 Techline-April09-H-D 110" CVO - Part IV: The cylinder liners and other issues
This article is continued in the next thread.
This month we continue with an excerpt from Chapter 3: H-D 110" CVO from Donny’s Unauthorized Technical Guide to Harley-Davidson 1936 to Present, Volume II. (Some content has been altered to fit AIM’s style and format.)
As my ma used to say, “The proof is in the pudding.” I’m not sure what that exactly means, but cutting a known, excellent cylinder like the TC 88 in half to view the crosssectional construction and compare it to a similarly cut, problematic rear CVO 110 will show the problem firsthand, debunking some theories and lending credence to others. Once we did this, the first thing Machinist “Marvelous” Martin noticed is that the TC 88 sleeve is a different cast-iron alloy composition. Marvelous had to cut the TC 88 cylinder in half at a much slower pace with less intense cutting. The CVO 110 cylinder was cut much more easily, as the iron alloy is softer. The TC 88 sleeve is about 0.030" thicker on each side, for a total of about 0.060" (1/16"), than the CVO sleeve. So the TC 88 cylinder would take more effort to cut because of the thickness. However, it’s still a harder material.
The second observation is that the construction of both cylinders looks to be the same. Both cylinders have a cast spiny lock construction. No wonder the CVO 110 cylinder liner refused to budge in my 20-ton hydraulic press! And as we also discussed last month, the cylinder wall thickness is also a red herring since when a TC 88 cylinder, which has a 0.162"-thick wall, is bored out to a TC 95 configuration, the cylinder liner thickness is approximately 0.100". That’s the same as the CVO 110’s.
The Missing Clue
Something was still bothering me. There was a missing clue. My TC 103 has the same liner thickness as the CVO 110. It is subjected to similar heat in the rear cylinder; perhaps more because I increased the compression ratio to 10.5:1, which is much more than a CVO 110’s 9.3:1 ratio. Actually, there wasn’t more heat because I also installed dual Jagg 10-core oil coolers and made some fuel mixture modifications. However, my 103 is still a hot-running engine. I’ve ridden my bike long and hard in very hot weather, but I’ve never had any problems. Why is the cylinder liner in the CVO 110 shifting or moving when it does not occur in the other Harley-Davidson Twin Cam, S&S, or JIMS cylinders?
Was the missing clue in the cross-sections of the two cylinders? I asked Steve to smash out part of the liner — at the top and bottom of the cross sections — on both the TC 88 and the problematic CVO 110 cylinders. That’s when the answer lay before us on the workbench. The thickness of these pieces was not the clue, even though the CVO 110 liner at the top of the cylinder deck is 0.060" less than the equivalent TC 88 measurement. Both the thicknesses of the TC 88 and the CVO 110 are equal at the bottom of the liner just before the flange. The thickness of the broken piece of TC 110 top liner is 0.150" and the thickness of the broken piece of bottom liner is 0.160". The thickness of the broken piece of TC 88 top liner is 0.210", while the thickness of the broken piece of the bottom liner is 0.160".
The smashed liner pieces gave me the answer I was looking for. I would never have found the cause if I had only cut the cylinders in half. As far as I know, no one has looked underneath the spiny lock construction! The CVO 110 cylinder liner is a spiny lock cast with the alloy cylinder body up to within 0.625" (5/8") of the cylinder’s head gasket surface. The other Twin Cam cylinders have cast-iron sleeves that are spiny-lock-cast with the cylinder alloy up to a distance of 0.094" (3/32") from the cylinder’s head gasket surface. That’s a big difference!
The 0.625" area at the top of the CVO 110 cylinder attempts to hold the liner rigid and at one with the cylinder body via fine striations that circle the inner diameter of the liner and the outer diameter of the cylinder body. These fine striations mate and ostensibly prevent liner movement.
However, the striations prove unsuccessful with the hotter rear cylinder. Under normal heat, this method would probably work as evidenced by the front cylinder where the liner does not shift under normal operating conditions. The cast-iron cylinder sleeve dimensions are not spiny-locked with the alloy cylinder body at the bottom of the cylinders, just above the protruding cylinder flanges. But this is another red herring. The TC 88 dimension is 0.250" (1/4"), while the CVO 110 is 0.156" (5/32"). Any expansion or movement has no effect on the O-rings between the engine case and the bottom deck of the cylinder (cylinder and dowel pin O-rings), or the piston support, since this area is below piston ring travel.
The accompanying Cylinder Liner Comparative Dimensions Chart shows the measurements for various sections of different cylinders. I measured the cylinder liner thickness from the external flange at the bottom of the cylinder. The width or thickness of the internal top liner and the internal bottom liner is from the pieces Steve, my head wrench, broke off a TC 88 and a CVO 110 cylinder. The Axtell measurements are from what I can see on the outside, since I did not cut one in half to remove pieces of the liner. The flange length of the Axtell cylinder is much longer than H-D cylinders, providing more rigidity, support, and stability for both the cylinder and its piston. The piston at BDC must stop, and change axis and direction. The piston needs all the support it can get in this area with all that it must contend with.
Why the Rear Gasket?
The H-D dealer’s mechanic (because I cannot believe the factory had a part in this) who rebuilt the engine the last time for my customer used a handheld sanding disk to grind the head gasket surface to clean it up. He was trying to solve a slight warping problem the wrong way. The warping we found was not resolved, so it continued to add to the problem. We fixed this problem the proper way, by precisely grinding it on a milling machine. “Marvelous” Martin, machinist extraordinaire, planed 0.007" off the rear head gasket surface in order to make it flat. The front head is okay, but we equalized it with the rear and took 0.007" off it also. The manual says to replace the head if warping is 0.006" or more. The modern way to restore components is to replace them. Planing works exceptionally well, restoring parts to their original working condition. The warping occurs across the two rear head ports (intake and exhaust), close to the dowels, so this could be the cause of the oil leak. The rear head warps from the center to the sides. The head gasket surface warps on the rear head only. The front cylinder head could possibly warp also from the excess heat of a mistimed engine. This is not normal on a properly timed motor.
Improper Heat-Treating
Improper heat-treating at the factory could possibly be a cause of head warping under high temperatures, especially in the shrouded rear cylinder head. This is where the air/fuel ratio goes above stoichiometric, anywhere from 14.8:1 well into the 15s with some reports going to an air/fuel ratio of 16.0:1. If this were an annealing problem, where heat-treating removes gases, stabilizing the alloy material to ensure the aluminum cannot shift under operating temperatures, it would also happen to the front head. Now we will need to add the head warping with the shifty top cylinder liner to arrive at a conclusion.
We cannot fix the symptomatic problems until we know how to fix the cause. Fixing symptoms will give longer engine life, but not long enough, as the root cause will return. Potential fixes will eliminate both problems through redesign and different metallurgy to combat warpage, and a better spiny-lock-liner-to-cylinder-body construction that goes to very near the top of the CVO 110 liner. However, these redesigns are still attacking only symptoms. For example, another symptom repair would be to use a thicker fibrous gasket like that of the TC 88 to take up gasket surface roughness and minor warping. The CVO gasket is a newer technology that requires a flat, smooth surface to function correctly. It’s also thinner than its TC 88 counterpart. The cause of the shifting top liner, head warping, and rear head gasket oil leak is excess heat combined with parts not built strong enough to endure it. And that brings to mind a couple of questions.
The first is what is the source of the excess heat? The second is why is excess heat occurring on only 2007 and later engines and not the earlier ones?
EPA Perfection
Two relatively new phenomena are part of the punishing demands for an air-cooled engine by the Environmental Protection Agency (EPA). They are
stoichiometric air/fuel ratios (see October, November, and December ’08 issues), and closed-loop electronic fuel injection (EFI). I suppose the acronymists will designate OLEFI and CLEFI to represent open-loop and closed-loop EFI.
The magic number for EPA guidelines, and thus the ratio during closed loop operation of an EFI, is 14.7. Everything in the engine management system including the sensors, electronic control module (ECM or ECU), and EFI revolves around this stoichiometric number of 14.7 parts air per one part fuel (gasoline). The stoichiometric ratio is the optimum air/fuel ratio, where all the available oxygen in the air combines with all the fuel available for burning in the combustion chamber. The stoichiometric air/fuel ratio is different for various fuels. Gasoline is 14.7:1, diesel is 14.6:1, methanol is 6.4:1, and ethanol is 9.0:1. Predecessors to the Twin Cam had less cooling fin area and contained more existing heat inside the engine. They also ran a richer air/fuel ratio, below today’s closed-loop, EFI-mandated ratio of 14.7:1. How do we burn such a lean mixture of fuel? Heat is the short answer.
Lambda is the actual air/fuel ratio (AFR) divided by the stoichiometric ratio for that particular fuel. The formula is: Lambda = actual AFR stoichiometric AFR. For example, if the actual air/fuel ratio is 14.7:1, as it is with gasoline when at the EPA-desired ratio, divided by the stoichiometric ratio for gasoline, which is also 14.7, the lambda is 1.
Therefore, if the lambda is 1, then the AFR is equal to stoichiometric. Let’s do another one: if the actual air/fuel ratio is 14.3:1, then the formula is 14.3 —: 14.7, which gives us a lambda of 0.973. A rich running engine that, by definition, has an AFR ratio less than stoichiometric has a lambda less than 1. One more: if the actual air/fuel ratio is 15.2:1, then the formula is 15.2 —: 14.7, which gives us a lambda of 1.034. Conversely, a lean running engine that, by definition, has an AFR ratio greater than stoichiometric has a lambda greater than 1. In short, we will get maximum horsepower and torque with a lambda slightly less than 1, which translates into stoichiometric under 14.7 parts air to one part of fuel. That’s no surprise.
Article continues in next thread. Check back issue for pix and extra information. |
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