rocker arm adjustment

[minifridge1138]

I know I have some valve clatter.
The service manual says the rocker studs should be tightened to 50 ft-lbs.
Should I just use a torque wrench or should I go through the engine running adjustment procedure?

All opinions welcome.

Thanks!!!

 

[Hib Halverson]

The tightness of the rocker studs in the head is probably not an issue.

The rocker arm nuts are not tightened to 50 lbs/ft. In fact, they are not tightened to any specific value.

Here's the easy way to adjust your valves:

Start with the left bank then do the right. Start at the front of the engine. Turn the crankshaft by hand. Adjust the intake when the exhaust starts to open. Adjust the exhaust when the intake starts to close.

Loosen the rocker nut just until you can easily "twirl" the pushrod with your fingers but when you move the rocker, you can't feel any clearance. Then tighten it just a tiny bit until you feel resistance to your twirling of the pushrod. Move on to the next valve.

After you adjust each valve that way, then go back and give each rocker arm nut another 1/2-3/4 turn. Put the covers back on and road test.

You can do this with the engine cold.

Lastly, if this is a case where the engine has always run ok, but recently you've developed one or more noisy valves, first I'd check valve lift to make sure the camshaft is not failing.

 

[minifridge1138]

Ok, thanks for the tips.

And you're right, that torque spec is for the rocker arm studs, not the adjustment nuts.

 

[TimAT]

When you adjust the rockers, if one nut feels easier to turn than the others, replace it. That tells you the crimp on the nut is going away and it will not hold it's adjustment.

My preference is to adjust them hot and running. Messy, but it works. And with it running, you can SEE the rockers moving. If one is going away, most of the time you can see it. Not always, but most of the time.

 

[Hib Halverson]

If a cam lobe has failed, indeed, you can see that with a visual inspection...quite easy turning the engine by hand, more difficult and messy if the engine's running...but you can se it. If you believe there is a cam lobe which is failing but it has not yet flat, the only way to know for sure is to measure the valve lift, divide the the rocker ratio then compare that to the lobe lift figure listed in the FSM.

 

[wishuwerehere82]

I have used both the twirl and tighten method and the clatter and adjust methods, but my auto parts guy turned me onto a method that works better than both of them.

1) Get a good vacuum guage.
2) Get a cheap pair of valve covers that you can cut up.
3) Cut a slot in the valve covers to access the rocker nuts.

Now with the engine warm, take off the valve covers and put the slotted ones on for adjusment purposes.
Then hook up the vacuum gauge to the intake manifold vacuum port.

The idea is to adjust the rocker arms until you get the highest vacuum reading on the intake manifold.
Make sure the engine does NOT go above idle RPM or you will spray oil all over the place.
Start with one side, and one by one, loosen the rocker nut until you see the vacuum gauge drop. Then tighten the nut until you see the guage reach the highest vacuum reading. Continue down the bank of rockers until you finished one side, then do the other side until you have the highest overall vacuum reading at the intake manifold.

I did the twirl and tighten method and achieved around 18" of vacuum on my L83.
After using the vacuum gauge method, my intake vacuum rose to 21" vacuum at idle, and runs much smoother and powerful than before.

Just one more way to skin a cat.

 

[Curtis]

After using the vacuum gauge method, my intake vacuum rose to 21" vacuum at idle, and runs much smoother and powerful than before.

Just one more way to skin a cat.[/quote]

My brain is in a fog and I don't understand why the guage method raises vacuum. It seems to suggest to me that this method is putting the adjustment at the point where only the play is taken out between the lifter and the pushrod and the plunger in the lifter is not preloaded in any way, which may effectively shorten the camshaft duration or lower cam overlap. Can you explain this a little more please? Why greater vacuum and why better performance?

 

[minifridge1138]

I'm just guessing but....

By starting with the rocket loose, it causes the valve to open less. This reduces the amount of air that can enter and exit the combustion chamber and therefore reducing vacuum.

As you tighten the rocker arm, you are increasing air flow and engine vaccum.
When vaccum reaches its peak, the valve is opening all the way. This is zero lash and factory spec.

If a rocker is overtightened then you are putting extra pressure on the pushrod and cam. The engine will use more power to open the valve and that is less power to the wheels. It could also be so tight that the valve is not closing all the way. That would mimic cam overlap and reduce vacuum.

By stopping at max vacum it is not too tight and not too loose.

 

[wishuwerehere82]

Minifridge hit it on the head.
Static adjustment takes the average value of 1/2 to 3/4 turn and pre-loads the springs in the lifters to 50% of their travel height.
By doing it with the vacuum gauge, you get maximum valve lift and maximum airflow and are dynamically using a combination of the spring and the oil pressure inside the lifter to do it.
The average position of the nut is very close to where it would be doing it statically, but that extra couple of degrees + - gets it right in the sweet spot where the valve is opening and closing at just the right time.

Plus, it gives you a chance to watch the amount of lift on the rockers and the oil flow out the pushrods in case you are having a worn cam lobe.

 

[Vettehead Mikey]

I'm curious to know how this method assures that the lifter piston ends up in the middle of it's travel as per design.

BTW- having a lifter piston sitting at the top bottom or middle of it's travel doesn't increase or decrease valve opening or timing at all. Hydraulic lifters are designed to self-eliminate all lash that would affect either opening or timing. Don't confuse this with a solid lifter set up.

 

[wallyknoch]

The tightness of the rocker studs in the head is probably not an issue.

The rocker arm nuts are not tightened to 50 lbs/ft. In fact, they are not tightened to any specific value.

Here's the easy way to adjust your valves:

Start with the left bank then do the right. Start at the front of the engine. Turn the crankshaft by hand. Adjust the intake when the exhaust starts to open. Adjust the exhaust when the intake starts to close.

Loosen the rocker nut just until you can easily "twirl" the pushrod with your fingers but when you move the rocker, you can't feel any clearance. Then tighten it just a tiny bit until you feel resistance to your twirling of the pushrod. Move on to the next valve.

After you adjust each valve that way, then go back and give each rocker arm nut another 1/2-3/4 turn. Put the covers back on and road test.

You can do this with the engine cold.

Lastly, if this is a case where the engine has always run ok, but recently you've developed one or more noisy valves, first I'd check valve lift to make sure the camshaft is not failing.

All you need to know,..

You may try rotating the engine with the alternator and a socket on the nut holding the fan and pulley. You may have to tighten the belt to prevent it from slipping. This would avoid searching for the crank bolt and use of the starter to roll it over. It would turn easier if the plugs were out but its not necessary.,..