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Synopsis: There is NO such thing as "Glaze Breaking." That's because there's no such thing, in a cylinder, as "glaze" - the word implies a deposit of foreign materials of some sort on your cylinder's surface. Unless you've been running with Teflon in your oil or some such silly thing as that, from whence would the foreign materials have come? Cylinders don't "glaze." Brake drums glaze - brake shoe material can actually become deposited on the drum surface, but cylinders don't.
No, what you've got is a smooth, polished, machine surface - just the thing for your new rings to seal against, once their high spots have been rubbed off in a careful and responsible break-in process. One which does NOT need to be preceeded by using the crudest of all the machine tools to scratch, abrade, trash, dog, bullyrag, and otherwise screw up your lovely smooth cylinder.
You see, the point is that, providing you use cast-iron piston rings, the rings will bed in to the shiny cylinder surface with few problems, and in a short time, too! Turns out that running an abrasive hone unecessarily through your cylinder will only serve to:
A number of years ago, I had the privilege of studying the Automotive Arts under than excellent teacher, as part of the work toward a degree in Industrial Education at the University of British Columbia. Said teacher, one Peter Trant, was a studious kind of guy, yet also a serious wrenchead - his qualifications included actually having worked in the business for a number of years, as well as the obvious academic ones. In short, the guy knew his stuff, both in terms of hands-on activity, and bookish research and knowledge.
So did many of the rest of the class. We had a number of folk on board who were "retreading" from a life in the trades to that of the high school teacher of Industrial Ed., so there was a good mix of bookworms and hands-on guys.
One day, Peter got us off to a good start as a debating society by introducing the proposition that there are three totally obsolete Old Wive's Tales in mechanics - procedures that are performed with no basis in reality, just "because." These were
When he told us that these are all in most cases a complete waste of time, and in many cases actually bad, a great cacaphony arose among the many, and there was much wailing, moaning, and gnashing of teeth. Not to mention arguing. A lot of these guys, myself included, had been doing these for years, and were not about to listen to this little punk tell them they'd been wasting their time. It helped a little to hear him say that he'd wasted much of his own time in these ways before his conversion, but not much. We, individually and as a group, attacked these propositions with a vengeance, but eventually all came to agree with this "new logic."
What began to help more was when he brought out the reprints of articles covering actual lab research done by the SAE - Society of Automotive Engineers - to support these claims. Yes, the SAE had actually done research to check this out, and they had been found seriously wanting. Here's how it went for honing:
A hone, you see, is a crude piece of work designed to remove metal, more or less at random. It's only necessity is as a first stage of polishing, in the case, and only in the case, of a cylinder having been rebored by a boring bar. For those of you who haven't thought much about it, let's look at what a boring bar does:
A boring bar is a piece of bar, into which is mounted a cutting tool, which is rotated inside the cylinder being rebored, while simultaneously being passed down its length. As it rotates, passing through a very tightly-controlled radius, it machine-cuts the cylinder walls to a precise diameter - within a fraction of a thousandth of an inch. In fact, if the bar setup is in good condition, any difference in radius between the start of the cut, at one end of the cylinder, and the end of the cut, at the other, will be attributable only to tool wear.
The only problem with this procedure is that, no matter how fine the "feed rate," - along the axis of the cylinder being bored - there will be a minute "threading effect" - the tool is after all cutting in a spiral. This is offset by such things as rounding the cutting edge of the tool somewhat, and by fine feed rates, but there's still a slight threading effect.
Because of this threading effect, the surface isn't entirely smooth, particularly to a piston running up and down it - across the path which had been followed by the cutting tool. For this reason, we apply a SLIGHT bit of crude technology for the finish - we run a rotating abrasive tool up and down the bore for a bit, to begin the process of polishing which will be completed by the rings and even the pistons themselves. We don't go nuts with this thing, and we certainly don't rely on it to take out major bites of material - in the thousandths, for instance. We use it only to begin the polishing process, getting out that "thread effect" and preparing the cylinder for final polishing by action of running the engine - "break-in," or "wear-in," depending on dialect.
This crude honing is not without problems which must be dealt with. First of all, it will result in further removal of material - beyond that which was done by the boring bar. This is allowed for by the machinist who sets up the bar, though - he makes the hole too tight to begin with, to allow for the extra thou or two that will be taken out with the hone. Note that this means that the pre-honed bore is too small for the piston at this point! - Although the honing will create the extra size to make for the proper clearance. (But what if you're honing a bore that's already a bit large for the piston? - The first thing to think about!)
A second problem is that the abrasive is making scratches in the cylinder, and at the bottom of these scratches will be found grindings formed by the process - fine powder of metal removed from the wall, as well as pieces of the actual abrasive itself. Needless to say, what is not removed of these will eventually mix with the oil when the machine is run, and will contribute to an accelerated wear rate until they are washed out and removed by filtration and oil changes. The SAE research found that this was a significant problem - bits of carborundum appeared in the oil for a number of changes, and the wear rate was considerably accelerated during this time. So they investigated - horror of horrors - not honing at all!
This turned out not to work well in the case of rebores. First of all, there has been no threading effect of the boring bar, but rather the smooth even surface of a well-worn-in cylinder wall brought to a mirror-like finish by previous running. In fact, they found it to be as detrimental in these cases to touch that beautifully-finished cylinder with a hone as it was not to in the cases of fresh rebores!
This is not theory here. It is the conclusion of an intensive research project, involving re-ringing used bores in like engines, some being honed, or "de-glazed," as the Old Wives like to call it, and the others just having the rings replaced and the cylinders left alone. The results were the same in every case - after being run for a period of time, - the equivalent of thousands of miles of use - the honed engines IN EVERY CASE burned more oil, and upon disassembly and inspection, IN EVERY CASE had developed significantly greater clearances - piston, ring end gap, all bearings, the works - than the unhoned engines. Although not expected by many to do so, the unhoned engines in ALL cases and at ALL STAGES burned less oil, and had worn significantly less than their honed counterparts. That is the result of the research. Now for the explanation.
When you hone a cylinder, you are running an abrasive surface up and down it. This creates random scratches, and removes metal. These scratches, miniature valleys, accumulate debris in their roots. The debris is composed of bits of expensive cylinder metal and also of carborundum and/or other grinding material - the cylinder is removing grit from the hone as the hone is removing metal from the cylinder. Moreover, you have now created a new "base level" for your cylinder after it has done its new wear-in. What remains of your previous cylinder surface, at, say, 3.100 in. is now "high spots" above your soon-to-be cylinder surface of maybe 3.104 (assuming .002 deep scratches.) And as this rough mess of peaks wears down, the metal which comes off becomes "grinding compound," polluting your oil, to wear out all your other components as well, such as bearing and even gear surfaces. And, worst of all, once the high spots have been removed, the new cylinder diameter is now .004" larger, meaning an extra .004" of piston clearance - above and beyond what was already there from the previous running!
Why would you want to pollute your engine thusly? Only because you've bought OWT #1 - you must "deglaze" your shiny, beautifully polished cylinder in order to "seat your rings." Well, it turned out that this wasn't necessary. They _did_ find that chrome rings don't seat well, if at all, in wear-polished (don't call it "glazed - that's something else again) cylinders. Turns out they need the roughness of a honed cylinder to seat properly, as both they and the cylinder go through a regrettable but necessary (only in the case of a fresh rebore!) period of wearing each other down. But polished cylinders _will_ seat cast iron rings just fine. So, in a nutshell, here's all you do: Don't hone cylinders, do use cast iron rings. If you hone, you will be treated to greater ring gap, more piston clearance, and greater engine wear as your engine goes through a completely unecessary break-in period, wearing itself back into a fit.
If you've experienced problems with oil burning after a re-ring, it's not because you didn't "de-glaze" properly, but because
Now, for the case of honing with rebores. In these cases, it is a necessary evil. For this reason, assembly clearances are set in anticipation of the rapid wear which is inevitable in the first few hours of engine life. Furthermore, a great deal of care must be taken to get as much of the grindings as possible out of the bottoms of the scratches - washing with hot water and soap, repeated scrubbing with clean rags and light engine oil until the rags come out perfectly clean, such procedures will pay in reduced engine wear during the break in period, and thus a considerably tighter engine for the balance of its service.
During run-in, as the rings wear the cylinders down to the bottom of the hone scratches, the ring gaps and piston clearances are going to increase a big bunch at first. You need to change oil and filter often, as your oil will be highly polluted by the flying chunks as this process takes place. In the SAE study, engine oil analysis showed initially high production of wear metals being produced in the oil, dropping off sharply as the engine went through this stage.
In the case of the non-honed re-ring, the only wear taking place is the comparitively much milder running-in of the softer cast iron ring surfaces. As anyone who has machined it will tell you, cast iron is almost a lubricant compared to chrome moly and even wear-hardened, polished cylinder surfaces, although they are also cast iron.
Once the break-in process was completed, the findings were that there was virtually NO increase in piston clearance due to cylinder wear, and considerably less increase in ring end gap due to ring wear, since the wear is essentially limited to seating - wearing off of the high spots only. Furthermore, oil consumption was much lower, and cylinder sealng (compression test) much better. Conclusion: it's madness to hone cylinders on a simple re-ring.
What to do if this news has come to you late? Such as after you've done a re-ring and found that you're having oil consumption and/or compression problems. Well, obviously, it's time to go back in there and see how much damage OWT#1 has done. Check your cylinder diameter, at both ends and in the middle in all directions, and make sure your clearances aren't too great. It's nice to do this with all the fancy bore gauges and such, but you can get a good idea by just putting a ring square in the cylinder, and checking the end gap with a feeler gauge at various places from top to bottom. A variation of .003 means one of .001 in diameter. Too much variation - more than .010 - tells me it's past time to rebore. Lots of people are fussier than I - let your service manual be your guide.
Check the piston fit in the cylinder at various places by seeing how big a feeler gauge you can get in there - preferably a wire gauge. If things aren't looking too loose, be sure this next time to use cast iron rings, verifying the ring gap for each of them at different places in the bore before installing. And, needless to say, leave that hone alone!
If you find you have to rebore, then of course you'll have to follow up with the hone. Be sure the rebore man leaves a little extra meat in the cylinder for the hone to take out - .002 is plenty, I think. And once you've honed, with the finest hone that will take out the "threads," you must be VERY careful to remove as much of that grinding compound as possible from the bottom of the grooves your crude tool has left behind. To do this, the recommended way is to scrub the cylinder repeatedly with clean rags soaked in 20 weight oil until they come out clean - and it will take a surprising number of rags for this to occur. Once they're clean, you haven't taken _all_ the grindings out, and of course, the high spots coming off will create more grinding compound, so don't be stingy on the oil filter elements or oil changes until satisfactory break-in has had time to occur.
And what will be the sign of satisfactory break-in? You guessed it - disassembly will reveal nice, smooth, shiny cylinder walls - just like the ones we used to run a hone through until they were the mess we mistakenly called "deglazing."
A Little Addendum
Got into a discussion on this on the Royal Enfield egroup the other day, and found myself adding to this. Here's how it went:
(Of course, if you're already convinced, and need no reiteration, then just click on outta here.
"Glaze" busting
On 2000-06-03 royalenfield@egroups.com said:
>Kevin!
>Thank You, I will do then a light glaze-busting.
>Risto
I will try one last time: (Don't ask me why)
1) There IS no "glaze"! That's a polished surface. Call it
"final machining" done by the last set of rings. It's a
wonderfully smooth surface of a certain size.
Microscopically, it looks like this:
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2) If you run a hone through it, lightly or heavily, you rough
it up, and create low spots. It then looks like this:
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Until it "runs in" to a new bigger size that looks like
this:
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3) Your new rings, and your piston, must get the surface
smooth again, by wearing down the high spots (what is
left of the old polished surface - NOT a "glaze" -to the
level of the low spots. This results in
a) accelerated wear of all engine parts, due to the
"grinding compound" effect of the metal being worn
off as your cyinder is ground to the oversize of the
bottom of the wear spots - as well as the GCE of the
abrasive residue which will inevitably be left in the
low spots - at the bottom of the grooves created by
the unnecessary hone.
b) A final (after break-in) size of the cylinder being
larger, the piston being smaller, and the ring gaps
being larger once this unnecessary abuse of your
surfaces has been completed.
I've told you that the reason I stopped honing polished bores, and
using cast-iron rings on rering jobs was because the SAE research
report found that identical engines treated both ways, and then
run for a fairly long interval after reassembly showed that:
a) The "deglazed engines" showed lower compression and
significantly greater wear upon being dissassembled and
examined than those which were not "deglazed."
b) The "deglazed" engines oil consumption was higher during
the so-called "breakin" period than that of the others, and
continued to be higher throughout the virtual service life.
(These were test bed engines.)
c) Periodic compression checks revealed that at all stages, the
compression on the deglazes engines was lower.
Furthermore, I've also said that I've built many engines since that
day in 1969, and I've never had a problem with bad ring sealing, poor
compression, or oil burning on any engine I've done since that time -
although I did have some troubles of this sort with engines I DID
"deglaze" before that.
And finally: there is no such thing as "deglazing." Honing is a
final process used to take the boring bar marks down to a smoother
(smoother, not smooth) surface after machining. The machinist
purposely bores slightly oversize, to allow for the metal the hone is
going to take out, and hones to a slight oversize, to allow for the
metal that is inevitably going to be lost as the piston and rings
take out the high spots left by the hone.
So what more do you need? Join HA (honer's anonymous) today! (My name's
Pete Snidal, and I'm a honer.) Become a recovering honer, and enjoy less
trouble and longer rering life! Or don't - see if _I_ care!