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Author Topic: Rocker Arm Adjustment (was: Engine Noise Diagnosing Challenge)  (Read 6160 times)

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mithral7

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Okay engine gurus... here's a challenge... or maybe I'm just stupid,

But I have an engine tick/clack/tap that I can not diagnose.

Is this the right location on the forum for such a question?

Engine is '73 455 with TH400 A/T. 40K easy driven miles on professional rebuild with slight mods.  Q-Jet carb.  Electronic Ignition kit.

Symptons:
- From top of engine, a mild ticking sound from the driver's side.
- From bottom, a louder tapping/clacking sound toward back of engine, definitely in front of automatic transmission.
- With a mechanics stethoscope the sound is loudest from the exhaust, second loudest from the manifold, third loudest from the driver side valve cover.
- Oil is changed.  Good oil pressure.  No water in oil.
- Coolant/Thermostat just changed.  Water temps within spec.
- Engine is tuned with new spark plugs.
- Looking for exhaust leaks but haven't found one yet.
- Noise is there at startup with cold engine.  No noticeable change when hot.
- Noise increases in frequency (as in speed, not sound pitch) relative to increasing RPM.
- No increase in volume at higher RPM.
- Timing light test suggests an upper engine issue.

Maybe an exhaust leak, maybe something serious?

I dunno.

Need some good advice before I start tearing things apart with fingers crossed.

« Last Edit: June 27, 2007, 11:31:10 AM by mithral7 »

miketransamkid

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Re: Engine Noise Diagnosing Challenge
« Reply #1 on: June 21, 2007, 12:26:33 PM »
I had a loud clunk noise that i thought was a rod knock. turned out to be a broken flexplate. Almost sheered all of the flexplate bolts off at the crank.


Click/clack/tap noise from the top of the engine? Sounds like valve train related too much valve lash? Is it a solid or hydraulic cam? Does it miss or run a little bit rough?


A valve cover wouldnt be that much to take off in car. An exhaust leak at the header/manifold woul also give you a tick noise. Can you listen by the exhaust side of the head and tell which side is louder?

mithral7

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Re: Engine Noise Diagnosing Challenge
« Reply #2 on: June 21, 2007, 04:43:03 PM »
Thanks Mike,

I just finished shimming my starter.  I took a look at the flex plate and it appears in good order.

It has hydraulic valves.  It does not miss, and is running normal as far as I can tell.  I tune it myself and I can identify no performance problems.

I tried isolating a location for an exhaust leak and as yet can find none.

I tried using one of those mechanic stethoscopes where you place a small metal rod onto a piece of the engine and listen for noise.  The ticking vibrations are strongest on the exhaust manifold, less so on the valve covers and block.

I almost wonder if it is an exhaust valve issue.  But I just can't seem to isolate the sound to one specific location.

I may have to bite the bullet and pull off the valve cover.  In the mean time... I'm open to all the advice I can get before I start tearing things down.

miketransamkid

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Re: Engine Noise Diagnosing Challenge
« Reply #3 on: June 22, 2007, 08:08:23 AM »
Well if you think its a valve issue. Put a vacuum gauge on it on manifold vacuum. If its fluttering like crazy then it would be a valve and it would also run like crap. And generally witha blown exhaust gasket you would see black deposits on the block where the leak was eminating from. its one of those things where you just have to start eliminating things i.e valve lash. and like you did with the flywheel.

mithral7

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Re: Engine Noise Diagnosing Challenge
« Reply #4 on: June 22, 2007, 04:09:29 PM »
Hmmm... no out of the ordinary blackness or color changes around the header/exhaust gaskets.  I'm probably just hoping it is an exhaust leak because that would be less intrusive to fix.

I'll see if I can acquire a vaccum guage somewhere and try that test.

Since there are no obvious performance problems a couple folks have suggested it may just be a sticking or gunked up lifter.  I am recommended to run a quart of tranny fluid in the oil for 100 miles and then change the oil.

If that doesn't work I guess it's time to stop being a chicken and pull the valve covers.

mithral7

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Re: Engine Noise Diagnosing Challenge
« Reply #5 on: June 23, 2007, 05:35:54 PM »
Thanks for the suggestions, Mike.

I found the cause of the tick.  It was due to a loose rocker arm nut.  Zoinks.

A readjustment of all rocker arm nuts identified 11 nuts that required adjustment.  Double Zoinks.

Static compression tests good in all 8 cylinders.

Lifters seem okay, for now.

Anyone have suggestions for replacement lifters?






miketransamkid

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Re: Engine Noise Diagnosing Challenge
« Reply #6 on: June 27, 2007, 11:15:06 AM »
Awsome Glad to hear you found the source of your noise.

mithral7

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Re: Rocker Arm Adjustment (was: Engine Noise Diagnosing Challenge)
« Reply #7 on: June 27, 2007, 11:48:57 AM »
Thanks Mike, I should have guessed it was a loose rocker arm nut.

And I see we have no obligatory "rocker arm adjustment" thread yet?

Anyone wish to comment on the appropriate method for setting or torquing factory Pontiac Rocker Arms and nuts?

Option One is to adjust so that rockers, rods, lifters are just touching (neutral position?) the tighten 1/4 to 1/2 turn.

Option Two (like in Chilton's) is to adjust the rockers to basically neutral as above, and then slowing torque to 20lb/ft.

I've tried it both ways, successfully.

Sometimes I think my engine runs a tad better using Option One, but then the nuts sometimes vibrate too loose and I have this problem as noted in earlier in this discussion, requiring readjustment from time to time.

Right now I am trying Option Two.  The engine seems to run very smooth and it starts easier.  Whe I put my foot into it, the car still spins the tires and still chirps when shifting to 2nd.

(I also chose the messy method of adjust/torque while running due to some time constraints.)

I noticed that torquing according to Option Two requires turning the nuts about one full turn instead of 1/2 turn.  I also found web instructions that call for adjusting the nuts anywhere from 1/4 to a full turn anyway.   And I just can't see where 1/2 turn versus a full turn makes that much of a difference when using hydraulic lifters.

Maybe someone can educate me otherwise?
Thanks,

National Firebird and Trans Am Club Message Board

Re: Rocker Arm Adjustment (was: Engine Noise Diagnosing Challenge)
« Reply #7 on: June 27, 2007, 11:48:57 AM »


 

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