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Old 08-29-2014, 10:14 PM   #1
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Leaking exhaust

My new to me '94 30' LY M/H has a noise that sounds a little like a loose valve lifter but it goes completely away at idle and under light load. It gets loud under heavy load. Does this sound like an exhaust leak? I understand that the 454s are prone to cracked exhaust manifolds. I can't see any leak or obvious cracks. Could it be a worn rocker arm? I seem to recall that a loose rocker is noisy at idle? It's been many years since I've had this kind of problem and I guess I've forgotten more then I remember.
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Old 08-30-2014, 04:59 AM   #2
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It sounds a little like engine knock. Are you using premium?

If your are running regular or mid-grade (half-regular/half-premium) gas, I'd mix in some premium as soon as you get room in your tank (below half).

If you are using premium from an off-brand, discount gas station, you might want to try a tank from a major oil company station, or a gas station at Costco, WalMart or other major chain store.
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Old 08-30-2014, 07:10 AM   #3
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You need a trained ear to listen to your engine.
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Old 08-30-2014, 08:20 AM   #4
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Thanks for the quick reply, Phoenix and Carl. Ping (or engine knock) is a very short sharp click (like a hammer striking solid metal) while this sound is more sustained and tinnier. And I think by '94 this engine should have a knock sensor which would retard the spark at the on set of knock? But higher octane gas would be worth a try. Yes, sadly my ear has lost it's training and some of it's sensitivity in the last 50 years or so. When I get back to Texas I'll pull the valve covers and check for a loose or worn rocker. My first thought was an exhaust leak but it should be detectable at idle, shouldn't it? And a valve lifter that is leaking down will be worse at idle and go away at higher speeds as I recall.

Surely someone on this forum has had this problem.
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Old 08-30-2014, 08:22 AM   #5
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Most exhaust leaks I have heard was on acceleration.
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Old 08-30-2014, 08:49 AM   #6
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Exhaust leaks are more obvious during periods of high exhaust flow. Acceleration and up hill climbs would make it more audible. I'm betting it is an exhaust leak based on the history of the 454. Broken exhaust studs more then likely.
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Old 08-30-2014, 10:34 AM   #7
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If it is a manifold leak you don't want to let it go for long because it will pit the head making it impossible to seal. Try the high octane and see if it goes away. If it makes the noise when you rev the engine in neutral it is probably a leak. Headers are notorious for leaking. Cast iron manifolds are more stable and less prone to leaks unless they crack.

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Old 11-23-2014, 05:19 PM   #8
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You might check the connection from the headers/ manifold into the exhaust pipe. There is a donut gasket there that is prone to leaking.
Easy to check with the engine running.
Cheep and easy to fix too.
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Old 11-24-2014, 10:09 AM   #9
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I had both exhaust manifolds replaced (they were warped) and that fixed it. Have put a couple thousand miles on it since and it runs great. Had to replace the spark plug wires also as they were falling apart. This engine now has about 103,000 miles on it... how long can I expect it to last?
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Old 11-24-2014, 11:39 AM   #10
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Leaking exhaust

Hard to say with a 454, but keep oil and water in it and the chances are very good that it will go another 100K without serious issues.


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Old 11-25-2014, 12:44 AM   #11
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Quote:
Originally Posted by J. Morgan View Post
Hard to say with a 454, but keep oil and water in it and the chances are very good that it will go another 100K without serious issues.


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+1

Had 454 in Chevy go over 200k miles before other 'running gear' issues forced me to sell ... I towed horse trailers, fully loaded at highway speeds... The 454 is a good engine..

There are some 'improvements' you could do... like pre-oilers, fuel injection, etc..

However, the 'best' advice I could offer is... 'don't rev the engine to try to warm it up faster"... when you 'rev' the engine, especially when cold, you put a high load on the main crankshaft and connecting rod journals (bearings) when the 'tolerances' are at their greatest...

Instead ... Start the engine with as little 'throttle change'... If your carb is not working properly, get it fixed or replaced so your engine starts and runs properly.... There are some decent REPLACEMENT carbs available through 'after market' sales which will require careful modifications.. not to be done by a novice... but can actually help a motor last longer because it is being properly fed.... such is life..

Oh.. if you have another 'exhaust leak'.. pour some Marvel Mystery oil down the carb throat once engine is warm... observe the exhaust... you will see the MM oil smoke coming from the 'leaky' spot...
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Old 11-25-2014, 12:52 AM   #12
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P.S... I would 'rebuild' a 454 in a heartbeat. You can make more power, be more fuel efficient.. etc... and have a real beast of a motor...and reliable..

A few steps will improve your experience..

-Have the block 'long bored',
-have the block and heads 'trued'/decked (this is where they machine them to closer tolerance for level than stock builds and give better gasket sealing)
-replace ALL bolts inside the engine... main and connecting rod journals, heads..
-do NOT bore cylinders unless absolutely necessary.. just a fresh 'crosshatch' hone to remove any 'shine' on the cylinder walls (the tiny grooves actually help hold oil and improve performance
-new pistons
-new hydraulic cam and cam followers..(lifters)
-new valves and springs and spring keepers
-new Oil pump...

There are a few others to do, but these are the basics...
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