GMC 12648846 Lifter Assembly, Valve

Before taking out the camshaft, measure the lobe lift to ascertain the extent of cam lobe wear. Put number one piston at TDC on compression stroke. Then open the rocker arm nuts by loosening up the valve cover to access pushrods. A dial indicator should be set up on the engine and a plunger placed against the top of the first pushrod. Zeroing will then follow and this can be done by turning crankshaft slowly in the normal direction of rotation until it reaches its maximum lobe lift position which shows that it has fully opened. Note down this measurement and repeat for other valves. If cam lobes have been worn down below specified limits, mount a new camshaft. To test for noisy lash adjuster, use a mechanic's stethoscope or a length of hose near each valve while listening for excessive clearance in valvetrain. Any defective lash adjuster is identified through noise produced. This requires removing cylinder head to remove lash adjusters. The removal tool used may either be magnet or scribe but lash adjuster guides help in separating them from the cylinder head. These are then washed and checked whether they have score marks, uneven wear and scuffing too. In addition, inspect rollers for damage or wear and replace them if necessary. To pull out a camshaft one should remove front cover with timing chains as well as sprockets on them; there will also need removal bolts together with oil pump drive as well as thrust plate of camshaft before you carefully withdraw it from block after which bearing journals are cleaned and examined for any destructions; size of bearing journals and camshaft lobes measured where obvious inspection of lobes revealing discoloration, score marks, chipped areas pitting, deformation etcetera indicates that they can no longer serve while some other good conditions along with correct measurements will allow further utilization thus lubricating these components such as bearing journal alongside their respective lobes through assembly lube should be done in a way that it easily slides into the engine after which thrust plate is put back with its bolts tightened while oil pump drive is reinstalled thus where lash adjusters are still intact, they may be reinstalled at their original locations and then coated using assembly lube. On the other hand, lash adjuster bores are also lubricated by engine oil prior to installing them whereby; pushrods as well as pushrod guides should be positioned while rocker arms together with rocker arm retaining nuts are tightened.

Begin with taking off the camshaft by unscrewing or unbolting the rocker arms, push rods, intake manifolds, timing chains, cam sprocket and balance shaft drive gear; in addition, you may have to do away with such things as fan radiator and condenser. Place the lash adjusters in a labeled box and disconnect the lash adjuster retainer. A special tool can be employed together with magnet or even your fingers to extract the lash adjusters from their bores. Remove the camshaft retainer plate and use three 6-inch long, 5/16-18 bolts as a handle to remove the camshaft from block. When inspecting clean lash adjuster & cam shaft using solvent checking for wear on both of them. The journals as well as cam lobes should be checked for wear. Measure. If its damaged then it must be replaced along with bearings. To lubricate bearing journals and cam lobes with assembly lube, the camshaft will finally slide into engine during installation. Fix other parts like this: install that thrust plate for a Cam Shaft; balance shaft drive gear plus also timing chain & sprockets. Lubricate lash adjusters using clean engine oil then fix them within block. The rest of installation is opposite to that of removing these components. Cooling system should be refilled at last because we are starting again after changing an engine oil filter. Finally start engine (run) and check there are no leaks.

Rocker arms can be pivoted away from the pushrods by removing the valve covers and loosening the rocker arm nuts before removal to measure camshaft lobe lift. The plunger on a dial indicator is to be positioned directly above the first pushrod, which is mounted on the engine. Disconnect the engine's electrical connectors from the distributor. Rotate the engine very slowly until it comes to rest with this pushrod sitting against its lowest point (base circle of camshaft lobe) then zero dial readout. As an effect of rotating crankshaft in normal direction indicator needle reaches its highest peak and starts reversing showing maximum cam lobe lift. Write this down and make check for all lobes comparing results obtained. If cam lobe lift is 0.003 inches less than specified, there will be a need for new camshaft installation since there has been a wear out of cam lobe. Also, remove fan shrouds, fan, radiator and condenser if applicable. Carefully remove them while properly labeling and storing before lifting off Lash Adjuster retainer. One must always be careful never to try to extract a camshaft with the Lash Adjusters left inside. Lash Adjuster removal from bores can also take different directions depending on what one wants to do next or how many Lash Adjusters are being replaced at once or maybe whether one has no other option but replace all of them because they are so bad that individual replacement would not solve anything here otherwise there could be no further discussion where others may simply call for removal with every other thing remaining intact Some other methods may include using tongs or pliers etc., By holding onto this chain while forcing it outwards (meaning our efforts are aimed at removing without damaging crankcase bearings which are located near bottom part). At this juncture, note carefully how two torx screws have been used here as well as appropriate directionality provided by manufacturer themselves. Three 6-inch long, 5/16-18 bolts can be threaded into the camshaft sprocket bolt holes to serve as handles when pulling on the camshaft, thus preventing any possible damage to bearings straight out. During an examination, there are several features that indicate damage in form of wear of cam lobes and bearing journals. Obtain a micrometer and take measurements of each cam journal's diameter and also determine height of every cam lobe using these results compared against appropriate tolerances. Should any journal have a diameter less than what it ought to be, then replace the particular camshaft. The procedure for changing these bearings is normally outsourced to automotive machine shops due to difficulties involved since they use specific tools and are manned by experts in this field. Once again, lubricate both camshaft bearing journals along with the cams lobes utilizing assembly lube meant for these parts, then gently slide it into block without damaging those sensitive lower ends of crankcase bearings near mounting points near crankcase face. As soon as position (dowel pin) after pivoting cylinder head in clockwise direction has been reached (that means 3 o'clock), lock it through tightening the thrust plate. By aligning dowel pins also confirming position of balancer shaft timing marks install balance shaft drive gear accordingly. Next, install the timing chain and gears in their right place using clean engine oil on Lash Adjusters when returning them into their respective bores because old Lash Adjusters may be reused if one is not installing new cams together with new Lash Adjusters too as was mentioned above or which case always follows after changing some worn out stock ones Finally, do everything else you did back but change oil before starting engine and put another filter.

To take off the camshaft, first disconnect the cable from the negative battery terminal and release fuel system pressure. From there on, remove; radiator, auxiliary automatic transmission fluid cooler (if equipped), power steering cooler, air conditioning condenser, valve covers, intake manifold, rocker arms, pushrods, timing chain and sprockets, and cylinder heads. Before you remove the lifters arrange to store them in a labeled container. Remove lash adjusters and camshaft retainer plate using a bolt as a handle to carefully pull out camshaft. To check out the camshaft measure lobe height and base circle for lobe lift determination; compare with specifications and replace the camshaft if necessary. Check the camshaft bearing journals for wear or damage; use a micrometer to measure them. Inspect the camshafts lobes for discoloration; score marks; chipped areas; unalike wear. Clean and inspect lash adjuster bodies for damage, wear and proper roller function. Put in place by lubricating bearing journals and lobes with assembly lube before sliding it into the engine, securing it with the Cam Thrust Plate. Install timing chain and sprockets , camshaft position sensor, lash adjusters As well as this refill cooling system, change oil, new oil filter installation precede start up-run engine process.

After installing the camshaft, you should: 1. Refill the cooling system. 2. Change the engine oil and filter. 3. Start the engine and check for leaks.

The lifters should be stored in a clearly labeled box before removing them.

If the cam lobe lift is 0.003 inches less than specified during the measurement, it indicates cam lobe wear, necessitating the installation of a new camshaft.

After removing the lifters, you should clean them and inspect them for scuffing, score marks, and uneven wear. Additionally, check the rollers for wear and damage. Replace the lifters if necessary.

The steps for installing the camshaft are as follows:1. Lubricate the camshaft bearing journals and cam lobes with assembly lube.2. Slide the camshaft into the engine.3. Install the camshaft thrust plate.4. Install the balance shaft drive gear.5. Install the timing chain and sprockets.6. Lubricate the lifters with clean engine oil.7. Install the lifters in the block.8. Complete the installation in reverse order of removal.

After installing the camshaft, proceed to install the balance shaft drive gear, aligning the dowel pin and ensuring proper alignment of the balance shaft timing marks. Then, install the timing chain and sprockets.

The lifters should be stored in a clearly labeled box before removing them.

During inspection of the camshaft, you should:1. Clean the lifter and camshaft with solvent.2. Check for wear and damage on the lifter and camshaft.3. Measure the journals and cam lobes for wear.4. Replace the camshaft and bearings if they are damaged.

There is 1 lifter per order