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Old 03-04-2021, 06:27 PM   #1
BRENT in 10-uh-C
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Default What is Engine 'Break-in'??

I engaged in a small post on social media where several people were recommending to a hobbyist that a rebuilt engine needs to go thru a 'break-in', ..and (more emphatically) during that time, the engine RPMs needs to be varied (-from idle to up & down the RPM range.). I asked "why" does this all need to happen, ...and no one could seem to give me an (intelligent) answer other than auto manufacturers suggested this.

So I'll ask here where I know the responses to my question will be much more accurate!!



Let me start by giving my theory as to why their advice is a bunch of nonsense on 21st century Model-A engine rebuilds;

  • The term Engine 'break-in' is really just an old phrase justifying the reasoning for allowing an engine to use internal friction of mismatched components to prematurely wear to a specification instead of using proper machining methods to obtain that desired clearance specification. (See Point #4 below)

  • The engine RPM does not need to be varied, -and it is likely preferable to run at a single RPM with enough RPM speed to provide splash oiling that all parts receive a constant coating. Altering this engine speed does nothing to increase longevity or better ring sealing on a properly machined & assembled engine.

  • After initial start-up of a rebuilt engine, the engine only needs to run long enough where various metals and gaskets can thermally expand. If the deck surface of the cylinder case and the cylinder head have a good RA finish, -and if the head gasket is of quality, then upon the components cooled to room temperature, the stud nuts can be retightened to compensate for any gasket compression. The (mis)use of gasket sealers (Copper Kote, et/al) often hinders the thermal expansion & contraction of the gasket which will affect fastener torque ratings being met.
  • Use of inferior machining techniques and/or worn machines causes cylinder bores to not be truly cylindrical. The use of 220 grit Diamond stones at roughly a 35 cross-hash will produce a finish that a cast iron ring can easily seal to. When poor quality machines and/or stones are used, the concentricity of the bore is compromised creating a need for the rings to scrub against that cross-hashing longer so the ring(s) can shape themselves to conform to the non-concentric shape of the cylinder bore. Additionally, a properly burnished cast bearing does not need additional run time for it become 'fitted' to a crankshaft journal pin. If a rebuilt engine requires a 'run-in' period for the bearings to clearance themselves, then either poor machining practices or machines themselves (crankshaft grinder or line-boring) were used.

The above are just my opinions, ...and I welcome theories that either corroborate or contradict my reasoning for Model-A engines not needing a rebuilt engine break-in period with the machining technology of today.
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Old 03-04-2021, 06:42 PM   #2
Mister Moose
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Default Re: What is Engine 'Break-in'??

My Model A engine rebuilder instructed me to run for short periods of 10 minutes and then a cool down. The explanation was the rope rear seal would burn if run for too long, that it needed to seat from wear over a longer period of time. If the engine was run too long the rear seal would carbonize from the frictional heat before the seal was worn in.

*Edit I was also instructed to use mineral oil for the first 500 miles for better seating, AD oils were too slick.

Aircraft cylinders have the diamond cross hatch pattern you describe. On brand new engines (I flew a lot of them) I was instructed by Continental to run at no less than 75% or even 80% for the first 10 hours. The explanation was the higher power settings gave higher cylinder pressures, and this would expand the rings to seat effectively. If the engine was "babied" when new, the cylinder walls would glaze and the rings would never seat. I'd expect an aircraft engine would be machined to state of the art. The engine was shipped with mineral oil, which would stay in for the first 50 hours, and then go to synthetic.

Outboard engines (2 cycle) were different still. OMC and Mercury instructed to run below half power for the first several hours, gradually increasing the power thereafter, and not to run at a constant power setting.

Obviously different machining methods and different materials lead to different instructions.

Last edited by Mister Moose; 03-04-2021 at 06:49 PM.
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Old 03-04-2021, 06:45 PM   #3
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Default Re: What is Engine 'Break-in'??

Hmmmmm. I recently had my engine rebuilt. I know 2 things:

1) My rebuilder was very specific about me running it at varyed sppeds, and not on jack-stands either. 20 - 30 MPH for 20 to 30 miles to start with. He also wanted me to use very specific oil, but then he gave me a bottle of ZDP to add to that oil. I have already ran the engine around the neighborhoods for about 30 miles.

2) The reason my engine needed to be rebuilt to start with was because my crankshaft snapped. When you speak of machining techniques, I recall sending my crankshaft over to what I thought was the most notable shop for Model-A engines I knew of. That expensive place in PA. It was machined wrong. I had it turned, counterwighted, and balanced. It was also balanced and matchmarked with the flywheel and pressure plate.
Turns out there were 2 surprises to that machine work.

Brent, I'm interested to see the further comments to this thread since I am not a machinist expert.
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Old 03-04-2021, 06:51 PM   #4
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Default Re: What is Engine 'Break-in'??

Was this a case where someone had rebuilt the engine himself, or had bought the rebuilt engine from a builder? If the latter, you definitely follow the builder's advice, not random people on message boards (present company excepted, naturally). The builder has an incentive to minimize come-backs, so he should be giving advice that works on his engines.
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Old 03-04-2021, 07:02 PM   #5
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Default Re: What is Engine 'Break-in'??

Not wanting to start anything . When should the first oil change be done. I am right now waiting for my oil to fully drain from newly rebuilt engine. Oil is cheap and I have the time, I am doing it at 250 miles then from this point on every 500 - 700 miles.
Brent and others what is your opinion on the mileage of the first oil change. I do enjoy and value the wisdom, thoughts of the group as whole.
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Old 03-04-2021, 07:09 PM   #6
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Default Re: What is Engine 'Break-in'??

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I agree with both Brent and Moose. In 1930, a model a engine probably required a break in period. In 2021 a new Corvette does not. My question would be: do/can modern parts and machining eliminate the need on our old engines? Are their any builders of these old engines that can do the work to the required precision?
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Old 03-04-2021, 07:35 PM   #7
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Default Re: What is Engine 'Break-in'??

My take is that break-in of engines from decades ago is solid. Heat cycles and moderate engine speeds are good to keep spot temperatures down until surface friction is reduced by the break-in process. My own experience has convinced me long ago that varying RPM's does help seat rings better. A corvette engine has the advantage of a modern cooling system, high pressure oiling, speed limits and gearing that won't strain engine parts, and especially the advantage of modern metallurgy that older engines do not. There is a huge difference between the life-span of modern crankshafts vs those made even during the fifties and sixties.
edit:
Regarding ring seating; the varying cylinder pressures associated with increased throttle and decreased throttle (esp under load) help the rings seat. Whenever I rebuild one of my bikes, the first thing I do is get riding in the hills. This is true for four-strokes but especially true for two-stroke engines which I have rebuilt countless times.

The cylinder honing process used today in new modern engines is a far cry from the old days..
Here's an article which explains plateau honing...
https://www.productionmachining.com/...cation-control

Last edited by kawagumby; 03-04-2021 at 08:33 PM.
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Old 03-04-2021, 07:50 PM   #8
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Default Re: What is Engine 'Break-in'??

I'm in pretty much the same camp as Stingray70 and kawagumby. New engines these days are made to tolerances not possible when our cars were made and out of materials not available using techniques they couldn't dream of. An engine rebuilt by the best workshop today will only be to about the standard Ford attained in the day. I don't think it is reasonable to compare a new engine with a Model A engine, new or rebuilt.
The engineers of the day knew what they were on about and they were quite strong in their recommendations that an engine be run in properly. That'll do me when dealing with one of their engines.
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Old 03-04-2021, 09:55 PM   #9
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Default Re: What is Engine 'Break-in'??

When did Ford start running the engines in on electric motors? I've seen the flathead V8's but what about the I4's?
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Old 03-04-2021, 10:07 PM   #10
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Default Re: What is Engine 'Break-in'??

Ford was "burning in" Model T engines in the teens with external sources.
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Old 03-04-2021, 10:15 PM   #11
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Default Re: What is Engine 'Break-in'??

I was maintenance supervisor for a 250 tractor/500 trailer fleet.During that time the fleet was in transition and I oversaw the rebuild of 40 CAT 3406E diesel engines.The truck would come in,we would kit it,slap on heads and bearings,inspect the rest and ship it..put the truck right back out spending 90% of its time fully loaded.no failures,no accelerated wear noticed in oil samples..build it correctly and run it.
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Old 03-05-2021, 01:29 AM   #12
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Default Re: What is Engine 'Break-in'??

Modern engines and modern engine builds using modern components (IE roller cams, roller rockers, etc) don't suffer from the same issues as hydraulic or solid flat tappet cam setups. Incorrect break-in of a flat tappet cam is a notorious cause of flattened lobes. I've done it and have seen it done many, many times.

I worked in a machine shop with a cam grinder who had 50 years under his belt and he told every customer the same thing, break in the cam. Vary the rpm for 10-15 mins, don't let it idle. Keep the oil pressure up and the lifters spinning (flat tappet cam lobes are ground with a ramp to force the lifters to spin to prevent them from wearing a flat spot in them). The dyno shop we use does the same thing and they test motors day in and day out. They wouldn't waste 20 mins of dyno time if it wasn't necessary.

Now, how that concerns a Model A? If I was swapping in a new cam, I'd break it in. Rings, new pistons, etc. Probably not.
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Old 03-05-2021, 07:20 AM   #13
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Default Re: What is Engine 'Break-in'??

The Model T engines were indeed "burned in." The engine was assembled with the main bearings so tight that the crankshaft could not be turned by hand. The engine was mounted on the burn in machine up side down and oil was applied by an oil can to the main bearings. The crankshaft was turned over with a large electric motor until the bearings were literally so hot that the oil was smoking. When the bearings cooled down the babbett was fitted to the crankshaft with the right clearance. The rod bearings and the rest of the engine was fitted during the breakin period.

In my experience, the bearings will tighten up when hot and when cool again will have the correct clearance. For my newly rebuilt Model T engine, I could not crank it if I stalled it when hot. I had to wait until it cooled off. These were babbett bearings. I am not sure if the same thing is true of insert bearings.
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Old 03-05-2021, 08:38 AM   #14
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Default Re: What is Engine 'Break-in'??

The Corvette has been used in a couple of post as a comparison but I took a tour of the plant in Bowling Green, KY and the last thing they did to a corvette was put it on a dyno and open it wide open! Same with the Harley factory in PA. Don't know if its right or wrong but that is just what they do.
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Old 03-05-2021, 08:54 AM   #15
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Default Re: What is Engine 'Break-in'??

I've built flat tappet, roller lifter and hydraulic lifter cammed engines, with cast and forged camshafts, been in the trade 40 + years, have never seen a cam fail on break in.

The ones that amuse me the most is the snake oil salesmen selling zinc additives. Modern oil designs do work, additives to aide load and shear, as well as detergents help us...but the high dollar 'racing' additives you must have to break in a cam?.. its a myth perpetrated by those who profit off the product.
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Old 03-05-2021, 10:24 AM   #16
BRENT in 10-uh-C
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Default Re: What is Engine 'Break-in'??

Quote:
Originally Posted by PotvinV8 View Post
Modern engines and modern engine builds using modern components (IE roller cams, roller rockers, etc) don't suffer from the same issues as hydraulic or solid flat tappet cam setups. Incorrect break-in of a flat tappet cam is a notorious cause of flattened lobes. I've done it and have seen it done many, many times.

I worked in a machine shop with a cam grinder who had 50 years under his belt and he told every customer the same thing, break in the cam. Vary the rpm for 10-15 mins, don't let it idle. Keep the oil pressure up and the lifters spinning (flat tappet cam lobes are ground with a ramp to force the lifters to spin to prevent them from wearing a flat spot in them). The dyno shop we use does the same thing and they test motors day in and day out. They wouldn't waste 20 mins of dyno time if it wasn't necessary.

Now, how that concerns a Model A? If I was swapping in a new cam, I'd break it in. Rings, new pistons, etc. Probably not.

Unfortunately you are leaving out several things in forming your opinion. When you factor in the quality of lubrication has changed immensely over time, the wear additives in modern engine oil alone allow for less chance of premature wear. We now have modern cam lubes that are meant to circumvent cam wear as it is very hard to wipe off this lube.

You also hit on one major thing that many Model-A rebuilders overlook. Tappet bores are often worn, and when a tappet is pressed against worn bore walls, it generally only has pressure contact in the extreme lower and opposite side upper. This generally causes a tappet to be unable to rotate. So when this machining step is omitted, the engine rebuilder is hoping that varying the RPMs will try to make the tappet rotate enough where the camshaft lobe will not be wiped out.

With all due respect to your camshaft grinding friend, there is MUCH in technology that has changed where his methods are obsolete. The engine machining tooling and supplies are different now. It isn't just engine machining that has changed in 50 years, ...look at paint & materials, battery technology, gasoline, fabrics, etc. and notice how much has changed.


I will also share with you that any performance Dyno shop that runs an engine for 15 minutes is doing that out of ignorance, -or you are mistaken. They have never done any of my engines that way, -and I have many close friends in the performance engine business and they don't dyno that way either. In the class we race in, a top quality engine is between $35-$40k, These engines are good for 1,000-1,200 laps. With lap times under 20 seconds, every 3-4 laps equals a minute. At an average cost of $35 per lap, I would not be interested in wasting $2,000.00 of run-time just sitting on a dyno listening to it run! Neither is anyone else!!
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Old 03-05-2021, 10:30 AM   #17
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Default Re: What is Engine 'Break-in'??

Quote:
Originally Posted by nkaminar View Post
The Model T engines were indeed "burned in." The engine was assembled with the main bearings so tight that the crankshaft could not be turned by hand. The engine was mounted on the burn in machine up side down and oil was applied by an oil can to the main bearings. The crankshaft was turned over with a large electric motor until the bearings were literally so hot that the oil was smoking. When the bearings cooled down the babbett was fitted to the crankshaft with the right clearance. The rod bearings and the rest of the engine was fitted during the breakin period.

In my experience, the bearings will tighten up when hot and when cool again will have the correct clearance. For my newly rebuilt Model T engine, I could not crank it if I stalled it when hot. I had to wait until it cooled off. These were babbett bearings. I am not sure if the same thing is true of insert bearings.
This is a sign of poor engine machining where the journal pin is not truly round, -and/or has taper from a plunge grinding with a worn machine. Often times, engine rebuilders will assemble an engine tight like you are describing with the hopes that it will clearance itself.
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Old 03-05-2021, 10:49 AM   #18
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Quote:
Originally Posted by Synchro909 View Post
I'm in pretty much the same camp as Stingray70 and kawagumby. New engines these days are made to tolerances not possible when our cars were made and out of materials not available using techniques they couldn't dream of. An engine rebuilt by the best workshop today will only be to about the standard Ford attained in the day. I don't think it is reasonable to compare a new engine with a Model A engine, new or rebuilt.
The engineers of the day knew what they were on about and they were quite strong in their recommendations that an engine be run in properly. That's do me when dealing with one of their engines.
This is not really an accurate statement. As I mentioned above, technology has changed immensely, so people should not assume anything. Ford engineers were dealing with several differences between their technological timeframe and today's. Ford was dealing with unseasoned cast which today's machine shop typically has seasoned castings to work with. Second, Ford engineers did not have near the quality of engine oils like today. The machines that we use today in the rebuilding industry can hold tolerances that even OE production engines do not try to meet. (This is why performance shops offer 'blueprinted' engines)

As mentioned above, the abrasives used for machining in the day vs. today are hugely different. Today, most rebuild shops are using diamond and CBN stones where the tolerances can be held to tenths measurements. Additionally, parts such as the alloys in modern pistons, the modern ring compositions, and today's valve & guide materials allow for much tighter tolerances to be used. Therefore we can (-and should) be producing a product that is much better than original with respect to longevity. We do this in other areas of the restoration such as the quality of paints, fabrics, tires, glass, etc. So why do we accept less when it comes to engines?
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Old 03-05-2021, 11:22 AM   #19
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Default Re: What is Engine 'Break-in'??

I don't have sufficient theoretical nor practical knowledge to be able to comment credibly on this. However, I want to compliment Brent on his occasional thought-provoking comments calling into question many of our long-held but not necessarily re-thought practices.

So often we accept what have been traditional practices without going back to fundamentals and examining if the practices are supportable. For example, I was taught many eons ago to always dunk head studs and nuts in STP before torque. Why? Because "that's the better way to do it". We now realize that the friction of the threads on the nuts is a fundamental part of the torque spec unless we are given a "wet" torque value by the engineers. Wet torque to a dry torque spec may result in overstressing.

Rethinking the old saws is never a bad thing to do.

Respectful discussion is how we all learn, and this is a great forum for this. Keep it up, Brent!

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Old 03-05-2021, 11:42 AM   #20
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Default Re: What is Engine 'Break-in'??

"The (mis)use of gasket sealers (Copper Kote, et/al) often hinders the thermal expansion & contraction of the gasket which will affect fastener torque ratings being met."

Brent, are you saying not to use any gasket sealant on a new head gasket?
What gasket do you recomend for Snyders 5.5 head ? Thanks !Mike

Last edited by Mikeinnj; 03-07-2021 at 03:59 PM. Reason: typo
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