350 with bottom end knock. opinions?

[1972_Buford]

unknown amount of mileage 72 C20 th400 with a 350. Started to hear a knock possibly coming from bottom end. Guessing it is not a good thing. is it possible to pull pan without lifting engine?? Need to take a look at bearings I am guessing.

any opinions?? I already drained oil which came out normal, dirty, but normal. Thinking tomorrow about pulling pan if I can do it in truck.

-B

[69GWC]

Yeah you can, take the motor mounts loose and then you can jack it up from there.
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[1972_Buford]

I was hoping to do it without moving motor at all but I am guessing that isn't possibly? Looks like a lot of room but I am not sure pan will clear caps on way out.
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[trac209]

Originally Posted by 1972_Buford

I was hoping to do it without moving motor at all but I am guessing that isn't possibly? Looks like a lot of room but I am not sure pan will clear caps on way out.
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On 2wd you can do just that with a stock pan. You might have to rotate the crank to clear the throws but the pan will come out. I've done this on several 67 72 trucks.
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[1972_Buford]

Thanks. Still hearing a noise too. When I am just cruising and let off gas to let engine slow down I' ll hear a rattling noise. Hope it isn't a spun bearing.
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[Stocker]

Could be a cracked flex plate....

[1972_Buford]

Just has that out and everything looked good
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[100%Chevy]

Check for loose harmonic balancer.The key can wear,making a knocking noise.
Mike.

[geezer#99]

Could be detonating too!! Check your timing! PLug off the vacuum advance to the distributor and see if the noise goes away first.

[1972_Buford]

Checked balancer. Timing seems to be on. Definitely sounds like a knocking vs detonation. Thanks for the option though. I'll check it too. I was going to do an oil change so the pan was already empty. Thought I may as well drop pan to see if anything was going on in there before I put new oil in there and waste it. Keep'em coming. Will be looking for more options if I don't find anything with oil pan. Have pan dropped but ran out of day light to get it all the way out. I'll be checking it tomorrow
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[1972_Buford]

Got the pan out today. Had to jack motor up a little to get it out. The pan would only go back so far before hitting flexplate and only tilt down soo much with block.

So on to the pan contents. Nothing in the pan that showed a major malfunction. The pan looked like it had some pieces of old cork gasket in it but could have been from when I took it off. No metal shavings that I could see. A good thing also came from this, the engine was leaking oil pretty decently from the back but I couldn't find it and just assumed it was the rear main. Turns out the rear oil pan gasket was put in cock-eyed and was more than likely the cause of the leak. It also had a ton of RTV sealer on the gaskets, including the front and rear rubber gaskets. Going to pick up gaskets today and put it all back in. just finished getting it all cleaned up.

I also noticed the wire going to the HEI is cracked. This could be a reason why it dies intermittently. I'll repair this with some new wire and go from there. Maybe just better to take the plunge and get a new wiring harness.

Keeping up the good fight.

-B

[100%Chevy]

While the pans off,it's a great time to check the bearings for wear!
And,re-torque.
You may find the reason for the knock.
Something else to check is the fuel pump push rod-Can sound like a rod knocking or a lifter ticking when worn.Or,when the fuel pump spring is bad,same thing.
Mike.

[jocko]

yep - it sounds like you didn't isolate your problem with the pan off. Hate to admit it sounds like a rod or crank bearing - and that won't show up in metal shavings in the pan until, well, until it's too late. Is the sound getting worse as time goes by?

Re-torqueing not a bad idea - but keep in mind you cannot visually tell if the bearing is spun without removing the con rod cap (for a rod bearing) or the crank main bearing caps (for a main bearing).

If the knock persists - and I hope it doesn't - a stethoscope (borrowed) would pay dividends. If it's in the lower end of the motor (i.e. not just a sticky lifter or loose valve) and you've eliminated everything else (harmonic balancer, flexplate, etc...), it's time to pull the motor.

[trac209]

Don't button it back up with a bearing check!
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[1972_Buford]

Chasing it down is annoying. So I sat under it while it was running and it sounds like it is coming from the top side. On the top side passenger it sounds like a loose lifter. When I got the oil pan gaskets I bought a set of valve cover gaskets too since I figured I was going to. Adjust those as well.

I fired it up and ran it until warm. I gave it a little gas and it bogs down or acts like a lack of gas. Takes a few seconds to rev up actually. Might be chasing two different problems.

As far as the rattle I noticed what looks like a valve on the passenger side exhaust manifold. Heat riser valve? Maybe? Regardless, there is no spring. On it so I think this is the rattling culprit. Also it doesn't move too much. Could this blockage because what stalls the motor? Wondering if it is frozen closed. The guy who had it before ( not an electrician) said he hadn't run it in over a year so I am kind I just chasing problems. Thanks again for all the replies I really appreciate the help and ideas.
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[1972_Buford]

Double post sorry

[Stocker]

Originally Posted by 1972_Buford

As far as the rattle I noticed what looks like a valve on the passenger side exhaust manifold. Heat riser valve? Maybe? Regardless, there is no spring. On it so I think this is the rattling culprit. Also it doesn't move too much. Could this blockage because what stalls the motor? Wondering if it is frozen closed.

Yup, heat riser. It should move freely through a 90 degree arc.... and IIRC, there should be a spring. If it's frozen closed, the engine will run but power will be down b/c exhaust from pass. side will be forced up through the intake manifold (which could be blocked by carbon buildup). It helps during cold startup in cold weather, but you can run without it as long as your choke works. I took mine off years ago.