Aluminum vs Cast Iron Noise Levels

[unclewill]

Ok, I fired up my 482 with all aluminum top end, hydraulic cam and boy is it noisy underhood!  Has anyone else noticed much higher mechanical noise levels with aluminum heads (over cast iron) or should I be concerned?  Other than a slight wiggle on the vacuum gauge, all seems good so far.  And it pulls 15 lbs of vacuum at idle too!

[chris401]

Concerning any aluminum engine it does to me. Even injector noise will radiate through the aluminum intake.

I have never been around an aluminum head FE that had quiet exhaust or hydraulic lifters, but I suspect they are no different than any other engine.

[Drew Pojedinec]

Huh, I never noticed.  That is interesting

Of course I work on 2stroke diesels in a metal box for a living, so my decibel acceptance level is off the charts......

[blykins]

Some hydraulic roller cams are noisy.  If you have lash in the valvetrain, you will hear noise.  But one head/block material will not be noisier than another. 

[unclewill]

My cam is hydraulic flat tappet.  The sound is a loud mechanical whirring, probably the valvetrain.  It's not a bad sound, just much louder than the old engine.  I figured you guys who run these on dynos all the time may have noticed a difference if there is one.

[TJ]

Any interference going on?...push rod to intake, push rod to rocker, etc ?  They can run right, have nice vacuum, and still be beating themselves to death.

[e philpott]

take the belts off and see if the noise goes away , in case it's a alternator or water pump

[TorinoBP88]

According the website below, the damping of cast iron may be between 10 to 100 more than aluminum (dont know where an engine block fits into that scale.  I do know motorcycles use rubber and other trucks to quiet mechanical noise of an engine:

http://www.atlasfdry.com/grayiron-damping.htm

[WConley]

I'm with the guys above who think it's something different mechanically in the engine.  Iron actually transmits sound really well, and when it's the size of an engine block, will be particularly good at the frequencies humans can hear. 

Aluminum is less stiff, so it will respond better to lower frequencies than iron.  This means an aluminum thing the size of an engine block will make a "duller" sound with more lower frequency energy.

Think about it.  There are tons of big cast iron bells the size of engines out there.  When's the last time you saw a bell that size in aluminum?  A big aluminum bell would make a duller sound, where the iron has that richer "ring" full of high frequency sound.

[unclewill]

I'm going to pop a valve cover and have a look see.  I like the belt removal idea too.  The oil is clear and clean after 20 min break in and about 10 miles of driving.  Cast iron manifolds are much quieter than headers so that's what got me thinking...

[unclewill]

The engine just hasn't been running right, vacuum fluctuates regularly at idle, pulled plugs, mixture looks right on, compression test showed low pressure on #3, pulled valve cover and pondering a perfect valvetrain then noticed the bottoms of the rockers are making contact with the outer valvespring retainer ring!  Pulled factory adjustable rockers, "detailed" the bottoms of the rockers - basically removed excess casting flash, reinstall.  Restarted the engine, seems quieter...will do the other side tomorrow.
Anyone have this problem before?

[Drew Pojedinec]

Yes and no (as far as having that problem)

Just about all factory adjustables that have made it into my ownership have had witness marks from the retainer, so as a habit I spend a few hours with a sandroll and a carbide bit and clean up all the casting flash.
The seam under the rocker and the oiling hole for the pushrod cup get the most attention.

[unclewill]

I just hope it didn't kill my cam and lifters.

[Drew Pojedinec]

After cleaning up the rocker arms, how was the vacuum, steadier?

As long as the lash hasn't changed, I don't see how the cam and lifters would be ruined.
If any damage would be done, I'd think the valve guides would have taken the brunt of it due to the valve spring being pushed over before the valve was pressed straight down.   *shrugs*  Dunno tho.

I'd think the fluctuating vacuum would have been caused by the valves not fully seating perfectly every time.

and not to be telling you something that you do not currently know..... but proper engine assembly is putting everything together, checking everything, turning the engine, checking for interactions between parts, adjusting as needed, rechecking, measuring, putting it all back together, rechecking because you weren't 100% sure, taking it all apart, etc.  This is all the more critical when dealing with a host of parts from a handful of different suppliers.  It took me probably an entire day to get my factoryish rocker set up to where I was happy they would do the job well. 

Anyway, good luck, hope this is the last of your issues.

[unclewill]

Thanks, Drew.  Yes the vacuum was steadier, but not yet perfect.  Today I'll do the drivers side to fully correct the issue - it's harder because the brake booster and M/C have to come out first.  I agree that the cam and lifters are probably OK, but I need to worry about at least one thing at all times. Also, the lash should be very close so I'm not making any adjustments.  I also agree taht the valves just weren't seating consistently giving me wacky cylinder pressures and the engine just "fell apart" above 3500 rpm.  Only about 70 miles on the car + break in time so hopefully no harm done.
Anyone using factory adjustable rockers needs to be aware of this clearance issue and be sure to correct it.  The loud clicking I heard could easily be misconstrued as "normal" solid lifter noise - I was puzzled because I'm running a hydraulic cam.  Other symptoms pointed to lean main jets or a vacuum leak: small backfires with revs, soft power at mid-high rpm, inconsistent idle.  This is a red herring!  If rockers with witness marks are common, than lots of people are running around with this problem.
It was the rhythmic vacuum fluctuation that clued me in to an issue with the valvetrain and a slight polishing of the outside of the valve spring retainer rings was evident upon VERY close inspection.  Thankfully a simple fix with a die grinder and cutting wheel.  More to come...