Noise question

[78Chev]

Last summer I rebuilt my 6.2 red block using a reputable machine shop, measuring to be sure everything was in spec, following the procedures found here on TDP, etc. It has a rebuilt 4911 pump with 6.5 injectors, J intake, Banks Turbo, the who 9 yards. I timed it with a digital meter (it was within spec; don't remember the numbers offhand). It starts and runs great. I couldn't be happier with that. So, what am I complaining about?

I've heard Robyn say that these "critters make all kinds of strange noises" or something to that effect. Well mine, under acceleration from idle sounds sort of like valves floating, that kind of noise. When I romp on it I get good boost and it sounds like I would expect. It's just this first bit of acceleration from idle that sounds strange to me. Is this one of those "strange critter noises" or do you have some other hypotheses about it? Could it be some artifact from my rebuilding process? I've been suspect of this 4911 from the beginning. (BTW: the reason for the complete rebuild was that the engine I purchased had Chinese 6.5 heads on them that were junk, which I found out after the tear down...)

I'm no expert on this stuff, just a shade tree mechanic who likes to work on this stuff. Your thoughts are appreciated.
Randy

[john8662]

My '86 has and noise like you're referring to. I'm 90% sure it's an exhaust leak. My exhaust system isn't the Banks unit either, it's a custom one of my design that has no union in the middle. I've made the advised 1" X 3/8" pipe adapters to install on the connection to the exhaust manifold on the driver's side, but haven't installed them. I did this on the '82 pickup and it helped a bunch on that engine (same configuration as the 86), but different turbo, and it's different ;) .

My best suggestion is to find a digital recording device that you can inport the audio onto the computer and upload it (I have the means to help you there) for us to listen to...

As far as cylinder head work, I'll bet the machine work brought the heads back to the correct specifications. Proper valve recession, proper end stem heights, and spring pressures, shimmed or not.

J

[78Chev]

I do think you a right about an exhaust leak. I've worked hard at sealing up at the turbo, left manifold, and crossover joint. I think i might have a leak next to an exhaust port; maybe the manifold needs to be milled or has a crack in it. I also still get the tick, although much softer now, that occurs only when there is exhaust pressure on the turbo and before the engine gets up to operating speed. I should have looked closer at that but I was so into getting the internals correct that it's easy to overlook the obvious stuff! Thanks, John, it would be great if this is it.
Randy