® The Seven Deadly Sins of Custom Bike Building, Sin #5: Ignorance of OEM Specification or Technique

Sigh. My, this one will be difficult to keep to just a few pragraphs. This area, more than any other, exemplifies the saying, "Don't bring to high performance work low performance thinking." The fact is, I have seen more bad work of this type than any other.

A few years ago one of the national motorcycle magazines ran an article about a pretty well known vintage bike builder, displaying one of his creations on a full page inside. Right away something stuck out to me. The front axle clamps were on backward. The bike was otherwise beautiful and the builder gifted, and I realize this is not really a big deal. But it is a good example of what I am talking about: presumably high performance work done in low performance ways. Think about it. Here we have a bike presumably built to perform better than stock; I mean that is most people's expectations, that the builder is somehow ahead of the game, specifications-wise. But in reality he (and I know and respect him) isn't even aware of the stock specifications, let alone those that might be better. The point is you can't rise above the factory if you don't even make it up to the factory's level. Wouldn't you say this is so? Said another way, you can't have high performance if you're missing even meeting standard performance. It's an impossibility.

There are a lot more of these kinds of things I see where folks have ignored the factory's way to their detriment. Honda SOHC oil filter bolts is another prime example of a factory specification folks ignore thinking they know better. There are actually two important specifications inside the stock bolts. First, they contain within them a carefully designed relief valve system, a kind of safety valve designed to bypass the oil filter in the event it becomes clogged in order to save the engine. And it is designed to do the same thing in the event the conditions are so cold that the oil is to thick to flow readily yet someone is revving the engine anyway. Do you really think the makers of the aftermarket bolts have devoted the same careful engineering into their copies of this part? Think about it. And it gets worse, for there is the second overlooked spec. Honda's oil filter bolt appeared first on the 1969 CB750. The first production run of ths bike actually included a bolt having a 14mm head, just like some of the aftermarket ones (many are even 17mm), rather than the 12mm headed bolt that quickly became standard and that everyone is familiar with. A lot of folks probably think that 12mm head is too small, mainly because they tear it up. What they don't realize is Honda themselves reduced the head of the stock bolt from 14mm to 12mm for a reason. Look closely at the bolt and you will see it has a large built-in flat washer, which is there to apply adequate pressure on the aluminum oil filter case. The geometry of this bolt makes its large flat area multiply torque, and thus it tends to stick tightly and not want to come back off again. Not incidentally, the bolt's original 14mm spec promoted over-tightening, further aggravating the situation and additionally causing oil filter case distortion and oil leaks at the case. Honda realized this before the second production run and made the head smaller so folks wouldn't overtighten the bolt (a smaller wrench is also shorter), taking care of both problems. But what do folks do? They put these badly-engineered 14mm -- and more likely today 17mm -- oil bolts on, unknowningly undoing all of Honda's careful and reasonable intentions. This is what I mean when I say, some of these folks think they're one up on Honda but are actually moving backward. Low performance thinking. Not even up to (what is in some of their minds) the more pedestrian stock performance.

And still cafe and chopper and brat bike builders and parts purveyors are poo-hooing the long-established and very real prohibition against dressing Honda valves. What is it with these folks? Haven't they ever seen receded valves? Don't they know the valves are so soft they are often junk in just 25,000 miles? What is grinding them going to do but waste them prematurely? Again, folks who want you to think they are high performance people, but who are obviously stuck in the low performance world. They "dis" the factory's specs, but are ignorant of what they are. They claim to know better, but don't even know what they should know.

The uninformed shunning of stock point ignition is another example. I have had much to say on my website about the stock Honda point ignition as it compares with the common aftermarket Dyna S and similar simple points replacement systems. You have only one reasonable argument for not keeping point ignition, and that is the contact points' necessity to be replaced every 12 to 15 thousand miles. There is no adjustment advantage in Dynas, because if anything they are equally as difficut to set up as is a points system. Nor is there a performance advantage, as the only thing a Dyna S or its like replaces is the points. The system is still Kettering in design, with all that that means in terms of strengths and weaknesses. The fact is, a carefully set up points assembly will perform exactly like a Dyna, a reality that I have proven on customer's motorcycles for decades, and most recently only a few weeks ago on a customer's GL1000.

While on the subject of ignitions, it is timely to mention spark plug wires. You often see colored spark plug wires on modified motorcycles. There is no advantage on a 70s or 80s Honda. The stock wires are stainless steel, not resistive core as are automotive and Harley wires, which means 80 percent or more of those for sale as accessory plug wires. But even if you use good metal core aftermarket wires, make sure they are attached correctly. This means their coil ends clean and correctly attached to stock coils, or their terminals soldered on, not simply crimped, if the coils also are aftermarket, and of course the plug caps properly screwed on tight. Plug wire installations create more problems than they solve when performed by the unknowing.

Obviously, this concept is not limited to motorcycles of any one origin, for if anything, Harley owners and builders are just as complicit. Take for example the use of aluminum pushrods in built H-D engines. No way would I do that, not after seeing the 600 in-lb valve springs that are required to keep high valve lift stroker engines from exploding. Or how about S&S Super carburetors? If you really think that's a good carb, just do this: Get a well set up and adjusted RevTech or Mikuni or a leaned-on Keihin on there -- even an SU! And see what happens. You won't be able to throw that Super far enough! Then there are straight pipes, which by now everyone has to realize sacrifice function for form.

One more, and one I feel strongly about. I am saddened when I am rebuilding a set of carburetors and find that in all the bike's 30 to 40 years of maintenance, it never received a proper tune-up. This fact is evident whenever I find idle screw mixture limiter tabs or flags still intact. Whatever someone has told you, it was and is still today NOT unlawful to remove these limiters, and was and is in fact NECESSARY to properly adjust the carburetors. Further, and more to the point of this article, it is especially poignant and ironic when said carburetors have a jet kit, aftermarket needles or similar modifications. Again, supposedly "high performance" actions combined with low performance thinking.

We could go much further down this road, this survey of ostensibly high performance work that is done in low performance ways. But I'll just mention in passing Barnett clutch discs. The most neophyte mechanic in the shop was aware of this stuff being crap back in the 70s. Why has no one picked up on it after all these many years? How about stock clutches that are misadjusted? I see this on every bike that comes into my shop. And big bore kits that are installed into haphazardly machined cylinders, oil line kits installed on V4s whose real need is not oil system modifications at all. Like I say, it all boils down to an ignorance of the factory specification.

I'll say it again. You folks that think you're one-upping the factory (and I'm no slave to OEM), when you don't even know why and how the factory does what they do, how can you possibly be making an improvement on it? "Low performance cowboys."

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