PLEASE HELP! Deep Engine Knock...Head Scatcher

[wild4wheels]

OK, 71 Longhorn 350. Had somebody that owed me money doing some "easy" work for me. I needed the valve cover gaskets and intake gaskets replaced due to some leaks.. not the only ones mind you but a good place to start.

It is a 63000 actual mile truck mind you and ran like a top in the summer months. Had some hesitation during winter months...another mechanic said that the valley under the manifold was plugged and need to be cleaned out.

So, this guy took off the valve covers, carb, distributor, coil, manifold, water neck etc....next day replaced the gaskets cleaned the valley..carbon build up on heads, reasembled and heard a loud, deep knockpass. side. called it a tick...no friggen way...it's a knock. He called a mechanic buddy of his over. and tried to pin point it. He told him to do it all over again..start over..maybe he had forgot something..did everything a second time...same thing..mechanic buddy came over again..adjusted some valves...thought it was the fuel pump..replaced that..STILL has the friggen knock. he thinks its now a lifter..ANY IDEAS? Prior to this I didn;t even have as much of a flutter of a lifter...I told him to count his sockets...dropped something in there? dunno..pulling what little hair I have left out...

[jef5150]

Originally Posted by wild4wheels

So, this guy took off the valve covers, carb, distributor, coil, manifold, water neck etc.... reasembled and heard a loud, deep knock

from what i read the " first attempt", this guy replaced "ONLY GASKETS and made no mechanical adjustments......Its very easy to drop a nut,washer,or bolt into an engine with no manifold on....That would be my first thought.

Originally Posted by wild4wheels

mechanic buddy came over again adjusted some valves, he thinks its now a lifter,

well if he couldnt adjust the lifter noise out and thinks you need to replace 1 of them,why didnt he tell you which lifter was bad????


jeff

[mrein3]

Originally Posted by wild4wheels

stuff deleted...
So, this guy took off the valve covers, carb, distributor, coil, manifold, water neck etc....next day replaced the gaskets cleaned the valley..carbon build up on heads, reasembled and heard a loud, deep knockpass. side. called it a tick...no friggen way...it's a knock. He called a mechanic buddy of his over. and tried to pin point it. He told him to do it all over again..start over..maybe he had forgot something..did everything a second time...same thing..mechanic buddy came over again..adjusted some valves...thought it was the fuel pump..replaced that..STILL has the friggen knock. he thinks its now a lifter..ANY IDEAS? Prior to this I didn;t even have as much of a flutter of a lifter...I told him to count his sockets...dropped something in there? dunno..pulling what little hair I have left out...

I'll guess that while he "cleaned the valley..carbon build up on heads" he knocked a piece of carbon down into the engine. Now that chunk is striking a valve as that piston comes up to the top.

If that is true, your best case scenario is take the heads off, remove offending chunk of carbon, reassemble and move on.

Middle case: damaged valve, need to do a valve job.

Worst case: Piston is damaged and you need a total rebuild.

What a shame with only 63k on the clock.

[sneakysnake]

My guess is something got dropped down the intake port also.

[68gmsee]

My take: It's hard to imagine anyone dropping a socket or other similar object after taking the intake manifold out and not see it. A snake magnet might retreive any object that would have fallen in the ports.

A small piece of carbon keeping the valve open could be the case if you had a miss. You certainly would notice that and could be easily checked with a compression tester before removing the heads.

I'd take a mechanics stethoscope or 3 foot section of garden hose (my favorite) and try to isolate the locaton of the noise. If it's a lifter that can be easily replaced. If it's a rod bearing or piston pin then it's certainly going to entail more work.

At this point, it's time to take it to a reputable shop, though. Good luck and let us know what you find.

[hdflstf]

How about checking the spark plug wires make sure the firing order is right.

[68gmsee]

Originally Posted by hdflstf

How about checking the spark plug wires make sure the firing order is right.

I would think that you should be able to hear it missing out, but it's a good point... Don't take anything for granted.

[wild4wheels]

If something did get down in the ports...if it is carbon, you think I should try doing a top engine clean either with the GM TEC or Seafoam? I just talked to a guy that says you can use tranny fluid that does the same thing..a search online backs it up. He says that he, as a precaution, had vaccumed the ports prior to reassembly. He doesn't think we are getting as much oil at the lifters as we should, could carbon be affecting this? Could the oil pump have "coincidentally" gone bad?

[68gmsee]

If you suspect that it's a lifter, here's a post from a week or so ago...
http://67-72chevytrucks.com/vboard/s...12&postcount=6

And here's the thread. He used some seafoam to loosen up the lifter.
http://67-72chevytrucks.com/vboard/s...12#post2843012

You didn't mention the oil pressure. If your oil pump gave out, it wouldn't be all of a sudden unless something broke. Then you wouldn't have pressure at all.

If you're not familiar with engine noises have a professional mechanic listen to the engine. They pretty much can diagnose the sound and isolate it from a bad lifter, piston rod bearing, piston slap, main bearing, etc...

Also, as a reminder, on these old engines, 63,000 miles was considered high mileage back then. These days that would be just broken in...

[wild4wheels]

Thanks all for the feedback thus far! According to the gauge in the truck, oil pressure is normal, and it does move slightly when I rev the motor..so I assume it is working. I m not a mechanic, thats for sure, but when I first heard it, my initial reaction was a rod. They took the valve cover off and started the motor..it took a few minutes but they all got oil eventually..just not a gusher throwing oil all over, hence the question about the oil pump. I guess at this point it wouldn't hurt to do the Top End Cleaning?

[68gmsee]

The total oil pressure is determined by not only the pump but the condition of the crankshaft bearings, camshaft, lifters, etc. In other words if they are nice and tight, the oil pressure is higher, if they are worn the oil escapes pressure is less.

In new or rebuilt engines the pushrods will definitely squirt oil out and make a mess. On older engines it will ooze out with just weak spurts.

I would definitely be concerned if you supect an oil pressure problem. Either clogged filter or worn pump or other. It can cause major bearing failures.

What I would do is to make sure I had clean oil and try some additive like "seafoam" to see if it will loosen up any gummed up lifters. Then I would drain it and try a heavier weight oil. Maybe 20-50 and see if your pressure goes up.

If you still hear a knock, I still say you need to have a professional mech give you his opinion...

[Gray Ghost]

OK...if it is a knock it probably isn't a lifter or a valve. Knocking sounds are usually something below the heads like a rod. It could also be something loose in there as most have said. I'd pull the heads for sure and check for damage on the piston.

Last week I saw a piston that had a chunk missing off the top edge....weird since nothing hit it....it just flaked off.

[cparman]

Ok here is my 2 cents, in the order I would go after it.

1 someone in the post made mention of crossed plug wire? If you veryfy the the firing order is correct, I would start the engine and pull one spark plug wire off at a time and see if the noise goes away when you remove one of the 8 plug wires. IF SO the noise in in that specific cylinder, and it is probably a rod/main. with no spark in a specific cylinder, a rod brg noise will be much less.

A TRAINED EAR SHOULD BE ABLE TO DISTINGUISH FROM AN UPPER END NOISE OR LOWER END NOISE

2 Carbon is a possibility. I used plain old water. whith the engine running, hold the rpm a little above idle 1500 or so ,a dn slowly pour water into the carb. after the engine stumbles let it recover and see if the noise changes. You may need to do this a time or two, to get the noise to completely go away.

3 if the noise is still there, then you probably have a nut bolt etc on top of a piston, and the head is comming off.

hope this helps

[wild4wheels]

Number 6 cylinder...is like 85..the rest are all testing right at around 120.

[biggreen292]

i'd give that cylinder a leakdown test next, see if the air escapes to the oil pan, intake manifold, or exhaust.

when he did the intake did he change the oil after? usually when you pull an intake off some coolant gets into the valley and into the oil, coolant wipes out bearings quite affectively.

my regal had a noise i swore to be a rod but turned out to be a collpased lifter/flattened cam lobe.

[71 super]

Do you have access to a timing light? IF so try the following: with engine running hook up the light and point it at the timing tab. Listen to the noise while watching the light flash, if the sound is in sequence with the light look at the bottom end, if the sound is twice the flash of the light the problem is in the top end. With the sound of things and the iea that the intake was carboned up I would lean toward carbon. Pull the plug out of #6 and spin the motor over a couple of times and see if you get any thing to come out. If it is something in the lower end it should sho up in the oil pressure. When you rev the engine what direction does the guage travel ? Up good, down wiped out bearings bad. Did the guy by chance use kerosene or other solvent to clean carbon hen he took the top end apart, if so he could have wiped out the bearings by striping all of the oil from them- effectively causing a dry start-up. Hope this helps...

[airdale94]

The distributor is not installed correctly. It's possible to get the oil pump drive rod cocked slightly. You will still have oil pressure and the distributor will seat, but you will have a loud knock.

If the speed of the knock increases uniformly with eng. RPM something isn't installed right. A dropped bolt or socket would make a "rattling" noise.