I’ll try to keep this shorts What’s the break-in procedure for new pistons and rings? I rebuilt a 4.0 (reman head, decked by machine shop and bored over, crankshaft grind at machine shop, all new bearings, new pistons and rings). I’m using the old camshaft and lifters; which I thoroughly cleaned.

I read camshaft and lifter break-in is idle at 2000 rpm for 20 minutes; and while that is going on the rings break in too. Since I did not install a new cam and lifters, is the break-in for pistons and rings different? I put rotella 15w-40 in it and I’m thinking I should drain it and try a different oil for break-in.

 

The higher speed break in is usually used to splash oil onto the cam to get the lifters to be well lubed as they seat on the cam lobes..not needed in your case. Everything else is a much longer ( rings) break in...days to weeks. The important part here is NOT to use synthetic. Its too slippery and doesn't let the rings wear in. You must use conventional oil for the first several thousand miles. With a full break in you change it after the first half hour. You should still do that. Then change oi after the first 500-1000. Then regular changes at 3000. After 10K you can shift to synthetic. Have you primed the oil system...I used an old distributor with the gear knocked off to pump oil and rotate engine for a good bit to verify oils in bearings and pushrods. At minimum...make sure your oil filter is completely full with oil before install. DO NOT REV past idle until oil pressure is good and the engine is quiet ...for a jeep. Ask me how i know that. With new bearings, you should not need 15w-40. 10-40 or 10-30 should be fine for your 30 min break in our going to dump it in a few min anyway. Did you get new cam bearings also, or did you just do rods and mains?

 

Yes I primed the oil pump already. I was thinking the same about new bearings and not needing 15w-40. I’ll have to drain it and find something else.
Yes the camshaft bearings, rod and main bearings have been changed. I think cam bearings would have been destroyed in the hot tank at the machine shop. Nonetheless, I wanted new bearings for the cam too.

Thank you for the information. So, no hi rev since no cam break-in. Aside from not revving high unless oil pressure is present; What is the procedure am I doing for the 30 minute break-in, that requires an oil change afterwards? Also, what am I doing for the longer break-in procedure for the first 500-1000 miles (then another oil change) ?

 

The 30 min break in is to get everything wet and clean any sh*t and debris that might be left from the build. The next couple of hundred miles is normal running without stomping on it to see if you can make 4800 rpm,s. Then change out to clean any shavings that might be left from the rings wearing themselves in. Once you hit your 3000 mile oil change you can do whatever you want while running dino oil till 10k...then run whatever you want

 

I’m not certain you mentioned what do I do to the engine or jeep during the 30 minute break in. You did say NO NEED to rev to 2k for 20 minutes. But did suggest a 30 minute break in period but did not mention what to do…
I appreciate your patience

 

You don't need to do anything special since you're not breaking anything in. Make sure you have above 30 lbs of oil pressure within several seconds or shut it down. Let it idle for 5 min and if it sounds good, rev it to 2k for 10 seconds, then go back to idle. After a couple of minutes, back to 2k for 30 seconds...hopefully your pressure is up above 40 and then back down to idle. Check your temps and pressures. If it all looks good, a few more cycles and after 20 min or so shut it down and attempt to drain into a clean pan or bucket so you can get a good look at it. If its all ok, change oil and filter and your good for 1000 and next oil change...then just normal 3000 intervals. At 10k you can move to synthetics if you want. The backstory to my first stroker break-in disaster. I was misguided? , or mis interpreted the need to get to 2000 rpm to lube the cam lobes as quickly as possible. 5 seconds after my oil pressure showed 40, i hit the gas....well the pressure showed 40 but most of the bearings were barely lubed and i went through the first minute of breaking at 2000 with dry bearings . The engine was loud and hot. When i drained the oil out it looked like silver paint. I didn't know exactly what that meant then. At 5 or 10 k miles i had rod knock. Dropped the pan and changed out all the rod and crank bearings..I think that motor went another 75k before the cam gear ground down and it was done at 340k. Moral of the story...if cam break in....let idle for a minute or two till all lubed and pressurized and then rev for cam break in...that was my old 92, stroked to 4.7 with a high lift cam and springs.

 

Ouch, that had to be such a bummer and frustrating. I almost went ahead and did a new cam and lifters too but not unless I absolutely need to. I’ve heard aftermarket cams for 4.0 or garbage but I don’t have experience with that. But I am a believer that metal isn’t what it use to be. I made sure to use assembly lube on all bearings and metal to metal contact surfaces.

Well since you’re the only one who has done an engine rebuild thank you for commenting and giving some insight. I’ll try what you suggested, after I drain and fill with the lighter 10w-30. I don’t run synthetic anymore but thanks for mentioning the 10k. I’ve also heard a suggested initial break-in procedure of driving up to 40mph then letting off the throttle so the engine does “engine breaking” to help seat the rings.

 

Hey..might be too late, but did you swap out those ridiculous torx bolts at the top of bellhousing for plain old grade 8 hex bolts of same length

 

Since no one really thinks about torx bits, I ended up reused them as a security measure so no one can steal my engine...
No I didn't bother replacing since i have the socket and thin ratchet to get to them from the top, through the engine compartment. Last time I did it the old fashioned way from underneath, connecting all my extensions together. The ratchet is from harbor freight called pittsburgh pro. The flex head is half the thickness of a normal ratchet. You have to entirely remove all the engine mounts and brackets to allow the engine to tilt forward enough to get to torx bolts but the ratchet gets in there with no firewall rubbing. Basically its the same amount of work without having the lay on your back, kinking your neck and getting grime in your eyes.

 

For what it's worth:

What you are breaking in is the new rings into the new cylinder wall honing. (this is assuming good oil pressure)
The usual advice on breaking in rings is for maybe the first ​​​​​ hundred miles don't go nuts on the rpm but vary the engine speed frequently... don't just sit there at 2500 rpm for an hour. I think the idea is to try to suck an adequate an adequate amount of oil into the ringsYou'll hear different opinions...hey it's not their engine

here's one of many
https://www.enginebuildermag.com/2018/05/how-to-break-in-your-piston-rings-the-right-way/

 

Thanks for your input, I’ve heard that too. I’m torn between if I should absolutely use break-in oil (and if so, do I need 6 quarts) or if I use just conventional 10w-30. I want to get it right the first time and not have the rings not seal properly. My engine burned oil prior to the rebuild and I don’t want that to happen again. At 300,000 Im sure the old oil rings were not doing much at scraping the oil off the cylinder walls; I took a few old oil rings off the old pistons and placed them in the cylinder that they weren’t even touching the walls.

 

I think you're over thinking this:
Your choices are use "normal" oil , go through the vary the speeds and don't get nuts with the rpm drill for a couple hundred miles and change the oil and filter to get the scrap metal out or do the same thing with the initial fill being break in oil.
If it lets you sleep better use break in oil, won't hurt any thing.

BTW if you find oil that means the engine won't need work after 300k please post here