excess valve train noise (LT1 solid lifters)

[Jerome P.]

I have noticed when I initially start my car that I am getting a lot of clicking (excessive) from under the right valve cover. The excessive clicking does go away, for the most part, after the engines runs for awhile and the valve train noise becomes more like that of a solid lifter car. The engine runs smooth and the exhaust sounds normal. Before I take the valve cover off to inspect are there any thoughts on what I might find or expect to find and what might be causing this noise?

[Dan P.]

Re: excess valve train noise (LT1 solid lifters)

Noise? I call that music!

Seriously though, sounds like you might have lash set too wide one one or two valves. There are a few threads on setting lash - both hot and cold techniques - in the archives.

[Jerome P.]

Re: excess valve train noise (LT1 solid lifters)

I agree; solid lifers are music to the ears. However, the excess noise does go away after the engine runs for awhile. Which I think is strange. I will look in the archieves, but would appreciate your additional thoughts and that of others.

Jerry

[Duke W.]

Re: excess valve train noise (LT1 solid lifters)

Google my name with "Corvette" and you will find a paper co-authored by John Hinckley and me. The latest revision IIRC is 12/07.

Adjust your valves (cold) using the recommended indexing scheme and clearances.

If you have any noise after doing this it is something other than valve lash.

Duke

[Jerome P.]

Re: excess valve train noise (LT1 solid lifters)

Thanks Duke.

I guess the question or thought I have is -- Why does the excessive clicking go away after the engine runs for awhile? I know I will have to get into the valve train, but thought I could get a feel or an idea before taking the valve cover off.

Again the engine runs smooth and the exhuast sounds normal at all times.

Your thoughts.

Jerry

[Duke W.]

Re: excess valve train noise (LT1 solid lifters)

LT-1's have forged pistons fit at about .0035". It could be a case of cold piston slap, but getting the valve lash set right is always a good thing to do.

If you can isolate the location along the length of the valve cover, give the nearby components a very close look. You might even what to remove the rocker arms in that area and give the pushrods, rockers, and balls a very close inspection for galling or wear and measure to see if all valves achieve full lift.

Measure and record all the "before" clearances before you reset them. Excessive lash on one valve might make more noise than others, and it could be intermittent.

Of course, all of the above are just possibilities. At some point you have to open it up and start looking.

Duke

[Bryan M.]

Re: excess valve train noise (LT1 solid lifters)

I have noticed when I initially start my car that I am getting a lot of clicking (excessive) from under the right valve cover. The excessive clicking does go away, for the most part, after the engines runs for awhile and the valve train noise becomes more like that of a solid lifter car. The engine runs smooth and the exhaust sounds normal. Before I take the valve cover off to inspect are there any thoughts on what I might find or expect to find and what might be causing this noise?

Jerome,
Could it be the AIR pump making the noise?

[Bill M.]

Re: excess valve train noise (LT1 solid lifters)

This was noisy.

[Duke W.]

Re: excess valve train noise (LT1 solid lifters)

Ohhhhhhh, that's a nice one! Once wear progresses through the thin surface hardening it goes very fast. Good rocker arms should just appear burnished on the contact surfaces. Any ridge you can feel with your fingernail means it's wearing and should be replaced.

Duke

[Stuart F.]

Re: excess valve train noise (LT1 solid lifters)

Nice picture Bill. Have not seen one of those since the 60's. They make excellent feeler gauge punch presses.

Stu Fox

[Bill S.]

Re: excess valve train noise (LT1 solid lifters)

i read the PDF on cold setting lash but it did not meantion 427. can this be used to set my valves on my L72?

[Duke W.]

Re: excess valve train noise (LT1 solid lifters)

I don't have precise specs for lash on big blocks, because I've never gotten a precise handle on the actual rocker arm ratio behavior as I have on small blocks.

You can use the recommended indexing scheme and for now I recommend (slightly modified) '65 L-78 recommended lash of .020/.022". The L-72 and later SHB big blocks used the same basic cam, but for some reason GM loosened the clearance recommendation.

If you have aluminum heads set them .002" tighter than above.

All of the above clearances are ENGINE COLD!

Duke

[Richard F.]

Re: excess valve train noise (LT1 solid lifters)

Duke, I am running a Crane version of the L72 cam, with closed chamber aluminum heads. Crane and most recent GM both recommend .024/.028 HOT. After letting the motor cool, I checked mine and found them all to be around .022/.024. Am I understanding you correctly that you recommend .018/.020 COLD? So I am sitting at .022/.024 COLD. Am I causing myself potential harm?

[Duke W.]

Re: excess valve train noise (LT1 solid lifters)

Depending on operating conditions, actual running clearance varies, so setting clearance is established so that running clearance will be somewhere in an acceptable range for anticipated operating conditions.

Under all operating conditions lash should be taken up before the tops of the clearance ramps, which are .012" on both lobes. (The BB SHP cam uses the same lobe on both sides.)

Actual lash at the valve depends on actual rocker ratio, which varies. It is not constant. On an OE machined small block I measured 1.37:1 at the lash point and 1.44:1 at max lift with an approximate 0.3" lobe.

If big block rocker ratio follows this pattern the lash point/max lift ratio range would be 1.55/1.63.

The data I have indicates the ratio range is greater than above, but the data was not sufficiently consistent to draw final conclusions. Also, it came from an engine that had both the block and heads surfaces machined, and this tends to increase the rocker ratio range.

GM specs are generally based on clearance ramp height times "design" rocker ratio, but they typically don't achieve the design value and vary - increasing with increasing lift.

So based on 1.7 times the .012" clearance ramp height the largest running clearance we want is 0.204", which is the L-78 spec on the inlet side (.020"). GM added .004" on the exhaust side to compensate for exhaust valve stem expansion. This amount is arbitrary was not done on any SB cams.

I have never measured a signficant difference between "hot" (engine idling or just after shutdown) and cold, so I don't agree with adding anything to the computed setting clearance. The larger the exhaust valve, the hotter it will run, but unless the engine is being run hard (like road racing), I don't think there is much exhaust valve stem expansion relative to (cast iron) head expansion. Since you can't run the engine "hard" for very long in normal road use, I don't think any arbitrary amount of setting clearance should be added.

Too little clearance could cause the valve not to fully seat, but the clearance ramps on OE cams are generous and the chance of this happening with slightly "tight" setting clearances is nil.

On the other hand if clearance is loose and not taken in until above the tops of the clearance ramp the valve will see more opening and closing shock and this can contribute to valve seat recession. And that's why some mechanical lifter engines are noisy. If clearance is taken up before the tops of the clearance ramps, the valvetrain should not be much noisier than hydraulic lifters. In fact, it should be hard to tell.

So, until I get some consistent measurements for OE machined big block rocker ratio behavior, I recommend the L-78 spec on the inlet side (.020") and add .002" (half the OE .004") on the exhaust side as a compromise.

There is no magic valve clearance setting number - just as their is no magic spark advance number, but arriving at rational setting clerances requires detailed understanding of cam lobe design and rocker ratio behaviour with consideration for operating conditions.

If you measure the rocker ratio behavior on your engine, you can compute the setting clearances that are best for your engine.

Duke

[Jerome P.]

Re: excess valve train noise (LT1 solid lifters)

Duke, Thanks for everything. You seem to be the shell answer man.

I still have not gotten the valve cover off. However, I am still wondering what is causing the excess noise on initial start up and lasting (intermittently) until the engine warms up. The engine was rebuilt 6,000 miles ago, never driven hard, and never had this noise until several days ago. If it is cold piston slap, wouldn't it have been present before? And wouldn't excess lash noise not go away as the engine warms up? But, the noise sounds like execssive lash until the engine warms or is running for 4/5 minutes.

Again the engine runs smooth at all times and does not burn any oil. The exhuast (both left and right) sound good from initial start up through warm up.

Is there anything else you can think of that would be causing this, given the above info?