Just a heads up on the Holley cover- not sure if anyone else has experienced this, but it seems as if the aluminum cover acts as an amplifier for chain noise... Just buttoned an engine all back up and went with the Aluminum cover... you can hear every little rattle that chain makes with the holley cover. I tore back apart and changed chain set to be sure it wasnt too sloppy...new cloyes deflection was imperceptibly different to the 150k mile roller that was on it...and not a whole lot different than the last one I tore down. Thinking about going back with the plastic.
Edit- sounds like a metal rattle at idle... Removed drive belt and no change to noise. Checked inside of cover for witness marks and chain didnt appear to be hitting inside of cover.
Wow. Wondering if there's room for a layer of carefully-trimmed Dynamat on top of that cover?
I was really thinking of upgrading to that aluminum cover down the road, but at the same time
I don't want to amplify the chain noise? Thanks for the heads-up based on your firsthand experience!
You've done this? And saw the behavior you described?
Closest I've gotten in person was careful observation of ignition timing jumping all around on a
SBC with a suspected loose timing chain. (When you got to certain engine speeds the ignition timing
was chaotic looking -- most folks were blaming this on the timing light itself?)
After replacing the worn-out factory chain with a Cloyes True Roller, using the same timing light,
the spark advance was *way smoother* when held at a steady rpm, even at the speeds where
the harmonics were previously making the sloppy chain really flutter?
Needless to say, the engine ran both smoother & quieter. Of course this was before GM had
added the CKP and CMP sensors so that we can see this directly (see attached #1) instead of
inferring it from using a stroboscopic timing light to 'freeze' a mark cut on the harmonic balancer.
...but I've been seriously considering doing exactly what I described on my '99 L29 using my
own trusty Tek 475. (The thought process was to compare real time scope readings to what
the scan tool is averaging out to a single CMP Ret #.)
EDIT: A scope is a very useful tool for making sense out of mysteries under the hood. If you
haven't already seen this, here I'm testing out a Knock Sensor that we added to an engine
being built for lots of boost. I've used the 475 as a last resort in order to fix a lot of the
'resisting repair' problems, but AFAIK this is currently the only video of it in use.
(Knock Sensor waveform test - old video, 2010-era picture quality.)
Listen, if you do hook up your scope, be sure to take a short video and share the wealth. I've
had a hankering to do this, and would have accomplished it already, except for packing for the
upcoming move is stealing precious time away from the good stuff like this.
BTW, good to know there's at least one other Tek 475 enthusiast still in the game. :0)
Fascinating idea
I'll have to pull out the old Tektronics 475 and give this a whirl.
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