Every other day, I answer comments on ICB where people eager to get onto the Royal Enfield bandwagon have one question that never seems to go away. Which is better, Royal Enfield Unit Construction Engine or the Royal Enfield Cast Iron Engine? Now, here’s the answer, it is the Unit Construction Engine that is better. Period. And If you really are interested to know why it is so, you must read ahead.
Here’s a quick comparison and if you really want to understand more about the intricacies of the different Royal engines, you need to read the post below this comparison. However, for a quick comparo, click on the images to enlarge.
I own, rather owned a 2009 Royal Enfield Bullet Machismo 500LB which I bought mainly because of it being the most powerful Royal Enfields around at that time and age. I also bought the AVL engined Bullet because it was better than the cast iron engine in terms of reliability as well as performance. In due time, I began working on my Bullet on my own. But the 500cc AVL Lean Burn still required a lot of maintenance, especially if ridden hard. So, here is Royal Enfield’s latest solution, the Unit Construction Engine.
First of all let me explain what the UCE is all about. Previously, the Bullets, both cast iron engine and AVL LB engines used to come with three parts put together, called the Pre-Unit Construction Engine. The engine, gearbox and clutch cases were three different units altogether connected to each other independently. So what happened was you needed to change oil at three places each time. Now, that is a messy thing to do, and also considering the various gaskets that required replacement frequently, in simple terms, it was maintenance heavy.
Also, since the engine was separate from the gearbox and the clutch, a lot of power used to get lost in terms of transmission losses as the set up is not as efficient as modern engines. so, not only were the Cast Iron and AVL LB Bullets delivering lesser mileage but they were also making lesser power at the rear wheel even though they were making decent power at the crank shaft. Here are some figures. The Cast Iron and AVL 350cc engines both produced 18 Bhp at the crank, but this figure went down to 12 Bhp at the rear wheel. Power loss: A whopping 33%. Culprit: Transmission losses.
Now, the UCE 350cc engine produces about 19.8 Bhp at the crank shaft. At the rear wheel, the power is about 16 Bhp. So, that is only 20% power lost in transmission losses, which while still a lot in terms of modern motorcycles, is fair enough for a Royal Enfield, which is a low revving, big single. Also, the Unit Construction Engine is more fuel efficient than both the Cast Iron and AVL Lean Burn engine by almost 20%. While the 350cc CI and AVL engines used to deliver 35 kmpl, the UCE engine consistently returns 45 kmpl.
Now, let’s look at why I’m rating the UCE engine higher than the CI or AVL engine. First of all, let’s begin with the valve train. The UCE engine now uses hydraulic valve lifters(tappets) to instead of the conventional tappet arrangement. What happens in the UCE engine is, pressurized oil drives the pushrods in the engine. Due to the oil pressure being able to remain constant for long periods of time, the pushrods don’t cause the valve clearances to change like they used to in the older engines. So, you get more consistent performance. In other words, riding hard won’t make your valves loose anymore.
While I wouldn’t call the hydraulic tappets totally maintenance free, for street riding purposes they should do fine for at least 20,000 kilometers before needing any kind of attention. Coming to the Cast Iron and AVL engines, which use solid tappets to move the pushrods, very often the pushrods become loose thus requiring constant adjustment. So, you would have seen many Bulleeteers constantly running to their mechanics to get their “tappets adjusted”. So, not for nothing they said that the mechanic is the Bullet’s and the Bulleteer’s best friend.
The third big change in the UCE engine is that of longevity. The UCE engine will last longer than the Cast Iron as well as the AVL engine even if you ride hard. Here’s exactly why. Ask a Bulleteer who rides hard about how long his Cast iron Bullet will last at 120 kph. Chances are that he would say that he doesn’t even dare taking his Bullet to those speeds. Let’s find out why. The Cast Iron Bullets used to come with a floating bush big end. The floating bush worked well until it was immersed in oil and there was enough flow. Yes, flow, rather oil flow is the big buzzword here.
In, Cast Iron Bullets, piston type oil pumps were used. These oil pumps circulated about 1 liter of oil per minute at 5,500 rpm which is almost half the Bullet’s oil capacity. Now, at 5500 rpm, when the engine is revving at it’s very top, just 1 liter of oil circulating to cool down the engine means only one thing. Bad engine cooling. Oil, as you must be aware is the blood of the engine. Apart from lubrication, more importantly it helps keeping the engine cool by absorbing heat off the metal parts unto itself and then circulating it continuously to dissipate heat.
On the cast iron engines, which were designed in the 1950s, this simply does not happen efficiently enough. To be fair, speeds in the 50s and 60s were quite low as roads weren’t as well developed as they are now. The Bullet, back then was a decent ride but the Cast Iron engine has simply outlived it’s purpose. Brutal it may sound, but that is the truth. Royal Enfield attempted to make some amends in the late nineties when they headed to Austrian engine design firm, AVL. AVL gave birth to the AVL range of engines, whose biggest advantages were a better oil pump and a roller type big end bearing.
The AVL engines featured a gear driven oil pump which used to pump double the oil per minute when compared to the Cast Iron engine at 2.42 liters at 5,500 rpm. So, more oil being circulated means that the heat is being dissipated better. Also, the roller end bearings work better than the floating bush. The other big change was the aluminum block which, being the biggest advantage of the AVL engine also forced the engine to be the least popular. While Aluminum dissipates heat better, it also muffles less sound. So, the AVL engines were prone to valve train clatter.
This is one reason why a lot of Royal Enfield enthusiasts sill preferred the cast iron engine for it’s soulful thump even though the AVL engine was vastly superior to the cast iron engine. Now, think about this, if you would prefer thumping at 40 kph all day on a highway, you may still prefer the Cast Iron engine. For everything else, the AVL engine is better. But then again, the AVL engine is still inferior to the latest kid in town, the UCE engine as the UCE engine has improved valve train apart from a lot of other improvements too.
For starters, the UCE engine uses a rotary type oil pump which pumps our 9.5 liters of oil ever minute at 5,500 rpm. This is full four times more than the AVL engine and a whopping 9 times more than the 9 times than the cast iron engine. Obviously, if you’ve gotten till here, you’ll know how increased oil circulation will improve the longevity of the engine. For the record, my good friend Adrian’s 2008 Thunderbird UCE350 has managed to run strongly even after 60,000 kilometers with absolutely no repair work done to the engine thus far.
Just take a look at the sheer volume of oil being pumped in the UCE engine, which is many times more than the Cast Iron or the AVL engine could ever manage.
Also, the UCE engine comes with a anti-backlash system engineered into the cams which makes sure that the cam backlash is kept to the bare minimum, which increases the cam life as well as maintains consistent engine performance even under hard riding. Bulleteers will understand how frustrating backlash can be on Cast Iron and AVL engined bullets, which though featuring adjustable cam spindles were still troublesome if ridden at speeds of 80 kph and above frequently. Also, the UCE engine has a piston ring designs that eliminates blow by.
Getting into crankcase blow by is another topic for another day. So, you must understand that a lower blow by means lesser oil getting wasted or lower crank case pressures. Two more changes are an auto decompressor assembly that sits on the UCE engine’s exhaust cam that makes starting easier. The UCE Bullet is almost as easy to start as say a Karizma or a Unicorn and now, that is a huge change, isn’t it? Finally, the UCE engine also has an auto primary chain tensioner which makes sure that the primary chain has just enough tension to ensure best performance and least maintenance.
If you’ve read this much, first of all I thank you for your patience. I also am sure that armed with so much more knowledge about Unit Construction Engine Bullets, you can now confidently choose as to which Royal Enfield suits you, either a new one or a used one. Also, the future clearly belongs to the Unit Construction Engine and in due course of time, spare parts for the Cast Iron and AVL engines will begin to dry up. In fact, parts for the AVL engine and the CI500 engine are already scarce.
Well, the thump obviously will be muffled in the long stroke UCE engine, which still remains a big, low revving single true to Royal Enfield’s heritage and is not quite an appliance bike like say the Pulsar or the Unicorn. And before I go, remember, Royal Enfield themselves offer a 40,000 kilometer/two year warranty on the UCE bullets while they used to offer only 10,000 km/1 year warranty on the Cast iron and AVL engines. So, that itself says a lot about how much the manufacturer trusts the UCE over the CI and AVL engines, doesn’t it? So, choose wisely and yes, Happy Thumping!