Date: Thu, 14 Mar 1996 18:05:28 -0800 (PST)
From: Peter Snidal
Lemme see, now............ having fun about Tri engines being made into air compressors is OK, but cracks about rubberframes and eternal gearbox rebuilding is pointless flaming..............(?) <scratch> <scratch>
Oh, well, anyway, here's another cut-out-and-save:
OLD WIVE'S TALE #2: ALWAYS REAM YOUR RIDGES By Pete Snidal
I was really happy, that morning in '69, to be convinced that ridge reaming bites the big one. Primarily because, although I had tried every fancy-ass ridge reamer I had been able to lay my hands on, my sense of juvenile perfectionism had always been really assaulted by the fact that I could *never* get the top of the cylinder looking as if it had never had a ridge. Try as I may, I would *always* end up with some ridge left on one side of the bore, and usually a low spot on the other.
So why did I never run into broken top rings in engines thus "deridged" and put back into service? A better question, which logically follows from the answer to the first, would be "Why did I ever bother trying to ream them out in the first place?"
Because, as it turns out, the top ring *never* hits the ridge, or the portions of the ridge left behind, or the hole where you went too far, anyway.
Why not? Well, think about it. As the old top ring was rubbing up and down in the bore, flopping around up at tdc, grinding/bashing/worrying a low spot in the cylinder and/or leaving an unworn ridge in the untravelled upper region, said ring was also getting worried down to a vertical size which made it looser in the ring land. (The groove around the piston into which it fits). When it is replaced with a newer, thicker ring, the n,t ring won't be able to travel as far up the cylinder.
'S'truth. At times when you are replacing the big end as well, this lower reach is compounded even more, so the difference is even greater. But either way, so the argument goes, the new top ring can't make it up high enough to contact the ridge. So don't worry about it. Leave it alone. This too was verified scientifically in the SAE tests.
And, in any event, I could never find a ridge reamer that would do the job clean enough to avoid damage to a piston ring fluttering against it at 6000 cps anyway. If you can't do the job right, why do it at all?
So, you may ask, Why do they make ridge reamers, then? Well, the explanation they gave us that fateful day was that their sole purpose is simply to facilitate removal of the pistons in severe cases of cylinder ridge. There are times when the ridge is so bad that you have to pound like mad on the bottom of the rod to get the piston out, and you fear breaking a land. This in automotive applications, where the piston comes out the top of the cylinder. Well, if it's that bad, you may as well ream the ridges first. And, since it's going to need a rebore anyway, it doesn't matter if you mess up the top a bit. Just don't do such a neat job. Just don't hog it down past what will be your finished rebore diameter.
But, other than that, ridge reaming is for the birds.
Date: Wed, 13 Mar 1996 09:01:21 -0800 (PST)
From: Peter Snidal
Saw a mention once again of honing cylinders or not. Since this is not yet a FAQ on the home page (hint, hint - Chuck), I post it once again. Apologies to those who have seen it before:
OLD WIVE'S TALES REBUKED By Pete Snidal
We've all heard of Old Wives Tales - stories passed around from generation to generation. Stories which have probably never had a validity check, but nonetheless live on in veracity simply because they're so old, and they've passed through so many hands. Someone you respected in your younger years told it to you, and you pass it on to someone who respects you many years later.
Faith is a good thing, in church. Not necessarily such a GT (TM) in other places, such as the shop. Here is the first of a series of OWT's which hopefully will illustrate:
Old Wives Tale #1: To Hone or Not To Hone:
Before we even begin to look at honing, we first should look at its precursor, boring cylinders.
It's not too bright to say, "bore the sucker while it's apart anyway." There's only so many bores in a set of barrels, and pistons aren't cheap. How you decide whether or not to bore is to check the clearances. Also, check the size of the piston itself, and interior mike the bores. If the bores are straight, and even if you have excessive clearance, but the clearance is due mostly to piston wear,(being aluminium, surprise, surprise, they wear much faster than the cast iron cylinders) you can often just replace the old pistons with new ones, and not bother with the bore job. Why use up an oversize on a perfectly good cylinder if you don't have to? I have personally put fresh pistons in old cylinders with good results many times. Clearance is the key here. That is, clearance at all places in the bore, and in all directions, particularly fore-and-aft at the piston skirt.
Now, let me blow a few minds over honing:
I was once in attendance at an Auto Mechanics course at Technical College, dancing through the hoops for a degree in Industrial Ed. One topic we kicked to death in there was the subject of honing and ridge reaming cylinders. It all came about when the instructor greeted us one morning with the news that you should *never* hone cylinders except to finish a bore job, and that it's *pointless* to ream ridges, unless you need to get the piston out. (Cars)
What an uproar! Most of us had had a fair amount of experience with engines, and we were pretty incensed. You *have* to "deglaze," or the rings will never seat! You *have* to deridge, or the new rings will hit the ridge and break on the first stroke! Everybody knows that!
Well, our instructor, who was a pretty savvy guy, knocked the wind out of the sails of the more scientifically inclined among us with one move: he handed out some reprints of actual SAE test results involving deglazing/not deglazing rering jobs, and ditto for ridge reams. It seemed that the compression test figures after 10000 miles were *better* by far for the unhoned engines. Also the increases in piston clearance were less, as was the bore wear, and - get this - they also showed *significantly* less bearing wear.
How come? Well, it seems that when you scuff up a perfectly good smooth cylinder with a rude sort of carborundum device, you are in fact only putting scratches on it, giving us a new, larger diameter at their base - sort of like root and pitch diameters in a nut, say. And when you put it back together, the new rings and this rough surface proceed to grind each other down until smoothness is re-attained. By this time, needless to say, you have larger ring gaps, due to more ring wear, and more piston clearance, since the cylinder has been taken down now to the base diameter of the honing scratches. And the valuable metal so removed has been converted into grinding compound circulating in your oil, so you have also reduced the size of your piston, and contributed significantly to wear of all the other parts as well, from rocker bearings to cam bearings to timing chain rollers to rods and mains.
Proven. Scientifically demonstrated in an actual SAE sponsored research project. But you gotta *deglaze* or the rings will never seat, correct? Well, yes and no, Chet. Although it is true that *chrome* rings are so hard and smooth that it can take from a long time to forever for the cylinder to wear them to perfect fit, this is *not* the case for Cast Iron rings. In fact, that's the secret. Chrome rings only in rough (honed) bores. And hone bores only when you have to, ie as the final "finish" of a bore job. Since the boring bar tool in effect runs a screw thread down the bore in its journey toward the land of largerness, it is necessary to do a final "polish" with a somewhat cruder tool - the hone. This is the *only* reason to put a hone in a cylinder. And when it's done, the machinist has purposely left some extra meat in there for the hone to finish to final diameter. And the final diameter is a tad small as well, in anticipation of the initially rapid wear that is inevitable as the new rings and the scratchy bore get acquainted. This is also the reason for very careful cleaning of said bores before assembly, and for very frequent oil and filter changes, until the motor has stopped manufacturing grinding compound during the break-in process.
Back to re-ring jobs. Turns out there is just plain no reason to muck up that lovely smooth bore with a hone. None. Cast Iron rings will seat just fine on a smooth bore. And wear a lot less in the process. Ditto for the bore. So check the clearances, select the new pistons option if you like, and be sure to use Cast Iron rings. But don't subject your engine to a bearing grind job just because your mom always told you to hone your bores. It's silly.
I imagine this will shake up a few readers of brit-iron. I know it shook up me and my classmates that fateful day in '69. But I rebuilt my 544 Volvo in that class that year, and followed the prof's advice. And it seated its rings just fine, in a few hundred miles. And I haven't honed a cylinder on anything since - probably 30 or 40 rebuilds later.
And I've never had rings fail to seat. And I know all those engines lasted longer than they otherwise would have. In fact, I put 117,000 miles on a 235 Chevyvan rebuilt this way. The van was into its 200K range when I did it, and it burnt no oil (<1qt/1000) when it finally rusted its way to the big Toyota factory in the sky.
I could tell you of lots of others, but that's sufficient, I think. Trust me - Throw Away That Hone. Unless, of course, you're Boring.(tee hee)
Date: 15 Mar 1996 15:39:03 +0000
From: "Cornforth, Bob" <Bob.Cornforth@mcl.co.uk>
G'day reamers and honers,
Much as I enjoy Peter's articles (the honing one was a belter), I must be missing the right brain cells to follow this one. If you put a new ring in a new bore, it Top dead centres at a point, let's call it x thou from the top, using the ruins of my algebra teaching. If the ring wears 2 thou, then it tops out at x+2thou down the bore, as the thinner ring will be slopping around at the bottom of the land as the piston goes up. This is where some of the ridge will end when you rebuild it. If you then stick a new ring in, it's going to run over the last 2 thou innit?
I suggest the reasons no-one bust a ring are as follows and in this order:-
I'm sorry if the SAE have proof that de-ridged engines a worse than ridgy ones, but I suspect it's because of other things, like (flight of fantasy music) the ridge acting as a additional squish band (fresh outbreak of sobbing from philosophy students)
IMHO
I'll set mesel up, you shoot me down
Bob
850 Puma Weslake Triton ( Ridge racer)
750 Morgo Bonnie (Honey I shrunk the rings)
Date: Wed, 22 May 1996 11:40:00 -0700 (MST)
From: Charles Falco
On May 21 Tim Mcpherson wrote:
> I disagree with powder coating jugs... it makes the cyl. hold too
much
> heat. Powder coating is almost a ceramic finish the same thing that
> they use in heaters and BBQ to hold in heat!!! this would reduce
the
> life of your motor greatly.. it would look great but it wouldn't
run.
Tim, you're mixing together different properties. Powder coating is very much an organic coating, with all the attributes (e.g. flexibility) and disadvantages (e.g. inability to withstand high temperatures) that implies. Just because powder coatings are applied using heat does not in any way make them equivalent to ceramics; which also are applied using heat (although, in their case, using much higher temperatures). Also, just because ceramics are used to coat heaters does not mean they "hold in" heat. The principle reason ceramics are useful on heater elements is because, since they are already oxides, they don't oxidise like most metals would do in that application. The thickness of a particular coating material, its thermal conductivity, and its emissivity all determine its usefulness as a coating for an air-cooled cylinder. A standard black paint and a powder black paint will have roughly the same thermal conductivity and emissivity. However, powder coatings are typically much thicker (~0.015" vs. ~0.002"), which reduces the heat flow across the paint, and thus increases the temperature gradient as compared to the case with a "standard" paint. What that means is that the cylinder will run hotter, as Tim said. However, the reason isn't quite the one he gave.
Charles Falco
14.4 Replacing Broken Cylinder Fins
Date: Mon, 7 Oct 1996 12:47:22 PDT
From: John Head.
As two of the fins on the head of my ES2 were broken and missing I needed to make replacement ones, as well as attach them. Fortunately for me these were on the very top, and bottom of the head. Therefore welding in this area did not pose a problem . For donor fins I broke a few large pieces from an old commando cylinder that I had laying around. The first step in matching and repairing the broken fins is to grind the ragged edges of the broken area of your part in order to achieve as straight, an area as possible ( forming a single straight line, or intersecting straight lines as necessary being careful to remove only as little an area as possible) from one side of the broken fin to the Otherwise gives you a clean area to mate up to.
I then slipped a piece of paper under this cleaned area and traced the lines onto it, as well as where the fins outer edge should be, onto the paper. This piece of paper then becomes your master or template in which to make your replacement fin(s) from. To get the outside contour of the replacement fin template you need to estimate where the edges should be, based upon the next adjacent fin. If the fin to be repaired is on the top, it will probably be slightly smaller than the fin below it, and if the fin is on the bottom of the cylinder, or head it will probably be slightly larger than the adjacent fin.
Your next step is to take your master paper template, and try to match it up as best you can to the outside (cast)edge of the broken commando (or whatever) fins that will be your donor. When an area is found that matches the outside contour of your master you simply trace the fin shape including the actual straight lines that will be your cut area onto the donor fin, and carefully cut the shape out. The flat areas are the areas that will be butt- welded to the cleaned and flattened areas of your head, or cylinder. As the donor fins that I broke off the commando were slightly thicker than the ones on my 53 ES2 at the butt areas I took my Dremel tool (high speed rotary hand held grinder) and removed material from the bottom side ( non show side) until the thickness matched the butted area. Grinding on the non show side prevents altering the cast look of the finished job. Once I was satisfied that the fin was a good fit I ground a 45degree chamfer on the fin, and its mating surface ( head, or cylinder ) from the show side. This will be the area that your welder will fill when he attaches the two pieces.
I did not braze my pieces on, however I was told that It could have been done. If you choose to do so I would not chamfer the mating surfaces on the contrary you will want as close a match as possible. Before I took my pieces to the welder (make sure he has past experience welding cast iron) I made a support piece out of wood that I slipped under the fins in order to support, and align it perfectly until the pieces were tack welded in place. If possible ask your welder just to tack the fins in place first, then remove your support piece, and carefully check the alignment. As your are trying to match parallel surfaces any small misalignment is very noticeable and once he fills in the fillet grooves, if it isn't right you need to grind out the weld and start over again. I found this out the hard way! However I was able to partially grind through the weld, to the point where I could CAREFULLY bend the fin back into alignment, and had the welder re-weld the fin. All that is left at this point is to carefully grind down the weld to the original surface of the fin and you are done. One more thing that I did to recreate that " as cast " look to the weld before I painted It was to take an old chisel, or nail , or other various sharp objects and CAREFULLY tap this area in order to create small irregular craters which recreate the cast look. I hope that this helps in some way.
John Head