Restorer32

Breaking in an engine

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Opening a discussion.  What does "breaking in" an engine actually mean? What physical changes happen as an engine is being "broken in" ?  Why is it suggested to run an engine at different speeds and under different loads during the "break in " period? What different forces are working on an engine at idle versus an engine under load?  What does "seating the rings" actually mean? 

Edited by Restorer32
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Most owners manual give instructions for breaking in a new car engine. Basically, take it easy fo a specific number of miles

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Yes, but why ? That is the question. There are 1000 ways folks say is the best way to " break in"  an engine. What does "breaking in an engine" actually do to the engine? 

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"Breaking in" an engine is basically getting the piston rings to properly seal against the cylinder walls.

 

In the old days, this was important because of the material and tolerances in the engine.

 

Modern engines don't really need a break in period, as the tolerances are so close that everything is basically seated from the factory.

 

There's not a lot of science to discuss, unless you get into analysis of tolerances, materials, machining and honing methods, and so forth.

 

Even Hastings, on their website, sort of glosses over the subject, see attached. https://www.hastingspistonrings.com/tech-tips-faqs/compression-ring-seating

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Freshly machined parts have a certain finish and fitment.  Breaking in an engine runs these parts under specific conditions so that they "wear-in" together, essentially polishing the surfaces of parts that wear on one another.  For older engines with conventional piston rings (as opposed to low-tension rings) and flat tappet cams and lifters (as opposed to roller lifters), this is an important process.  Both the rings and the lifters are primarily lubricated by splash oil, even in relatively new engines.  Running the engine at 2000-2500 RPM for the first 20 minutes or so ensures that the crank throws splash enough oil on these surfaces to prevent galling or damage during this critical wear-in period.

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Hey who opened this can o' worms???  Just kidding.  It's a worthy discussion of course.  Here's all my manual says about new car break-in....

Breakin.jpg

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I am told by the old guys that running a new engine at a constant speed will promote a ring ridge.

Therefore they recommend to vary speeds for the first 500 miles or so.

They will also say that a new engine should have oil with a lot of zinc in it, I guess that must harden some surfaces, especially around the cam and lifters.

I'm no metallurgist but I have rebuilt a lot of engines and don't have failures, so maybe this is good advice.

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25 minutes ago, JACK M said:

Therefore they recommend to vary speeds for the first 500 miles or so.

They will also say that a new engine should have oil with a lot of zinc in it, I guess that must harden some surfaces, especially around the cam and lifters.

 

This information is correct.  I was talking about the first 20 minutes once a rebuilt engine is fired for the first time, to break in the cam.  This is talking about the first 500 miles of actual driving.

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2 hours ago, JACK M said:

I am told by the old guys that running a new engine at a constant speed will promote a ring ridge.

This is the sort of thing this thread seems to be aimed at. ...... WHY? HOW?

 

Lets think about this (I am making this up as I go!). The piston goes up and the rings are forced to the bottom of the grooves in the piston. The piston is pushed onto the small bush and the rod is pushed onto the crankshaft. Is it possible that there is a certain speed at which the inertia of the piston and rod at direction change means they move UP a little further and actually pull the bearings rather than push on them? Hmmm. But if that were the case, why did they specify low speeds like 30 mph? No, that can't be it.

 

Maybe varying speeds means the engine will be working, coasting, working lightly and so on. When the engine works, more fuel is burnt and the combustion chamber temperatures might increase? On coasting, those temperatures reduce. Maybe this temperature cycling is really what the designers want? At constant speed, there is no temperature cycling. And at fast idle with no work, the temperatures are lower and over a fairly constant cycle.

 

So if it is temperature cycling the designers want, why? Maybe expansion of the components at high temperatures causes more friction and the high spots can wear off a little. With a lower temperature period following, any local friction-induced high temperatures can dissipate without doing damage. The next higher temp. cycle, more high spot wear occurs?

 

But this doesn't explain the ring ridge at constant speed. Is it possible this is a myth?

Edited by Spinneyhill (see edit history)

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This is what Dyke's 18th Ed. 1937 says about it.

IMG_0769.thumb.JPG.f2f956d5fd0be712a3dafb6adfc5650b.JPG

IMG_0770.thumb.JPG.e45b66e1e4159aa95c5d7d0364051bea.JPG

 

Note also the paragraph near the top on the first image, starting "Remember one thing:" about the use of cheap oil! Still applies. :)

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2 hours ago, JACK M said:

 

I'm no metallurgist but I have rebuilt a lot of engines and don't have failures, so maybe this is good advice.

 

Interesting info emerging here.

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You have to think microscopically what the newly machined and ground surfaces are really like - sharp mountains and valleys.

 

The reason for varying the speed and load is to wear in the cast iron rings and bore without glazing them with microscopic wear particles jammed into the microscopic valleys.  Those sharp mountain peaks cause drag, so they give less friction when they wear smoother. But you need some of those tiny valleys kept clear to act as reservoirs to retain some oil. If they become clogged the surface won't lubricate the same.   

 

When you accelerate, the cylinder pressure increases. That pressure gets behind the rings thus pushing the rings outward against the bore. That's why rings have a top and bottom and beveled inner edges - to allow the high pressure gas to slip between the piston and ring.

 

When you lift your foot to slow down, the vacuum in the cylinder goes up and that high outward pressure on the rings goes down, thus helping to pull some fresh oil up past the ring faces to flush the wear particles into the oil pan.

 

If you've ever looked at drain oil after the first couple of hours of running-in new cast iron rings and a freshly honed bores, it shimmers with the iron particles. And there is so much fine particles suspended in the oil that you can write your name in the oil by holding a magnet just above the oil surface.   Sometimes it freaks out the customer the first time they see all that floating in relatively new oil.

Edited by PFitz (see edit history)
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Amsoil has recently come out with a very sophisticated SYNTHETIC BREAK IN OIL (!!!!!). Look it up. Their explanation is eye opening. They are very specific and info oriented , which you all will enjoy. As I always must say , I am not affiliated with , nor have any financial interest in Amsoil. I just use their lubricants. If you can prove better , I will change to it. The very best is none too good for my machinery.   - Carl 

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26 minutes ago, C Carl said:

Amsoil has recently come out with a very sophisticated SYNTHETIC BREAK IN OIL (!!!!!). Look it up. Their explanation is eye opening. They are very specific and info oriented , which you all will enjoy. As I always must say , I am not affiliated with , nor have any financial interest in Amsoil. I just use their lubricants. If you can prove better , I will change to it. The very best is none too good for my machinery.   - Carl 

 

 

Thanks, Carl. This explains it better than I could.

https://www.amsoil.com/shop/by-product/motor-oil/racing/break-in-oil-(sae-30)/

 

Anyone wanting to know more about what happens during break in, scroll down to read it all.

 

Paul

Edited by PFitz (see edit history)

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I have not read the above links, so if I am repeating information.....oops :).  One of the bigest issues with breaking in a new or rebuilt engine is, as stated above, causing and allowing the newly finishes, machined, honed parts to wear into each other. The reason for varing speeds and loads is to keep resonaces (think vibrations) from causing a repeating pattern of wear and therefore not making things wear togeather. It is a bit hard to explain how resonance happens in a heavy engine, but it definately can and does happen from time to time.  Think about how a wind chime vibrates to make a tone when the clapper hits the tubes. An engine firing at a constand rate and load does the same thing to the moving parts. By changing things a bit the place where something happens changes and therefore does not form a pattern.  This is what I have been told through the years and as a hobby machinist I have seen the results of vibration on precision fitted parts. I am sure there is much more to it, so I will keep an eye open for more information....

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