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What can cause noise heard at the rocker arm???

Old 03-24-2007, 07:44 PM
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Neither do I but when in doubt...
Look at the way the rocker attaches to the stud. If the stud was smaller diameter and the rocker was larger it could wobble around and create a noise? I am trying to rule everything out to avoid pulling the head only to find nothing wrong.
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Old 03-24-2007, 10:42 PM
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I hate to be the bearer of bad news... but from what I've heard, if the rocker geometry is correct, and the lash is adjusted correctly, it could be a bad cam lobe. The profile on a cam lobe "lowers" the valve onto the seat. If the lobe is excessively worn, it can let the valve hit the seat abruptly, causing noise. Valves don't just "pop open" and "pop shut". They are raised, accelerated to full opening, quickly lowered to "almost closed" and then lowered onto the seat. If you were to graph the valve timing on paper it is easy to see. If the cam lobe is worn down on the top, it will allow the valve to slap onto the seat causing noise. The noise you hear isn't in the excessive lash, but in the valve hammering onto the seat.
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Old 03-25-2007, 01:00 AM
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Reed, I can see a worn lobe giving some rocker/valve clearance tick if worn more than the valve lash adj. and not open the valve fully, but wouldn't it still lower and raise the lifter slowly (not abruptly) because that part of lobe profile of the ramps are near the base of the lobe and not the nose where most of the wear would occur? If so, then the valves would still open and close off seat at the same rate as a good cam.
??????????
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Old 03-25-2007, 05:03 AM
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A little history on the engine might be on order here. I omitted some details to help with clarity that now may need be of some relevance. This engine was fully rebuilt last summer. Heads, bored, forged pistons, rods, polished crank, rods, cam bearings, timing chain and gears, balanced, new oil pump, cooler and lines, fuel pump etc. It was assembled with lifers from another engine that had 50 hrs on it. Crane rollers with tie bars. Engine went together fired and broken in just fine. One anomaly was that rockers had to be set at 1 full turn to make them quite. This block was line bored and the short timing chain set was used.

Got it on the water late in the summer and put 25 hours in with no problems. Last run of the year I wrung it out pretty hard and 4 (don’t recall if was I or E) developed a slight rocker noise. While on the water I pulled the valve cover and snugged it down another ½ turn and it was fine. At assembly time I was not comfortable using used lifters but it was all I had. After having to re-adjust no 4 I decided to replace the lifters as I felt they perhaps were more tired than the 50 hours claimed to on them so I ordered a new set of lifters roller Morel thinking better safe then sorry.

It should be noted that in the 25 hours the valve train was silent except for the event with no 4 which was fine after re-adjusting. The thought was that the used lifters were more tired than we thought or perhaps they were mis labeled. The lifters came from a twin with one engine that had 300 hours and the other 50. The boxes could have got mixed up.

So to make a long story short this engine was running fine when put under cover in the fall. The only change was installing new lifters for peace of mind. That is when this fiasco with no 7 started.

To summarize:
Noise on 7 exhaust that does not seem to change between 3/8 and 1 turn preload. This leads me to believe adjustment is fine. Pressing hard on the valve end or pushrod end makes no change.
Swapped rockers with no change.
Lifters are pumped up and oil is flowing through pushrod and into rocker just fine.
Lifters seem to be pumped up as turning adjusting nut depresses valve. I need to verify if the valve raises after setting a bit. This would prove that the valve motion occurred because of hydraulic pressure rather than the lifter bore being bottomed out.

With the history and details I would hope to rule out the cam. They are roller lifters so unlikely the cam is flat especially since a visual inspection of old lifters shows nothing unusual.

Things left to check:
Geometry
Clearnace
Rocker stud
Valve keepers
Run with spark plug wire disconnected on 7 then 5

Looking for suggestions to isolate and rule out possibilities.

Last edited by BadDog; 03-25-2007 at 05:08 AM.
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Old 03-25-2007, 12:23 PM
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Originally Posted by US1 Fountain
Reed, I can see a worn lobe giving some rocker/valve clearance tick if worn more than the valve lash adj. and not open the valve fully, but wouldn't it still lower and raise the lifter slowly (not abruptly) because that part of lobe profile of the ramps are near the base of the lobe and not the nose where most of the wear would occur? If so, then the valves would still open and close off seat at the same rate as a good cam.
??????????
It depends on how the lobe is worn. I had some valve noise on my Mercedes. I thought it was a hydraulic compensator,(used to adjust the lash on a OHC engine). The compensator was ok, the lash was ok, but the cam follower had a flat spot worn into the face. It allowed the valve to hit upon lowering. Lash ok... but still noisy. I replaced the follower and the noised dissapeared.
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