Break-In Period on Rebuit/New Engine

This is my first rebuild I’ve ever done. I have an expert helping me with this rebuild. He rebuilt cars when he was younger. But, my only question is what brand oil should I run until my break-in period is over. I know regular conventional oil but, it’s 2014 and there isn’t much regular with no additives left. Any suggestions?

When I got my Goodwrench remanufactured diesel, I don’t remember any special oil issues. It did take 500 miles or so to loosen up so it would start ok. Had to replace the batteries too in the first couple hundred miles because of the starter drag.

If you go on E-Bay you’ll find a wide assortment of “engine break in oil” although I’m not sure that’s really necessary.

“No additives???”

Never heard that one before. To the contrary, I’ve heard you want to run an oil loaded up with Moly, ZDDP, and other extreme pressure additives to protect the cams until they’ve been broken in.

“No additives???
Never heard that one before”

I’ve heard it, and it is just as untrue today as it was when I first heard it back in the '60s.

Back in those days, there were some old-school mechanics who used to advise the addition of scouring powder to the oil in order to “wear-in” an engine during the break-in phase.
Yes, they were morons.


These morons actually advised to use Comet, or some such scouring powder . . . ?!

500 miles with convetional oil.

@db4690–I don’t recall exactly which scouring powder these old guys recommended using, as I simply walked away from them when they began spouting nonsense that was truly dangerous. If they used Comet or Ajax, they were also adding chlorine bleach to the crankcase, in addition to abrasives.

I don’t even want to know what the addition of chlorine bleach would do…

Years ago I took a 13 week auto-shop night class at the local high school. Twice a week, 3 hours a night. It wasn’t a sit and learn class. It was mostly just an opportunity to bring your own car into the school’s shop and use their lifts and tools to maintain/fix your car and have two instructors there to offer guidance. Two of the class members had been taking this same class for an entire year at that point. They were working together rebuilding a v8 engine in a Chevy pick-up truck. I happened to be present at the time of the first start up, after a year’s work. I noticed before the first crank attempt they poured a cheap, off-brand oil in, so I asked why be cheap on the oil? I mean after all, they’d just spent a year doing the rebuild. The instructor piped in, told me it was by design, that this particular oil brand had few additives, and that it was supposedly good for the first few hundred miles as the parts meshed, a little more friction & wear was needed. It didn’t really make sense to me then, and it still doesn’t. But that was the explanation. It started right up, on the second crank attempt.

I remember the cleaner that old school mechanics used to use back in my younger days. It was Bon Ami. I remember those yellow cans with with the little chick on front. I never was taught to use the stuff but I can remember a lot of old mechanics who did.

I remember the Bon Ami, their slogan was “hasn’t scratched yet”. They also used much finer abrasives than other cleansers.

I don’t know if this has anything to do with it, but Studebaker used to build engines with much tighter clearances than other makes and it used to take about 5000 miles to break one in to where it would get good gas mileage. Once broken in they got outstanding gas mileage for their day. Perhaps the cleanser was an attempt to hasten the process.

I also remember the Hudsons with chrome, nickel alloy blocks, you couldn’t use chrome rings in them or they would never break in. Had to be cast iron rings. Some mechanics would wipe down the cylinder bores with salt water to let them rust before honing. Don’t know why.

I was taught the reason for using ‘break-in’ oil with minimal wear additives is to properly seat the piston rings. On a freshly honed cylinder, the cylinder walls will have sharp peaks and valleys. With minimal wear additives, the rings will knock down these peaks within a few hundred miles of easy driving. This promotes better compression, lower leak-down, and maintain good oil film retention. With wear additives, the peaks will take longer to knock down and may prevent the rings from seating correctly, allowing for increased blowby and oil consumption. At first I was a bit skeptical, but I later read an article in a pilot’s magazine about an FAA study into overhaul procedures, and they confirmed this, complete with microscopic images of the cylinder walls after overhaul using break-in oil on one engine and standard av oil with typical wear additives on the other. The difference was dramatic and further testing, compression, leak-down, and oil consumption showed the break-in oil for the first few hours of operation greatly improved engine performance and engine life right after an overhaul.

What is it about the Bon Ami, Comet, or other scouring powders that we don’t believe in today that so many experienced engine rebuilders of yesteryear believed in?

Granted today’s engines are different, so those techniques may no longer be warranted. But are we saying what they were doing back then was wrong?

Use conventional oil in the correct weight (5w30, 10w30 ect.). Hopefully you used moly or engine build lube with lots of ZDDP to lube up the insides to prevent dry startup. If you have roller followers on the cam, you won’t really have to worry about cam break-in, only sliding followers.

If your engine has sliding followers (flat tappets) and a new cam, run it for 20-30 minutes at 2000-2500 rpm so the cam will properly break in. Shut it off and once it cools down a little, change the oil filter. Add oil to the fill mark and drive the car for 500-750 miles. Change the oil and filter. Done. If you want to run synthetic oil, do it a couple of oil changes later. Otherwise enjoy the product of your labor. Not many folks do this anymore!

I believe GM had a TSB in the late 1970’s to use Comet to help break in new engines with chrome rings. Start the engine, pour in a measured amount of Comet cleaner into the intake. I seem to recall you were allowed to do two treatments of this to seat the rings. If that didn’t do it then a teardown and honing of the cylinders was required.

@meanjoe75fan I have to run regular conventional oil with no additives to allow the pistons rings to seat properly.

Ok guys, I found some non-additive oil.
This past weekend I went into NAPA Auto and explained to them the issue or what I’m trying to do. They said “I’ve never had anyone ask that question before. But, we do have some oil with no additives. This here does have any additives see.” Well the oil we gave me was “NAPA SAE 30 non-additive” So, I will give it a shot. I only have to run this oil for 500 miles.

I still think you’re making a big mistake, especially if you have flat-tappet valves.

You need some ZDDP in there…heck, GM even makes an EOS additive to protect camshafts on initial break-in following a rebuild!

Leave the 1930’s oil tech for those who operate 1930’s technology…like piston-powered aviators!

Yes, many years ago GM had a factory bulletin advising dealership shops to correct a problem with high oil consumption by pouring a scouring powder through the carburetor. A local shop owner/friend had worked at a Chevrolet dealership when that occurred.

I have always filled new and rebuilt engines with the factory recommended oil and told the owners to drive normally. There was never a problem as a result and some of those engines ran 200,000+ miles.

On all of my 60/70s era big block rebuilds, the contact points get a generous application of break in lubricant on assembly. The cam is literally dripping with it including lifters etc. No need to have it in the oil then where it might interfere with proper break in of other parts. Then I run straight 30 weight conventional oil for the cam break in. After 20 minute run in, change oil and put in multi-vis oil I will be running from then on…Has worked for me for decades…