Issue link: https://read.dmtmag.com/i/693447
70 nJuly 2016n www.thunderpress.net THUNDER PRESS Rock 'n' Rods Funny (as in odd) that just a few weeks ago, I would get—almost simul- taneously— a comment about a col- umn I wrote three years back about TC crank "scissoring," and a "restoration project" in the form of a 1974 Triumph Trident T150V. Trains of thought erupt. Discuss? Well, let's take them kind of in order, starting with the comment. David Lindsey on April 30, 2016 6:37 p.m. wrote: "My 2003 FXDL has a manual primary chain adjuster. It started puk- ing oil into the breather after 40,000 miles. It had cam chain tensioners changed at 28,000 miles worn but still together. Crank is scissored out of spec. Oil pump damaged, not scavenging oil from crank and cam cavity causing excessive oil carried through breather. Cam plate damaged, pinion bushing damaged. The automatic primary tensioner in a 2007 Ultra Glide has taken transmission main shaft bear- ing and seal, rear primary seal, clutch and crank seal and bear- ing out at 37,000 miles of a lady's bike I'm repairing. These same problems exist in the new Twin Cams. Don't fi x what isn't broken but this has been estab- lished as bad design." It might sound a little cold… but I wish David had taken some sound advice a while ago. It might very well have kept him from having to write that comment, to say nothing of potentially preventing his engine issues. The advice? Don't fool around with the older cam plate, oil pump, etc. arrangement on Twinkies and hope for the best. Purchase and install the H-D upgrade kit #25284-11, along with all the other stuff required mentioned in the fi ne print (#25285-08 spacer kit, #17045-99D cam service kit, #25566-06 drive gear retention kit)! Is he right in saying the stock arrangement for his bike is "estab- lished as bad design?" Probably, but he's been out using it and knew that, all along. So, no sense lamenting after it bit him. Better to deal with it head on, before there's trouble. Fix what isn't broken before it breaks if you damn well see it coming! Some things. First, I think it's fair to say that the list of troubles his bike is affl icted with, culminating with a scissored crank, comes down to (and originates with) oiling issues, heat-generated stress on the rods and metal fatigue (probably including an oval-ed big end on the rod). Second, the SE upgrade kit deals effec- tively with preventing all that! Most especially improved oiling. Do not underestimate how important that is! Lastly, it dawns on me, I'm every bit as much a procrastinating cheapskate as he is, or at least I might be. I say that because, while he debated until his motorcycle made the decision for him, I'm doing the same thing as this is written. And it all comes down to connecting rods! Which brings us to a brief rehash of technical stuff regarding H-D oiling and my new, old British Triple. Both machines could be described as archaic in their respective approaches to these critical issues. H-D with its knife and fork rods and low-pressure oiling and the Brit sled with its… well… let's just get on with it, shall we? Making the connection We might as well start with some basics; late-model (2007–on) Harleys use (what I believe to be) a type of (steel) powdered metal rod, with no big-end thrust washers and no small- end bushing. There needs to be that all-important microscopically thin fi lm of oil in there somewhere, doesn't there? Said lubricant is dispersed (we hope) via a notoriously low-pressured system. All of which is in most peril of malfunction or failure at two points in the engine "use" cycle—idling and wide-friggin' open! (The fact that the oiling system is better than it was on David's 2003 model facilitates use of the new-type rods but doesn't obviate certain realities.) At one extreme you have very little lubricant fl owing to critical hot spots like the little end of the rods. At the other, you have mas- sive stress loads on both ends of the rods, at the same time and under con- ditions when over-heated oil is likely to fail in its dual roles of cooling and lubricating. In a sharp contrast of design, but working under the same conditions and constraints, we have the Trident. As some of you Anglophiles might know, Edward Turner did something insane back in 1937, when he designed his game-changing parallel twin. He used a material designed by Rolls-Royce for their aircraft program, specifi cally "R.R. 56," to make connecting rods. Often erroneously called "aluminum," these Hiduminium (for "High Duty") connecting rods do use bolted-on caps (like cars) but the cap itself is made of steel and employs split plain bearing inserts at the big ends. Triumphs use a high-pressure oiling system. The Trident, in particular, needs over 70 lbs. of pressure to live and was the fi rst motorcycle to be issued an oil cooler as standard equipment. In other words, it couldn't be much more different than the Harley approach! Add to that the state-of-the-art material used in the Harley rods versus the ancient alloy used in the British rods and you have the makings of an entertaining discus- sion, right? Stronger or longer? The 'net is full of chat about Harley rods going oval at the big end and the aftermarket "solutions" abound, more than ready to help. Almost all of them involve "stronger" rods. Same thing, on a much smaller scale, applies to replacement rods for Triples. This situation exists because Harley owners fear material weak- ness in their new factory rods and Brit-wits fear old age and fatigue in theirs. Since "fear," as the seminars teach, stands for "false expectations appearing real," we might want a few more facts before reaching an expen- sive decision, in either case. Trouble is, not being metallurgists, we aren't really qualifi ed to separate the facts from the crap in most instances. It's complicated! Puts me in mind of a great old Jimmy Stewart movie No Highway In The Sky. (Available on YouTube, if you haven't seen it, or need a refresher viewing.) Stewart plays a nerdy scientist who realizes that metal fatigue is going to make the tail of his company's latest airliner fall off! His experiments prove that, after a certain number of fl ight hours (1,440, I think it was) the metal will fail with no warning and no clues whatsoever! One moment the structure is sound and the next, catastrophically lethal. Connecting rods are like that, with one important difference. Connecting rods have no real known conditions for longevity and reliability! You don't get a predictable "life" of X number of hours or dependable parameters for functional failure. Since no one knows when, or how, all you get is a nasty surprise when a rod effs up! So, we hedge our bets and cover our butts with "stronger" rods. As though that was all there was to it. But what the OEM Harley rods are I-beam style. You can see one popular variation (H-beam) in the above pic, but there are more. Besides materials, lubrication, heat, loads, stresses and basic engine design, this is an important aspect of connecting rod design. In the end, the key is to balance all these elements with a design that stays happy in its intended work for as long as possible. Once upon a time, this was the way to a high-performance connecting rod! DIY lightening, polishing (hopefully shot-peening) and more really did make a difference. The thing I'm fas- cinated with is how these rods resisted being turned into shiny pretzels, metallurgy being what it was before World War II. What is known is that these things fl exed at high rpm but rarely broke, so maybe that notion of elasticity in the material is what kept them alive. Of course, back then, if you bent 'em you could bang 'em straight again!