Reinstalling Timing Chains on the U-20
If possible, BEFORE disassembly, it is best to set the engine to cylinder #1 at TDC, confirm the distributor's rotor is pointing to #1 cylinder, and the top ears of the camshaft, for #1, are both pointing upwards. This will make it simpler to replace the chains by keeping everything in proper synch.
If the engine has been complete torn down, then it is a matter of starting from scratch. Biggest concern is to NOT bolt the head on the block, then start rotating the engine. Some valveFs will always be open, and it the piston hits them, even while turning by hand, you may still bend the valve.
First: Rotate the crank so piston #1 is at TDC. You'll notice the crankshaftFs woodruff key is pointing straight up. You should be able to spin the jackshaft around, so the woodruff key is roughly at 8:00. Double check to see what the distributor rotor is pointed, it should be at #1 cylinder. Quite common to discover someone who was messing with timing chains last time set the distributor wrongly.
Now, while the lower chain and gears are on the bench, point the markers towards each. Wrap the chain around the gears, and slide the whole thing in place onto the crank and jackshaft gear. [The factory manual has a thing about little dimples, and counting links. Usually the newer crankshaft gears only have one mark on them, not two like ones I saw some years back.]
Second: now rotate the crankshaft 90 degrees to the left (we just want to lower #1 & #4 pistons while we fit the cylinder head.
Third: place the head on the engine block. Rotate the camshaft until the locating dowel is straight up. #1 valve lobes on the cam should be pointing up (at 10:00 and 2:00 positions). At this point, I usually like to install the head with just two head bolts - just snug them down.
Fourth: Rotate the crankshaft back - 90 degrees to the right. Just confirm that the woodruff key is pointing up. Now install the upper timing chain.
Fifth: I rotate the crank, by hand, around twice to make certain there are no problems with clearance between valves and pistons. Bringing the engine back to #1 TDC.
Optional, but a good idea, I like to use a dial indicator and timing wheel to confirm the opening/closing time of the camshaft.
Sixth: Remove the cam sprocket, and use that handy support (upper guide) to hold it in place. Remove the head. All the timing components should be set up without any problem! Always remember to set the head down on its side.
Do not overlook the oil slinger on the front crankshaft, the raised portion faces you (it goes on AFTER the crank gear is in place).
Install the front cover seal while the cover is still off.
Jackshaft modification: have a machine shop drill and tap the hole to accept a 7/16-20tpi stud. It should be installed no further than the first oil hole (In all honesty, only time IFve seen jackshafts snap at the nose are on engines that have been revFd to 8,000 rpm. Oh, one failed at a stop light!)
Front Cover: if you replace those studs in the upper portion with bolts, youFll be able to get at the timing chains next time without having to pull the cylinder head.
Check the Crank Pulley: Before installing the head, slip the front pulley in place. With a dial indicator on the piston, check that the pulleyFs largest notch lines up with the front cover pointer. Just nice to make sure TDC on the pulley is actually TDC at the motor.
Lower chain guide: I do not bother installing them. Not sure the original idea for the guide, but most fail and have a portion of them end up down by the oil pan.
TomFs quick check on camshaft timing: With the engine at TDC on # 1 cylinder, look at the lobes on #4. They should both be opening the valves the same amount, with either the symmetrical SU or SOLEX camshaft. It is an easy and quick way to confirm the camshaft is installed correctly. (If you have a custom ground Asymmetrical camshaft, then refer to your grind card).
©1996, Thomas Walter