breaking(lapping) in a new engine

[dolson]

Time to time the question comes up as to the proper procedure for (I prefer to call it) lapping in a new engine.

Advice runs from; Pay your money hit the starter button and ride it like you stole it. To, following the factory recommended guidelines.

If I may please indulge me with my thoughts on this.

The reason I prefer to call this period "lapping in" is that is what one is doing. Polishing metal pieces and form fitting different parts together by literally rubbing them together usually with a moisture barrier (oil) between the parts so that they do not actually touch. The oil acts as a lubricant and coolant and flushes minute metal particles away from the mating surfaces so they won't gall or burn the mating surfaces in the polishing and burnishing process.

No matter how fine a machining process (4 microns in the case of our crankshafts), you will always have hills and valleys on any part be it journals, bearings, whatever. The higher degree of polish, the smoother the parts are, also the greater the surface area. The greater the surface area the greater the load bearing and less heat and stress are being built up as a result of friction.
I know that one might think that the greater the surface area the greater the friction and heat, but when a surface is not polished, friction and heat are more localized to the hills I mentioned and they get really hot. In some cases hot enough to change the metal and not for the good. A polished surface absorbs this friction heat and is able to dissipate this heat better. Also, two polished surfaces will slide together easier than two rough surfaces.

As for how to lap in a motor, there basically are two schools of thought. Cane it's back side off from "0" miles or a regimented procedure. Actually, either one will do it. Since the mid 1960's I've built many engines. Most were racing engines. And about all of those were run-in long enough to break in the cam and then they had the ever lovin' bejeebers hammered out of them.
I didn't care about them as long as they did what I needed them to do, once. To me they were Dixie cups. I was running .0045 clearances, heavier oil and a lot of pressure to keep things from touching.

The long term engines I always did differently. A more regimented procedure. I Never baby an engine, they all have to earn their keep. But I worked them giving them a chance to breath so to speak.

The results that I have seen having been in the inside of an engine a time or two are that the hammer them type of break-in is ok for short term. It will get the job done quickly providing nothing bad happens. Like two bare pieces of metal whizzing around touching together. But I haven't seen this as a good long term solution.

They just don't have the longevity that a progressively lapped in engine does. Strong for short term but not for the long haul. They'll start making metal, bearing clearances will open up, etc.
Sooner or later this will happen.

Here we go, this is my busy theory.
As I said before, no matter how fine a machining process one has, there will be hills and valleys on the surfaces. The lapping in process is used to polish the hills down to the level of the valleys. This is done by friction which causes heat. When new, the distance from the top of the hills to the bottom of the valleys is the greatest. The heat caused by friction is greatest on the top of the hills. The faster the reciprocating mass is spun, the greater is the heat that is generated. It is also more localized to the tops of the hills.
All metals have a temperature where they start to break down. For the typical steel, around 650-700* F. For instance, a high speed steel drill bit. Anybody here drill something and start to hear the bit squeal? You've heated it beyond it's critical temperature and it started to break down and shed metal and get dull. Where, if you would have kept the RPM's down and used less pressure and more cutting fluid the bit will remain sharper longer. Heat is the enemy of metal.

This I feel is what is going on during a run it like you stole it break-in. Heat is localized to the tip of the hill and due to the high RPM, the temp. at that very localized spot is exceeding the metal's critical temp. and instead of polishing, the hill gets weak and soft and the minute particles start shredding and tearing off. Also, because metal expands as it gets hotter, that localized hill is getting hotter than the surrounding area, expanding and consequentially getting weaker and softer leading to increased wear in that spot down the road.

The above is in general.

I mentioned that I've built engines with about .0045 bearing clearance. This took into account heat expansion, oil pressure retention things like that.
Our triples have about .001-.0015 clearance. Pull out a dollar bill. That's .003 thick. Now, split that in half, then half again and you have the clearance on either side of our journals. Pardon me, but that's tighter than a B.... Well, that's really tight! And there's not much wiggle room there. There will be a lot of localized heat and the faster you spin it initially new, the hotter it will get.

So, the rotating mass in our engines is built to a very tight tolerance and come from the factory with a very fine finish, but that doesn't negate the necessity of doing the final polishing ourselves. That takes care of the bottom end.

Next, a lot of folks worry, IMHO, too much about the reciprocating mass. The breaking in of the pistons, rings and cylinder walls. Here again, we are lapping in the fit of the rings to the cylinder walls to make an effective seal, keeping the hot expanding gasses inside the combustion chamber and not leaking past the rings and walls. I have seen changes over the years and the improvements made in both materials used and initial bore finish is truly amazing. They seal quicker, better and longer lasting than ever before.

To me, it is important during the initial break-in or, here again lapping of parts, to keep the BMEP=Brake Mean Effective Pressure high.

BMEP is a theoretical average pressure in the combustion chambers. The higher the BMEP, the more efficient the engine is running at that time. Power can be said to be the same with high BMEP and lower RPM's or lower BMEP at higher RPM's.

So, higher BMEP is good. What do we do with that pressure? Taking a look at the top of a piston crown you may, depending on the application, see little tiny holes drilled around the circumference of the piston. Most hi-pref. applications have them. These holes lead to the inside of the top compression ring groove in the piston. This is to pressurize and force the top compression ring into contact with the cylinder wall. The higher the BMEP, the more force is applied to the back side of the ring pushing it into the wall providing a better seal.

Higher BMEP, as said, occurs at LOWER RPM with a greater throttle opening. Higher BMEP also keeps the combustion chamber and cylinder walls cleaner aiding in a better seal.

So, to put this all together, for longevity breaking, or lapping in a new engine is best done at high BMEP and lower RPM. This has several advantages.

1: You are running the engine in at it's maximum efficiency.

2: It's lapping and polishing the bottom end rotating parts at a lower RPM keeping metal heat as low as passable.

3: The combustion chamber pressure remains high aiding in sealing the piston compression rings. The oil rings are just there to provide a controlled amount of lubrication to the cylinder walls.

Another benefit of a controlled breaking-in procedure is at the upper top end.

How many of you watch NASCAR? Those that do, you will see in every race, cars that drop out or get way behind. The crews that are interviewed usually say that the engine dropped a valve or some other upper end trouble. A vast majority of these failures are due to valve spring failures.
A coil spring working in compression, meaning that when you compress it it's force is exerted out-wards from the center. Versus a tension spring, like a screen door spring, that when stretched wants to return to it's original shape.

Coil springs when new require a break-in too. Take a new coil spring and work it and pretty soon it will take a "set" or achieve a normalcy. You would see that if you take two identical springs and measure their length, that measurement would be the same. Then take one of the springs and work it. Compress it and let it relax. Keep doing this over and over. Then compare the two springs. You will see that the one you worked is visibly shorter that the other new, unworked spring. It has taken it's set and achieved it's normalcy which it should maintain for it's life.
Even though for a given application taking into account cam profile, valve size and weight, identical valve springs made from the same spring wire stock will take a set differently. That's why, after a true blueprinting one of the things a builder will check is the valve spring tension and length after a nominal engine run-in. Tension and lengths will change and then he will shim the springs as necessary to get all the springs the same. Adjusting preload if you will. Any spring that falls outside of a certain percentage will be replaced and the process starts over. (It's the attention to the little details)

Anyhow, if you start whacking a new spring before it's had a chance to achieve it's set, or normalcy, there is the greater possibility that stress fractures may develop in the molecules resulting in a weakness at that point. This could lead simply to a weaker spring that won't last over the long haul or even a collapsed and failed spring. So, they need a little working in too.


In summary, I look at the application. Race motors I never got emotionally involved with and didn't care whether they looked like junk on the inside after a race or not. After every race they were rebuilt anyway. As long as they did what I needed them to do. This included everything from little 292's to 494 and 523 ci B.B.F.'s and pretty much everything in between. That's just car motors.

My Sprint is a different thing altogether. She's my companion and emotional investment and after much deliberation I want to keep her for the long run. So her lapping in I handled very deliberately.

I kept to Triumph's recommend mileage and RPM schedule.
After the first 100 miles I could feel things relaxing and mileage improved.

After that I started to work her a bit. I'm blessed in that I live in an area with hills and mountains all around. The best way to get the BMEP up is to accelerate up a hill in as high a gear as you can without lugging the engine. You are packing in the air and fuel without buzzing the engine too much. You folks in Texas or Florida will just have to play on the ON-Ramps :razz: .

But this is it in a nut shell what I did. Up the hill then giving her a chance to breath and wash the cylinders down going down hill. All the time during the first 1000 miles getting more and more aggressive with the throttle. But, still staying within the RPM limits as we went along.

At 500 miles we changed the oil and filter, putting back in the normal break-in oil. Which BTW is a very good oil.
After 1000 miles we were pretty much riding normal, but I would still get on her going up hill.

Changed the oil again at 1500 miles. Again with the normal new engine break-in oil.

At the 3000 mile mark the oil was changed again this time going with a full synthetic oil. There really is no hurry to go with full synthetic as some would have you to believe.

During her life so far she has reached several milestones considering her engine characteristics.

100 miles, 1200 miles, 3500 miles, 5000 miles and, the last I think at about 7500 miles. At each point there was a change. More spinning, better mileage, something I could feel.

These are just my thoughts on the subject based on a few years of what I've observed. Those of you who find yourselves in the enviable position of running in a new engine are certainly capable of making up your own minds as to how you want to go about it.

I would make these cautions.

Lugging an engine is certain death. Lugging=being at too high a gear at too low an RPM asking for too much effort. This will pound the bottom end resulting in metal to metal contact and or putting enough pressure on the oil so it will actually blow particles of metal off the journals or bearings. Keep the BMEP high without lugging.

Sustained steady state freeway speeds. Parts stretch to a certain extent and need to. The higher the RPM the more things like rods stretch. You want to have full throttle and RPM capabilities. Loafing along at a RPM establishes wear patterns. The piston ring, for instance, will only go so far up the cylinder wall. The wear pattern establishes a ridge at the upper travel of the ring on the cylinder wall. This was more prevalent in older cast iron blocks but still is applicable to these more modern materials.

When RPM is increased, the rods stretch more and the ring will go higher, and catching on the lip that was formed at the lower RPM will wear faster or break or even deform the ring groove depending on the size of the lip and RPM involved. So, vary the RPM and run her up as you can to whatever limits you decide.

That's about all I'll have to say on this, So, go ahead and flame away :-D

Don

[REGULATOR]

sounds good to me, I actually followed Triumphs schedule almost perfectly on my break -in period, was a celebration of sorts removing the decal on the tank when completed.
I think my bike runs even stronger now that I'm getting closer to 12,000 miles on it

[rodneybrown]

Mr. Dolson,
I go along with a lot of what you say but not all. One point I agree on is that 500 miles is too early to go full synthetic on Triumphs. Let's make a point here, Triumph recommends going to full synthetic Mobil 1 4T Racing at 500 miles. On my next bike I will dump the oil and filter at about 100 miles and put more "breakin oil" until at least 1000 miles, maybe even a bit more. That I would do for the rings to "lap in" but as far as the rest of the engine I'm not sure I buy all that you say. First, remember the days of "blue printing" engines. Don't hear much about that anymore do you? Also, you used to hear about breaking in to knock off the burrs. Don't hear much about that either. I am NOT saying to bury it in the red from day one, but machine tolerances are MUCH, MUCH better now. (Anyone out there have a 1965 BSA Lighting Rocket or T120 with a 100K miles and original main bearings?) In your discussion of valve springs I think you may have touched on something else besides the lapping in. The engine needs to get heat treated just like a spring or a good knife. Whether it is hardening or anealing, metal parts of an engine do heat treat themselves during breakin to some degree. All I know is I have babied engines during the breakin period on too many vehicles and the results were less than what I expected. I ran both my RS and ST incrementally harder from first start and they both ran well. No matter what you do, I believe applying common sense tempered with a bit of mechanical aptitude, is the best path rather than absolute application of a manufacturer's decree who may have other motives in mind rather than giving you a strong, long lived motor.

[ This message was edited by: rodneybrown on 2006-03-12 14:50 ]

[AlaskaSprint]

Don -- Excellent info. on the ins and outs of running in a new engine -- thanks.

It sounds like you think periodic (not sustained) full throttle is OK within the factory break-in rev limits? Is that correct?

When I broke in my 05 Sprint last August, mostly on day rides from Missoula MT over Lolo Pass - Hwy. 12 in Montana and Idaho (what a great road to break in a Sprint on!), I used full throttle out of every corner, but within the factory limits plus 1,000 revs after 100 miles.

So far so good (2,200 miles), but I won't really know until I put about 60 or 80,000 miles on her, will I?

Cheers,
Jack

[Whisperinsmith]

Don, again more great info. Thanks. But now I wished that I kept the break-in oil in longer. I did exactly what the book said to do. After 500 (600 in my case) the dealer put synthetic in.

[pushr0d]

Dolson,

Nice work, thanks!

However, you don't address engine braking during the "lapping-in" process.

I was told by Scott Bartels to avoid engine braking during the period. His belief is that (if I've got this right) it is important to keep pressure on the piston until the rings are properly seated.

He also mentioned the rev limits, the avoidance of lugging the engine, and the variance of speed on the road.

I don't know if his system is 100% correct, but I've "broken-in" a H-D Evo and two Triumph 955's and none of them use(d) any oil to speak of.

Again, thanks for your post!

Steve

[dolson]

I was told by Scott Bartels to avoid engine braking during the period. His belief is that (if I've got this right) it is important to keep pressure on the piston until the rings are properly seated.

I totally agree with keeping the BMEP as high as you can for several reasons.

But I don't think that a little engine is as harmful as the other facts you brought up. Like, you can't be under power all the time.

Again, this is just my observations. My thoughts are that under engine braking there is always a little raw fuel going in the chambers. Not much but a little. For a very brief instant there is more fuel than it can handle and burn. This will wash down the cylinder walls a bit. Really, no harm in that as the oil scraper rings will wipe it again. But, I sure wouldn't want to go down a long down grade like that.

Don

[ST-ern]

Excellent post Mr D.

[upNorth]

On 2006-03-13 19:47, ST-ern wrote:
Excellent post Mr D.

Yes, thank you for the information. Especially timely for me as I am expecting delivery of a new Sprint any day.

FWIW, I broke in my Thunderbird exactly as recommended except for going about 600 miles before the first oil change. 39,000 miles later, the engine is as strong as ever.

[Green01SprintST]

I wore in my 01 as you described with the addition of engine braking. I had the break-in oil changed out at 600 miles and replaced with Mobil 1 per the manufacturer recomendation and so far, after 25 thousand miles, the engine runs like a top.

I believe engine braking during initial break-in is useful in that it creates higher than normal vacuum in the engine and would tend to draw oil into the combustion chamber past valve seals and rings, sort of a reverse flush if you will. Does it really work? I have no hard evidence that it does or does not, only the fact that my engine uses virtually no oil between 5K mile changes and, as I said, runs like a top.

Your results may vary.