® The Seven Deadly Sins of Custom Bike Building, Sin #4: Unwarranted Faith in Aftermarket Parts

Aftermarket parts. Big subject; more so than folks who don't work in the industry realize. Any longtime dealer tech can tell you of many incidences where non-original parts had to be drilled or bent or welded, or machined or whatever, to make them fit. Case savers, fairings, saddlebag kits, different handlebars, floorboards, whatever. We always dreaded the accessory whose manufacturer claimed, "universal fit." Yeah, right. I can still remember drilling aftermarket Gold Wing engine guards so I could synchronize the carburetors, and notching saddlebag guards just to be able to change rear brake pads. Very very common. While the necessity of remanufacturing the parts isn't as common as it once was in the aftermarket world, in some ways the situation is actually worse than it was in the 70s. Because today the part in most cases fits, but then doesn't perform properly. Shops all over the globe are reporting bad results from aftermarket clutch levers on newer bikes, for example. In many cases the levers actually change the way the engine runs, because an incompatiblity with the bike's clutch switch causes changes in the engine's ECU. Another current issue is aftermarket billet engine covers that leak or interfere with proper cam chain tensioner operation. And there is still much more.

Once you have worked on the inside of the industry, and understand how carefully the OEMs make their parts, and how each part affects the other, you come away with a new appreciation for factory engineering, and a more jaundiced view of aftermarket replacement parts. The fact is, the powersports aftermarket industry has never approached the kind of fitment assurance and functional reliability enjoyed by its auto counterpart. Not at all. Motorcycle owners should not assume the same kind of situation exists as if you were to go to your local Autozone and pick up a new water pump. There just is no comparison. Ninety percent of aftermarket parts for non-racing, road-going motorcycles are just plain junk. If they fit right they won't adjust right. If they adjust right they don't work right. If they work right they don't wear right. And if they do any of these things right they have other drawbacks, such as the case of aftermarket foam air filters whose oil runs off of them and pollutes the bike's intake system! You can't win so much of the time with aftermarket parts.

Besides all this, the most persistent problem with aftermarket parts and what defines them today is that with many, their performance doesn't come close to matching their claims. In a few cases the situation is bad enough that you have to wonder how the makers of the stuff stay in business, such as in the case of carburetor rebuild kits. Take just the Honda vintage DOHC four line, the 750, 900, 1000, and 1100 series of motorcycles made between 1979 and 1983. Aftermarket carburetor kits for these carbs are crap. They're just no good. Their metal parts are known causers of engine performance issues, and their rubber parts are sub-par as well. The manufacturers of these kits just don't bring to their product the level of engineering inherent in the original. How can they, with immeasurably fewer resources?

Aftermarket gaskets are a big deal. Those of us involved in the vintage world have discovered what dealer techs knew all along: that Vesrah and Athena and their ilk just aren't worth the effort, unless you happen to like taking your engine apart again right after rebuilding. I learned about Vesrah gaskets the hard way, when as a shop tech I tried using them on Suzuki and Kawasaki and Honda maintenance services. The rubber Vesrah valve cover gaskets were softer and more prone to heat distortion, and just wouldn't stop leaking. Their paper cylinder base and head gaskets for Honda fours were made thicker than stock, leading to insufficiently compressed Honda and Kawasaki oil gallery sealing o-rings, and thus consistent and aggravating leaks. On Athena cylinder base gaskets for the SOHC Honda 750, the dowel holes are misaligned, leading to gasket tears on assembly. The head gaskets, compared with stock look like little more than reinforced cardboard and deteriorate after less than a hundred miles of use. And the rubber parts in these brands' kits? Forget it. Even Athena and Vesrah's most ardent defenders admit you can't use their rubber bits but have to go with OEM. When it comes to aftermarket engine gaskets, Cometic is the only brand I would even consider using today, and that only if I couln't get the original. Their 1970s and 1980s Honda and Kawasaki head gaskets at any rate are almost indistinguishable from OEM.

Now aftermarket exhausts. Wow! A whole subject by itself. In fact I have had much to say about aftermarket exhausts elsewhere on my site. For now, I'll say only that they flunk nearly all the criterion we have put on the table in this article, and some of them all at once! Aftermarket exhausts for vintage Japanese motorcycles have always, and continue to, fit badly, leak, interfere with suspension or other chassis points, reduce ground clearance, are noisy, require repacking, are constructed at about the quality level of frozen dinner trays, employ incredibly ugly mounting hardware...and I could go on and on. To be fair, there are a few out there that rise above the rest. Supertrapp, for one. Something 70s and 80s Japanese bike owners need to realize though, any claims of engine performance increases with systems made for these bikes are insincere at best. And my opinion on how these systems look, which could be said to be their major attribute, is most are ugly, looking as they do (and are) cheaply manufacturered, poorly engineered, high profit margin collections of under-sink plumbing tubing.

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