So I got the L79 started for the first time since it started it's long Winter's nap. It cranked a bit but fired up. Rear lifters clacked a bit until the oil pressure worked its way to the back. It fast idled fine and after it warmed up the warm idle was fine. Oil pressure stayed at 60 the whole time. Ran great.
Once it was warmed up and idled down, I noticed a fairly loud whistle. Couldn't really place it, thought maybe it was a whine from the alternator, maybe a bearing going bad. I got out my stethoscope and the alternator sounded fine. Rockers sounded fine. Distributor sounded fine. Water pump sounded fine. Still couldn't place the whine/whistle. Seemed to be coming from both sides. Thought maybe it was the carb. I pulled the air cleaner and it got more prominent. No air intake whistle, that's a different kind of sound. This was high pitched and got more shrill as the engine sped up. No leaks from the carb, no loose fittings anywhere. Didn't seem to be any vacuum leaks as it ran and idled just great.
Out of a loss for anything else to check, I stuck my thumb in the crankcase air intake pipe, the one that connects from the air cleaner to the back of the block. It didn't stop the whistle right away, but if I left my thumb in the pipe thus plugging it, in a few seconds the whistle went away entirely. If I take my thumb out of the pipe, it takes a second or two before the whistle comes back. I could feel the engine vacuum pulling on my thumb slightly as the rest of the PCV was still hooked up to carb vacuum so the PCV system is sound the engine would appear to be well sealed. These engines don't use a PCV valve, there is just a restrictive orifice inside the main carb body that acts as a valve somewhat. Anyway, it has never caused a problem and the orifice isn't blocked because I can feel vacuum. But if air is allowed to pass through the system, there is the whistle. To further confuse things, if I pull the PCV vacuum line off the oil fill spout and plug it the whistle continues so I have to assume the whistle is NOT in the carb.
I have absolutely no idea where to take this issue from here nor can I even think of what could be causing the whistle. Most especially, I have no idea where to continue to look for the actual source of the whistle. If it was a leaking intake manifold or carb base gasket you'd think the whistle would get louder if I blocked off the PCV intake air source because it would be trying to pull even more air through the leak. I can't imagine the baffle inside the lifter valley is the source since it has no moving parts and the noise continues even when the vacuum source is removed thus preventing any air from passing through the baffle.
Any thoughts at all out there?
Once it was warmed up and idled down, I noticed a fairly loud whistle. Couldn't really place it, thought maybe it was a whine from the alternator, maybe a bearing going bad. I got out my stethoscope and the alternator sounded fine. Rockers sounded fine. Distributor sounded fine. Water pump sounded fine. Still couldn't place the whine/whistle. Seemed to be coming from both sides. Thought maybe it was the carb. I pulled the air cleaner and it got more prominent. No air intake whistle, that's a different kind of sound. This was high pitched and got more shrill as the engine sped up. No leaks from the carb, no loose fittings anywhere. Didn't seem to be any vacuum leaks as it ran and idled just great.
Out of a loss for anything else to check, I stuck my thumb in the crankcase air intake pipe, the one that connects from the air cleaner to the back of the block. It didn't stop the whistle right away, but if I left my thumb in the pipe thus plugging it, in a few seconds the whistle went away entirely. If I take my thumb out of the pipe, it takes a second or two before the whistle comes back. I could feel the engine vacuum pulling on my thumb slightly as the rest of the PCV was still hooked up to carb vacuum so the PCV system is sound the engine would appear to be well sealed. These engines don't use a PCV valve, there is just a restrictive orifice inside the main carb body that acts as a valve somewhat. Anyway, it has never caused a problem and the orifice isn't blocked because I can feel vacuum. But if air is allowed to pass through the system, there is the whistle. To further confuse things, if I pull the PCV vacuum line off the oil fill spout and plug it the whistle continues so I have to assume the whistle is NOT in the carb.
I have absolutely no idea where to take this issue from here nor can I even think of what could be causing the whistle. Most especially, I have no idea where to continue to look for the actual source of the whistle. If it was a leaking intake manifold or carb base gasket you'd think the whistle would get louder if I blocked off the PCV intake air source because it would be trying to pull even more air through the leak. I can't imagine the baffle inside the lifter valley is the source since it has no moving parts and the noise continues even when the vacuum source is removed thus preventing any air from passing through the baffle.
Any thoughts at all out there?
