Like most NOOB's, I am terrified of the flat tappet/ring seating process!What is the reasoning behind not using synthetic oil for breaking in a flat tappet engine?I have seen opinions that state it is because of ring seating, but I have also read that moly rings seat immediately and it has nothing to do with oil.If you have read the oil blog of "540 Rat" https://540ratblog.wordpress.com/ all the "break in" oils are of very sub-standard protection and vary so much in formulation that it is apparent that there is no rhyme or reason to any of this.I almost think Mobil 1 5W30 is an ideal oil for this purpose because "5W30 Mobil 1, Advanced Full Synthetic, API SN, GM dexos 1 approved = 117,799 psi" is in the "Fantastic" category and it is affordable @$23 at Wallyworld.In contrast "30wt Brad Penn, Penn Grade 1, Break-In Oil, conventional = 56,020 psi" is in the "UNDESIRABLE wear protection" catagory!?All the break in oil are of dubious value protection-wise.I will not cheap out on this break in process....if I have to spend $10 a quart I will...but I don't see the logic in any of this?C'mon guys....fire away!

My 17 Jeep has had synth since new, and at 20,000 + miles, it still uses oil. I don't know if it will ever seal up.

All i can tell ya is i used the Amsoil break in oil to break in the flat tappet in my brand new 511. Think i paid 8$/qt. The company says its designed to seat rings quick and efficietly. After break in i used Brad Penn 20/50 (which i get for $5/qt) for about 200 miles. I now have Amsoil Dominator 15/50 in it. Very good oil with lots of additives. The cam was nitrated and inner springs removed for break in. All went well. Some just use the cheapest oil they can find and add a can of STP oil treatment. Not me. I like and use good oil. You might find more info on bobstheoilguy.

That 540rat dude was exposed on speedtalk years ago as a fraud. His test methods are rediculous and he uses a gear oil test to test engine oil.

Ignore anything that guy says.

Buy a QUALITY mineral break in oil and use it. I just did my own engine about two years ago. SFT cam with 145 on the seat and 400 over the nose with double springs. I didn't go through any of the crap of pulling the inner springs. Everything went fine.

The biggest issue with ring seating is to NOT slop a bunch of oil on the rings when you assemble the engine. I wipe the bores clean with Marvels Mystery oil until the paper towels come out clean. Some guys use ATF. Some use WD-40 even. Doesn't matter. Just get the bores clean.

Once that is done, I use a small amount of a QUALITY assembly lube on the SKIRTS of the piston so the SKIRTS have a thin coating on them and put the Pistons in. That's all you need for lube.

Make sure you have the correct lube on the cam. Make sure the lifters rotate in the bore. Make sure the engine starts. Don't sit there and crank on it. Prefill the carb.

Set the TOTAL timing at 40-45* BTDC before starting the engine. Don't try to time the engine at TDC. Too little timing is worse than too much on start up.

See...this is why there is no stupid question and the internet is a dangerous place!I had no idea about 540Rat....sounded good and made sense.I will go with Comp Cams break in oil.I think 10W30 should be good and $6.99 per Qt at Summit.

That 540rat dude was exposed on speedtalk years ago as a fraud

X2 - very annoying person to exchange views with, little engineering knowledge.

(slightly) off topic, there is a VG read on piston rings breakin on www.mototuneusa.com scroll down til you get to & click on "breakin secrets". the jist of it is to load the eng hard on breakin & that you get one shot to get excellent leakdown numbers as opposed to good ones. it is a motorcycle site but the principle would be the same & they state that. I am a believer in doing a final hone with a BRM flex (dingleberry) hone with file fit moly rings (for most apps) & following BRM instructions ex they want you to bore to size then use their hone with no 3 stone honing & I dont agree with that part. As said clean the eng/cyls THOROUGHLY. I would remove the inner springs tho, cam failures happen regularly (might be different reasons tho). As said, plenty of timing & you want everything dead on so it fires IMMEDIATELY. several helpers, one to set the timing, one to spot leaks, one to add trans fluid, YOU in the drivers seat to man the throttle (to goose it) & watch the gauges & shout orders! If a leak or issue shut it down right then & there, dont think about anything just do it & fix it & fire it back up.

This debate will never end. I try to pay attention to what is used and recommended by top engine builders, across multiple disciplines, on any number of subjects. They can't agree on anything and they see the results everyday.

Even before I heard of 540rat - that would be today - I prefer Amsoil stuff based on what I see in the filter and the parts when it comes apart. I've done the break it in with dino oil deal, and synthetic from the beginning deal, and never really saw a difference. But then my stuff was never after every last bit of power and a little crude compared to what a high end builder would provide. I just wanted it to stay together.

"What is the reasoning behind not using synthetic oil for breaking in a flat tappet engine?"

I didn't see this main question directly addressed?

I am NOT an engine builder, but this my understanding, Syn oil is not favored for break in as its too slippery. The intent is to lap both the lifters and the cam lobes. Very high idle(2000 rpm?) is desired as it keeps everything oiled and oil cooled at the lapping surface. Additionally, the higher break in speed to me is somewhat analogous to driving on sand, slow and you dig in and get stuck (wipe a lifter), fast, you float across the top surface, lapping all the while, Syn oil and reg oils work to prevent that process.

The reason not to use synthetic on break in is to get the rings seated. Today, in 2018 I think if the bores are finished correctly and the rings aren't slathered in oil the rings will already be seated.

Regular engine oil has to have a bunch of additives you don't need for break in. That's why I don't use it. The cam is essentially lubed by dry film lubrication and not an it film so cam break in means nothing to synthetic oil.

Do you think OEMS that have engines that are required synthetic break them in with coonventional oil?
Doug

Yes it's about the ring seal.

Good question because most all new cars I work on use 0-20 synthetic from the factory but they are all overhead cam engines with fairly light springs(never measured them) but they compress very easily.
I work with guys that still dunk their pistons in motor oil during assembly and I have to laugh. The new engines I have rebuilt use a very thin low tension rings and all I use is a little spray of lube(like WD40)and they break in right away.
So has anybody ever driven their car to break it in as opposed to just letting it run with a fan in front of it. I would think cycling the engine through the gears would seat the rings and cam quicker

Gus

Wow, I guess I've done everything wrong using synthetic oil to build race engines for the last 43 years. I think it's time to quit!

This isn't arguing, but trying to learn something...don't the OEMs use a machine to spin the shortblock briefly prior to full assembly? Guess the bearings get assembly lube and then they spin it to seat the rings prior to the heads going on? Or is this not the case at all?

All I've ever heard (like many others) is that synthetic is too slippery and won't let rings seat...even w/ proper wall finish, etc. I've never done it, always used conventional oil. I figure the "break in" oil is gonna get changed soon anyway and the synthetic is more expensive, so I see no reason to take a chance?

FWIW...I use assembly lube everywhere but the cylinder walls, which get a light coat of conventional motor oil. Rings get sprayed w/ WD-40. This has worked very well for me.

My Chrysler Zone Technical Rep told me around 1995, that the Cummins engine plant used filtered oil to fire them up. That oil was then drained, filtered and reused until the analysis required a refresh.

I follow the American engine rebulders association guidelines,
https://gafiero.akroncdnr.com/docs/BreakIn.pdf

on breaking in a new or rebuilt engine.

When I went to Viper training the first time Mopar told me that all the Viper engines use Synthetic oil. But they also said they are run first at the factory with non-synthetic oil to seat the rings faster. Then after that they get synthetic before they leave the factory. They told me the synthetic is slippery and that's why they don't run it in a fresh eng. I was told its best to seat the rings and run them on non-synthetic first and then after ring seating and cam break-in if a flat tappet then switch to synthetic. Course I first went to Viper training in 1992 so this may have changed some since then and others may not agree with it. But I myself still go by that and break engines in on non-synthetic. Course I don't run synthetic in my cars anyway. Ron