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INSPECTION OF CAMSHAFT AND RELATED PARTS After the camshaft has been cleaned, check each lobe (Fgr__67) for scoring, scuffing, fractured surface, pitting, and signs of abnormal wear; also check for plugged oil passages. Premature lobe and lifter wear is generally caused by metal-to-metal contact between the cam lobe and the lifter bottom due to inadequate lubrication. Wear normally begins within the first few minutes of operation. It’s the result of insufficient lubrication. To check cam lobe wear, measure the lobe height with a micrometer. Measure from the heel to the nose and then again 90 degrees from the original measurement. Record the measurement for each intake and exhaust lobe. Any variation in height indicates wear. Also check the measurements against the manufacturer's specifications. Measure each camshaft journal in several places to determine if it’s worn. If a journal is 0.001 inch (0.0254 mm) or more below the manufacturer's specifications, it should be replaced. The camshaft should also be checked for straightness with a dial indicator. Place the camshaft on V-blocks. Position the dial indicator on the center bearing journal and slowly rotate the camshaft. If the dial indicator shows runout (a 0.002-inch [0.0508 mm] deviation), the camshaft is not straight and must be replaced. If the engine has a worn or damaged camshaft, identify the cause and fix the problem before installing a new camshaft, lifters, and/or followers. Timing Components The timing belt or chain and crankshaft/camshaft gears (sprockets) should be inspected and replaced if damaged or worn. A timing gear with cracks, spalling, or excessive tooth wear is an indication of improper backlash (either insufficient or excessive). Excess backlash causes the noise as the gears' teeth make violent contact. This overloading causes accelerated tooth wear and breakage. Insufficient backlash can cause the gears to bind. It can also cause high contact forces that can rupture the oil film between the teeth, causing spalling and wear. Gear backlash is checked with a dial indicator. Check the movement between the camshaft and crankshaft gears at six equally spaced teeth. Hold the gear firmly against the block while making the check. Refer to specifications for backlash limits. Lifters: When inspecting lifters, carefully check their bottoms and pushrod sockets. Wear should be off the center of the lobe and there should be no signs of edge contact. If they show abnormal wear, scoring, or pitting, they should be replaced. Any lifter that has its contact face worn flat or concave must also be replaced. Lifter bottoms are normally spherical. Technically, normal lifter wear is referred to as adhesive or galling wear. It results from two solid surfaces (camshaft lobe and lifter face) rubbing on each other. The two surfaces tend to weld together. Fortunately, proper lubrication retards this process. However, excessive loading will accelerate the wear process (Fgr__ 68). Excessive loading is caused by incorrectly matched valve springs (too much spring pressure), old lifters on a new camshaft, or new lifters on an old camshaft. Hydraulic lifters should be removed, disassembled, cleaned, and checked. Check the lifter's leak down with a leakdown tester. Lifter leakdown rate is important. If the lifters leak down too quickly, noisy operation will result. If the lifters don’t match specifications, they should be replaced, along with the camshaft. Never install old flat lifters with a new camshaft or new lifters on a used camshaft. INSTALLATION OF CAMSHAFT AND RELATED PARTS Before installing the camshaft and balance shafts with their bearings, coat all parts with assembly lubricant. This lubricant should have an extreme pressure (EP) lubricant rating. This helps prevent scuffing and galling during initial startup. It should also have excellent adhesion to prevent the lubricant from draining off the parts during engine reassembly. Camshaft Bearings: Although the installation of camshaft bearings can be done after the short block is assembled, it may be easier to align the bearings' oil holes when the crankshaft is not installed. Keep in mind that any engine block that needed to have its main bearing bore alignment corrected due to distortion is likely to have camshaft bearing bore misalignment problems. OHV cam bearings are normally press-fit into the block or head using a bushing driver and hammer (Fgr__69). The bearing at the rear of the block should be installed first. The camshaft journals may have different diameters, with the smallest being on the rear of the block and each journal being progressively larger. The new bearing is fit over the tool's expanding mandrel and the tool is set into the block. A guide cone is used to keep the tool centered in the bore. Once the bearing is at the outside of its bore, rotate the bearing to align the oil hole in the bearing with the oil hole in the block. On blocks with grooves behind the bearings, the bearing should be installed with the oil hole at the 2 o'clock position as viewed from the front. While holding the centering cone against the outside bore, drive the bearing into its bore. If the cone and tool are allowed to move while inserting the bearings, the bearing can be damaged. While driving the bearings into their bore, be careful not to shave metal off the backs of the bearings. This galling may cause a buildup of metal between the outside of the bearing and the housing bore and result in less clearance. To prevent galling, housing bores should be chamfered. Camshaft: Wipe off each cam bearing with a lint-free cloth, then thoroughly coat the camshaft lobes, bearing journals, and distributor drive gear (if there is one) with assembly lube. Also lubricate the lifters. Most premature cam wear develops within the first few minutes of operation. Prelubrication helps to prevent this. Use the lubricant recommended by the manufacturer. The camshaft should be carefully installed to avoid damaging the bearings with the edge of a cam lobe or journal. Keep it straight while installing it. A threaded bolt in the front of the camshaft helps guide the cam in place. An alternative is to install the camshaft while the block rests on its end. When the camshaft is in place, install the thrust plate and the timing gear. Be sure to align the thrust plate with the woodruff key. Never hammer a gear or sprocket onto the shaft. Heating steel gears helps with installation. Don’t heat fiber gears. When installing the gears, be sure to keep the gear square and aligned with the keyway at all times. Once the shaft is completely in the block, the shaft should be able to be turned by hand. If the cam does not turn, check for a damaged bearing, a nick on the cam's journal, or a slight misalignment of the block journals. If the bearing clearance is too small, some technicians ream away a slight amount of the bearing; others hone the bearing. Both of these need to be done carefully. The best way to increase the clearance is to cut the camshaft journals on a lathe. Reaming or honing the inside diameter of cam bearings is not recommended because grit may become embedded in bearing surfaces, which will cause shaft wear. CRANKSHAFT AND CAMSHAFT TIMING USING SERVICE INFORMATION Normally, camshaft timing marks are shown in the engine section of a service manual under the heading Timing Belt or Chain R&R. During most engine rebuilds, a completely new timing assembly is installed. The camshaft drive must be installed so that the camshaft and crankshaft are in time with each other. Both sprockets are held in position by a key or possibly a pin. There are factory timing marks on the crankshaft and camshaft gears or sprockets (Fgr__70). The timing must be positioned according to the manufacturer's instructions. SHOP TALK -- Make sure the timing marks are precisely matched. If the gears are misaligned by one gear tooth, the timing will be off by about 17 degrees. The chain is installed on the crankshaft gear first, then around the camshaft sprocket. Never wind a chain onto the gears. Also, a screwdriver, prybar, or hammer should never be used to force a chain into position. Prying or pounding on the chain will damage the links, causing the chain to stretch and fail. Carefully place the entire assembly as a unit onto the shafts by pressing both gears evenly, keeping the key ways aligned. While keeping the gears parallel and aligned, gently tap them in place. SHOP TALK -- There are some OHV engines that are interference engines. If the crankshaft-to-camshaft timing is not correct, the pushrods normally bend when the engine is started. Double-check the alignment. Some manufacturers recommend additional checks of the camshaft after it has been inserted in the block. These include a check of the clearance between the camshaft gear and the backing plate. This check is made with a feeler gauge. This clearance can often be corrected by repositioning the camshaft gear. Camshaft end play is measured with a dial indicator. As the camshaft is moved back and forth in the block, the indicator will read the amount of movement. Compare this to specifications. End play can be corrected by changing the size of the shim behind the thrust plate or by replacing the thrust plate. Some engines limit the end play with a cam button. A nylon button or Torrington bearing sets on a spring and is installed between the gear and timing chain cover. === Camshaft to crankshaft Align marks Align marks Balance shaft to camshaft Fgr__70 Camshaft-to-crankshaft and camshaft-to-balance shaft timing marks. === A camshaft is designed to open and close the valves at the correct time. The camshaft, crankshaft, timing gears or sprockets, and timing chains or belts are made to specifications. Those specifications will include a range of acceptable tolerances. This means there is no guarantee that the timing assembly will provide exactly what the camshaft was intended to do. Overall engine performance can be affected by a few degrees of misalignment. Many performance engine builders degree the camshaft to precisely match the position of the camshaft with the crank shaft. Degreeing a cam is highly recommended when installing a performance camshaft. An engine with a properly degreed camshaft will be more efficient than one without a degreed cam. The exact procedure for degreeing camshafts varies with each engine design. The procedures must be followed exactly as stated by the cam manufacturer. Degreeing the cam requires a degree wheel, a stable pointer that can be attached to the block, a dial indicator with a mount, a positive TDC stop tool, the specification sheet for the camshaft, and the parts necessary to adjust the mounting of the timing gears. The latter are necessary to position the gears at their correct positions. === Balance Shafts--Balance shafts are serviced in the same way as crank shafts. Each bearing and journal should be cleaned and carefully inspected. All worn or damaged parts should be replaced. The oil clearance of the shafts and bearings should be checked with Plastigage. Place the balance shaft half bearings into the crankcase and then position the balance shaft(s) onto the bearings. Then lay a strip of Plastigage across each journal. Insert the matching bearing halves into the balance shaft housing and tighten the housing bolts to specifications and in the proper sequence. Now remove the housing bolts and housing. Measure the Plastigage at its widest point. Compare the readings to specifications. If the oil clearance is excessive, measure the shaft bore and the shaft(s) journals. Determine the cause of excessive clearances and replace the bearing or balance shaft. Remove the Plastigage completely after measuring. To install the balance shaft assembly, install the bearings in the crankcase and housing. Apply a light coat of clean engine oil to the bearings. The shafts need to be properly timed to the crankshaft. On some engines there are two balance shafts; these must be timed to each other, in addition to the crankshaft (Fgr__71). Align the timing marks of the balance shaft(s). Set the shaft(s) into position in the block. Set the housing with bearings over the shafts. Install and tighten the housing bolts. In most cases these bolts should be tightened in two steps and in a prescribed sequence. === Fgr__71 Balance shafts must be timed to each other and the crankshaft. Reference holes--Timing marks === Lifters--Before installing the lifters into the lifter bores, generously coat the lifter bores with assembly lube. Coat the lifters and/or followers one at a time as they are being installed. After they have been installed, rotate the camshaft to check for binding or misalignment. SHOP TALK -- Some technicians submerge the hydraulic lifters in clean oil to allow them to fill with oil before installing them. === Fgr__72 The different ways an oil pump is driven by the crankshaft. Outer rotor Inner rotor Pick-up tube Relief valve Crankshaft Oil pan; Strainer === Next: Oil Pumps Prev.: Installing Pistons and Connecting Rods Home Article Index top of page |
