The small volume of the combustion chambers of this engine also does not allow the possibility of opening the valve at the moment when the piston is near TDC. This can happen if the chain or camshaft is not properly aligned with the crankshaft. In this case, the valve will collide with the piston and the engine will fail.
To chain (2) camshaft drive (8) did not sag and did not make noise, it must be constantly stretched. For this, a plastic-coated tensioner shoe is used (4), which is pressed against the chain by a spring-loaded tensioner piston (2). There is an oil damper to dampen chain vibrations (3), which prevents the tensioner piston from swinging. The opposite branch of the chain on both sides is enclosed between the soothing strips (7).
Oil pump (6) driven by a separate chain. This short chain is often the cause of howling noises in older engines because it does not have a tensioner and therefore can oscillate when the engine is running.
Caution: Do not rotate the camshaft or crankshaft while the drive chain is removed as this can cause the valves to hit the pistons, resulting in costly repairs.
Withdrawal
Set the piston of the first cylinder to TDC on the compression stroke.
Remove the valve cover. Make sure the #1 piston is at TDC on the compression stroke (rocker arms of the first cylinder do not compress the valve springs).
Remove the top drive chain cover. Note the location of the camshaft alignment marks, which should now line up. On engines with six cylinders, the line drawn through the two opposite camshaft sprocket mounting bolts must be strictly vertical, and the line drawn through the other two bolts must be horizontal. Also, the dowel pin hole should be in the bottom left corner (between 7 and 8 o'clock).
Caution: Since the engine is mounted at an angle in the engine bay, all horizontal and vertical references for camshaft adjustments are in relation to the crankshaft, not to the ground.
Block the crankshaft with a wrench by installing it on the center bolt of the vibration damper, then loosen (but don't shoot) four bolts securing the sprocket to the camshaft. Be very careful not to turn the camshaft or crankshaft.
Note: Camshaft sprocket bolts on some early models have locking tabs. Bend them back before loosening the bolts.
Remove the lower drive chain cover.
Loosen and remove the four camshaft sprocket bolts, then move the chain away from the crankshaft sprocket and carefully remove the chain from the engine along with the camshaft sprocket.
Inspection
Asterisks
Inspect the crankshaft and camshaft sprocket teeth for signs of wear. If the sprocket is worn, the working sides of the teeth will be slightly concave. In this case, the sprockets must be replaced.
Attention: The crankshaft sprocket is pressed onto the crankshaft and can only be removed with a puller after removing the key and oil pump. It is recommended to install a new sprocket on the crankshaft, preheating it to 200°C. For this reason, if the crankshaft sprocket needs to be replaced, it is recommended to remove the crankshaft, take it to a body shop and have the sprocket replaced by a specialist.
Drive chain
The chain should be changed if it cannot be tensioned sufficiently (excessive noise during operation) or if the sprockets are worn. It is recommended to change the chain every time the engine is overhauled.
Chain guide and tensioner
Inspect the chain guide and tensioner guide for grooves made by the chain. Replace them if they are excessively worn. The guides can be replaced after the circlips have been removed.
Shake the tensioner plunger and check that the ball located inside is tapping. If no sound is heard, replace the plunger.
Blow first into the closed end of the plunger, then into its slotted end. In the first case, air should not pass through the plunger, and in the second, it should flow freely through it. If not, replace the tensioner.
Installation
Install the tensioner guide and chain guide.
Temporarily install the lower drive chain cover and vibration damper, check the alignment of the alignment marks of the shaft elbows and remove the vibration damper and cover again.
Route the drive chain over the crankshaft sprocket and then over the camshaft sprocket, and placing the chain between the chain guide and tensioner guide, install the sprocket onto the camshaft. Make sure the timing marks on the camshaft are aligned.
Then install in the reverse order of removal.