Z24 - Time for a valve adjustment!

[Mighty Burger]

Hey guys. I've posted here once before and you were all really helpful with getting me started on some basics and making my truck run better. I thought I'd come back to ask about this. My 1983 Datsun 720 4WD with a 2.4L engine has a rattling noise, almost like it sounds like a diesel. The sound gets more noticeable when it warms up (which I've noticed takes a while. Looking under the hood, it seems like the fan runs all the time, could this be a thermostat issue?). I think it needs a valve adjustment. I changed the oil recently just for general maintenance and it hasn't affected the noise, so it isn't an issue caused by dirty motor oil. I've noticed a couple other symptoms that I think could be caused by it needing a valve adjustment, like idling really poorly when it hasn't warmed up yet, and I don't want to look into those any further until I adjust the valves.

 

I was looking all over trying to figure out how to do this and I'm a little confused on a few things. I want to get this straight so I don't misadjust any valves and ruin my engine. My confusion is about the process once I have the valve cover off. Here's what I found. There's four cylinders and two valves per cylinder - one intake, one exhaust. The valves on the left (passenger) side are the intake and the valves on the right (driver) side are exhaust, and they both should have a gap of .012" correct?

My biggest confusion is about rotating the engine. First, how do I rotate it? Some people said to use a socket and a long ratchet to rotate it. Well.. which way?? Clockwise if you were standing in front of the truck looking under the hood?? Besides I don't have any really long ratchets or pipe to extend the handle of one to turn the engine, would just putting it into 5th and pushing it down the road until it's where it needs to be work? And how in the world do I know when piston #1 is at TDC? Is there any way I could see that just by looking under the valve cover? (I don't know what I'm going to see under the valve cover any pictures would be great.)

How much time do I have to do all of this before it cools down too much?

[menac1ty]

The valves by the intake manifold (that's the carb side) are intake valves and the ones to the opposite side (exhaust manifold) are the exhaust valves. The spec is 0.012" that's right. Have someone start the engine and take note of which way it rotates, then spin it that way with your wrench. You could use another pulley if you can't reach the crank pulley but I wouldn't recommend it much, I was used the alternator pulley to do this job. Alternatively you can jack up on of the rear tires, put it in 5th gear and spin that tire by hand, would be a lot easier if someone would spin that for you while you adjust the valves tho.

The way to see if piston #1 is at TDC: Remove the distributor cap and spin the engine until the rotor is just about pointing at #1 spark wire, then look at the markings at the passenger side crank pulley, there are some numbers there and a mark on the crank pulley itself, it goes 20 10 and 0. Spin the engine until that mark is at 0. You're now at TDC. Another way is that both exhaust and intake valves are closed for #1 at TDC.

 

First go for a drive (at least 15 mins) to really warm things up, including the oil cause if you warm it up at idle then the only thing at adequate temp is the coolant temp.

Then shut the engine off, remove everything in the way, loosen the valve cover fasteners a bit and then start the engine again let it run for like a minute or two. Shut it off again and remove the valve cover completely. Do the adjustment and double check to see if you've done it right and tightened the locking nuts enough. Then put the valve cover back on and use two fasteners to just secure it into place, DO NOT TIGHTEN THEM. It will prevent engine vibrations from throwing the cover off and the oil pressure at idle is so low the it won't leak from the sides and make a mess. Start the engine and let it run for a minute then take the cover off and recheck the clearance. After you're done, replace the cover gasket and install it regularly this time. This is an extra step I always do to make sure it didn't cool off much during adjustment to throw off my clearance and also to double check.

And remember: ALWAYS set the lash on the loose side and not on the tight side, but no so loose that a bigger feeler blade could slip through easily.  

[Mighty Burger]

On 11/26/2019 at 10:06 AM, menac1ty said:

The valves by the intake manifold (that's the carb side) are intake valves and the ones to the opposite side (exhaust manifold) are the exhaust valves. The spec is 0.012" that's right. Have someone start the engine and take note of which way it rotates, then spin it that way with your wrench. You could use another pulley if you can't reach the crank pulley but I wouldn't recommend it much, I was used the alternator pulley to do this job. Alternatively you can jack up on of the rear tires, put it in 5th gear and spin that tire by hand, would be a lot easier if someone would spin that for you while you adjust the valves tho.

The way to see if piston #1 is at TDC: Remove the distributor cap and spin the engine until the rotor is just about pointing at #1 spark wire, then look at the markings at the passenger side crank pulley, there are some numbers there and a mark on the crank pulley itself, it goes 20 10 and 0. Spin the engine until that mark is at 0. You're now at TDC. Another way is that both exhaust and intake valves are closed for #1 at TDC.

 

First go for a drive (at least 15 mins) to really warm things up, including the oil cause if you warm it up at idle then the only thing at adequate temp is the coolant temp.

Then shut the engine off, remove everything in the way, loosen the valve cover fasteners a bit and then start the engine again let it run for like a minute or two. Shut it off again and remove the valve cover completely. Do the adjustment and double check to see if you've done it right and tightened the locking nuts enough. Then put the valve cover back on and use two fasteners to just secure it into place, DO NOT TIGHTEN THEM. It will prevent engine vibrations from throwing the cover off and the oil pressure at idle is so low the it won't leak from the sides and make a mess. Start the engine and let it run for a minute then take the cover off and recheck the clearance. After you're done, replace the cover gasket and install it regularly this time. This is an extra step I always do to make sure it didn't cool off much during adjustment to throw off my clearance and also to double check.

And remember: ALWAYS set the lash on the loose side and not on the tight side, but no so loose that a bigger feeler blade could slip through easily.  

Thank you. The detailed instructions help a ton. I'll post any updates on this. Thanks for the help!

[datzenmike]

With engine hot quickly loosen all lock nuts to save time later. It will rotate either way but clockwise as viewed from the front is the way it runs. Set to TDC on #1 while hot. Both valves on one should be closed and cam lobes pointing down at 8 and 4 o'clock, again as viewed from the front. Set the following valves...

 

Intake and exhaust on #1 cylinder. Both are closed

Intake on #2.  Only intake is closed

Exhaust on #3. Only exhaust is closed

 

Turn engine ONE turn and up to TDC. Cam lobes on #1 at 10 and 2 o'clock. This is TDC on the exhaust stroke on #1

 

Exhaust on #2

Intake on #3

Both valves on #4

 

At one minute per valve you're done in under 8 minutes (more likely well under 4 minutes) and you only needed to turn the engine once after initial set up to TDC on the exhaust stroke. More than fast enough to set the valves before the engine cools.