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1982 Honda CX500TC Turbo
1983 Honda CX650TD Turbo


Valve Train Problems

Now let us shift our focus from the electrical domain to the mechanical. As if the electrical system shortcomings are not enough to swallow, the CX Turbo has a nasty dose of mechanical ones also. The problems mainly arise in the valve train, specifically the camshaft, rocker arms, and the valves and their guides. The tips of the valve stems develop pitting, the lobes of the camshaft develop pitting, and the rocker arms wear prematurely. It is not uncommon to observe gross deterioration in these areas on a Turbo with even less than ten thousand miles on the clock. Keeping the valve clearances adjusted is important on any bike, but even performing this maintenance procedure religiously will not prevent the damage I am referring to. I will describe the damage which occurs on each part, along with several theories on why the damage occurs.

Each valve is acted upon by a screw tappet attached to the upper rocker arm. The screw tip itself will first begin to show evidence of fatigue, then increasing pitting. The surface of the valve stem where the screw strikes will also experience the same fate. The screws are simple to replace, but pitted valve stems require replacement, a major and expensive job. At one time, I theorized that the relatively soft screws pitted first, thus eventually causing the mating surface of the valve stem to pit also. A friend of mine, Tim Deinhard, theorized that more frequent oil changes might alleviate the problem. Both of these theories were (expensively) put to rest on one of my Turbos.

It is true that using pitted screw tappets will both cause and accelerate valve stem pitting. However, at one point, all the valves on my 15,000-mile Turbo were pitted, so I replaced them all with stock Honda valves, along with eight fresh screw tappets. I replaced the oil with a synthetic, and adjusted the valves. Only one thousand miles later, I went back in to inspect the parts and was shocked at what I found. My original theory was that the screws would pit first, causing any subsequent damage to the valves. What I found instead were eight screws in perfect condition riding on top of valve stems that were already beginning to pit! So much for the oil and screw theories. It appears that what we are experiencing is the result of one of two things. The first possibility is that the Honda valves are insufficiently hardened. The second possibility is that our engines are experiencing a lubrication deficiency rivaling that of the pre-1986 Honda V-four engines.

For those who may be wondering what is so dire about pitted valve stems, consider the following. When you slide a .005" feeler gauge between the tip of the screw tappet and the flat surface of the end of the exhaust valve stem and adjust to that dimension, that is the clearance you end up with. Now imagine a side view of a valve which is pitting at the tip. The surface of the valve stem is no longer flat, but is actually dished down slightly into the valve. When you go to slide your feeler gauge in, it slides between the screw tappet and the upper edges of the dished portion of the valve. So you adjust the valve in this manner to .005" clearance. Is that the actual clearance you get? Not at all. The actual clearance is .005" plus an undetermined additional amount equivalent to the depth of the pitting. Your flat feeler gauge cannot "reach" into the pit to measure it, but your screw tappet does travel the addition distance. If you attempt to adjust your pitted valves, you will have an excessive clearance. This causes increased pounding upon the valve, which leads to even deeper pitting. This yields an even larger clearance discrepancy at the next adjustment, and so on and so forth. If the pitting problem is not addressed, the tips of the valves will deteriorate ever more rapidly. Unfortunately as far as I know, there is nothing that can be done about this. At one point I thought I had found the answer in a valve lash cap. This is basically a crown for a valve stem. It slips on top of a pitted valve stem to create a fresh surface on which the screw can act. However, the lash caps I installed very quickly deteriorated to the point of uselessness. I removed them and sent them back to my supplier. Later he had them hardness tested, and they were found to have wildly varying hardnesses. His source refused to give up their source, so he and I were stuck. If you can find lash caps of the proper size and have them hardness tested before use, that may be your best bet. Otherwise, if your valve stems are pitting, you might consider adjusting your pitted valves .001" tighter in an attempt to compensate for the dished valve. This is sloppy at best, since one doesn't really know how deep the pit is, and your hardfacing has already been breached.

Another area of the valve train subject to excessive wear are the upper rocker arms and their shafts. Aluminum bushings are pressed into the rocker arms. Over time, these bushings wear into an oblong shape, making consistent valve clearance adjustments difficult. (A more likely area to suspect if your valve adjustments seem to quickly "pop" out of adjustment, are the faces of the cam followers. The edge of the follower can wear into the lobe of the cam, creating a ridge between the worn surface and the virgin surface. When rotating the crank by hand to perform a valve adjustment, the follower can ride up onto the ridge. If you adjust your valves under this condition, once you start your engine the follower will pop back down into it's normal wear track, causing the valve clearance to open up.) Even in my normally aspirated CX500 engine, by 60,000 miles the rocker arm bushings were so worn that the shaft had worn completely through the entire bushing and was beginning to ride on the steel itself of the rocker arm! Fortunately, upper rocker arms and shafts are easy to replace, although not cheap.

Still another area of the valve train subject to abnormal deterioration is the camshaft. Between Tim Deinhard and myself, we have disassembled about seven CX Turbo engines with mileages from less than ten thousand to over thirty thousand miles. On the lobes of all cams, we observed varying degrees of pitting, from "disconcerting", to "Oh-my-God"! I used the term deterioration above since all of the cams measured within lift specifications. Our cams do not wear abnormally, they break down structurally, causing small to large pits on the face of the lobes. If the problem stems from bad Honda parts, you may be able to sidestep the whole problem by sending your pitted cam to:

Jim will perform a grind-weld-grind job on your cam with hardened steel. Price runs about $175 per cam if Megacycle already has a master for it, which they do for the CX650 Turbo thanks to Tim Deinhard and myself. Tim Deinhard and I pooled our CX650 Turbo cams and sent them to Jim. We also sent Jim a brand new CX650 Turbo cam for him to create a master from. Jim is used to creating new radical cam profiles for racers, so be sure to mention that all you want is a stock profile grind-weld-grind. If you have a CX500 Turbo cam you want redone, you will need to ask Jim if he has a master. If not, he will need to create a master for that cam, which will cost a considerable amount more for the initial cam, not to mention that he will need to be supplied with an unworn, new cam from which to make his master. None of the reground cams Tim and I have installed have been removed and inspected, so we cannot conclude that they will not pit as a Honda cam will. Since the nature of Jim's business requires he supply top-notch quality goods to serious racers, I trust that the durability of his cams are at least equal to Honda's. However, there is still a chance that even a Megacycle cam could pit, if the problem is not a part problem, but rather a lack of lubrication.

To sum up the valve train problems, I would not rule out the lubrication deficiency theory. For starters, there just seem to be too many parts wearing out and pitting in the CX Turbo engines to be attributable solely to an isolated parts problem. Second, it is well known that Honda has pulled a few real boners in mechanical design in the past, including all pre-1986 V-four engines: Sabre, Magna and Interceptor. All of these engines suffered lack of lubrication in the valve train, causing camshafts to wear out. The Interceptor also was known for smoking it's connecting rods. Now, production numbers for our Turbos were so miniscule compared to those of other bikes, that to expect any acknowledgment from Honda that our CX Turbo's may have a lubrication problem akin to the V-fours would be laughable. In any case, what could anyone do about it? Here is what I do. I ride my CX Turbos and savor their incomparably unique roll-on power, but with the full knowledge that in twenty thousand or so miles I will need to go through the engine and replace key components. That is the CX Turbo trade-off. We are proud owners of rare and unique bikes, and therefore should be willing to sink a little more time, money and effort into preserving them than we would for a more plebeian mount.


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