Royal Enfield Unit Construction(UCE) Engine vs Royal Enfield Cast Iron (CI) Engine!

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.

2011 Royal Enfield UCE500 Classic Chrome

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.

Royal Enfield Unit Construction UCE Engine Advantages

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.

Unit Construction Engined Royal Enfield Classic 500 Military

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.

Cast Iron Engined Royal Enfield STD350

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.

AVL Engined Royal Enfield Machismo 350

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!

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April 5, 2011 | By Jay Prashanth · Tags:

Comments

19 Responses to “Royal Enfield Unit Construction(UCE) Engine vs Royal Enfield Cast Iron (CI) Engine!”

Rohan on April 5th, 2011 10:24 pm

Excellent post my man! I’m buying UCE anyways…a tad bit sad that I wont need to open her up too often.
Jay Prashanth on April 5th, 2011 10:34 pm

Glad you understand dude. Lotsa folks are getting stuck up with the thump thingy and they don’t realize the hassles of it all. A vintage bike is just that, vintage.

Meanwhile, here’s something that’s even more interesting, Read this->http://www.indiancarsbikes.in/motorcycles/royal-enfields-uce500-engine-dump-fuel-injection-carburetted-icb-exclusive-34230/

Cheers,

Jay
krishna on April 6th, 2011 1:37 am

awesome post bro hope it opens some eyes who still wanna stick to CI….i have TBTS and it offer only 1 year warranty nt two…
Potha on April 6th, 2011 4:49 pm

Thanks Jay,

It was very informative read. Please do keep posting these type of technical articles.

What do you think about RE going back to Carb, it looks like we are being short changed instead of offering kits to upgrade to O2 set up?
Jay Prashanth on April 6th, 2011 5:19 pm

Potha,

As you know Royal Enfield should have offered the o2 sensor in the FI system right from the beginning. Since they wanted to keep costs low, they refrained from doing so. As you say, Royal Enfield as a goodwill measure should offer the o2 sensor kit for existing customers if at all they are really serious about satisfying their customers. But in India, unfortunately very few manufacturers really bother about a satisfied customer. Any which ways, the carbed UCE500 is not yet a certainty even though the RTO shows an entry. Also, it may not be offered on the Classic and instead the Machismo might get the carbed UCE500. So, I won’t comment on that, just as yet. We’ll keep you updated as and when we receive any information regarding the carbed UCE500.

Cheers,

Jay
Satyabrata Sarkar on June 18th, 2011 4:35 pm

Hi,
I own a enfield classic -350(1995).I argee with you that the UCE is much more advance and much more better than the old cast engine.Also the availability of spare is tough. But then also I personally feel that enfield is not for riding at 100 or 110 kmph, because enfield is like a elephant which doesn’t care about anything but goes on slowly on its defined path. Also the main identity of enfield is its vibration and sound which has been reduced in the newer versions.I have tried the new enfield of one of my friend, but I didn’t get the same feelings as of my own enfield. There is no much difference in new enfield and Karizma or Pulsar 220.Although this all are my personal views, I don’t know how many people will agree with these thing or not.
roshy n j on June 23rd, 2011 4:58 pm

i trusts the UCE
Raghav on July 20th, 2011 11:07 pm

Hi Jay,

That was a very informative & outstanding post i have read so far.

Have booked a bullet 350cc uce, expecting delivery by the end of this month or early next month.

All these days i was very skeptical about the transformation of RE from ci, avl to uce but now after reading your post, i must say that am relieved & breathing easy to book a uce rather than ci or avl, yes the thump is quite different & missing but other updated technology & advancements have been matched up to the standards & have made it hassle free

Thanks for that eye opening post

Keep it up buddy :-)

Raghav
Mahesh on August 14th, 2011 3:47 am

nice article,find it very helpful.Thank You
Vado on September 15th, 2011 11:17 pm

Hi,
I have Bullet 350 for the last 5 years (with old CI engine). I love the bike for the thump and heavy weight and comfortable riding too… It is definitely a gorgeous and cult bike to have! I can’t even call Karizma or Unicorn a bike compared to Bullet! But.. I must admit that maintenance costs are quite high. Also I have 4-5 major or moderate issues every year when I need to get bike into service. Say, this year – clotch plates gone, low decompression, spark-plug thread gone… I’ m not even mentioning here countless brakes and clotch adjustments, oil leakages, very low mileage (25-30 km/l).
So in few days I’m buying new Bullet Electra 350 with UCE. I’m feeling it is time to change. It is still Enfield Bullet after all.
But I know that I will surely miss my old Bullet like an ex-girlfriend that I loved much but who was causing me too much troubles…
Peace!
vikky on October 31st, 2011 4:37 pm

Jay Prasanth… I doubt how well will UCE stand the test of time as CI did.. lets wait n watch but i bow to you for a such an insightful review.. God bless you Man!! Bullets’s unique identity was it’s THUMP which made heads turn n could hear it from far distance that ya a bullet is going somewhere around us But yes Truth is always bitter.. New UCE makes one feel like its kind of Japanese bike with Bullet outfits.. But i do care for environment and better sake of RE to continue on its production to next decade or else Govt will shut it down as it happened to YEZDI.. I am using and proud owner of 1994 model cast iron bullet but soon going to shift to newer bullet with UCE n Thanks to you for changing my perception..
Jay Prashanth on October 31st, 2011 4:59 pm

Vikram,

Thank you for the kind words. Glad you’re shifting to the UCE but I hope you’ll keep your CI350, cos you’ve got a classic there. Happy thumping!

Cheers,

Jay
vikky on October 31st, 2011 6:50 pm

Jay,

Thanks but for a middle class man it’s hard to keep a collection of Royal Enfield.. I will probably get a good thumping silencer for a new 350UCE to pacify. So it’s nature’s rule.. old one has to give way for the New ones.. But my Love for the Old Classic 350cc for its robustness n thumping will never diminish & will never be replaced by any bike.. Happy Thuming to you dude!!
Lakshminarayan Kashyap on January 6th, 2012 8:30 pm

Thanks man. An awesome post. Wanted to know the real facts about RE motorcycle engines. I think I know better now and clearer than I knew the engines before.

Though, I am planning on the new Thunderbird 500cc released yesterday in New Delhi at the Auto Expo 2012. Impressed with the Fuel Injected engines of my friend’s Classic 500. Plus projector headlamps, disc brakes on both brakes, etc, I really think it’ll be in demand far more than any other competitor.

Long live RE !! :)
Aditya on January 22nd, 2012 1:08 pm

The best and the ultimate comparison between engines used in RE motorcycles. Reading this comparison helped me make the final decision of buying a UCE powered RE motorcycle and made me a regular here at Indiancarsbikes.in. In the comparison above, it has been indicated that RE offers 2 years of warranty on UCE motorcycles, but sadly it is not the case in India. Unlike some countries in the West where they get 2 years of warranty, here in India we have only 1 year warranty on all RE motorcycles.
Hitesh Sharma on January 24th, 2012 12:27 am

Thanks for such a wonderful and informative article.
i already booked RE Classic 350 two weeks back but was still in doubt till reading this article on whether to go for new uce or the old cast iron engine model i.e. used bullet. googling for the same got me here and now after reading this article i am clear about the technical differences and will definitely be going for new UCE model.
Regards
John on January 31st, 2012 1:57 pm

Good article there Jay, thanks for sharing the technical aspects and the advantages of UCE Engine. I’ve had a 1978 model for the last 12 years and have just got rid of it, looking forward to riding the UCE.
Lets just say ive traded in the white elephant :-))
/S/
harshad on February 3rd, 2012 12:45 pm

Jay,
That was awesome review man. I was in dilemma whether to buy new bullet or not. I was looking for insight on CIs and UCEs and after reading your post I am relived and all my doubts are cleared. You rock. Booked Electra twinspark UCE.
Will Barclay on February 4th, 2012 4:26 pm

Sorry, I still want the real, cast iron engine. Lets go through the supposed advantages of the UCE:
1. OIL FLOW – My Cast Iron Engine has a high capacity bronze oil pump for more than double the oil flow than the engine was originally designed for. Advantage negated.
2. HYDRAULIC TAPPETS – This is the one thing that I wish the Cast Iron Engine had and is perhaps the only true advantage of the new engine. I do enjoy setting my own valve clearance though and anyone who does not should probably not be riding Bullets at all.
3. Economy / Efficiency: My Cast Iron engine has been fitted with mixture control that allows the rider to adjust the fuel/air mixture while on the move. this allows the rider to use the amount of fuel appropriate to the situation resulting in better power and cooling when required and better economy when available, just like a light aircraft. RESULT: My cast iron engine gets better fuel economy than the new engines when operating in the real world!
4. CYLINDER BARREL: My “Cast Iron Engine” uses an aluminum alloy barrel as well leaving no advantage here for the new engines.
5. DECOMPRESSOR: I never had a use for the decompressor and so use that hole in the head of my Cast Iron Engine for another spark plug with an independent ignition system (with its own coil). RESULT: Easier starting, better economy, more power, and a redundant system more reliable than the new electronic ignition.
6. ADJUSTABLE CAM SPINDLE: Not a factor
7. The roller bearing I have fitted to my crankshaft means that it is happy to go 120kph (or much faster) all day long. The new engines cannot keep up.
8. I am producing about 48hp at the crankshaft and losing a lot in the inefficient gearbox, but I still bring a lot more power to the road than anything now coming out of the factory. and I do it reliably, using less fuel, on a motorcycle much more true to its heritage and to the reason that we ride Bullets. I would never ride a Pulsar, but I would rather ride that than a new “imitation” bullet.