How to Detect Valve Train Instability
 

What are things to look for that would indicate that a valve train has instability issues (before an engine/component failure)? Parts inspection? A unique symptom from the way the engine is running?

I would say to put a dial indicator on the end of the rocker stud and see how much movement you have when you crank it over.

That wouldn't show an issue at higher rpm/load where it becomes a problem. I think you just need to go with proven combinations or a proven engine builder.

I agree with a proven combination. But that is the only way I know of to check for any valve train movement.

I understand the use proven parts and proven engine builder to minimize possibility of valve train instability in an engine.

The question is after the engine is built and running. Is there any indication of a harmonics related valve train instability that have also shown up on new parts such as the cam lobe, hydraulic lifter roller, push rod, valve spring, valve spring retainer and locks, valve, valve guide or roller rocker after lets say about 25 hours running or a dyno session or how the engine performs or running characteristics such as valve train noise if the engine has valve train instability?

Try taking off the spring retainers. See if you have to beat the locks out of them.

There was a video link posted recently in regards to that. It's amazing how much movement there can potentially be with simply rolling the engine over. Imagine what it's doing at 6,000 rpm. Can be time consuming and often overlooked but so important. Correct length pushrods for starters and offset rockers might be needed as well as stud girdles. If money isn't a factor I personally really like the Jesel sportsman series shaft rockers.

That's why I made sure I did girdles this time... I want it to be solid as a rock..

could you somehow hook an oscilloscope to the block to see if you have an odd major harmonic or something??

Run it till it breaks! Valvetrain stability is a relative thing , Even horrible setups are stable somewhere in there operating range.

Is the cam radical? Whats the setup? Cam, lifters, pushrods, spring specs, max rpm, etc.

The engine is a new build still in the tuning stage. I am planning ahead for season to learn what to look for as to running clues or parts condition that indicate valve train instability before any big bang (hopefully). Previous engine I was lucky and it lasted 350 hours untill refresh. Found that exhaust valve train had insufficient spring for the heavy valve and 5800 rpm. Exhaust valve seats heavy brinneling. Lucky was that those WOT runs were a minute portion of that 350 hours. Subsequently Performance Trends Engine Analyzer Pro software modeling of that engine showed how bad the lofting would be and cam markings confirmed it. Current engine is designed to have no lofting running to 5600 rpm power peak. However I do not know if harmonics could still cause instability and damage so I want all the insight as to what to look for when engine is running and parts condition inspection after some running. I really don't want to get into all the details on my engine in this post. Lots of my other posts here in on all aspects of its history back to 2005. It is a NA engine, 520ci currently with custom cam and valve train I designed for max WOT power. I do not plan to improve or 'upgrade' anything unless testing shows it is needed.

The suggestion to check spring retainer lock tightness is the kind of info I am looking for.

The oscilloscope thought as well in the form of maybe a linear knock sensor mounted to the heads and recording signal to lap top as audio file for audio playback and/or for later processing through spectrum analyzer software.

What else in parts condition or running characteristics is symptomatic evidence of valve train instability?

Base engine is a GM Gen7 BBC, hydraulic roller lifters, stud mounted aluminum roller rockers, iron heads, wet exhaust.

Was that 5800 rpm with stock cam , springs, and lifters when you had evidence of instability? If not , what were the installed and open pressures?

While the exhaust valves can be heavy, they still typically arent as heavy as a intake valve, or heavier I should say , being that they are significantly smaller in diameter. If valve weight was the issue, I think you would be seeing it on the intake side as well.

A typical manley severe duty 3/8 intake valve, 2.19 dia, is roughly 145 grams, and close to that for a 1.880 inconel ex valve. Knock about 20 or 25 grams or so off those numbers, for an 11/32 valve like most aftermarket perf valves.

The battle the exhaust side faces, is opening against cylinder pressure and seat pressure at same time. This can put added stress on the lifters hyd mechanism, pushrod, rocker, etc. Pushrods that are gonna deflect, are most likely to do so on the exhaust side of things .

Have you ever compared the weights of bbc valvetrain components to those of an LS series? That'd be interesting.

They are lighter for sure. Like 30 plus grams when compared to a 3/8 bbc valve. Rightfully so, as they are smaller valves, with smaller stems.

Still looking for more things to look for that would indicate that a valve train has instability issues (before an engine/component failure). Parts condition symptomatic of value train instability issue inspection? A unique symptom from the way the engine is running associated train instability?

Take the rocker arms off and look at the top of the valve to look for cross marks which is an indication of valve float and/or instability in the spring setup. Also check rocker arm wheels for flat spots or erosion which is usually an indication of side load. These are just a few simple things to check while it's together.

Excellent! Thank you. I saw some cross marks on valve stem ends from the previous engine that I mentioned earlier that had valve float issues.

First I have heard a 'side load' issue mentioned. What causes that?

The push rod guide plates not being properly aligned, the rocker arm not being perfectly perpendicular to the valve or on aftermarket heads, the pushrods hitting the inside of the head.

OK. Thanks again.

You can have your combo SpinTron tested to find problems before installing. The cost is not horrible but can add up if you need to make multiple changes and retest.

What has been changed, upgraded, rebuilt since your last build?

Any time.

Here's an example of what you DON'T want to see.
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they have those cheapy valve spring testers which hook on the valve and are kinda like a flex beam torque wrench. quickie method of checking for failing spring.

What the.....

An engine I fixed last year

Interesting thought, would need a vibration sensor with the proper bandwidth.

setting the heads up properly to begin with is critical... valve springs, correct length pushrods, good rocker arms, these all play a roll, but the valve spring stack is the most commonly overlooked thing in head construction/assembly, spring surge is a component killer!!! a very wise man taught me that, and a well placed video confirmed it...

So, being like .250 away from coil bind, is no good ? Lol

Were these Raylar setups? I'm asking because I get the itch from time to time to do the Raylar kits on mine.

Spintron testing is a good value compared to a broken valve train. When you are running at + 4000 RPM you can't hear much and and the odds are you will do signicant damage if something in the valve train fails. If you use solid lifters, a good indicator is you have to adjust the valves. When the valve train is stable, nothing moves.

Were you able to determine what was wrong with the engine valve train configuration that caused this damage?

Raylar parts in the engine are the intake and stroker kit only. In my mind a fully engineered Raylar engine upgrade package would be one of the safest routes since it is just that...fully engineered and proven and you know what power you will get. Knowing what I know now if I had to do it over again that is the route I would take as a do it yourselfer. It would have saved me a lot of $$$ as well.

I have one of those and have used it over the years as you suggest. Thanks.

Thank You

How to detect valve train instability?----well, one way is when you start seeing little white surrender flags start popping out of your engine compartment. :party-smiley-004:

So the push rods should never touch the push rod guide plates?

Well I checked the valve stem tips after about 5 hours running. Most of it lower rpm. The witness mark on the valve stem tip is narrow and in the center. However there are lots of them not just one and all at different angular positions to each other. Like an asterisk "*". Only looked at even bank so far and each and every valve stem tip is marked like that. Five valves had previous use but I cleaned up their tips, maybe not well enough but three were brand new. Only been up to WOT 5800 rpm briefly twice with the rest 5000 rpm or mostly below that trying to tune the Holley EFI. From just a glance at the cam lobes from lifter galley they look nice with smooth even roller lifter witness mark track.

I am afraid to ask for comments.

sounds like the valves are rotating. don't know if a bad thing or not. they used to design them to rotate. heck, they still do, but not at real spring pressures and lifts.

No rotators under valve springs. Valve springs are PAC1255X Beehive springs with PAC retainers and keepers which seem to lock onto the valve stem and make assembly rigid. Previous setup was Comp Cam 929 springs with Comp Cam retainers and keepers which seemed to be a more free fitting assembly with valve stem. The Comp Cam spring and retainers produced a single rocker arm roller witness mark on the valve stem tip. Previous cam was less lift/aggressive.

Not concerned about rotation by itself assuming it is not the signature of something more insidious (damaging) going on. I guess a different question would be is valve rotation normal with the PAC beehive spring and retainer system?