Wednesday, May 28, 2014

Some Reflections on American V-Twin Motorcycle Engines

I have worked as a mechanic at both Harley-Davidson and Victory shops in a part-time capacity for sixteen years, and I own both makes of bike. I have ridden countless bikes and worked on all kinds of stuff. Here I offer some thoughts about these engines with which I have the most experience.


The Harley-Davidson Twin-Cam Big Twin Engine (TC): This is, of course, the current version of the all-time icon of v-twin motorcycle engines—the Big Twin (BT). The BT has come a long way and is better than ever. Harley’s days of quality-control problems are long over, although the TC still has some design features that can cause some problems of their own.

A few negatives: The cam-drive system has had some problems, as the very small tensioners pressing against the little drive chains in the gear-case can wear and sometimes fail, although this problem has been addressed to some extent. Switching over to a gear system requires an exquisitely small pinion shaft run-out specification that can be difficult to achieve. If the run-out is too great, the wobbling against the gear teeth can be dangerous, which is why Harley uses a chain in the first place, since a chain can accommodate much greater run-out.

Also, as the air-cooled TC has gotten ever larger during the displacement wars, the heat stress has become a major problem for the exhaust valves, which are getting so hot that they can burn up. Also, the temperature difference between the intake and exhaust sides of the head can become so radical that the aluminum head itself can actually distort, causing head gasket failure. Harley is now offering the “Wet-Head” engine on some of its touring bikes, which is actually running coolant through little radiators in the fairing lowers and then up through passages in the heads that surround the exhaust valves. The other models still have to make due without this cooling.

The TC bikes have separate engines, primary drives, and transmissions, all of which have to be bolted together. This increases the number of gaskets, seals, and o-rings required for oil control. This gives the bike more opportunities for leaks.

The final-drive pulley is sandwiched between the primary drive and the transmission, making the belts, which cannot be split and reconnected, a major operation to replace. The primary drive must be separated from the engine and transmission to access the belt. Most riders don’t have the tools, skills, or knowledge to dive into this particular mess, so they’ll have to open their wallets on that one!

With all that said, I would argue that the TC is a fine engine overall. The positives: The TC has a legacy, a look, and a soul that no other engine possesses. It is butter smooth, torquey as hell, and sounds like no other engine on earth. I adore the BT transmissions—they are incredibly smooth to operate and shifting them is a joy.


The Harley-Davidson Evolution Sportster Engine (XL): Another Harley icon. Rubber-mounted in the frame since 2004. The XL was once the hottest motorcycle engine on earth. Well, no longer, but its legacy cannot be questioned. I have owned an XL since 1995. I love it now more than ever. Here are my thoughts on the XL:

A few negatives: Older XLs, like mine, were mounted directly to the frame. They will make your fillings hop out of your teeth. The newer, rubber-mounted XLs are much smoother, but the frame became significantly heavier, affecting the power-to-weight ratio. Older XLs feel lighter, narrower, and more nimble than the new ones, although the vibrations are the price for that.

Whereas the older XLs had a “cartridge” transmission, allowing the tranny to be removed from the engine without splitting the cases, the newer ones require case splitting. I am fortunate to have the older design.

Older XLs had a major problem with rocker-cover-gasket leaks, although the gaskets have gotten better and the newer XLs have a different design, thereby minimizing the problem.

A few positives: The XL has straight push-rods, unlike the angled push-rods of the BTs, making for a sturdy valve train. The gear-case uses only gears without chains, and it has been bullet-proof for decades. The engine is a unit construction, eliminating the need to fasten three systems together, making for a strong unit with fewer leak opportunities. The drive belt is off to the right side of the engine, making belt changes far simpler. XLs have not suffered from the heat stresses of the TCs, but that is simply because they are smaller (74 vs. 103 cubic inches). Instead of the long, double-row chain of the BT, the XL uses a shorter, triple-row chain, making for a primary drive that never dies (mine has gone for 110,000 miles and shows no signs of stopping).

I have great appreciation for the TC engine, but I prefer the XL engine myself. If the XL engine were simply enlarged to the size of the TC, well, buh-bye Big Twin! The sheer design of the XL is vastly superior and Harley hit a home run when they designed it.


The Victory Freedom V-Twin Engine (VIC): Victory has existed since 1998 and has made unbelievable progress in a short period of time. Here are my thoughts on the VIC:

A few negatives: Well, it’s another big v-twin engine. Nothing too radical there. And for people accustomed to push-rods, it might look a little off. The older VICs were fugley. I mean FUGLEY. I find the newer VICs to be quite attractive, however. The trannys on Victorys have always been clunky. I mean CLUNK! No one will miss when you click into first at the light. Due to the unit construction, tranny work requires case splitting, and this is a major operation on the massive engine of the Victory, which is 106 cubic inches and weighs somewhere around 250 pounds. Luckily, Victory engineers have made some frame mods to simplify engine work, but it still won’t be as easy as it is with a Harley.

A few positives: Four valves per head makes for an excellent flow of gasses. The single-overhead cam allows for hydraulically adjusted valve trains (which BTs and XLs also enjoy with their push-rod designs), making for a no-maintenance valve train. Oil passages for cooling (the oil pump has a pump for lubrication and one for cooling) in the cylinders and heads allow for a degree of cooling that air-cooled engines cannot achieve, and without the need for a different fluid. Long cam-chain tensioners ensure a long tensioner life. Unit construction is very similar to the XL, with a direct-drive transmission that exits the right side of the engine, making belts easier to change. Gear-driven counter-balancers in the crankcase manage excessive vibration without the need for rubber mounts (some TCs also do this). The primary drive is entirely gear driven, eliminating any need to adjust a primary chain.

So here is my overall take on these three fine engines. My heart belongs to the XL. It was my first bike, which I bought new in 1995, and it is still my daily rider. Why is it STILL a daily rider? Because it’s a freaking XL, and the XL design is awesome!

If I bought a brand-new bike today, what would it be? The Victory. The VIC engine is a masterpiece of engine design, and my experience with my own Victory has proven that the engine is stupidly reliable and oil tight. My 2004 Victory TC lives in the desert, has a sidecar on it, toured the country twice, has 50K on it, and has neither leaked a drop of oil nor required any engine or transmission repairs of any kind.

Although I appreciate the TC, I wouldn’t buy one, personally. The soul of Harley lives in my XL perfectly well. The XL is, in fact, the longest-running continuously manufactured motorcycle in history. Talk about a legacy! So I will keep my XL forever and buy new Victorys.


And then came Indian… Indian, manufactured by Polaris (as is Victory), now has a 111 cubic inch v-twin push-rod engine. Its under-square design guarantees broad, massive torque. I do not have sufficient experience to opine much on this topic, so we’ll have to see what happens. Having studied the design features of the Indian engine, I am still convinced that the Victory engine is ultimately the best design, but then, not everything depends entirely on the engine! You must choose the bike that speaks to your soul! Happy riding!

6 comments:

  1. I would like to say this is very nice blog having great information & beneficial for us. For more information you can visit Used Engines Motorcycle

    ReplyDelete
  2. Excellent summary, thanks for posting

    ReplyDelete
  3. Thank you for sharing your expertise. I'm currently eyeballing the 2016 Indian Dark Horse. What do you think about them removing the oil cooler on that model? Are they really that confident about the air cooling on the 111 while steering that bike around in slow city traffic? I wish Victory made better looking bikes. They are just so...bland...

    ReplyDelete
    Replies
    1. Bland compared to what, Come on. Take a look at the tank on my 05 Pin, and it came that way, a pre-scuplted teardrop. Who wants a big fat rounded tsnk, anyway. You need to get un to a Vic dealer, sit on and ride one, and the, - - perhaps retink your post.!

      Delete
    2. Bland compared to what, Come on. Take a look at the tank on my 05 Pin, and it came that way, a pre-scuplted teardrop. Who wants a big fat rounded tsnk, anyway. You need to get un to a Vic dealer, sit on and ride one, and the, - - perhaps retink your post.!

      Delete
  4. Thanks for the update you have nicely covered this topic. keep it up. ring rolling forging

    ReplyDelete