Long story. And stupid, too. Lots of stupid.

Cherojakee

Haha sounds like a good story. Probably wasn't funny at the time tho.

may pop

X2 to being on track for a low budget rebuild. Clean clean clean. Oil the new bearings before torquing them. Lube the cylinders. Pour oil over the new head/valve train so it is not run dry Change oil and filter after an hour or so of running for cheap insurance if any crude was left inside.

Ron

Cherojakee

Thanks for the advice. I've been cleaning parts and putting clean oil on everything. So you recommend an oil change after about an hour of break in? I've read about that, but didnt know if it still applied for a partial rebuild.

Cherojakee

Got the new parts in and running. The budget rebuild ended up costing around $1000. Did a little preventiative maintenance too while I had it apart. Rear main seal, gaskets and tightened flex plate bolts. Is running better and quieter than when I bought it with 87k on odometer.

Ran a 20 minute break in for the lifters/cam last night. Oil pressure was good around 40. Now today the oil pressure dropped to around 10 at idle and 25 driving. I was thinking maybe oil pump got some gunk in it. Anything else that might cause that?

s346k

cam bearings

Cherojakee

Thanks seems like low pressure is a common occurrence after rebuild.

may pop

s346k
You are absolutely correct on the cam bearings. They are often forgotten by DIY guys and are a common cause of low pressure especially when coolant ( it is corrosive to the coatings on bearings) has mixed with engine oil. Installing them with the engine in the vehicle is not an easy task like rod bearings.

moparado

No blasting here texastaz38 you're right, piston knurling was done a lot back in the day.
Piston knurling has some advantages like holding oil a little better and it will quiet minor piston slapping in the original bore.

IMO, right or wrong.
I think whether knurling should be done instead of a complete rebore with new pistons depends on how long one plans to keep the vehicle.

I considered piston knurling decades ago when rebuilding an old Chrysler 318 engine.
Instead, ended up getting it bored .020" over then buying new pistons/rings to fit.

I think the potential problem with knurling with some of these 4.0 pistons is the pistons are already prone to cracking likely due to excessive mileage wear causing out of tolerance micro slapping fatiguing the piston skirt metal until it finally cracks or cheap metal or a combination of both, who knows.

The pistons could already be stressed even with microscopic cracks and knurling could possibly stress the metal even more.
If one piston cracked, odds are another one will crack eventually.

If i had a cracked piston and intended to keep the vehicle for a long while, i for one would get the cylinders bored over with new pistons and rings.
In the least if money was an issue, i'd cross hatch hone the cylinders then replace all the pistons/rings.

Motojunky

Not to turn this into a knurling thread, but I've seen it done on wrist pins in dirt bikes to avoid splitting the cases and rebuilding the crank to replace a connecting rod worn out at the small end. I hadn't thought of it for a piston slap application.

OP - thanks for keeping us posted. Great info for others who may be considering a similar rebuild.