I am having problems with vavle knock. Last week I started hearing a pretty good knock from the driver's side of the engine toward the front. I tightened up the exhaust manifold bolts and the manifold to the exhaust, just in case it was that.

I just got done doing an adjustment on that side. It sounds exactly like it did before I adjusted them. It is not very loud at idle or revving, but under load it is pretty loud.

I losten the nut until the rod spins freely, then tighten until I feel the rod harder to turn, then tighten another 1/2 turn. At this point the rod is pretty tight. Hard to turn with fingers. Then I tighten the hex lock nut as tight as it will go. Now, when I feel the rod again, it is MORE LOOSE than before I tightened the hex lock nut.

What is the deal here? Is it even my valve, or could it be something else even?

 

Could be your cam going flat, I had one go and it knocked no matter how I adjusted it.

 

Forgot to mention. Less than 500 miles on new cam and lifters. Cam was broken in with cam lube at 2000 rpm for 15 minutes.

 

Yank the valve covers to check for valve movement. Could be a flat cam. I had one go bad and I did everything right too. It doesnt make sense that you tighten it down and then it loosens spontaneously. Might be a lifter problem too. You tighten yours tighter than I would mine and yours is still clattering and getting loose? Dont sound good. I still vote for bad cam. Once you tighten the lifter past the pre load it shouldn't get loose again, in fact, as it gets hot it should get tighter due to expansion. I'm no mechanic, but just passing on personal experience.

 

One more thing, could it be a broken valve spring? Might make it clatter no matter what.

 

Good advice above. Do those to assure valve springs are ok and cam lobes are all the same.

I adjusted my ProMagnums like that but didn't check em after adjustment since the lifter might lose oil.

Also, what sequence did you use to assure that the valve was on the seat?

 

Anyone think it is a matter of the roller rockers being adjusted incorrectly? I think I am not doing something right on the rockers, or perhaps I need to tighten more than 1/2 turn. I'd rather try the easy things first

I followed lars' valve adjustment from the corvettefaq.com site.


[Modified by Rhys, 11:31 PM 10/5/2001]

 

Last year I had a motor with a XE274 with my 1.6 rollers. IMO loose is better than over tight. I did not have a hydro cam motor in years. So anything with a locking allen will change the lash - Even on rollers. tighten them down till where you baerly roll them and set the allen. Then push down on the back of the rocker and see if you can fit a .012 under the tip warm motor to valve clearance.

 

I've been building engines for over 35 years, and I don't care what any person or book says.... based on my solid EXPERIENCE in this area (as a professional engine builder), hydraulic lifters/valves/rockers should NOT be adjusted using the "spin the pushrod" method. Here is the reason: The little springs inside the lifters DO NOT all have the same tension, AND, the amount of oil in each lifter retained by the check valve is NOT the same in each lifter. The oil determines the point where the plunger locks up solid. Each lifter has its own "personality, and each will exert a different amount of resistance to plunger movement. When you adjust the rocker while spinning the pushrod, there is no way to tell how far you actually have depressed the plunger in the lifter. The result is, some are loose, and some are way too tight. In extreme cases, the engine will not even start because at least one valve in each cylinder remains open at all times... no compresion. You can also do major valve/valve guide/piston/cylinder head damage by doing this.

Forget the "spin the pushrod" idea.

Follow the shop manual procedure for valve adjustment... this varies based on firing order, and, firing order varies by engine. Adjust each rocker for zero lash, and follow up with another 1/2, 3/4, or 1 turn- this also varies. Some engines call for 1/2 turn, some 3/4, some 1 full turn of the adjusting nut. Here is how you determine "zero lash"-
Following the correct order, doing one valve at a time, loosen up the nut so that you can "feel" clearance between the rocker tip and the valve tip. That is, while you are loosening the nut, GENTLY rock the rocker... you can feel when there is clearance. Slowly tighten the nut while you continue to GENTLY rock the rocker, uintil the clearance goes away (zero lash). Then make your final turn. While you are rocking the rocker, you must be careful not to depress the lifter plunger... even the slightest plunger travel will result in a bad adjustment. The trick is to be GENTLE... and you will be able to feel the clearance without depressing the lifter plunger.

Shop manual adjustment procedures say "x turns from zero lash". Spinning a pushrod will not tell you when a hydraulic lifter is at "zero lash" point because all lifters do not exert the same amount of resistance at a given amount of depression. Solid lifters are a different story.

I'm not trying to rain on anyones parade here, but it yanks my chain when I hear people trying to adjust lifters using the "spin" method. It's just another witch hunt. Hope this sheds some light on the topic.

 

I discovered what Tom454 says the hard way. The spin method stinks, you're sure to lash the valves too tight. Do it the way Tom says and you'll have no trouble.

Eric

 

Well, I just adjusted the 1-3-5-7 valves (where the noise is coming from) the way Tom said, and there is no difference in sound. I decided to try an adjustment while running. At that point, I could tell that the noise was definately coming from underneath the head.

Tightening of looseing the valves really only changed the noise for a second or two, then went back to the same sound.

So now the question is, valve seat (less than 500 miles on the heads) or lifter, or something else?

When I replaced the cam and lifters, one of the 16 would not compress at all, and I took it back and exchanged it. It is not the same one that is making the sound now.

All the valves seem to be going up and down the same amount of travel


[Modified by Rhys, 11:16 AM 10/6/2001]

 

Did you have the seats replaced when you did the heads? maybe a seat has come out of the head. this would pretty much make it impossible to adjust. could a piston be impacting a valve or the head? I had a 427 with big domes that made piston contact with the edge of the combustion chamber. check the guides to make sure they are still in the hole. I've had bronze replacement guides come out too. A quick way to eliminate possibilities is to do a compression check. By the way, if you understand your looking for zero lash, the spin the pushrod method works fine. The trick is making sure your on the the base circle of the lobe.

 

Yes, the seats (and everything else) were replaced on the heads. The HP and torque as well as performance is good. The only problem is the very loud knock under load.

Valve springs are not borken, checked that also.

I guess I will do a compression check next.


[Modified by Rhys, 12:08 PM 10/6/2001]

 

Well, with no other suggestions, I guess my only choice at this point is pull the manifold and replace the lifters in that area.

I may get trick flow heads while I am at it.

 

Rhys...

I assume you meant "while running" , not "under load". These are two different conditions.

"Tightening of looseing the valves really only changed the noise for a second or two, then went back to the same sound."

If altering the valve train geometry actually made the noise go away, then it is a safe bet that your valve seats are okay. Changing lash adjustment will not make a valve seat problem go away. It will also not make a wasted cam lobe re-appear.
This also rules out wrist pins, and rod bearings.

My guess would be bad lifter(s). By pressing on the rocker arm during adjustment, you may have momentarily removed excess lash in the particular location. The ability of a lifter to function depends on its current leak-down rate.... which takes a "leak down" tester to determine. Sounds like you have a few weak lifters. Also, dirt or metal filings inside a lifter will cause the same problem. So will low oil pressure.

Of course.... brain surgery over the internet is difficult. You may find that your tire pressure is too low. :crazy:

 

No, it knocks much more under load. That is... In gear or when pushing the accel pedal more and more while driving. Idle in neutral and neutral pedal while driving, not so much noise.

I am going to try replacing the 4 lifters in that area. How much are trick flow heads? :D

I appreciate the input Tom.


[Modified by Rhys, 9:52 AM 10/8/2001]

 

Well.... there are some contradicting points here...

If you can make the noise go away at idle temporarily by adjusting the rockers, then it cannot be detonation.
But since it acts up more under load.... it sounds like detonation/timing.
This is the "brain surgery" part. There is a critical piece of information missing here. Wonder what it is.

You may also have a bent valve if you adjusted the rockers too tight, even if for a few minutes. If a valve kisses a piston, it can bend and then stick in the valve guide. This typically makes more noise under load.

I don't know what the current prices are on heads these days. I have trouble just remembering where my keys are.

 

What are your thoughts on it being a rod bearing?

 

Rod bearing and lifter/valve noise sound entirely different.
A rod bearing will be a dull thud, or knock. Valves/lifters exhibit a tick.

Try loosening up a single rocker until you hear a noticeable tick from it. Readjust that rocker to get it back to normal.
Memorize that sound.
If your other sound is entirely different, then it could be a rod bearing or a wrist pin or ring/piston slap.

The reason I ruled out these other problems is because you said the noise went away temporarily when you fiddled with the rocker arms(s). If this is, in fact, the case, then it cannot be a rod bearing.

 

Well, I did some further investigation. I loosened the #1 cylinder valves until they started ticking. Then tightened. The knock sound did go away for a second or two when tightening the exhaust valve. The knock also seemed to quiet a bit doing that on the intake valve also. It may have been the engine slowing down a bit though. Also, revving the motor quickly make the knock sound apparent, gradually raising the rpm, you can barely hear the knock.

Also, diconnecting the plug wire also made the knock go away. Changing the plug and plug wire had no affect.