In another thread on this forum regarding FE cranks, some of us "accidentally" hi-jacked the thread. In order to be a good FTE citizen, I am moving this discussion into a new thread.

I decided to summarize portions of the original thread so that new readers would not have to go read the other thread. If you find all of this to be too many words for you, please do not waste your time wading through it and then complain. This thread is about getting to the bottom of a simple question that requires a complex answer. I hope we can draw from FTE resources on both the side of real, first-person hands-on in-the-shop experience on one hand AND education & industrial experience in metallurgy & engineering on the other. I am repeating 100% of my posts. If my summaries of others' ideas are incomplete, I invite them to repeat and amplify their ideas in this thread.

It will not help if there are a lot of posts about opinions -- this is not a poll or even a democracy. It is an effort to find a real explanation about why blocks seem to have different hardnesses in their cylinder walls. If you do not understand a technical point, you are probably not alone, so feel free to ask for an explanation.

The other thread started to become hi-jacked: Crank strength is important, but at high horsepower, the block's strength and rigidity becomes an issue. Then which block is best, which block is strongest, what alloy differences there are in blocks, and finally, why are some blocks harder to bore than others were all brought up. (Remember hardness and strength go together in metals, so hardness is not irrelevant to a strength discussion.) Is high nickel content a myth? What causes some blocks to be harder to bore than others - is it overheating?

I contributed to the hi-jack by posting: From Steve Christ's Big Block Ford Engines: "All FT blocks are cast of high-grade-alloy iron with manganese, silicon, and other alloys added to improve durability."

continued next post . . .

 

And then I added: "Other alloys" could definitely include nickel and chromium in small quantities, especially if some scrap iron was added to virgin iron, which is likely. (If someone KNOWS that Ford used 100% virgin iron, please feel free to contradict me.) While these alloys do improve the "durability" of the blocks, it is unlikely that any extreme difference would show up during boring.

"High-grade-alloy iron" does NOT mean "high-alloy" - it most likely means that the alloy percentages are very low, but "highly controlled'. Carbon content in cast iron is already 3-4 times what is in high-carbon steel, and although the content can vary, the properties are not very dependent on carbon content once it is over 3%.

Regarding overheating, or anything I can think of, a cylinder wall should not be able to get harder from an overheat because the iron has to reach over 1300 degrees Fahrenheit in order for a transfromation to austenite to take place and then it would have to be quenched rapidly to form martensite (the hard form of an iron-carbon solid solution).

I am not saying that some blocks are not harder to bore than others, & I certainly will entertain a dialog on this subject. I am just saying that it is hard to see quench & temper hardening occurring during an engine overheat unless it got driven off a bridge into ice-water.

I am still trying to understand why some blocks are difficult to bore - I take that as an observed fact. Many of us had had a flywheel that had hard spots from severe abuse. These can make turning impossible and hence flywheel grinding has taken over. This is a different situation. The face of a cool flywheel is subjected to some severe clutch slipping and can get red hot while the majority of the flywheel volume remains cool and the heat is transferred rapidly, giving the quench. An overheated engine or any operating circumstance that comes to my mind, does not give the same situation as the flywheel example.

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The question of quench-hardening of the cylinder's inside surface by oil or coolant was broached and I responded: Considering quench-hardening is fine, but the mass of the oil is nowhere near enough to cool the wall rapidly enough - think quench hardening by spraying hot oil droplets on the red-hot part instead of stirring it in a tank of cool oil. Also the oil control ring keeps the oil from getting to the upper half of the cylinder. I will allow that there might be a shallow surface effect, but someone will have to tell me that the top half of the cylinder acted different than the bottom half during boring for me to believe that the oil is doing the quenching.

The coolant in the water jacket might be the correct temperature for a slow (marginal) quench, but it is separated by the cylinder wall's thickness. This is why I mentioned the flywheel example where a rapidly changing thermal situation results in hardening. This is also how induction and flame-hardening work. The surface of a cool piece of metal is suddenly heated near red hot and just as suddenly cooled by the mass of metal under the surface. In the case of a running engine, everything is in sort of a "steady state". The cylinder inside wall surface is at its operating temperature and the coolant is at its operating temperature. The small thickness of the cylinder has a rather severe temperature gradient which is possible because cast iron is not a very good conductor of heat. Upon overheating, everything just gets hotter, water goes to steam, the whole cylinder wall can go red hot, but there is nothing cool around to give a good quench.

My resident metallurgist (PhD-Materials-Stanford, really) and I (only a MS in Materials) are kicking this around. All we have come up with so far is that scuffing by severe ring friction might lead to carbide formation in the glazed area. Is it observed that the hard area continues at the bottom of the cylinder past the ring travel?

We will pick up in this thread is with the following question:

What is going on with blocks that are harder to bore than others? Is it metallurgy (nickel?) or the block's history (for example: overheating or other abuse) OR BOTH?

 

One thing I want to clear up, especially due to my PM's with Archie, is the statement I made about a 360 block from a '70's pickup being harder to bore than a passenger 390 block I had.

Big difference? One was from about 1974, the other from 1968. So it's not a "truck" vs. "passenger car" thing. It's more likely it's an earlier casting made with different stuff.

And on edit: "harder to bore" means my machinist wanted to cut it shallower on each pass. So it needed more passes. Not so much that it was "harder".

 

I'll add that others had run into glazed cylinder walls that were highly resistant to boring until rigid-honed through a thin, hard glaze. The leading thoughts are alloy content vs heat treatment from overheating, and each side has refuted the other.

I am still wanting some more who either owned the block (like Art) or were the machinist to further describe this phenomon. I have heard of it, but all my experience in this is second hand. The main questions I have at this point are was the hard area from top to bottom of the cylinder and how deep was it?

 

I dont have a damn bitta knowledge on any of this but tend to rationalize things when possible. So I will go to Russ's no water left and only oil to splash on the walls. If the wall are hot enough te piston rings will speread the oil thin enough to have what we see in a pan of hot oil Iie (steam) from from the oil ? could be considered smoke ? I guess I'm asking what is the stuff lthat leaves the top of hot oil and what would it's effect be in the situation of it's precsence in the cylinder wall scenrio..? Just fishing here.. sorry if it's a stupider than stupid response..

edit:I should probably clear up my theory here. The piston would spread the oil on the way up the steam trailing off beneath the piston being scraped back down on the power/intake strokes.

 

Hey, Redmanbob, any number can play . . . My problem with the "oil quenching theory" is that oil can only absorb so much heat energy per ounce, so there might be some effect at the bottom where the oil splash hits the most. Anything in the bottom half of the ring travel will get less oil; anything above the highest travel of the oil control ring does not get much oil at all. The heat is distributed in the opposite direction - hot at the top and not so hot at the bottom, especially if the coolant has been boiled off in an extreme overheat.

You are correct that if the oil is heated enough to leave the cylinder wall as oil fumes (a gas) more heat will be removed because it takes energy to go from liquid to gas. This still seems to me to not be a rapid enough cooling rate to be that required for a quench-hardening effect in a low (or no) alloy cast iron.

If someone can post experiences of whether the whole cylinder wall was the same hardness, or just the top or bottom, then we can get farther.

P.S: The approximate 1,300 degrees F temperature required for quench-harden cast-iron is near the temperature where the aluminum pistons would be melting. I am not saying that a badly overheated engine cannot get this hot - I am just trying to show what kind of temperature we are talking about. I re-ringed my Dad's 390 after a lower coolant hose loss caused a bad overheating. The pistons survived, but cam bearings were starting to melt! The engine ran another 50,000 miles, but had a small crack in the block that let combustion gases into the water jacket. The new rings seated and the engine ran fine so long as the radiator was kept topped off.

 

And thinking even more about this, my machinist's reason for cutting the block slower was that to hone it out afterwards was a pain in the ***.

As in, the metal just moved around, it didn't "cut". My understanding was that the one block that cut well and fast was more brittle.

 

Probably we all already know this, but I'll throw it out anyway:

Remember that the earlier blocks (probably 1972 and earlier) were cast at DIF, and the later ones at MCC. Would it be that hard to think they changed the alloy a bit when they moved over the casting location?

 

Art, I can only try to explain what you & others describe. Grey cast iron is inherently brittle - that is the kind you find in blocks. (I mention this to distinguish blocks from cranks where Ford pioneered nodular iron, which is NOT nearly as brittle.)

If the metal was "moving around" the cutting tool (plowing is what machinists call it), this was a sign of softness and even ductility (the opposites of hardness & brittleness, respectively). I am afraid that this behaviour may just be too "distant" from describing to explain with out more data, such as a hardness test. It definitely has "morphed" into something quite different than RapidRuss' situation. He had to hone first to get through the glazed layer before he could bore.

It is my understanding that the reason that rigid honing up to as much as the last five thousandths of a cylinder bore job is desirable is that there microcracks that one would expect from boring a brittle material like cast iron. The slower, gentler process of honing removes the layer that includes these cracks, while maintaining a true cylinder and getting good size control.

Kurt, good point, Changing foundries would make for changes in composition, but even would changes in sources of scrap iron & steel available - even ore sources would all play into this discussion. The products of the manufacturing world are not as homogenious as one might expect. There is a real reason that aero-space manufacturing has tighter requirements - they need it and they pay for it. The automotive world is all about saving pennies and even 1/100th of pennies. Sometimes we hot-rodders forget that most engines were intended for low-stress lives. The exceptions are the FT's and 427's and they do not have near the level of control that exists in aerospace.

 

First off, I'm not a machinist. I can't answer the question about hardness through the length of the bore.

The alloy question: When I got into the forums three years ago there was discussion over at net54 about the "high Nickel" alloy. If you decide to search the topic, look for posts by Dave Shoe. The guy has reviewed a number of old Ford documents including engineering specs. and blueprints. He had yet to find a specification for higher Nickle content. At this time, nothing supports the claim. He also pointed out that Ford used primarily Phosphorus for added wear resistance.

As an anecdotal side note, Rod Ciocotte worked in Ford's foundries. He noted that if a pour was too hot, they would throw rejected crankshafts in to cool the batch for pouring. So yes, there will be variables from pour to pour.

Mechanical variables: Russ mentioned over-heat, I don't think he could know every variable that preceded those blocks coming to his shop. I can't imagine him asking what the compression was like, or if it burned oil, or how long was it run after the initial overheat, or if the engine failed at the event. Just too many variables to say "all other things being equal".

Your friend mentioned friction as a source of heat? I think that's part of the process. You mentioned constant state in an overheat condition, and question how that much heat can be removed for a case hardening process. My first thought was of abusing a Honda I once owned. The last two miles to work one day it was overheating. I left it in gear (I was on the highway), turned the ignition off and held the throttle full open. The rapidly expanding air and fuel (hydrocarbons, hmmm) cooled the top end enough to drive a little further. I don't think that's the answer here, the duty cycle between heating and cooling favored heat.

Since I work in the rail industry, I see a wheel condition called Shelled tread. What happens is that the surface of the STEEL wheel heats so fast that the thermal shock causes seperation from the base material. I think the "constant state" is important for that very reason.

You have thrown out some interesting stats about changing a material's crystalline structure. You mentioned malleability as a function of composition, no mention of heat? You quoted your friend's observation of heat as a function of friction (did I understand that right?), why not friction as a function of pressure? We don't think of a piston like we do a forge, or rollers, or a shot-peen, but we can talk about thrust and non-thrust areas in the cylinder.

So here is my lowly torch jockey's theory: Heat the inner wall to a higher state of malleability and apply pressure, you are going to increase the surface density. We are not changing the structure, merely rearranging it?

I don't know, ask the guy with the PHD if it's plausible.

 

Thanks for your contribution, Hypoid.

We could list all the things that are NOT in blocks, but the list would be pretty long! All the same, I would say that there are small amounts of nickel in almost all cast-iron other than that is made from 100% virgin pig iron, made directly from iron ore. These small amounts of nickel would not change the behavior of a block's cylinder wall, no matter what the thermal history, so I agree with Hypoid - nickel is not likely to be part of the effect we are talking about.

Phosphorous is another interesting alloying element. In many cases (especially in steels) phosporous is considered to be detrimental in most applications. Iron ore already has varying amounts of phosphorous, sulfur, and silicon, in addition to the iron itself. The refining process takes out the oxygen and adds carbon. Phosphorous and sulfur are usually reduced as much is economically feasable, although there are, as always, exceptions. Silicon and other alloying metallic elements are added to cast-iron. Upon consultation with my expert, all I can say is that IF phosphorous is added to the better blocks, it is a special case, perhaps because the cast-iron rings are running on a cast-iron wall. (A practical point is that the FT engines had chrome rings, making me wonder about this idea.) In most cases the effect of phosphorous in cast iron is to make it even more brittle. What the Ford records may have shown is that they did not always control the phosphorous - usually foundrys try to get rid of phosphorous.

At this point let me define the word "maleable". It is used a lot of ways, but to a metallurgist it means that the material can be deformed with plastic flow occurring. It pretty much means the same thing as "ductile" but ductile is associated with tension and maleable with compression. I doubt that there is any large amount of plastic flow of the cast iron in even the most severe cases of overheating - that there could be small amounts of plastic flow is what I will talk about next.

Following what I think you might be thinking of, there may be mechanical, plastic movement happening where the rings act on the cylinder wall. In this case, we are talking about material motion that is very small, but possibly has the effect of changing the hardness of the cast-iron cylinder wall's surface. (Quench-hardening is unlikely - my position at this point, but I will try to be open to any counter-argument.)

If quench-hardening is out, then the next most likely effect to explain a thin, hard layer on the inside of the cylinder walls would be strain-hardening, or "work-hardening" as it is called in the shop environment. Very slight plastic distortions can give large increases in hardness in some alloys.

Many of you reading have had problems drilling holes in stainless steels. If you keep up the cutting pressure, you can drill successfully, but if you ease off the pressure a little, but keep the drill engaged with the cut, you suddenly find that the character of the material has changed almost instantly. (For reference, the hard layer created is very thin and if you immediately apply serious pressure, the drill will break through the hard layer and continue on its way through the hole. If you wait to long to do this, you can get some experience in friction welding and your drill bit's end will end up welded to the bottom of the hole.)

The problem with this explanation is that unless iron alloys have a serious amount of chrome and nickel, they do not exhibit much tendency to work-harden. I have a "theory": it is possible to imagine a severely abused & overheating engine that has chrome rings, experiencing a transfer of enough chromium to the cylinder wall to change the alloy to have a greater tenedancy to work-harden. This is a long shot, but I will try to develop it further IF a machinist can tell me that the thin, hard layer was primarily in the area of the ring travel.

It is time to hear from the machinists . . .

 

There is no doubt in my mind some of you may remember back to the days of the flatheads. We would see blocks with 10 thousands or more taper, ridges in cylinders that were just unbelievable. Then about 1955 things started to change and these conditions began to go away. I realize we have reduced the load on the cylinders with low tension rings, lubricants have improved, but so have the blocks. I have no doubt in your observation of introducing alloys into the castiron that is used, and I doubt any of the cast is virgin, so who knows what it has in it. It may also have the cylinders flame hardened, perhaps even stress relieved in an oven, but I doubt that temps high enough to achive that are attained once in operation. Also what you may be seeing in the boreing operation are the same condition found in large brake drums where local hard spots exsist due to the other alloys which seem to concentrate in what appear to be small pools in the casting. My two cents.

 

kotzy, thanks for joining this thread - I will add my reactions to some of your comments.

A lot of the wear in the early engines was because they did not have full-time oil filters, so the grit just went around & around, lapping the moving parts. Note that Ford started full flow oil filters when they stopped making flat-heads and went to overhead valves.

Big foundrys try to control both the desired and undesired alloying elements, but are limited by economic considerations. They usually do KNOW what the actual composition of each "heat" is, if only after the fact. (In the old days, sample "coupons" would be kept for chemical analysis. Now-a-days analysis can be done in minutes before the pour is started.) There are ups & downs in the availability of scrap, but none of the variations is likely to change the alloy enough to leave the category of low-alloy cast-iron, which is not that likely to work-harden.

Read my clutch example given earlier in this thread. The same thing applies to brake rotors and drums, although I would expect that their castings are even less well-controlled with respect to alloy & impurities. In these cases, a short-term clutch slip, or panic stop can heat the surface red-hot while the rest of the body of the cast iron is still relatively cool, and then sucks the temperature of the surface back down, resulting in quench-hardening.

My South Bend lathe bed is flame-hardened, but I do not know of any automotive applications of flame-hardening. Caterpillar and many other diesels use high-carbon steel removable cylinders that are probably heat-treated in furnaces and quenched in oil or water. I don't think any cylinder walls that are integral with a cast-iron block are likely to be hardened. Although they could be flame-hardened, I do not believe Ford would have bothered. They would have to be finish-bored, flame-hardened, and then honed & assembled. I do not believe that they would spend the $$$ for the extra operation. (I would love to have somebody prove me wrong - this is only my opinion. If any Ford were to have a flame-hardened cylinder walls in any engine, I would think it would be the 391.)

 

So let me ask: How does Manganese affect the alloy? The Steve Christ book pretty much says it's in the FT (mirror 105) blocks.