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overhead camshaft engine problems Q&A Review

Why do some modern car manuals instruct to start driving straight away, without waiting stationary to warmup the engine?

Older vehicles often needed a SHORT warm up, but not necessarily for the carburetor (we had chokes to compensate for that, both manual and automatic). The real problem was in the camshaft bearings and rocker arms that were used. Oil galleys (the passages for oil to lubricate moving parts), especially to those engines with overhead camshafts, were designed to drain oil BACK to the oil pan. It took a few moments for oil pressure to build up, and then for the oil to be pumped to all parts of the engine, especially bearing surfaces. Unfortunately, being impatient people, we often revved up the engine, trying to hurry-up the warm-up, which often resulted in a dry, or "spun" bearing.

I want to know everything about bikes. How do they work? What should be looked for before categorizing them into good and bad? What are cc, strokes, etc.?

In this answer I will be trying to make you understand the terms which you are going to face often on the web pages of different motorcycles. 4 Stroke Engine, A 4 stroke engine is the one in which the piston completes four separate strokes while turning a crankshaft. A stroke refers to the full travel of the piston along the cylinder, in either direction. 4 strokes can be categorized as following : (Please refer to this animation as I couldn't incorporate it in my answer ,Four-stroke engine, ) Intake: Open the intake valve(right one in the following diag.) so that air fuel mixture can come into the chamber. Compression: Compress the air fuel mixture. Power: While the mixture is fully compressed and piston is at its top most position, ignite the mixture using spark plug.Ignition leads to expansion of air-fuel mixture and thus forces the piston down to its bottom most position. Expansion: Exhaust valve (left one in above diag.) is opened and the piston forces the residual air-fuel mixture out of the chamber. These days all bike engines are of 4 strokes so their is no need to get further into it. Let's start focusing on more important aspects. 4 Valve and 2 Valve, In above diag. you can see there is one valve present for intake and one valve for exhaust of air fuel mixture hence the term 2 valve engine. In a 4 valve engine, there are 2 intake valves and 2 exhaust valves. Just as when you run at fast speeds you start taking breath from mouth as well, having 2 extra valves will help engine to get air-fuel mixture in sufficient amounts at higher rpms. Sports bike like R15 and CBR have 4 valve engine whereas 2 valve engines are more common in street bikes. SOHC and DOHC, In the engine diagram shown above, just above the rods attached to intake and exhaust valves, you can see two rotating pieces having a bulge outside. This mechanical piece is known as Cam and the bulge present at its surface helps to open and close the intake and exhaust valves just at right moments. Both cams used to be attached to a single rotating shaft, known as Camshaft, as shown in the following diagram. Fig. 1: The two bulgy pieces are Cams and the whole structure of cams and shaft/rod going through them is called Camshaft. Orange pieces are the rods connecting intake and exhaust valves. (Refer ,Camshaft, for complete animation) In a 2 valve engine a single camshaft is enough to open and close intake and exhaust valves by placing the cams at appropriate angles. Things get complicated in a 4 valve engine. There are two options to circumvent this problem : i) Use two camshafts, each camshaft having 2 cams for 2 inatke valves and other camshaft having cams for 2 exhaust valves. ii) Use single camshaft alongwith more complicated mechanism to operate all 4 valves. Hence, the name dervied are : SOHC : Single Overhead Camshaft DOHC : Double Overhead Camshaft Fig 2: 2 Valve SOHC Engine ( Image source ,Motorcycle Specifications, ) Fig 3: 2 Valve DOHC Engine ( Image source ,Motorcycle Specifications, ) As the camshafts are present just directly at the head of the engine, hence the name Overhead. Just to avoid any confusion, camshafts are present outside the engine but just above its head. DOHC layout has better valve opening and closing timings and more precise also but increases the weight and number of moving parts in engine. SOHC although will be lighter but we will have to use rocker arms to control the valves. CBR has 4 valve DOHC engine while R15 has 4 valve SOHC engine. 2 valve engine bikes have usual SOHC. Spark Plug, Position of spark plug plays key role in the efficient combustion of air-fuel mixture, as the ignition should spread evenly in the chamber. A 4 valve DOHC engine offers very favourable top central position for spark plug. In case of 4 valve SOHC engine, due to single camshaft present at top central position, spark plug is placed slightly away from this key position. Fig 4: 4 Valve DOHC Engine with spark plug in the middle of 4 vlaves (Image source ,http://www.caranddriver.com, ) Bajaj has been using DTSi technology which use two spark plugs instead of one for more efficient combustion although other key players are able to give equivalent benefits using only single spark plug. Air Cooled and Liquid Cooled, Air cooled engines are cooled naturally by outside air. They generally have fins present to dissipate more heat. Fig 5: Air cooled engine. (Image source ,http://zxj510228.en.ec21.com, ) Liquid cooled engine is surrounded by a continusouly flowing coolant which absorbs the heat and dissipate it at the radiator. Liquid cooling is used in the engines having high compression ratio, which can operate at high rpms as sports bike. Fig 6: Liquid cooled engine (Image source ,http://www.iamabiker.com, ) R15 and CBR use liquid cooled engine as opposed to air cooled engine in FZS, Gixxer, etc. Max Power and Max Torque, These parameters are of great importance to look out for while comparing motorcycles but they are very hard to understand and quite confusing. I am incorporating few words from this article ,http://www.bikesindia.org/reviews/difference-between-motorcycle-power-torque-explained-which-is-better.html, Power:, The Power produced by any engine is the capacity of that engine to take the motorcycle to its maximum speed. Torque:, The Torque generated by an engine is an entity which determines the pulling capacity of the bike. You will have to dive deep into this topic on your own. Displacement, As given on Wikipedia, engine displacement is the volume swept by the piston inside the cylinder of engine in a single movement from top dead centre (topmost position) to bottom dead centre (bottommost position), commonly specified in cubic centimeters(cc). Generally higher the displacement higher the torque and power you get. But there is no direct relationship between displacement and power. For example Honda CB Trigger with 150cc engine given max power of 14 bhp whereas Honda CBR 150R with 150cc engine gives max power of 18 bhp. So instead of looking just at displacement, give more weightage to maximum torque and maximum power the engine can deliver. Disc Brake and Drum Brake, In a disc brake, the brake pads squeeze the disc attached instead of the wheel, and the force is transmitted hydraulically instead of through a cable. Friction between the pads and the disc slows the disc down. Fig 7: Working of disc brake ( Image source ,http://auto.howstuffworks.com,) In drum brake set of shoes or pads press outward against a rotating cylinder-shaped part called brake drum. Disc brakes are superior to drum brakes in stopping vehicle, they dissipate heat better and also have less wear and tear. General trend is to have disc brakes in front, as momentum is transferred to the from while stopping, and drum brakes in rear due to cost constraints. High end bikes have disc brakes in both front and rear. Fuel Injection and Carburetor, Constant supply of air-fuel mixture in right proportions and in right amount to engine is of upmost importance and the amount should be adaptable according to the factors like the speed at which engine is running, load, etc. Before the advent of modern electronic sensors, this task was handled by a mechanical device called Carburetor. Fig 8: Carburetor (Image source ,http://www.rc-trucks.org,) Now days, carburetors are replaced with electronic Fuel Injection systems which gather engine operation information using various sensors and then decide the control over the air-fuel mixture. Carburetor are still popular in motorcycles and there is a heated debate between which one to use. Carburetors can be diagnosed by a mechanic in case you got unlucky in some remote area and their performance have been quite satisfactory until now. Fuel injection systems provide better fuel efficiency and power but to what extent is a topic of debate. Also if you got unlucky with fuel injection system in a remote area, then there is not much that you can do. There are lot of other factors which you can find on internet. Twinshock and Monoshock Rear Suspension, For rear suspension generally Twinshock absorbers are used but they add additional weight and get bendy and flexible in extreme riding conditions. Fig 9: Simplified view of twinshock absorber ( Image source ,The Car Maintenance Bibles, ) These problems can be overcomed by the use of Monoshock absorbers. Fig 10: Monoshock absorber ( Image source ,BikeAdvice.in,) Monoshock are more popular with high end sports bike and Twinshock with general street bikes. Full Fairing and Half Fairing, A motorcycle fairing is a shell placed over the fame of some motorcycles with primary purpose to reduce air drag. Full fairings cover both upper and lower portions of motorcycles, as distinct from a half fairing, which only has an upper section, and leaves the lower half of the motorcycle exposed. Fig 11: Full fairing, most portion of engine gets hidden behind the fairing. (Image source ,http://sv1000.lsn.net, ) Fig 12: Semi faired version of Karizma. (Image source ,Top Speed In,) Kerb Weight, Kerb weight is the total weight of a vehicle with standard equipment, all necessary operating consumables such as motor oil, transmission oil, coolant, air conditioning refrigerant, and a full tank of fuel, while not loaded with either passengers or cargo. So lesser the kerb weight more performance engine can provide. Wheelbase, Wheelbase is the distance between the centers of the front and rear wheels. Well the shorter it is the quicker a bike can turn and the longer it is the more stable it will be. That is why criusers like Bajaj Avenger have much greater wheelbase compared to other street and sports bikes. Fig 13: (Image source ,http://www.carbibles.com, ) More motorcycle geometry and handling factors can be read at ,Motorcycle Geometry 101,. Tubeless Tyres, Tubeless tyres do not require a separate inner tube and hence light weight and air leakage is slower in case of puncture. You can cover few more kilometers on motorcycle itself once tyre gets punctured. At the end of my answer, I will say that although the features described above play key role, factors which cannot be described but rather can only be experienced are handling, comfort, easiness in shifting gears, engine vibrations, noise and many more. I will also not recommend you to maximize the features described above as that will lead you only to Sports Bikes. Instead, first the select category from which you want your bike to be and then you can sort according to the above parameters. Bikes are broadly categorized as : Street Cruiser Sports Happy Hunting !!

Are the cylinder head and cam cover a matched set that can't be switched?

Are you talking overhead camshaft engine? With cam ‘caps’ with the cam bearing upper half as part of what you are calling ‘cam cover’ ? Holds the cam in the head? yes, those ARE matched sets and should NOT be interchanged. They are part of the head when the cam bearing journals are line bored. Some are actually cast with the head, drilled and tapped, and then fractured off the head so alignment stays perfect. More modern machining has the variances down to very small differences and you MIGHT get away with swapping. The consequences are pretty high. if you’re talking about the valve/cam cover ( that keeps the oil in and the world out) ..no, same make model year should be no problem

Why are most engines' time belts not made of chains instead of rubber which is less durable?

Hmm. I am old enough to remember the introduction of timing belts. The first one I saw was on the Pontiac Tempest single overhead cam 6 back in the sixties. When overhead camshaft engines first started appearing, the chains had to be longer to reach up to the overhead camshafts. This mean’t that the chains were heavier and had to be equipped with hydraulic tensioners and guides to prevent chain whip and to reduce timing errors. So, chains becane heavier, the tensioner sucked power, and everything became expensive to manufacture. So, manufacturers developed the toothed neoprene timing belt. It is lightweight, cheap to manufacture, has lower friction losses, and is less prone to whip. In the beginning the belts were not fully enclosed and bits of debris had a habit of getting in behind the teeth and destroying the belt. This started to give belts a bad rap. On the heels of the notorious Envoy Epic and Vauxhall Viva which GM imported into Canada, GM imported the Vauxhall Firenza with a toothed belt into Canada. Because the belts were not fully shrouded, engine failure abounded and prejudice rose. People blamed it on the belts being made of rubber, which they are not. Manufacturers soon shrouded the belt completely putting and end to this problem but the reputation lingered. Belts were actually quite common for a long time. My Mazda B2000 pickup had one, so did my Honda Civc, and my Saturn Vue with its 6-cylinder Honda Pilot engine. As time went by another changed happened. Most engines used to be of the non-interference type. If the belt broke and the camshaft stopped turning, the valves did not meet the pistons and the engine simply stopped. In the quest for more power, compression ratios rose, and newer 4-valve configurations made non-intereference engines a thing of the past. Oil and dust seeping into the belt shroud tended to shorten belt life. So manufacturers wisely decided to make a timing belt change mandatory, usually around 100,000 km to prevent any possibility of a belt failure causing catastrophic engine destruction. As manufacturers added air conditioning, power steering, turned their engines sideways, and made engine compartments more compact to save weght, a simple timing belt change became more difficult because of all the stuff in the way. People complained about getting steep bills of $800 to $1000 to change that damned belt. It was often a big stumbling block when trying to sell the car. The big questions was always has the belt been changed? If it hadn’t, the purchaser would bolt. The grumbles rose and manufacturers heard the complaints loud and clear. They started putting chains back in to spare the customer the belt chsnge. At first they tried to cut costs and weight using thinner and lighter single-row chains with disastrous results. Now, they are finally realizing that they have to use heavier chains or even double-row chains to preserve reliability. So that is the story. Now there are few engines that still use belts. Most are now chain driven. Belts are actually better in many respects…..if you protect them properly and make it easy to chsnge them.

What exactly is a "Hemi", and why should I want one in my truck?

Most people here have pointed out that “HEMI” is just a copyrighted trademark of Fiat Chrysler Corporation and doesn’t really tell you much about the engine. In fact, the engines produced by Chrysler are not really hemi’s, and hemi’s are not the most powerful or fuel efficient engines. In fact the four-valve per cylinder, dual overhead camshaft, variable valve timing engine in my four-cylinder Toyota provides a much better trade off between power and fuel economy. However, let me tell you where the Chrysler Hemi originated. After WWII, Zora Arkus-Duntov, a Belgian-born engineer, put the first “hemi” cylinder heads on an American V8. He was later called the "Father of the Corvette" after he started working for GM. See: ,Zora Arkus-Duntov - Wikipedia However, during WWII he fled to the US, and working for the US military, discovered that the flathead Ford V8 could rev to 6,000 rpm, going downhill in a tailwind. Since none of the racing engines he had worked on could rev to 6,000 rpm without throwing a rod, he found this intriguing. See: ,Ford flathead V8 engine - Wikipedia He started producing aluminum overhead valve, hemispherical combustion chamber heads for the flathead Ford V8 engine. The hemispherical design was not exactly new, but putting it on the flathead Ford was a game-changer. This solved a serious overheating problem with the Ford V8’s, in addition to which he could get over 300 hp out of the engines. It was called the Ardun head (from Arkus-Duntov), and you can still buy them, although his company went bankrupt shortly after the war. Duntov joined General Motors in 1953 after seeing the Corvette on display and took over development of that iconic sports car. In 1951, Chrysler came out with their first Hemi V8. However, people noted that the 1951 Chrysler Hemi looked a lot like of a set of 1947 iron Ardun heads atop a 1949 Cadillac shortblock V8. Duntov noted the similarities when they took the engine apart at GM, but he felt flattered that Chrysler had copied his design. He didn’t actually own the rights to anything because the hemispherical combustion chamber design was not exactly new. Chrysler did go on to trademark the name “Hemi”, though. The Chrysler Hemis were extremely powerful for an American V8 of the time, particularly the legendary 426 Hemi (7 liter) engine, but you have to remember that these times are different. Fuel costs are much higher and the old V8’s were incredible gas guzzlers. Nowadays when they tell you an engine is a “Hemi”, it just means they have saved money by not going to a much more efficient, four valve per cylinder, double overhead camshaft, variable valve timing configuration. You can get a lot more power out of a lot smaller, more fuel efficient engine these days - particularly if you put a turbocharger or two on it.

What’s the most stately motor car ever made?

Question: ,“What’s the most stately motor car ever made?” Really not possible to claim there was only one. Therefore, I will give you three examples of unquestionably elegant “stately” automobiles. The first would be the Bugatti Royale. The Bugatti Type 41 or Royale was produced from 1927 to 1933. Only seven were built and six still exist. The Royale was a massive car with a wheelbase of 169 inches and a length of 252 inches and a curb weight of 7,000 pounds. For comparison a Chevrolet Suburban is ,only ,224 inches long. The Royale was powered by ,12.7 (!) liter, magnificently finished Straight-8 with an overhead camshaft and three valves per cylinder. The engine was based on a French aircraft design. The cylinder head, with hemispherical combustion chambers, was integral with the block, eliminating head gasket problems. But that meant the entire engine had to be disassembled to grind the valves, a yearly procedure in that era. The engine produced about 300 horsepower. The Bugatti Royale chassis alone cost approximately $30,000. The coach built body cost extra. The Bugatti Royal wheel alone is gorgeous. The second of these “stately”cars would be the 1957 Cadillac Eldorado Brougham. The Eldorado Brougham in 1956 cost $13,074…twice as much as other Cadillacs and more than the Rolls-Royce Silver Cloud. It was powered by a 6.0 liter V-8 which breathed through twin 4-barrel carburetors. The Brougham’s roof was unpainted polished stainless steel. Its level of luxury can be imagined by noting that standard ammenities included crystal drink tumblers, cigarette and tissue dispensers, lipstick and an ,Arpège, atomizer with ,Lanvin, perfume, and a ladies' compact with powder puff, mirror and matching leather notebook, comb and mirror. The Eldorado Brougham was GM’s answer to the next example on my list of elegant automobiles, the 1956 Lincoln Continental Mark II. The 1956 Lincoln Continental Mark II was powered by a 6.0 liter V-8 producing 285 horsepower and 402 pound feet of torque. the engines for these cars were selected from the line and then blueprinted, i.e, disassembled, inspected, and reassembled with matched and balanced components. The quality control was exceptional with all employees involved in any way in its production or service being specially trained. This car was essentially hand built, rather than being produced on a normal assembly line. The Mark II’s hand assembled, expensive, wheel covers alone were works of art! I do not think anyone could deny that these three cars were truly elegant “stately” automobiles.

Do oil additives work? Do any of them do what they claim?

Question: “Do oil additives work? Do any of them do what they claim?” I have owned worked on and built high performance engines since the 1960’s With two ,possible, exceptions, under certain conditions, maybe, ,engine oil additives do not work, CAN CAUSE SERIOUS ENGINE DAMAGE, and at best are useless. The older additives, for example Marvel Mystery Oil and Sea Foam do nothing. The solvents in them are weak, added in minuscule amounts, and being volatile flash off from the oil as soon as the engine gets hot. Marvel Mystery oil is a 1923 mixture that according to the manufacturer contains mineral oil and tiny (less than 1%) amounts of diclorobenzene and tricresyl phosphate, i.e., it’s mineral oil. An NTSB (National Transportation Safety Board) analysis found that it contained 74% mineral oil, 25% white spirits (an extremely weak solvent), and 1% lard. Lard?! Sea Foam amusingly uses the marketing slogan “Not A Chemical!” (Guess they do not employ chemists or anyone with an education.) Sea Foam is a crude mixture of 60% kerosene, 25% naptha (a weak solvent previously used for dry cleaning), and 15% isopropyl alcohol. What you pour into your engine is essentially lamp oil mixed with dry cleaning solvent and rubbing alcohol. The two volatile solvents flash off and you are left with some kerosene in your engine diluting your Mobil-1. OK, these and all other of the older motor treatments cannot possibly do any good. But, at least if used in small quantities, they cannot do much harm either. But that is not true for some of the more modern engine oil additives. These use suspended solids such as molybdenum or PTFE (polytetrafluoroethylene) supposedly as an anti-wear agent. A heavily marketed version of these is Slick-50, marketed by Petrolon. ,Slick-50 and all similar additives are harmful to engines and can cause severe damage. ,I have had real world experience with that and have the receipts for two camshafts and a set of valve rockers arms to prove it. All engine oil additive companies spend a great deal of money on marketing. For most (all?) of these companies their marketing budget far exceeds their R&D budget. Slick-50 claimed in its advertising that its PTFE formulation would coat the moving metal parts in a car’s engine and reduce wear and extend the engine’s lifetime. I fell for that bullshit and was unaware that their marketing suspiciously ignored another property of Slick-50. Yes, the stuff did stick to moving metal parts. ,But it stuck a lot better to NON-MOVING metal parts, such as the SMALL PASSAGES IN OIL GALLERIES. I should have known better. After all I have been building high performance engines for decades. And I have torn down a lot of engines and measured their cylinder bores and bearings with micrometers. I know how engines work. And I conscientiously change engine oil and have exclusively used full synthetics (in my case Mobil-1) since it came out in the early 1970’s. But the theory behind Slick-50 an its clones seemed to make sense, and so I poured some into the perfectly maintained low mileage engine of my wife’s Infiniti G20t, hoping to extend the life of what was already know to be an extremely well designed and very durable DOHC engine. Maybe 10K miles later I heard this squeal coming form her engine when she started it up in the morning. It was sort of like the sound of a slipping fan belt but at a much higher pitch. It lasted seconds and then went away. She drove down the driveway on her way to work. Every mechanic hates that sound! That squeal means that something really bad is happening. ,It is a metal to metal squeal., The next day I asked her to pop open the hood and let me listen when she started the G20’s engine. The squeal was coming from the top of the engine, somewhere in or around the camshafts. I told my wife that I was driving her to work in my car. When I got back home I immediately pulled off the G20’s valve covers. On the Infiniti G20 the dual overhead camshafts and their rocker arms and the lifters receive their lubrication oil from two oil tubes connected the the oil galleries in the cylinder head and block. The tubes look like this. Each of those tubes has a series of holes drilled in it precisely sized and placed to provide a constant flow of oil under pressure to the camshaft lobes and the valve rockers and valve lifters. When I pulled off the G20’s valve covers I found that the PTFE in the ,Slick-50,, ,which had an undisclosed ability to deposit itself much more readily on non-moving than on moving parts, had formed little hard ant hill like deposits of PTFE in and around the oil distribution holes of the oil supply tube for the camshafts. THE SLICK-50 HAD CLOGGED THE HOLES AND STARVED THE CAMSHAFTS OF OIL. TWO OF THE CAMSHAFTS’ LOBES WERE BADLY WORN., I did not need a micrometer to measure this. The tops of the lobes were worn flat! I was forced to buy and replace two camshafts and a set of rocker arms and, of course, flush the engine and clean its oil passages. Rather than extend the life of the engine the addition of Slick-50 to the Mobil-1 engine oil had clogged oil passages and severely damaged it. OK, I had the skill and tools to replace the cams myself. I can only guess what that would have cost me if I had had to have the service performed at the dealership. With, ,perhaps,, a couple of exceptions, e.g. the use of a lead substitute added to the gasoline to lubricate the valves and valve seats of old engines that were designed for fuel containing tetraethyl lead, and ,maybe, the use of a phosphorus additive in the oil for older engines that do not have roller tappets, YOU SHOULD NOT PUT ANY ADDITIVE IN YOUR CAR’S OIL. If an additive actually worked, Mobil or Valvoline or Shell or Castrol’s highly skilled engineers or chemists would have already discovered it and added it. Additive companies sell snake oil. At best, they are useless…simply a waste of money. But some of them, such as Slick-50 and similar products, can and do cause serious engine damage. Note: Because of changes in environmental regulations the amount of zinc dialkyldithiophosphate in motor oil has been reduced or eliminated., That presents a problem for older cars, those whose engines were designed prior to the 1990s and used flat, rather than roller, valve tappets. The zinc dialkyldithiophosphate served as a lubricant protecting those flat tappets. Its absence will cause rapid wear. To prevent damage to the tappets on such engines it is necessary to use a motor oil that still contains some zinc dialkyldithiophosphate or use the additive ZDDP.

Why do big American V8s still not use overhead cams?

The overhead cams add complexity and reduce reliability without substantial benefits in most cases. The reason why the pushrods engines had issues at high RPM is that people didn’t understand, how big are the forces on the pushrods. The old-time pushrods flexed a lot, causing both distortion in the valve phasing and damage to the pushrods. Once this had been understood, the solution was simple: make stronger pushrods. And the way to make the stronger pushrods without increasing their weight is to increase their diameter, keeping the walls relatively thin. The NASCAR pushrod engines routinely run at 9000 RPM for hours at a time. An interesting thing is that the modern pushrod engines represent a development of the racing technology. If NASCAR weren’t limited to the pushrod engines, nobody would have bothered to think about fixing the weak pushrods. But the NASCAR teams had to work with this limitation, so they have spent the effort studying the problem and have discovered the simple solution. Granted, there are limits: if you want to go to 20000 RPM, you’ve still got to use the overhead camshafts and pneumatic springs. But what street cars have even the 9000 RPM redline? Pretty much none (well, except for rotaries, but that’s a separate story). So without the overhead cams you get a simpler, cheaper, more reliable, more compact, more serviceable, lighter package, with the better weight distribution (fewer heavy parts on top).

Is the Royal Enfield Himalayan 650 coming soon?

I am not sure about the Himalayan 650 cc . Let me explain , though some or many may disagree . The existing Himalayan is underpowered . That is one major complaint . But then few have complaints on its off roading capabilities . A bigger engine like the RE Interceptor’s would increase the vehicle weight. One major requirement of off roading is minimum vehicle weight especially when riding damp, sandy or mountainous terrain. Second the purpose is increasing the payload, without increasing the weight or improving the power to weight ratio. Yes, a 650 cc engine improves the power to weight ratio significantly as opposed to the current 411 cc . However the problem is that it adds weight to the motorcycle. If ithe bike is purpose built, the vehicle weight needs to be low without compromise on integrity . A Triumph tiger with a three cylinder engine dual overhead cam operating 12 engine valves ,weighs just 198 kgs. The Himalayan weighs 195kg with a single cylinder single overhead camshaft engine. The power/torque of Tiger is 95 brake horsepower and 79 newton metres . The difference shows up in the power to weight ratio as well, 0.5 brake horsepower per kg for the Tiger as against a measly 0.13 bhp per kg of the RE Himalayan ! Clearly the Himalayan has substantial scope for improvement. So what can be expected is improved performance from the engine with some or slight change in displacement . Perhaps a twin cylinder Dual overhead camshaft engine with four valves per cylinder? A lighter frame with lower saddle height would be a significant improvement . The purpose is making the biking experience inclusive rather than exclusive . Inclusion would allow shorter riders and women to take to off road biking . All Indians are not tall are they ? So can the power to weight ratio be improve in Himalayan ? I believe there is huge scope for improvement! Watch the video please ! Finally I ride a 500 cc RE desert storm and am short. By just removing the saddle springs alone brought the saddle height down to 775 mm. Removed the excesses , such as the rear seat solid stays and the ancient saree guard . RE is sexist and hasn’t woken up to the fact that modern women prefer to be on the saddle rather than the pillion . (For stubborn saree fans, there are scooters or cars!). Certainly these are not insurmountable engineering challenges missed by Siddhart Lal. So expect the new Himalayan to be lighter more powerful ! I am anxiously waiting to ride one before I hang up my riding boots !

Why do timing chains in modern car engines still stretch and fail when timing belts can last 90,000 miles or more?

In U.S. push-rod engines, the timing chains are very thick and very short, thus almost impossible to break. This includes virtually all 6 & 8 cylinder engines from the 1950’s until today (excluding flat-heads). As mentioned, they don’t stretch, but wear so that slop develops. Some have a tensioner on the return side to help minimize “chain flap”, but when very worn it can start slapping the side of the timing cover. The distance between the camshaft and crankshaft is so close that the chain and sprockets can be replaced with a gear-set as a racing upgrade. More noise, but no more valve-timing lag from wear. Lagged valve timing is not necessarily bad since that gives more torque at higher rpm’s (hence max horsepower). Indeed, many racers setup a new cam with valve lag for that reason, though the engine will run worse in daily-driving. The biggest problem is that some versions (my 1965 Chrysler 383) used a nylon sprocket on the camshaft to reduce noise and those can wear faster or break off a tooth to “skip timing”. I recently changed the “timing set” (sprockets & chain) in my 2002 Chrysler 3.8L V-6 at 260,000 miles and found it barely worn. My main goal was replacing the rubber seals, but a new set is so inexpensive it is wise to replace whenever in there after any significant mileage. In contrast, many Japanese and European V-8 engines have overhead camshafts (2 total) or double-overhead camshafts (4 total). Those have much longer, thinner chains which look more like a bicycle chain, and thus are much more prone to wear to the breaking point. The DOHC engines can be a very involved system of chains and sprockets. My only experience is my 1980’s M-B diesels which have a chain-driven single overhead camshaft. It is ~4x thicker than a bicycle chain and I haven’t read of one breaking. Since it is expensive and a difficult replacement, minor wear can be compensated by simply installing an inexpensive “offset key” on the camshaft sprocket. The biggest risk is that a tiny roller bearing in the mechanical vacuum pump can fail, leading to the innards sliding into the camshaft to jam it and destroy the engine. Not all M-B designs were brilliant or even advised. Re rubber timing belts, they have disappeared in current U.S. engines, after having been used extensively in 4 cylinder engines starting in the 1980’s (overhead camshafts). Several Japanese 4 cylinders used timing chains throughout. The belts never appreciably stretch, but they can snap or the teeth shred off. In some “interference engines”, that can cause the pistons to hit the valves. My 1996 Voyager 2.4L DOHC has a belt, which has failed twice. It is “non-interference”, though the valves could hit each other (very rare). The belt itself didn’t snap but rather both times a roller bearing on the tensioner or idler seized to jam/burn the belt. I recall the OE belt suggested changing every 60,000 miles, but replacements quote 120,000 miles. Since the roller bearings are outside the engine and get no lubrication other then their “permanent lube” (which isn’t forever), it is wise to also change those and get the best quality bearings you can find. Usually, cheap Chinese bearings come on replacement parts, so I prefer buying individual quality bearings (German or Japanese) and swap them with a hydraulic shop press when possible.

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