MILD THUNDER

iTrader: (3)

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

Rage

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?

Rage

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

MILD THUNDER

iTrader: (3)

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 .

bck

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

MILD THUNDER

iTrader: (3)

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.

Rage

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?

Panther

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.

Rage

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?

Panther

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.