Topic: Engine break in, how long?

[94MtnYote]

 Just had the engine rebuilt. how long should I wait for the motor to break in so I can to enjoy the full benefits of the throttle.

[LOL @ IFS]

Don't wait.  Go drive normally 'till it warms up a bit, then do some full throttle pulls in 2nd gear from 2K RPM- 4K RPM, then coast, and do again five or six times.  That's it.  The first 20 miles are critical, and if you wait too long, the rings won't seat and you'll need to re-ring and re-hone. 

Flooring it early on will force the rings against the cylinder walls, and the cross hatch honing will "shape" the rings to seal against the cylinder wall.  If you drive gently, this won't happen, and the honing will be worn off without the rings properly seating. 

[SolidAxle]

I'm not so sure on the full throttle thing. When my dad got his 340 rebuilt they told him for the first tank full of gas to drive easy on it, But keep the rpm changing as much as possible. after that they said he could hammer it. I rebuilt my engine at the same place my dad did, they take all of the engine they do and run them on a spin tester, (bolt machine to crank  and spin it with no spark plugs) the guys check oil pressure, compression etc. the engines are spun for about 10 minutes like this.
I think immediately doing full throttle pulls would put too much pressure on all the new parts which need to be worn in and work together.

Just my opinion 

Why not phone a machine shop, they know best?

[LOL @ IFS]

I think immediately doing full throttle pulls would put too much pressure on all the new parts which need to be worn in and work together.

You don't immediately go WOT... you warm it up by driving two or three miles normally and then do the pulls.  By that time, you will be able to tell if it's going to overheat or lacks oil pressure.  Think about it- the rings need to seat, right?  That's really the only part of a new engine that needs to "wear in" because the bores aren't completely round, and neither are the rings.  Also, why does everyone want that nice 60° crosshatch honing pattern on the cylinder walls?  It's not for looks.  It's so that the walls act as a file, removing the high spots on the rings so they seat completely.  However, that abrasiveness doesn't last that long, so you need to take advantage of it while you can.  In order to do that, you need to put more pressure on the rings, to force them against the cylinder walls.  How do you do that?  More throttle.  More throttle will increase your combustion pressure, forcing your rings against the cylinder walls.  Regarding the oil- use dino oil initially because synthetic is too slippery to allow the rings to seat.  You can use synthetic after the first oil change at 500 miles.

Why not phone a machine shop, they know best?

This sums it up perfectly:  http://www.mototuneusa.com/break_in_secrets.htm  The claims of power increase are of considerable debate, but the facts related to seating the rings remains undisputable.

The first engine I ever built was ruined because I listened to the "drive it gently for 1000 miles" advice the old guard gave me.  After driving it for 7000 miles and burning about eight quarts of oil, I tore it apart, reringed and rehoned, and put it back together (same brand rings, same machine shop for the honing).  I drove it for about five miles, then gave it short bursts for 15 miles or so, and proceeded to log somewhere around 80,000 miles on that engine between daily driving and track days before I sold it and never saw any blue smoke.  I've rebuilt somewhere around ten engines since for friends and myself and have been adamant about this break in procedure and have yet to produce a smoker.

To the OP, I've given you factual knowledge backed up by first hand experience.  What you do with that information is up to you.

[79coyotefrg]

Don't wait.  Go drive normally 'till it warms up a bit, then do some full throttle pulls in 2nd gear from 2K RPM- 4K RPM, then coast, and do again five or six times.  That's it.  The first 20 miles are critical, and if you wait too long, the rings won't seat and you'll need to re-ring and re-hone. 

Flooring it early on will force the rings against the cylinder walls, and the cross hatch honing will "shape" the rings to seal against the cylinder wall.  If you drive gently, this won't happen, and the honing will be worn off without the rings properly seating. 

i agree  totally  with this procedure,  only different i would  do it from 1500- 3500 rpm

this is very important  to do this

[unclejpl4x4]

I ran my engine around upand down 1500-2000 for 20 mins parked  then drove it around town for a few miles.

[OOPS]

I am a firm believer in break it in like you are going to drive it. That is within reason, do not fire it up and do a WOT pass down the block the first time. I also do an oil and filter change after 500 miles, motorcycles after 200 miles. I have never lost an engine because of my breakins or oil related failures. We did lose one 327 SBC when the clip on the oil pump was not installed right and it came off at 8,000 RPM's, 0 OP at those RPM's plays havoc on an engine.

[94MtnYote [OP]]

  Yesterday I was running around town and went to the dump, with around 30-40 miles on the rebuild. I hit the throttle pretty good a couple times to check it out on straight aways.
Just want to make sure I break this puppy in for the long haul

[SolidAxle]

Alright you guys have got me convinced. Sorry for my misleading comments. luckily nothing has happened to my dads car's motor and mine has 0 miles on it still.

[Cheesemaker]

This totally goes against everything that I've been told, or read.  Including guys that have been building motors for 30+ years! 

I've always been told that it's not about the rings, it's about the bearing on the bottom end, and the cam.   

[kneedownnate]

As important as break in is, lots of people don't bother with it and get lucky.  On the other hand, I was talking to a guy at a track day once who'd just purchased a honda 929 solely for track riding.  The only street riding he ever did was just to break it in, but he thought he was a little hard on it during break in and it was confirmed when they dynoed it later.  He was down a few hp from running it too hard.

We don't even break in a lot of engines at work.  I cringe any time we have to change an engine when the college kids are here, cause you know they hammer down as much as possible, and all too often they'll back off the throttle limiter so it can rev higher.

[RN37DD]

i agree with the 1500-2000 rpm for 20minutes to brake the cam in. then keep it below 3500-4000rpm for the first 500 miles.  lots of speed and throttle changes as you drive. braking the rings in is about combustion pressure. rpm without load is where you get the rings and cylinder's glazing. as long as the main and rod bearing have the right clearance you really don't have to worry about them.  i just pull apart a 20r that had a ton of miles on it.. and a bunch of over 6000rpm runs and both the main and rod bearings had no wear. after 500 miles change the oil  just run it the way you want to drive it. i kept my rebuild engine below 5000 rpms until after 1000 miles. i try to keep it below 6000 now. 

[79coyotefrg]

.......... braking the rings in is about combustion pressure. rpm without load is where you get the rings and cylinder's glazing. 

to seat the rings  you NEED  to  load  the rings,  low rpm  with load,  not hi rpm  with no load 

[RN37DD]

yes glazing is bad!!! rpm without load is bad!!! i never rev my motor unless it's in gear and pulling hard.

[bad luck]

i was told to not keep a constent speed for the first 500 miles and the change oil
and again at 1000 miles

[RynothealbinO]

Heres a paraphrase of a combination of my Haynes Manual, pesonal experience, and professional advice:  Allow to warm up for a few minutes to chech for leaks, making sure to keep between 1500 and 2000 RPMs if you are putting a new cam in for proper oil pressure, as soon as possible (no more than 5 minutes) drive it doing full throttle pulls from 30 to 50mph, closing the throttle all the way afterwards to decelerate, do this 10-12 times, and always make sure you keep the RPMs at least at 1500 for cam break in for the first 20 minutes.  After that drive the next 500 miles gently and vary the speed when it is possible.  I did this by doing a 300 mile drive on an engine with less than 100 miles on it (scary) and going between 4th and 5th gear and varying my speed from 55-65mph.  After 500 miles change the oil and start to drive normally (think normal person "normal").  Then change the oil at 2000 miles and consider the engine broken in (so go ahead and do those 7000RPM pulls lol).  The crutial thing is the first 20 minutes because you cant let it idle too low with a new cam, but you should also have a load on it, and probably keep it between 1500 and 3500RPMs.  However I have heard varied reports about when to use synthetic.  DO NOT use it for the first 500 miles because then therings will likely not seat right, but I have been told to wait until there are 5000 miles on the engine, which sounds high to me.  So does anyone know when I can go synthetic?  I have 2000 miles on it now, so I hope soon.