Royal Enfield J-Series 350 cc Engine: How Different Is The New Engine?

The Royal Enfield 350 cc has been the hero product of the Indian motorcycle brand, in the company's modern history, ever since Royal Enfield first started producing motorcycles in India in the 1950s. And the new 350 cc single overhead cam (SOHC) engine of the Royal Enfield Meteor 350 is the fourth generation 350 cc engine introduced by Royal Enfield ever since the brand started developing motorcycles in India. 

Also Read: 2021 Royal Enfield Classic 350 Review

The new J-Series engine has since been introduced in the new Classic 350 and the just launched 2023 Royal Enfield Bullet 350 as well, promising a level of refinement  Before we look at what all has changed, and if the new engine offers any significant advantages, let's first quickly look at how the 350 cc single-cylinder engine has evolved over the past two decades.

Also Read: Royal Enfield Meteor 350 Review

The Cast Iron 350 cc engine was used in Royal Enfield motorcycles for more than four decades and featured a separate gearbox, with a right-hand side shifter, as well as a unique neutral finder lever

The Royal Enfield 350 cc engine

The old Royal Enfield Bullet 350 continued with the same Cast Iron 350 cc engine well into the 1990s with a separate four-speed gearbox with a neutral finder lever, and a right hand side gear shifter. In 1999, Royal Enfield introduced the 350 cc aluminium engine, built in collaboration with Austria's automotive consulting firm AVL. The AVL 350 cc engine required oil changes at 5,000 km, compared to 3,000 km oil change intervals of the cast iron engine, and offered slightly higher revs, and better high-speed cruising ability. 

The AVL engine had a higher compression and shorter stroke when compared to the Cast Iron engine. It also required less tappet adjustments than the cast iron engine, but had its own share of problems. Engine clatter was one common issue, with cam-gear backlash being a source of noise and considerable heartburn for many owners. Meanwhile, the Cast Iron 350 cc soldiered on with a five-speed gearbox in the then new Royal Enfield Electra 5S, as well as the Standard Bullet 350.

Also Read: All You Need To Know About The RE Meteor 350

The first-generation Royal Enfield Thunderbird 350 came with the 350 cc AVL engine

By the mid-2000s, Royal Enfield engineers introduced a solution with adjustable cam spindles, which somewhat helped in reducing the cam gear backlash noise, but the aluminium engine still had some clatter. In 2008, the AVL engine was replaced by the new unit construction engine (UCE), which had an integrated five-speed gearbox, with the engine and gearbox in one common unit. The pushrods were hydraulic so did not require tappet adjustments, as was the case with the old cast iron and AVL engines.

Also Read: Royal Enfield Meteor 350 Vs Rivals' Price Comparison

The UCE 350 is still offered in the Royal Enfield Bullet 350 and the Royal Enfield Classic 350 models

The UCE engines had a reputation of being the most reliable 350 cc Royal Enfield engines, and were known to be more fuel-efficient than the AVL and Cast Iron engines. With a left-side gear-shifter across the Royal Enfield model range, the UCE 350, also known as the TwinSpark engine, due to the twin sparkplugs, became a runaway success. By the end of the decade, all Royal Enfield 350 cc motorcycles came with the new UCE 350 engine, including the Bullet 350, and with a five-speed gearbox. The Royal Enfield Classic 350 still continues to be the brand's bestselling model, contributing over 80 per cent of Royal Enfield's overall monthly sales.

Also Read: Royal Enfield Meteor 350 Launched; Prices Start At Rs. 1.76 Lakh

The new 349 cc single-cylinder air and oil cooled engine makes 20.2 bhp at 6,100 rpm and 27 Nm of peak torque at 4,000 rpm.

All-New 2020 Royal Enfield 350 cc OHC engine

Now, in 2020, Royal Enfield has introduced the all-new 350 cc engine with overhead camshaft (OHC) in the new Royal Enfield Meteor 350. Visually, the new engine's cases, particularly the clutch and crank cases, look similar to the bottom end covers of the Royal Enfield 650 cc parallel-twin engine. However, according to Royal Enfield, the new 350 cc engine doesn't share anything with the 650 cc twin, apart from a few bolts and fasteners. The new 350 cc single-cylinder, SOHC engine will be the new 350 cc platform for Royal Enfield, and is likely to replace the existing UCE 350. So, after the Meteor 350, the new engine will likely be introduced in newer models of the bestselling Royal Enfield Classic 350, as well as the Royal Enfield Bullet 350.

New 350 cc OHC engine is expected to replace the existing UCE 350 engine and has a bigger bore, but shorter stroke

Dimensions & Output

The new 350 cc engine's displacement has gone up from 346 cc in the UCE 350 to 349 cc, with an increase in bore from 70 mm to 72 mm, but stroke has been reduced from 90 mm to 85.8 mm. Compression ratio has changed to 9.5:1 on the new 350 cc SOHC engine from 8.5:1 on the UCE 350 engine. In terms of output, the new engine makes just about 1 bhp more than the older engine, but maximum power of 20.2 bhp is achieved at 6,100 rpm, compared to 19.1 bhp of the older UCE 350 at 5,250 rpm, effectively widening the usable rev range. Peak torque has gone down from 28 Nm at 4,000 rpm to 27 Nm at 4,000 rpm.

The cam gears have been replaced with a timing chain, along with the SOHC system, which results in less noise and more efficient valve timings.

Architecture

But output figures on paper are one thing; and what is more significant is the architecture, which has changed on the new 350 cc engine. The cam gears have been replaced with a timing chain, along with the SOHC system, which results in less noise and more efficient valve timings. The chain primary drive has been replaced with gear primary drive, which reduces transmission losses, and the primary balancer shaft reduces vibrations on the engine which is immediately apparent, the moment you fire up the new engine.

The new 350 cc engine makes 20.2 bhp at 6,100 rpm and 27 Nm at 4,000 rpm

Performance

All these changes have resulted in a very welcome change in the engine's performance. The trademark thump is still there, but the engine revs freer and higher, and with refinement, which is immediately likeable. The torque spread is wider though, across the rev range, with meaty torque available from as low as 2,400 rpm to over 4,500 rpm. The engine also runs smoother and is more refined across the rev range, thanks to the primary balancer shaft, and the single overhead cam helps in making the engine rev freer, with the redline at a higher 6,100 rpm than the UCE 350 cc engine. Oil changes on the new engine have also increased to 10,000 km, making it more maintenance friendly, although service intervals are still at 5,000 km.

The Royal Enfield Meteor 350 gets significant improvements to the Royal Enfield 350 cc platform

The future-proof 350 cc engine?

The new 350 cc SOHC engine has made its debut on the new Royal Enfield Meteor 350, a motorcycle which will not just be sold in India, but will also power Royal Enfield's global ambitions to establish leadership in the mid-size motorcycle segment. The Meteor 350 will be sold in global markets like Thailand, Brazil, and even in Europe and North America. While it may be the first model on the new 350 cc platform, it will not be the last. The Classic 350 already has this engine, and now, the Bullet 350, which will also be now positioned as a global product.