Krishna Kotiyal

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...dis is my project report of assynmnt given at TATA MOTORS PANTNAGAR..!!
...i njoed dat span...it was gr8 learning dere..!!

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Krishna Kotiyal

  1. 1. A PROJECT REPORT ON “PROBLEM SOLVING ON CAMSHAFT AND CAM LOCK ASSEMBLY” for the requirement of the degree of B.TECH (MECHANICAL) (2012)Under Supervision of: - Submitted by:-Mr. Amitesh Amarnath Krishna Gopal
  2. 2. PROJECT COMPLETION CERTIFICATEThis is to certify that Krishna Gopal, student of B.tech(ME) from has undertaken the project titled“Problem Solving On Cam Shaft and Cam Lock Assembly at Tata Motors – Pantnagar” underour guidance from 06th June 2012 to 05th July 2012 and has completed the said projectsuccessfully.During his training tenure he Ire overwhelmed, confident & hardworking. I wish him all the very bestfor future endeavors.External Guide’s Full SignatureDesignation Organization’s Seal Page 2 of 10
  3. 3. EXECUTIVE SUMMARYThe project was undertaken at TATA Motors Limited, Pantnagar, and the duration of the project wasfour weeks. The title of the project is “Problem Solving on Cam Shaft and Cam Lock Assembly atTata Motors – Pantnagar”.The main objective of the project was to understand and gather information about the engine andengine parts. Cam shaft is basically used to control the movement of inlet and exhaust valves withrespect to the other engine parts.Our basic need is to have proper injection of the fuel inside the cylinder for the proper and efficientworking of any engine, which is done by the help of injection timing.In this project a complete analysis of camshaft is done with the help of many seniors and colleagues. Page 3 of 10
  4. 4. CamshaftA camshaft is a shaft to which a cam is fastened or of which a cam forms anintegral part.UsesIn IC engines, the camshaft is used to operate poppet valves. Itthen consists of a cylindrical rod running the length of thecylinder bank with a number of oblong lobes protruding from it,one for each valve. The cams force the valves open by pressingon the valve, or on some intermediate mechanism as theyrotate.TimingA steel billet racing camshaft with noticeably broad lobes (very long duration)The relationship between the rotation of the camshaft and therotation of the crankshaft is of critical importance. Since thevalves control the flow of the air/fuel mixture intake andexhaust gases, they must be opened and closed at theappropriate time during the stroke of the piston. For thisreason, the camshaft is connected to the crankshaft eitherdirectly, via a gear mechanism, or indirectly via a belt or chaincalled a timing belt or timing chain. Direct drive using gears isunusual because the frequently reversing torque caused by theslope of the cams tends to quickly wear out gear teeth. Wheregears are used, they tend to be made from resilient fibre ratherthan metal, except in racing engines that have a highmaintenance routine. Fibre gears have a short life span andmust be replaced regularly, much like a cam belt. In somedesigns the camshaft also drives the distributor and the oil andfuel pumps. Some vehicles may have the power steering pump Page 4 of 10
  5. 5. driven by the camshaft. With some early fuel injection systems,cams on the camshaft would operate the fuel injectors.LiftThe camshaft "lift" is the resultant net rise of the valve from itsseat. The further the valve rises from its seat the more airflowcan be released, which is generally more beneficial. Greater lifthas some limitations. Firstly, the lift is limited by the increasedproximity of the valve head to the piston crown and secondlygreater effort is required to move the valves springs to higherstate of compression. Increased lift can also be limited by lobeclearance in the cylinder head construction, so higher lobesmay not necessarily clear the framework of the cylinder headcasing. Higher valve lift can have the same effect as increasedduration where valve overlap is less desirable.Higher lift allows accurate timing of airflow; although even byallowing a larger volume of air to pass in the relatively largeropening, the brevity of the typical duration with a higher liftcam results in less airflow than with a cam with lower lift butmore duration, all else being equal. On forced induction motorsthis higher lift could yield better results than longer duration,particularly on the intake side. Notably though, higher lift hasmore potential problems than increased duration, in particularas valve train rpm rises which can result in more inefficientrunning or loss of torque.Cams that have too high a resultant valve lift, and at high rpm,can result in what is called "valve bounce", where the valvespring tension is insufficient to keep the valve following the camat its apex. This could also be as a result of a very steep rise ofthe lobe and short duration, where the valve is effectively shotoff the end of the cam rather than have the valve follow thecams’ profile. This is typically what happens on a motor overrev. This is an occasion where the engine rpm exceeds theengine maximum design speed. The valve train is typically thelimiting factor in determining the maximum rpm the engine canmaintain either for a prolonged period or temporarily.Sometimes an over rev can cause engine failure where thevalve stems become bent as a result of colliding with the pistoncrowns. Page 5 of 10
  6. 6. PositionDepending on the location of the camshaft, the cams operatethe valves either directly or through a linkage of pushrods androckers. Direct operation involves a simpler mechanism andleads to fewer failures, but requires the camshaft to bepositioned at the top of the cylinders. In the past when engineswere not as reliable as today this was seen as too much bother,but in modern gasoline engines the overhead cam system,where the camshaft is on top of the cylinder head, is quitecommon. Page 6 of 10
  7. 7. CAMSHAFT FAILURE ANALYSISINTRODUCTIONCam failure is rarely caused by the cam itself. The only things we cancontrol during manufacture pertaining to cam lobe wear are lobe taper, lobehardness and surface finish. Of all the damaged cams we have checkedover the years, more than 99.99 percent have been manufactured correctly.Some people have the misconception that it is common for a cast iron flattappet cam to occasionally have a soft lobe. We have yet to see a cast ironflat tappet cam that had a soft lobe.When the cast core is made at the casting foundry, all the lobes are flamehardened. That process hardens all the lobes to a depth below the barrelof the core. That depth of hardness allows the finish cam grinder to finishgrind the cam lobes with Rockwell hardness above 50Rc. The generallyaccepted hardness on a finished cast cam should be between 48Rc to58Rc.All of the finished cams that we have checked are always above 50Rchardness on the lobes. Many outside factors, or a combination of factors,can cause cam failures. We will list some of the factors we have determinedthat may cause camshaft failure. Page 7 of 10
  8. 8. REASONS FOR CAM FAILURE 1. Lobe wear A) Incorrect break-in lubricant. Use only the Moly Paste, Part Number 99002-1 that is included with the cam. This Moly Paste must be applied to every cam lobe surface, and to the bottom of every lifter face of all flat tappet cams. Roller tappet cams only require engine oil to be applied to the lifters and cam. Also, apply the Moly Paste to the distributor gears on the cam and distributor for all camshafts. For extra protection, an anti-wear additive should be added, such as Crane Super Lube, Part Number 99003-1.B) Correct break-in procedure.After the correct break-in lubricant is applied to the cam and lifters, fill thecrankcase with fresh non-synthetic oil. Prime the oil system with a primingtool and an electric drill so that all oil passages and the oil filter are full of oil.Pre-set the ignition timing and prime the fuel system. Fill the cooling system.Start the engine. The engine should start quickly and run between 1500 and3000 rpm.C) Spring pressureNormal recommended spring seat pressure for most mild street-type flattappet cams is between 85 to 105 lbs. More radical street and raceapplications may use valve spring seat pressure between 105 to 130 lbs. Forstreet hydraulic roller cams, seat pressure should range from 105 to 140 lb.Spring seat pressure for mechanical street roller cams should not exceed150 lb. Race roller cams with high lift and spring pressure are notrecommended for street use, because of a lack of oil splash onto the cam atlow speed running to help cool the cam and lubricate the lifters. This highspring pressure causes the heat created at the cam to be transferred to theroller wheel, resulting in its early failure. Any springs that may be used mustbe assembled to the manufacturer’s recommended height. Never installsprings without verifying the correct assembled height and pressures.D) Mechanical interference.There are many factors that can cause mechanical interference. (1) Spring coil bind: This is when all of the coils of the spring (outside, Page 8 of 10
  9. 9. inside or flat damper) contact each other before the full lift of the valve. We recommend that the spring you are using be capable of traveling at least .060" more than the valve lift of the cam from its assembled height. (2) Retainer to seal/ valve guide boss interference. You need at least . 060" clearance between the bottom of the retainer and the seal or the top of the valve guide when the valve is at full lift. (3) Valve to piston interference: this occurs when a change in cam specs. (i.e.; lift, duration or centerline) is enough to cause this mechanical interference. Also: increased valve size, surfacing the block and/or cylinder head may cause this problem. If you have any doubt, piston to valve clearance should be checked. Minimum recommended clearance: .080" intake and .100" exhaust. (4) Rocker arm slot to stud interference: As you increase valve lift, the rocker arm swings farther on its axis. Therefore the slot in the bottom of the rocker arm may run out of travel, and the end of the slot will contact the stud and stop the movement of the rocker arm. The slot in the rocker arm must be able to travel at least .060" more than the full lift of the valve. Some engine families, like small block Chevrolet, have stamped steel rocker arms available in long and extra long slot versions for this purpose.2) Distributor gears wear.The main cause for distributor gear wear is the use of high volume or high-pressure oil pumps. We don’t recommend the use of these types of oilpumps. If you do run these types of oil pumps, you can expect short life ofthe cam and distributor gears, especially for low speed running, in street typeapplications. If you must run these types of oil pumps, you can increase thelife of the gears by adding more oil flow over the gear area to help cool off thepoint of contact.3) Camshaft end play.Some engines have a thrust plate to control the forward and backwardmovement of the cam. The recommended end play on these types ofengines is between .003" to .008". Many factors may cause this end play tobe changed. When installing a new cam, timing gears, or thrust plates, besure to verify end play after the cam bolts are torqued to factory specs. Ifthe end play is excessive, it will cause the cam to move back in the block,causing the side of the lobe to contact an adjacent lifter. Page 9 of 10
  10. 10. 4) Broken dowel pins or keys.The dowel pin or Woodruff key does not drive the cam; the torque of thetiming gear bolt, or bolts, against the front of the cam drives the cam. Somereasons for the dowel pin or key failing are: Bolts not being torqued to correctspecs; Incorrect bolts of a lower grade being used; Stretching and losingtorque; Not using the correct hardened washer that may distort and causetorque of the bolt to change; LocTite not being used; Or some interferencewith the cam and lifters or connecting rods causing the cam to stop rotation.5) Broken camA broken cam is usually caused by the cam being hit by a connecting rod, orother rotating parts of the engine coming loose and hitting the cam. Whenthis happens, the cam will usually break in more than two-pieces.Sometimes the cam will break in two pieces after a short time of usebecause of a crack or fracture in the cam due to rough handling duringshipping, or some time before installation. If a cam becomes cracked orfractured due to rough handling, it will generally not be straight.Most people will not have any means of checking cam straightness. As ageneral rule, if you can install the cam in the engine and install the timinggear, the cam should turn freely with just your finger pressure. There shouldnot be any drag or resistance in turning the cam. This free turning of thecam is assuming that if new cam bearings were installed, they were thecorrect parts and they were installed correctly. Page 10 of 10

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