What is Engine 'Break-in'??

[BRENT in 10-uh-C]

Originally Posted by Bud

Do modern builders bore and re-bush the tappet bores? I would think most do not, but I cannot be sure.

Former MAFCA Tech Director Jim Cannon and I were discussing this a week or so ago regarding someone he was helping on finding a noise. I have a special Go/No Go gauge made to check Tappet Bores diameters that is 0.5945 & 0.5960. The print calls for the bore size to be 0.5940" - 0.5945" and that was meant for about a 0.001 total clearance(-½ thou per side). As long as the .960 end does not fit into the bore, then I usually will let it go.

I would venture a guess that maybe less than 50% of the blocks I check are worn enough where the .596 will go in, -but many will have a lot of clearance with the .5945 portion of the gauge inserted.

Several of the Model-A vendors offer a 0.005" oversized tappet to use however set-up to accurately machine the block for these is a little labor intensive. Sure, it is not that hard to run a hand reamer thru the bore to "open it up", but if that is done without a fixture, then the bores can be out of alignment from each other and/or the camshaft. (You really need a fixture built to index off of the main bolt datums.) Like with most things, a good machinist can correct many of these problems if he has the budget to do so.

[Bud]

Is the original tappet drilled as I described, with the central drilled hole and the cross drill?

[GeneBob]

From reading through this I can see a few things that stand out:
1. Brent will always have a contradictory answer to anything and everything.
2. I am sure we are all impressed with the cost of the racing engines.
If the racing engines were properly broke-in, maybe they would last longer.
3. If you take your engine to a shop and ask them to apply their expertise and best judgement to the machining and assembly of your engine, LISTEN TO THEM. They put their blood, sweat and tears into becoming experts in engine rebuilding. When you get the engine back, it is a reflection of their work so they get to tell you how to handle the baby they just returned to you. Yes, you paid for their expertise but it is still their engine during the break-in period. If you do not listen to them and your engine craps out, see how far you get with "Well, I read a blog that said..."

[john in illinois]

Bud ,I think the tappets are continually oiled from the oil pump. It pumps oil out into the valve chamber , out the side drain pipe and to the timing cover.


John

[Mister Moose]

Originally Posted by GeneBob

From reading through this I can see a few things that stand out:
1. Brent will always have a contradictory answer to anything and everything.
2. I am sure we are all impressed with the cost of the racing engines.
If the racing engines were properly broke-in, maybe they would last longer.
3. If you take your engine to a shop and ask them to apply their expertise and best judgement to the machining and assembly of your engine, LISTEN TO THEM. They put their blood, sweat and tears into becoming experts in engine rebuilding. When you get the engine back, it is a reflection of their work so they get to tell you how to handle the baby they just returned to you. Yes, you paid for their expertise but it is still their engine during the warranty period. If you do not listen to them and your engine craps out, see how far you get with "Well, I read a blog that said..."

Fixed it for you.

It occurs to me that the degree of precision machining that goes on with your 90 year old engine overhaul will be a function of both how stock you decide to keep it and how much money you have the budget for modern improvements.

[BRENT in 10-uh-C]

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Originally Posted by GeneBob

From reading through this I can see a few things that stand out:
1. Brent will always have a contradictory answer to anything and everything.
2. I am sure we are all impressed with the cost of the racing engines.
If the racing engines were properly broke-in, maybe they would last longer.
3. If you take your engine to a shop and ask them to apply their expertise and best judgement to the machining and assembly of your engine, LISTEN TO THEM. They put their blood, sweat and tears into becoming experts in engine rebuilding. When you get the engine back, it is a reflection of their work so they get to tell you how to handle the baby they just returned to you. Yes, you paid for their expertise but it is still their engine during the break-in period. If you do not listen to them and your engine craps out, see how far you get with "Well, I read a blog that said..."

...........

[BRENT in 10-uh-C]

Originally Posted by Mister Moose

Fixed it for you.

It occurs to me that the degree of precision machining that goes on with your 90 year old engine overhaul will be a function of both how stock you decide to keep it and how much money you have the budget for modern improvements.

That shows how little he knows. Unlike rebuilt Model-A engines, racing engines do not come with any warranty expressed or implied.

I think your comment regarding a 90 year old engine overhaul is pretty accurate.

[Dave in MN]

Later....
I have a full schedule today, breaking down three engines and breaking in one!

Now it's later...And the engine is through with the "break-in"

"Dave, I do like your thinking regarding snapping the throttle closed to induce oil movement however I am unsure if it will work that way. Work with me to establish how this works. If the piston is at TDC, the oil that is on the cylinder walls is typically below the bottom oil ring as slinging it around is always under that control ring."......

Brent, I realize most of the oil on the cylinder wall is below the lowest ring. The assumption you make disregards or is not mentioning the oil deposited between and above the oil control rings and not factoring the machined slots and holes from the interior of the piston into the lowest oil ring groove. Oil is free to move in either direction through these lower ring groove openings. Excess oil removed/scraped from the walls is passed to the inside of the piston and oil from the oil mist in the crankcase is free to enter these areas in the reverse direction as well. The oil around the lowest ring is the oil I am trying to redistribute.

IMO: Blow-by past the top and middle rings will impact the oil within the lower ring assembly. Most often it will move the accumulated oil to the interior of the piston, would be my assessment. Quickly closing off the throttle plate on an engine at operating speed will change or maybe slightly reverse the oil movement around the lower oil ring(s).

My theory it that any change in the cylinder pressure, assuming there is some blow-by, will cause an interruption to the movement of the oil retained in the oil control ring assembly and could deposit some of that oil above the top ring of the assembly when the cylinder is trying to draw in air with the throttle plate closed. Doing so would provide a bit of additional oil to the middle ring and to a lesser degree to the top ring especially if these rings are not fully seated yet. My belief that I am redistributing some oil around and between the middle and top rings and is why I snap the carb closed a couple times early in the running.

My goal in snapping the throttle closed is to slow down the generation of heat being developed between the middle and top ring and the cylinder wall.

I can usually think of two reasons as to why I do something. While doing the "Snap the throttle closed" I am also listening to the engine perform. I am studying the result and listening for any errant sounds. I cannot say I have ever heard any but nonetheless, I am studying the result.

Thanks for your study Brent, it's always interesting.
Good Day,
Dave

[GeneBob]

There used to be 2 schools of thought on break-in; baby it for 600 miles to gradually wear in the parts and "run it like you stole it". I lean toward the baby it for a while but regardless of which you choose, you are breaking in the engine in the first few hours of operation. Simply stating that it doesn't need to be broken in does not change the reality of what is happening inside the engine. No amount of precision machining will change the fact that the engine is breaking in when first run.

[Flathead]

I think post #49 pretty much sums it up. Thanks GeneBob.

[daren007]

Do race car drivers and dragsters break in their engines.

[PotvinV8]

So the consensus says?

I haven't seen a single example in favor of the "anti-break-in crowd".

[alexiskai]

Originally Posted by Mikeinnj

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

This question got overlooked in the melee. Gasket sealant should not be needed on a rebuilt engine, where the block and head have been milled correctly with the correct surface roughness.

[BRENT in 10-uh-C]

Originally Posted by PotvinV8

So the consensus says?

I haven't seen a single example in favor of the "anti-break-in crowd".

Ummm, I think you have. If you read in some of the links you provided, it speaks of running an engine at a constant speed. That was the intent of the first post was to discuss the mindset of why varying the RPMs. Starting an engine to verify leaks and to build temps to thermally cycle the engine so retighten head nuts and like fasteners can be done is not really "breaking-in" an engine as this is done in a much shorter timeframe. In a subsequent conversation with a Model-A camshaft manufacturer, he agreed that he does not break-in his own engines.

Originally Posted by alexiskai

This question got overlooked in the melee. Gasket sealant should not be needed on a rebuilt engine, where the block and head have been milled correctly with the correct surface roughness.

Colin, Mike also reached out to me via a PM and I answered him there.

[BRENT in 10-uh-C]

Originally Posted by GeneBob

There used to be 2 schools of thought on break-in; baby it for 600 miles to gradually wear in the parts and "run it like you stole it". I lean toward the baby it for a while but regardless of which you choose, you are breaking in the engine in the first few hours of operation. Simply stating that it doesn't need to be broken in does not change the reality of what is happening inside the engine. No amount of precision machining will change the fact that the engine is breaking in when first run.

Yes, I agree how you say this. Maybe 600 miles to accomplish the rings sealing is excessive but I see your point.

Originally Posted by daren007

Do race car drivers and dragsters break in their engines.

No. A top-fuel dragster is generally rebuilt between racing rounds. Once reassembled, the engine is generally started to check for leaks, verify spark plug wires are installed correctly, to set ignition timing, and to seat the clutch plates. All of this takes place in less than 60 seconds. The next time the engine is started is prior to doing a burn-out.

In the NASCAR world, engines are started on the dyno and run long enough to bring to operating temps before the first pull is made. After the first pull, they will generally 'leak' the engine and then use a bore scope to check cylinder walls for abnormalities. They may make subsequent pulls to see if changing timing or jetting changes makes any performance gains, but generally the engine has sealed-up by the time it has reached operating temps (generally a couple minutes)

Just for clarification, there is a difference between warming up a new engine vs. breaking-in a new engine. Yes, both engines are operating however the length of time is vastly different, and the purpose is vastly different also.

[PotvinV8]

You haven't provided a single example supporting your case. I provided three.

I'm just trying to save someone the headache of pulling out a brand new cam with a flattened lobe. As far as engine break-in goes, that's the single biggest factor. Gasket sealing, ring sealing, etc is what it is. You can retorqued fasteners but you can't relube a flattened cam lobe because the engine was fired up and idled for 20 minutes while the operating futzed with the carb settings.

[johnneilson]

The articles referenced previously are for a different application, completely.
Apples to rhubarbs.
Cam material(s) and the PV specification does require breaking in the cam in some applications.

Most Model "A" motors, even the hot rodded ones do not require much of a break-in.
Cams do get spalled or have the nose flatted off, usually caused by other factors.

Even aircraft engines have this issue, but it is only at major rebuild time or if a cylinder is a substantially low output.

FWIW, the race motors will use a very different pist/ring combination that requires very little time to seal properly.

Best, John

[PotvinV8]

An interesting thread over on the "hot rod" forum...

https://www.jalopyjournal.com/forum/...stion.1223452/