 Techline-October08-Oil Coolers - Pt I - Adversary is Heat (cont.)
Pt I article continues
Lugging & Detonation
Lugging, which is running the engine at too few rpm in too high a gear, has always been a problem for some. Put another way, riding the bike at too few rpm causes lugging, the symptoms including anemic power and lurching. The cure for lugging is always downshifting to a lower gear, sometimes two gears lower. It is a huge problem with the torquey 2007 and later TC 96 with its supercharged primary gear ratios and high-ratio rear-drive pulleys. The TC 96 powertrain really cooks when ridden at the proper rpm ranges, but many H-D riders are having difficulty adjusting to these never-before-seen H-D ratios. Lugging exacerbates detonation as well as amplifying the much-complained-about fifth-gear chatter in the 2007 Cruise Drive six-speed transmissions. The cure for both maladies, on my bike anyway, seems to be putting the engine under load, in the proper gear, at a sufficiently high rpm. Riding at a higher speed in each gear than what traditional riders are accustomed to is necessary on 2006 Dynas and all 2007 Twin Cams. If transmission clatter or whine is an issue, install either the BAKER F6F helical gear replacement kit or the Harley-Davidson IDS rubber-stopped rear pulley kit to alleviate the noise.
Gear Ratios
The massive increase in the engine compensator sprocket from 25 to 34 teeth and the clutch sprocket from 36 to 46 teeth gives a primary ratio of 1.35 engine rotations for one rotation of the clutch hub, and, therefore, one rotation of the transmission mainshaft that the hub sits on. Compare this to the former primary ratio of 1.44 engine rotations for one rotation of the clutch hub and the transmission mainshaft. The final ratio for 1994-2006 Big Twins (except 2006 Dynas) is 3.15:1, thus turning the engine 3.15 times for one rotation of the rear wheel. The ratio for the 2006 Dyna is 2.88:1, so the engine turns 2.88 times per rotation of the rear wheel. Lastly, the final-drive ratio for all 2007-08 Big Twins is 2.78:1.
Therefore, the engine turns 2.78 times for each rotation of the rear wheel. The difference between the 2006 Dyna and all the 2007 and 2008 Twin Cams is a reduction of two teeth on the rear pulley of the 2007-08 models to 66 teeth from the 2006 Dyna’s 68 teeth. However, these are both reductions from all other 2006 and earlier Twin Cams, which have the traditional 70-tooth rear pulleys.
The overall gear ratio chart shows the number of engine revolutions required to turn the rear wheel one 360-degree turn. For example, in first gear a 2008 model takes 9.31 engine revolutions to rotate the rear wheel once while a 1999 Big Twin takes 10.81 engine revolutions to obtain the same goal in first gear. Overall gear ratios take into account the internal transmission ratios with the primary and secondary gear ratios while the final drive ratio is a simple multiplication of the primary ratio times the secondary ratio. These subjects are covered and explained in detail in volume one of my series Donny’s Unauthorized Technical Guide to Harley-Davidson, 1936-2008.
As you can see in the accompanying chart, the first domestic model showing its overall gear ratios when in a specific gear is the first king of the highway, the Shovelhead FLH Electra Glide. This bike uses a chain final drive and 51-tooth rear wheel sprocket combined with a four-speed transmission. Since they have a belt final drive, a 70-nub rear pulley is standard for the five-speed transmission on both a 1999 EFI-equipped Big Twin and the 2005 Twin Cam FLHT. The 2006 Dyna has a final drive pulley with 68 nubs, while it is 66 nubs for the final drive of all 2007-08 96" Twin Cams.
Harley-Davidson International (HDI) models generally have taller gearing for better highway touring because of increased speed limits in other countries. The taller gearing results mainly from a rear wheel pulley that’s smaller in diameter and, therefore, tooth count, than those used in the US. European final-drive pulleys are as low as 61 nubs for high-speed riding on the superbly designed and maintained autobahn-like highways of Europe.
I have a theory that will offend many. Some traditional riders are not used to these dramatic gear-ratio increases, so they ride in a lower rpm range without realizing it because that is what they have always safely done. I know there is an offensive noise in many 2007 transmissions. I also know that aggravating this transmission noise, along with engine detonation, is lugging, which is riding in a gear at too low a rpm. New riders many times lug older Harleys, but are unprepared for the supercharged gear ratios of the 2006 Dynas and 2007 and later Big Twins. However, the Dynas do not seem to present much of a problem because of their hot-rod nature. The 2007 to present baggers are a much different story. I mean, whoever heard of breaking in a new hog at up to 75 mph on the highway, which is what I did with my 2007 Street Glide with nary an adverse mark on the pistons. I know this because I hopped up my FLHXI after break-in and was anxious the see the pistons, which were still like new. Detonation exacerbated by lugging occurs when the rider incorrectly matches rpm to the gear engaged.
In low or first gear, rpm must start at idle, which is around 1000 rpm. The rider should twist the throttle, accelerating away from a stopped position, steadily increasing rpm through the powerband. Neither baby nor abuse the throttle, just twist it as in normal riding. Shift into the next gear near the top of the powerband. If shifting into the next gear at a low rpm, the bike will slowly surge, laboriously attempting to reach the comfort zone of the powerband. Pinging (detonation), emanating from the cylinders, will lend noise to this overworking of the engine. Difficulty gaining speed is a major indicator of either lugging or wind resistance. Speed will indicate which is the case. Going 50 mph in sixth gear is definitely lugging. When pushing the bike to 100 mph and over you encounter much wind resistance. Without the benefit of a water jacket with a cooling radiator that keeps engine temperatures within acceptable ranges, the poor Harley-Davidson air-cooled engines fall victim to the ravaging effects of detonation. While a water jacket is a cure for temperature control, it is not a Band-Aid to suppress the effects of rider lugging.
Air & Liquid Cooled
I always hear the ongoing controversy about whether oil coolers are necessary for a Big Twin or Sportster Harley-Davidson engine. Why there is not unanimous support for oil coolers is beyond me. Back in 1999, I even heard an H-D engineer (who wishes to remain anonymous for obvious reasons) say that he thought the factory did not recommend oil coolers for the new Twin Cams because the powers-that-be felt that the H-D rider would interpret their inclusion as an indication that there was something wrong with the new engine. I can say that, in all my discussions with factory executives and engineers, they were extremely proud of their Twin Cam development. They were also protective of their new baby. Their legitimate fear, as I interpreted it, was the traditional resistance to change by the Harley rider. Writers and mechanics like me would have leapt to Harley-Davidson’s defense if it were criticized for using an oil cooler on an air-cooled engine.
There are some Harleys, such as the V-Rod and the 2008 Buell 1125R, that do not need oil cooling because they already have temperature control. These engines are liquid-cooled via a water jacket that encases the engine. Liquid cooling keeps an engine’s operating temperatures within a predetermined lower range of temperatures. You may have seen on television or heard the stories of the V-Rod left running for a long time in a metal transport box in the Nevada desert with no air circulation whatsoever. An air-cooled engine like the Twin Cam would have suffered from the heat in short order, but the V-Rod did not miss a beat because its engine is liquid- cooled. Liquid cooling makes it eminently easier to plan ignition timing and certainly reduces, if not eliminates, detonation in most circumstances.
We are not so fortunate with an air-cooled engine that is subject to the vagaries of hot days and slow, rush-hour traffic. We are at the mercy of airflow in sufficient quantity to keep the engine within operating temperature confines. In addition, we have a rear cylinder that’s out of direct airflow and feeling the heat of the front cylinder. This gives us half the engine running at hotter temperatures than the other half, which may be running too hot in its own right. So, what is there not to get about the need for an oil cooler on an air-cooled engine? Liquid cooling an engine is the permanent and consistent solution. However, an oil cooler is a wonderful assist in lowering oil temperatures on air-cooled bikes by protecting the oil from oxidation breakdown.
Article concludes in the next thread. Check back issue for pix and more information. |
Linear Mode
