I have seen several post before recommending how to adust rockers. The recommendations always seen to vary. Specifically, how much turn after zero lash. I just finished installing LT4 1.6 roller rockers and still have clicking. I would like for them to be quieter. Please select your experience in adjusting your rockers. Any other comments welcome. Thanks.

 

I vote for all of the above.

 

Well....I did say all comments were welcome...so thanks CFI-EFI.. :rolleyes:

 

On my 91 they are a little noisy also.

 

Well, I don't know a good way to tell you this, but LT4 rockers are not adjustable. I just got through reinstalling factory rockers on my LT4 the other day and you simply torque them to 18 ft lbs (per Helms manual). Of course, the valve must be in the closed position.

 

The "stock" LT4 rockers are not adjustable. But the ones that come with the Hot cam kit and sold by GM as part# 12370838 is similar to the rockers used in the LT4 engine but are 3/8" adjustable. The stock LT4 have a 10mm trunion. On my 95 that had these rockers I adjusted them first to 1/2 turn but went to a little over 3/4 turn to quiet them down a bit. On all motors I do I start at 1/2 turn.

 

Rich is right of course. They are the GM 3/8 stud models. I call them LT4 'clones'. I did start at 1/2 turn, but they sound a little loose to me. I've already decided that I am gong to crank them down to 3/4 turn to see how that does. I need to pull the valve covers to finish polishing them anyway, so it's not much extra effort.


[Modified by 92corvette, 9:00 AM 11/18/2001]

 

Well, I see I got one vote for a full turn. That's what my book says they should be set to. I wonder why so few people use the suggested settings in the manual (including me)? Maybe personal experience with the 1.6 ratio rockers?



[Modified by 92corvette, 5:51 PM 11/18/2001]

 

You have to get used to the noise 'cause it's supposed to make it.
If you tighten them 1/2 to 3/4 turn after the push rod gets tight you have
them adjusted correctly. :yesnod:

 

the gm service manual says one full turn after zero lash. i did this and it idled rough i went to 3/4 turn and idle was fine.

 

vettedave is absolutely right.

Full roller rockers will always be noisey when adjusted properly (1/2 to 3/4 from zero lash). There won't be a tapping sound, but it will kind of resemble a sewing machine kind of mechanical noise. It does take a little getting used to.

 

1/4 turn is all that is needed and might allow for a few RPM more on the top end. Do not use the "spin the pushrod" method. Use the "vertical motion" method. When you can no longer move the rocker up and down, 1/4 more turn and you are done. Roller rockers are slightly more noisy than regular ones. I am not sure if the noise you are hearing will ever go away, but without hearing it, I just don't know...
Good Luck,

 

A tighter valve clearance will shift the powerband into the upper RPMs, a looser clearance will bias the power in the lower RPMs. These powerband shifts are hardly noticeable on a dyno. The powerband shifts with valve clearances occur in a similar manner to changing the camshaft.

 

Tightening the valve lash on a solid lifter cam a few thousandths will, in effect cause the cam to have more duration that it actually has ground into it. This is because the valve begins to open sooner and close later.

With a hydraulic cam, however, it doesn't work that way since the valve train parts are always solidly connected to each other. With a solid lifter cam, the valvetrain continually has slack in it as the engine runs and the lifter is on the base circle of the cam lobes.. Reducing this slack (lash) causes valve action begin earlier and continue longer. Most cam companies state not to go more than, say, .006 or so tighter than the lash specific on the cam card.

The purpose of setting lifter preload with a hydraulic cam is to set the moveable lifter plunger to about the center of it's travel. Depending on which camshaft book you read or who you talk to this can be anywhere from .020 to .050. CompCams and Crane give differing numbers.

.030 seems like the middle ground though.

Problem is that there is no way to actually see how much the lifter plunger is actually being depressed with the intake manifold on. With the manifold off, though, you can see and get a pretty good idea of how much the plunger is being depressed as you tighten the adjusting nut/poly-lock. I suppose you could rig up some sort of way to put a dial indicator on the plunger to actually measure the amount of depression, but the manifold would have to off.

The amount of lifter preload guys usually run varies from 1/4 turn to one full turn from zero lash, and as with most other things, depends on who you talk to as which one is the best. The trick, though, is to make absolutely sure that the lifter is on the base circle of the cam lobe when establishing zero lash and setting the preload.

With today's fast ramp (aggessive) cam lobes, this can be tricky and if the lifter is even a little bit onto the ramp when the preload is set, the adjustment will be off. The usual result when set too loosely is a slightly noisey valvetrain and a rough running engine when set too tightly.

Roller rockers make more noise than non roller types, so be prepared to accept a little more noise, even when correctly adjusted.

One way to establish which preload is best for you is to try the different settings and settle on the one that gives you the most satisfactory results. Whatever makes you happy, go with it.

I run one full turn from zero lash. Using less preload (like 1/4 turn) can allow a few hundred more RPMs before lifter pump up, but often results in a little more noise as the lifter plunger hits the retaining lock.

There are several different ways of setting the preload too. Some guys opt for the "engine running" method, others follow the directions in the service manuals (which most now say can be very inaccurate with aftermarket cams) and I saw one post of a mathmatical formula one guy uses.

If you watch the "Big Boys" at any National meet, you'll see they use the 'E/I - I/E' method, whereby you bump/turn over the engine while watching the Exhaust rocker and when it gets to a certain point, stop and set the INTAKE. Then bump while watching the Intake and when it gets to a certain point you set the EXHAUST. If using this method and the engine has been run before, you need to remove all lash then allow about a minute for the plunger to completely rise before establishing zero lash.

This is the method I use and recommend. Also, as someone else posted, I use the up and down method to establish zero lash rather than the 'twisting the pushrod' method. I wrote a doc file explaining the procedure that I email to guys who want to see and consider using it.

This lifter preload question falls into the same catagory as "Which spark plug is best?", "Which oil is best?", "Which tire is best?", etc. Talk to 10 different people and you'll get 11 different answers.

Hope this helps.

Jake

 

I think TPIS says to adjust at least one full turn preferably 1.5 turns. Is this wrong? Is the upgrade to 1.6 full roller rockers worth the trouble? :confused:
DO you see a gain in horsepower?

[Modified by SLOWBUSA, 9:33 PM 11/22/2001]


[Modified by SLOWBUSA, 10:21 PM 11/22/2001]

 

Do you think after spending $300 I would say it was not worth it :)

Aloha,
Larry

 

1.5 or more turns is NUTS!!! That is way too much!

 

:rolleyes: :lol:

Hey 2FST4U, thats what I thought. :crazy:

 

Well, 1/4 turn was ahead when I left hunting yesterday. Looks like 1/2 turn has nosed ahead. :)
Some great feedback in these posts though. i appreciate every one of them.
It looks like I am just going to have to find my own best setting by trying different ones. I still have to take the valve covers off for sme more polishing, so no big deal. I have also taken note of some of the reccomended procedures for adjusting. One important one is to use the up and down motion to find zero. I found that using the twisting method is easy to depress the lifter past zero very easy. Especially on the new lifters that I just put in and hadn't started up yet..
Thanks everyone...

 

So go 1/3 turn. :)