I bought a set of 1.6 roller rocker arms to replace standard 1.5 rocker arms the new set is stamped Chrome Molly just like the old ones but has the roller end and is shorter. So I have read in a article that the stock push rods are not correct length and may need to replace them with chrome Molly rods of correct length, a engine shop stated he can't tell if I really need to replace them without doing the install but most are just fine with stock rods. My question is when I turn the engine till valve is closed then tighten down the nut till the rocker is aligned correctly and touching the valve end, how far do I turn to correct adjustment for the rocker 1/2 Turn 1 full 1/4 ??? and can anyone tell me whether or not to get a tool to see what the correct length is nessary or take the vette to the engine shop and have him check the push rod length ?

 

Here is the standard method that GM has used for years to adjust their valves:

Adjusting valves on the 1985 Corvette:

1) Remove the spark plugs. This makes it much easier to turn the engine by hand.

2) I believe that the nut in the center of the bottom pulley on the balancer is 5/8”. Use a six point 5/8” socket to turn the engine over by hand to line up the timing marks. Place a finger in the spark plug hole for plug #1 as you turn the engine over. You are trying to determine if the engine is on compression as you line up the marks. If you feel the air pushing against your finger as you line up the marks, you have compression in cylinder #1. Align the timing marks.

3) Now adjust the valves as follows:
Intake #1, 2, 5 and 7 then adjust Exhaust 1, 3, 4 and 8.
Note: If you are not sure which valve is the intake and which is the exhaust, look down at the exhaust manifold. The exhaust valve will be right above the exhaust pipe for the cylinder you are looking at. The adjustment is made by slowly tightening the nut as your twist the push rod between your thumb and finger. When you feel resistance as you twist the rod...stop. Then tighten the nut 3/4 to 1 full turn.

4) Turn the engine 360 degrees and line up the timing marks again. Now adjust the following:
Intake 3, 4, 6 and 8 then adjust Exhaust 2, 5, 6 and 7.

You are now finished with your adjustment. I usually tighten the lock nut 3/4 turn after adjusting to zero lash.

If you are adjusting roller rockers with a locking Allan nut inside the nut, turn the adjusting nut about 1/2 of a turn and then tighten your Allan screw. Now turn the nut and the Allan screw at the same time the additional 1/4 turn. This will lock them tight.


Here is the method that Forum Member Joe C came up with which I feel is better because you can tell much better when you reach zero lash using the feeler gauge.

BTW, I tried something a little unconventional on adjusting hydraulic lifters. one thing that always bothered me is the statement "spin the pushrod until resistance is felt" that seems a little too subjective to me. so I tried this: I set "zero" lash with a .0015" feeler gauge while slowly turning the adjusting nut. {place the feeler gauge between the top of the valve stem and the rocker arm.} When I felt the feeler gauge grab, I was fairly confident I was about .001 from zero lash. at that point, I turned the adjusting nut 3/4 turn. I recently read that one turn is equivalent to .040" because of the thread pitch on the threaded rocker arm stud, so 3/4 turn should give you about .030" adjustment. I also read that within a hydraulic lifter there is .060 total plunger movement, and ideally you want to be just about in the middle of that range, or .030 inch. I don't know if I’m out in left field on what I did, but I feel I got a really consistent valve adjustment across the board. if you think you might have a tight cylinder, maybe give this a try - it seemed to work for me...

again, thanks for all your help - take care -

JoeC

 

I and a lot of people I know usually loosen the nut until the valve chatters, tighten it until it stops chattering, and go a 1/4 turn.

Never knew about GM's method.

 

this is the way to do it !

 

thanks much this is great info any opinion on the length of push rod ? I did buy a rod length checking tool if the length is less then .010 difference should I buy new rods ?

 

new rods on new rockers !!!! yes !!!

 

I never thought to remove the spark plugs to ease the spinning of the engine. Another way to tell if #1 is on the compression stroke is to place your hand on #1's rockers and as 0 degrees comes up they should both be closed i.e. no movement in the pushrods and rockers so do (3) above. If you feel movement then it is on the exhaust stroke so do (4) above.

Good luck!

 

engine only has 42000 miles

 

I mark my balancer off in 90 degree increments .
Bring #1 to TDC adjust both valves for that cylinder .1/2 to 3/4 after no more play
(Rotate the pushrod in your fingertips )
Do this through the firing order 18436572
I also have 3 sets of pushrods here , different lengths ....Let me know what length .

 

What year is your Vette? I put 1.5 / 1.6 full stainless roller rockers from PRW on my 1985 last winter and after a ton of research and answers from a gentleman at Scorpion found that the stock length was ok but to change to chrome moly for better strength. I recommend putting in fresh springs also. Everything worked perfectly and I can't begin to describe the performance increase, you will just have to feel that for yourself. I had a thread going on this also that might help you out, alot of people contributed some great info to it.

 

1993 Quazar Blue

 

It would have helped to know the year up front in the first post.

Since you have a 1993 with the opti....there is no timing mark on the balancer. The only way to do this now is to remove both valve covers, pull #1 plug, turn the engine by hand until you fell pressure in the #1 hole. Now watch the valves as you VERY SLOWLY turn the engine. When both valves to #1 are closed, then adjust the valves that I lsted above.

Now turn the engine and watch for #3 intake to full close and then adjust the other half listed.

 

For doing valves, the way I set them on all engines is by opposites.

The pairs of cylinders that are always at the same position are 1&6, 8&5, 4&7, 3&2 as long as you are running a standard SBC 18436572 firing order and not a 4-7/2-3 swap.

So if the exhaust on #1 starts to open, I know that the exhaust on #6 is on the base circle of the camshaft, same for the intake rockers. You can do it the method listed where you only have to put the crankshaft at two positions and it will work, but I assure you you'll spend more time double checking your work and it won't be any faster than the opposite method.

On to the rocker arms, the stock LT1 1.5 ratio is around .450"-.460" valve lift, the 1.6 ratio rockers put it to .470"-.480", if you measure the spring in a Rimac spring tester and put them to the installed height then compress them .480" from that you'll see they are very close to coil bind. I won't run stock valve springs on anything other than stock valve lift.

As for the pushrods, the pattern of the wipe on the back on the valve stems dictates their length.

 

well got the HB off and found that the distributor was rusted inside so replaced the whole distributor as the optical sensor was corroded too much to swap out with the other distributor that doesn't have a Mitsubishi sensor anyway the issues with intermittent miss was most likely the corrosion in the cap rotor and threw out the distributor if the new optispark fails I plan to just replace with a coil pack system I found that replaces the ECM... and doesn't use the optical trigger in the optispark I plan to wait till I get the push rod checking tool before I Finnish the rocker arm upgrade as I will need new rods thanks much everyone I am looking for the correct harmonic balancer up grade to a super damper or other stainless / alloy HB the new distributor is a replacement optispark II so that should be good for now any input on LS coli pack systems to replace the optispark

 

I do have a set of roller cam springs and retainers I plan to install they are around 193 psi the engine shop said he could lighten them up if I want to build the heads up for 6500+ rpm

 

If you have in intermittent miss and you have a spare opti, a easy trick to eliminate the optispark is to just unplug the one that is on the car and plug in the spare with a spare plug wire and plug running off of it. With the ignition key to run, spinning the new opti by hand will fire the plug cleanly if it is the old opti that is messed up.

Frequently it is not the Opti that is failing you but instead a coil, icm, or burnt plug wire.

I've used ATI Super Dampers on a F-Body before. It was a 7.5" Aluminum shell, steel hub balancer. Another great thing about the ATIs is that you can simply unbolt the three 3/8" 12 point bolts and the three T-45 Plus torxs bolts and the opti will come out without having to pull the hub for the balancers.

You can kind of get away with not using a T-45 Plus bit on the damper, but I highly advise against it as you will strip the torx bit or bolt and then be in trouble.


Now that I look it up, there is conflicting information about the Y-body version of this.

ATI website says to use 916096B which is just the hub for Y-body and then you would have the option of going with a 7.5" steel or aluminum shell 917015 or 917073 respectively.

Then summit says 917274 is the complete hub and balancer for a Y-body.

 

Whether you use new pushrods or not, which I would use what you have already with just a rocker ratio change. If you change to shorter pushrods you just cancel the increase in valv opening with going o a higher ratio rocker. Go any longer and you are at risk of excessive valve side loading. If you have changed to a higher flowing head or higher compression, then change to hardened pushrods.

 

???

You know that pushrod length has nothing to do with actual valve movement?

The increase in lift is done by moving the cup for the pushrod in the rocker towards the pivot point of the rocker arm.

 

True enough.
Changing pushrod length will change the angle that the rocker has on the valve....not much else. Stamped steel 1.6 rockers will use stock length pushrod with no issues.

 

New better than stock pushrods are always a good idea. Many things affect pushrod lenght, different brand rockers with the same ratio can use different lenght pushrods, because the pushrod cup height is not the same. Still many swap from 1.5 to 1.6 with no real problems using the same pushrod. I plan to swap 1.6 this spring myself and upgrade my springs. Before I install the 1st good spring I'll put on a pair of test springs, mark the valve tip with a sharpie, install the 1.6 rocker on an intake and exhaust and cycle the valve to check the sweep. Solid lifters with the differance measured form the hydraulic lifters would be ideal, but test springs are pretty wimpy. Once I get the sweep where I want it I'll order the set of pushrods that is closest.

FYI there are three ways to measure pushrod lenght I'm aware of, make sure your tool uses the method of the manufactuer you order from.