Techline-March09-H-D 110" CVO - Part III: The cylinders and other issues (cont.)

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This article concludes in the next thread.

Piston Thrust
This theory almost did not make it into this article, as it’s ridiculous. However, I don’t want it to survive, so let’s blast it. I can discount this bogus theory immediately. Pistons, whether in the front or rear of all 45-degree Harley-Davidson engines, thrust against the cylinder walls, particularly when changing axis (direction). Yes, it’s a legitimate argument to replace the awkward 45-degree angularity with a more friendly 56- or 60-degree design, but this is not the argument at hand. Every other Harley-Davidson cylinder, including the Knuckle, Pan, Shovel, Ironhead Sportster, and Evo survived piston thrust. The Twin Cam cylinder is shorter than all the aforementioned ones. Additionally, it is at one with its high-pressure, cast-in liner in spiny-lock construction. I would venture to say the Twin Cam cylinders are the strongest and most rigid of any in the history of Harley-Davidson. Furthermore, the ever-growing use of synthetic oil reduces the thrust pressure, as does the hypereutectic piston material and the Teflon coating on its thrust surfaces. Enough said!

Cylinder Not A Plug Fit
Normally, the lower exposed cylinder liners, known as flanges, fit tightly into the engine crankcases. This is known as a plug fit. The aluminum engine cases expand more and at a greater rate than the cast-iron cylinder liner appendages, so there is never an issue of squeezing the cylinder and distorting it. The plug fit adds the support of the engine case to the cylinders.

It surprised Steve and me to find that the outer diameter of the cylinder flanges on the CVO 110 is about 4.180", but the spigot hole in the engine cases is 4.208". This leaves 0.028" for some potential shifting. The cylinders sit over and hold down four equidistant cylinder studs. Once the male-threaded cylinder studs, which protrude from the base decks of the engine cases through the cylinders and heads, tighten down to specifications via threaded, hollow female-threaded bolts, it’s impossible for different component parts to move when cold.

As engine heating and cooling occurs, thermal expansion and contraction of the different components may induce some movement if there is pressure on the parts to shift when expanding and contracting. The cylinder and head’s loose fitment over the four cylinder studs also leaves room and may not discourage little movements. Metal expansion, even for alloys, is different because of diverse metallurgical content of various aluminum alloys (cylinders and engine cases). The thickness of the aluminum alloy engine cases is greater than that of the cylinders, giving subtle differences in expansion and contraction rates. The cast-iron cylinder liner will expand at a different rate than the crankcases and cylinder bodies.

Steve, Marvelous Marvin, and I stared at the cylinders with our combined Harley-Davidson mechanical experience, which totals over 120 years. Then we saw it: another clue. The cylinder liner is thicker in the cast-in spiny-lock cylinder than when the cylinder flange protrudes from the base of the cylinder. Steve postulated that this thicker portion of the liner must sit on the engine case spigot decking to add support for the cylinder liner lip’s potential shifting. But for this to work, the cylinder must be a plug fit into the engine case spigot holes. The CVO 110 does not offer this support, since it has a total of 0.028" extra room (0.014" on either side) between the cylinder flange and cases. Could the liner shift downward from the force of descending piston thrust and metal expansion without this engine case support? In other words, could this gap allow the cylinder liner to walk?

If the cylinder uses a spiny-lock cast-in cylinder liner this can’t happen. In addition, if this situation occurs in the problematic rear cylinder, why would it not repeat in the front one? These clues turned out to be red herrings. At Heavy Duty, we’ve seen many bored-out engine case spigots for bigger bore cylinders returned to stock displacement usage. While this is certainly not ideal, one must appreciate how difficult it is to make a round hole smaller. The point I’m making is that I have observed many of these situations over the years, and no appreciable shifting occurred.

Less Cooling Fin Area
The TC 88 has 11 fins, the same as the CVO 110. However, the length of the fins on the TC 88 is approximately 0.130" (1/8") to about 0.165" (5/32") longer all the way round the circumference of the cylinder, as well as from top to bottom. Therefore, the CVO 110 has a substantial reduction in fin area, as there is less length in its fins all the way around and top to bottom. This area of finning extrapolates into a substantial difference in total finned area between the two cylinders. The extra bore diameter of the CVO 110 requires more finning to circumnavigate the bigger cylinder, but it still has less fin area than the TC 88 cylinder. Furthermore, this total fin area differential will greatly affect the cooling capabilities of the two cylinders (the adequately cooled TC 88 cylinder and the inadequately cooled CVO 110). A thinking person would logically believe that this situation should be reversed, with the CVO 110 having more finned area than the smaller and cooler-running TC 88!

Why would the factory reduce the fin area on a hotter-running cylinder? I think it has to do with marketing the look of the V-twin engine, so important to the Harley rider. An increase in fin area to match that of the TC 88 and, hopefully, go beyond to dissipate the extra heat that is such a problem with the CVO 110 rear cylinder, in combination with the 0.250" wider bore, would produce a much fatter top end. The cylinder head fins would need to increase to be symmetrical with those of the cylinders. In my mind, this scenario is wonderful; just look at the extra cooling capabilities that would result. Of course, the other reason for fin area reduction might coincide with cost reduction or at least cost savings. However, the situation becomes worse with the TC 110 oil return passage. It’s closer to the cylinder bore than the other cylinders mentioned, which brings us to the next point.

Liner/Dowel Interference
I postulated that cylinder liner thickness is not an important factor in the TC 110 rear gasket failure because I have not seen or heard of a rear CVO 110 head gasket blow in regards to compression sealing. The cast-iron liner pushes up the gasket, still sealing in the compression, but causing a problem with sealing as the gasket encounters the aluminum alloy cylinder. The rear CVO 110 gasket seals on the inside compression area, but the gasket blows outward from the centrally located oil return dowel.
It appears that all the factory Twin Cam engine cylinder sizes use the same cylinder stud pattern, with the same distance between each. The gaskets for all the cylinder bores have the same stud-hole locations, but the CVO 110 oil passage is closer to the bore than on the TC 88 simply because the CVO 110 bore is larger. I’m sure this has legitimacy and becomes a symptom of the cause. The problem, thus far, is that the Motor Company is addressing a symptom instead of the cause.

Our inspections of the various Twin Cam cylinders resulted in some interesting observations and theories as we stared at them for weeks. The TC 88 inside liner is about 0.110" away from the dowel pin oil return hole.

The TC 95 inside liner is about 0.090" away from the dowel pin oil return hole. The TC 96 inside liner is about 0.110" away from the dowel pin oil return hole. The TC 103 inside liner is about 0.090" away from the dowel pin oil return hole. The CVO 110 inside liner is a paltry 0.030" away from the dowel pin oil return hole. A moving cylinder liner might well interfere with the dowel pin oil return hole passage, causing a leak, especially if the head warps due to excessive heat. But how can the liner move? The CVO 110 cylinder liner is virtually pressing on the dowel pin outer diameter. Heat expansion of the hotter liner may distort the dowel pin oil return hole and disrupt the gasket. It appears to me that a CVO 110 cylinder redesign is necessary in conjunction with dealing with excess heat from air/fuel mixture ratios well above 14.7:1.

Article concludes in the next thread. Check back issue for pix and extra information.