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

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This month we continue with an excerpt from Chapter 3: H-D 110" CVO from Donny’s Unauthorized Technical Guide to Harley-Davidson 1936-2008, Volume I. (Some content has been altered to fit AIM’s style and format.)

Okay, this is the biggie, or is it? From what I gather, most people are assuming that the head gasket problem on the CVO 110 rear head emanates from a shifting, separating, or moving cylinder liner. Liner separation seems to be the favorite description.

Many liners, especially in the old days, were a separate part from the cylinder itself. When worn, the mechanic simply pressed the old liner out of the cylinder and pressed in a new one. The 45-degree crosshatching in the old cylinders also served for oil retention in the cylinder wall to assist in piston-to-cylinder lubrication. The new liner would require boring (or at least honing) to crosshatch the cylinder walls to assist with piston ring break-in. Boring the new liner to eliminate bore tapering and out-of-round conditions was preferable to replacement. Honing, unless done with a sophisticated and expensive tool like a Sunnen hone, only follows the existing bore’s out-of-round and taper conditions, so this is not a good way to clean up a cylinder bore.

The Sunnen hone is the most expensive tool I’ve purchased for my shop, Heavy Duty Cycles, over the years. I saved and waited for five years before a good deal came up at an auction back in the early 1980s. And I still had to finance it. Then it took a few years more to purchase all the specially sized mandrels and hones to precision-fit every Harley-Davidson bushing and race. I still have that Sunnen hone!

Spiny Lock Liner
Twin Cam cylinders have a spiny-lock iron liner that is die-cast into the cylinder. The top of the cylinder liner is part of the head gasket surface. Machining the alloy cylinder and its cast-in liner flat for the head gasket surface occurs at the same time, so one cannot be higher or lower than the other. But if this is so, why can I hook my fingernail on the liner on a used rear CVO 110 cylinder?

I’m going to use a TC 88 cylinder for comparative purposes throughout my examination of the CVO 110, as well as in the accompanying photos. The TC 88 cylinders have been in use for nine years now, with nary a problem in many hundreds of thousands, if not millions, of Harley-Davidsons. Both the TC 88 and TC 96 cylinders are the same, with a 3-3/4" bore, a height of 4.930", and a cylinder base flange diameter of 4.180". However, the pistons are different because the TC 96 pistons were redesigned to lower their reciprocating weight and made shorter to clear the 3/8" increase in stroke.

As mentioned, the rear liner appears to be separating, with every indication that its cause is a problem with heat. When the Motor Company manufactures its cylinders, never mind the year or model, one of the final machining steps is to plane the top gasket deck surface perfectly flat for excellent gasket sealing capabilities. This machining procedure assumes the cast-iron cylinder liner and the aluminum cylinder body are one with each other.

The front CVO 110 cylinder liners that I’ve seen don’t seem to be separating, and they pass the fingernail-hooking test. However, these cylinders, like all Twin Cam cylinders, are identical and interchangeable. In fact, when I run my fingernail across the top cylinder deck gasket surface on a used and disassembled CVO 110 front cylinder — from the outside going in toward the cylinder bore — it’s a smooth progression. My nail does not hook or detect sudden changes in gasket surface height. The front cylinder, because it’s in the air stream, rarely broaches the extreme heat that the shrouded rear cylinder endures. Therefore, front cylinder liner separation is not an overt problem with a stoichiometric air/fuel mixture ratio of 14.7:1. Moreover, would a TC 88 cylinder suffer the same separation fate with newly instituted, closed-loop, 14.7:1 air/fuel ratios?

Well, the TC 96 cylinder is the same as the TC 88 cylinder! The TC 96 also must reach the same stoichiometric closed-loop air/fuel rations on both cylinders. Obviously, its shrouded rear cylinder must also suffer higher temperatures. However, there’s no wide spread problem with the rear TC 96 cylinders suffering the negative heat effects that plague the CVO 110s. After all, the heat-generating compression ratios are almost identical with only a 0.1 differential. The TC 96 is 9.2:1 while the CVO 110 is 9.3:1.
The clues are coming together. There must be a difference between the CVO cylinder construction and that of the TC 88/96 ones. When I run my fingernail across the top cylinder deck gasket surface on a used and disassembled CVO 110 rear cylinder, from the outside in toward the cylinder bore, it is not a smooth progression. My fingernail hooks on the edge of the cast-iron cylinder sleeve that is supposed to be flat and on the same level as the aluminum part of the top cylinder deck gasket surface. I did the same test on every used TC 88/96 cylinder in my store, of which there are many. Not once did my fingernail hook on any of them. They must be different than the CVO 110. I can now say definitively that the TC 88/96 cylinder will not suffer from a separating liner!

To press out the CVO 110 cylinder liner, Steve, my head mechanic, first had to heat up the CVO 110 rear cylinder on the press. When he did this, oil seeped out from between the liner and cylinder. At this point even Steve and I felt there might be some merit to the moving cylinder liner theory. But this engine design is too modern to have a separate cylinder liner. This is a throwaway society, and Harley-Davidson is no exception, as fewer actual repairs occur in favor of parts replacement. Replacement liners are for the rebuilders of yesteryear. Spiny-lock cylinder construction adds rigidity and support. This is one of the main tenets of the Twin Cam design philosophy. However, oil did seep from between the liner and the cast-alloy cylinder body.

Steve attempted to press out the CVO 110 rear cylinder liner with our 20-ton capacity press. It got scary. The press creaked and groaned under maximum effort. Steve put a longer activation bar on the press so he could move off to the side, farther from harm’s way. He was afraid the cylinder was going to shatter under the force applied. Finally, the press fixture began to bend. Steve had to stop. He was certain the cylinder was going to shatter. The cylinder liner did not move 0.001". We now know that the liner is not a separate part and yet it still fails the fingernail test.

Let me get a few more red herrings out of the way before I ask my machinist, Marvelous Martin, to cut a CVO 110 rear cylinder in half and then do the same to a TC 88/96 cylinder. We can then compare them and observe firsthand the actual cylinder liner construction in minute detail.

Is The Liner Too Thin?
I’ve received many e-mails complaining that the crux of the problem is that the CVO 110 cylinder liners are too thin. A typical one relates the theory that “regardless of the engine issue, most of the problems are traced back to the lean air/fuel ratio of 14.7:1. Face it, the rear cylinder gets the most heat, so while the front can marginally survive, the rear is expanding and contracting more, and with a thinner liner. Where is the mystery?” Some knowledgeable web sites offer the same explanation.

If the liner is too thin, why doesn’t the front cylinder at least exhibit milder symptoms to those of the identical rear cylinder? Well, I guess no one took the trouble to measure the liners of TC 88, TC 95, TC 96, and TC 103 cylinders to compare them with the CVO 110. My measurement for the CVO 110 actually came out to less than what the reader’s e-mail stated.

His measurement is 0.110" while mine is 0.100". Different tools and margins of error can account for this 0.010" differential, which is not a big deal for our comparisons. However, a margin of error this big would definitely cause problems in more precise applications.

I took the following measurements at the cylinder base where the liner flange exits the cylinder. The TC 88 cylinder has a 3-3/4" bore and a liner thickness of approximately 0.162". The TC 96 cylinder has a 3-3/4" bore and a liner thickness of approximately 0.162". The TC 95 cylinder has a 3-7/8" bore and a liner thickness of approximately 0.100". The TC 103 has a 3-7/8" bore and a liner thickness of approximately 0.100". This makes sense since they are the bored-out versions of the TC 88/96 cylinders. And the TC 110 cylinder has a 4" bore and a liner thickness of approximately 0.100". Well, I guess the measurements take care of the “too thin” argument as the TC 95, TC 103, and TC 110 liners all measure the same thickness, plus or minus 0.005". The TC 95 and TC 103 liners do not pose any untoward problems that I have observed — yet. The TC 95s are defunct because they’re bored-out versions of the discontinued TC 88 engine. These engines never had to operate under the stoichiometric air/fuel ratio of 14.7:1. The TC 103s may encounter heating problems with the rear cylinder if no fuel modification is undertaken after boring out a TC 96. But why would anyone bore a TC 96 into a TC 103 without installing an ignition/fuel modifier? My current three favorites are the Terminal Velocity, S&S IST (Intelligent Spark Technology), and the venerable Power Commander. I don’t think that liner thickness is a factor for the CVO 110 problems, although it could easily be made thicker in a cylinder redesign if it made people feel better.

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