Help I have to get to work on monday

[69GMCCustom]

So i replaced my manifold, and my carb, started the truck and it has a slight knocking sound that increases with rpm. I have no idea what could be causing this, and I need to get to work tomorrow morning! Any ideas?

[Boog]

Make sure the distributor cap is sitting on squarely. If it's tipped a bit the rotor will hit some of the terminals and sound just like a knock. Ask me how I know.

[into69z]

I hope the oil pump shaft stayed together and re-engaged with the distributor-did you check for oil pressure?

I don't want to make it worse but if your oil pressure was or is not where it should be-it could be bearings.......let's hope not!!

[69GMCCustom]

lol oh yeah I have oil pressure. I cranked it over the first time and it caught and I had forgotten to put the oil pressure sending unit back on. So I cleaned about a quart of oil off my engine. But it was only about a quart low so hopefully that wasnt enough to cause damage. It does come and go at times tho. The dist cap looks good. I've got oil on both my heads, adn the engine runs great, instant response, great idle, except that knocking sound comming from pass side, i think.

[71swb4x4]

Is it a deep knock or a "lighter" knock?
Exhaust leak? Loose rocker?

[69GMCCustom]

honestly if i had to guess I would say it sounds like a rocker is hitting the head cover, however I didn't replace them or do anything more to the heads other than replace the gasket covers. I'm not sure how to check for a loose rocker. It is loud enough to hear in the cab, but not loud enough to hear when revving.

[Frkypunk70]

Main bearings...just my guess
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[69GMCCustom]

Ok Its louder down near the oil pan....looks like i toasted berings in under 15 seconds. New Question...Anyone know a good place to get a 400 sbc rebuilt in Fresno? And probably the tranny too, it leaks.

[yob2kanobe]

You didnt leave a wrench or pliers in the valley did you? Ask me how I know...

[ryanroo]

seems unlikely that you would waste the bearings in that short a period of time and with only a quart missing from the pan. the sender should be after the mains in the oil circut so it wouldnt starve the bearings. if you did manange to ruin them there would be tattletale glitter in the oil.

[69GMCCustom]

no glitter in the oil at all. just that constant knocking at every rpm, no matter what. I'm pulling my oil pan off tomorrow, and if I find nothing wrong Ill pull off my intake again.

[Frkypunk70]

Not a whole lot of info here. Such as how many mile on the engine? What work has been done to it? Does it have a hei ignition? Could be real simple or a major problem. Knock that deep would normally be a spun bearing. Maybe the experts could chime in and let you know if a vac advance from possibly poor vacuum could make the same thing happen or loss of vac from the intake? Don't start rebuilding yet. Worse case scenario pick up a C list engine for 500 bucks and throw it in. It only take about an hour to throw a engine in these badboys...and that's if you supply the beer. When I made the initial statement it's what my mind was bread to think. Get some thoughts by the experts here first. You might have something simple that is the problem. Let us know how you make out.
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[69GMCCustom]

I bought the truck 6 weeks ago. The speedo was unhooked lol. The engine sounds great except for the knocking, that's whats throwing me off so much . If theres nothing that i can see wrong with the bottom end, then I'll open the top end back up and check it out.

[Boog]

It is possible a small bolt, washer or nut fell down into one of the intake runners of one of the heads and is sitting on top of the piston. If not very big it can get pounded into the piston top without bending a rod or cracking a cylinder. I have found a few over the years. Also a loose torque converter bolt can cause a hard knocking sound.
You could use a mechanics stethescope or a long piece of hose to helpl narrow the search for the source of the sound. Good luck with it.

[dukcaln]

Originally Posted by Boog

It is possible a small bolt, washer or nut fell down into one of the intake runners of one of the heads and is sitting on top of the piston. If not very big it can get pounded into the piston top without bending a rod or cracking a cylinder. I have found a few over the years. Also a loose torque converter bolt can cause a hard knocking sound.
You could use a mechanics stethescope or a long piece of hose to helpl narrow the search for the source of the sound. Good luck with it.

this happened to my dad in his 71....small washer planted it self on top a piston.........so it is possible

[71 GMCDRVR]

I recently had the same sound I thought it was valve lash but after resetting the valves a number of times it just got worse. pull your intake manifold and pull out your lifters and check em. if they are damaged you lost or are in the process of losing your cam. This is what was wrong with mine! Is the sound coming from the top end? rubber hose works great for finding these noises!!...................But make sure the lifters go back exactly as they came out, I might be preaching to the choir but I had to say it that's how I roached the cam

[bigguy69]

Mine done that but it ate the air cleaner stud. But mine cracked the block and head. So back to square one. I hope it is simple fix for you.
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[71 GMCDRVR]

After reading and thinking about it, it sounds exactly like mine did. It sounded like rockers it came and went for the first couple of weeks then just went downhill in a hurry. Any loss of power? Is it more of a tick? could also be a fuel knock, where is your timing set? Cheap gas? (I had all these problems when I switched motors)

[Stocker]

Originally Posted by 69GMCCustom

Ok Its louder down near the oil pan...

Auto trans? Thought mine had a rod knocking but the engine ran long enough to get me home from duck hunting. Turned out to be a cracked flex plate..... engine was fine.

[69GMCCustom]

Well tomorrow I am going to reset it to tdc, reassemble it, and fire it up again. If it still knocks I'll have to get a hoist to get a look at the bottom, I cant get the oil pan off with the engine in. The top looks good, however I did find a 1/4 inch long piece of copper wire in the valley, but the rods all look good, the heads look good, looking down into the ports? from the intake my valves have a nice patina, but not alot of gunk built up on them. I also thought about running a magnet inside my pistons thru the sparkplug holes to see if it picks up anytihing. I'm worried about removing my heads as I have read the process to tighten all the rockers, rotating the engine, however I have never done it. So hopefully I will have good news tomorrow.

[69GMCCustom]

btw as far as cheap gas, I was running chevron, and like I said the engine sounded great after i changed the manifold and carb, no missing, no hesitation, just a knock. Im worried about running it anywhere that way, dont want to tear up too much if its serious...know what i mean

[71 GMCDRVR]

Have you checked the lifters?

[OJ1988]

Loose converter bolt will make a knocking sound that increases with rpm.

[stsalvage]

its not that it happens all the time but the tourq converter might have one of the blades bent in it I seen it happe4n on my 350 when i hit the gear shifter in my power glide and put it in reverse at 55 miles per house was only there for 30 sec But i have a small tick in my motor but only happens when i put it on fast idal and it sounds like it coming from the bottom end

[71 GMCDRVR]

Does the sound get louder around 2500 rpm but stay the same there after even at a higher rpm? The reason I ask is at one point you said it almost sounds like a rocker hitting the valve cover. If thats the case it could be nothing more than a loose rocker or two or three (don,t ask me please)