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Old 09-12-2017, 01:36 PM   #1
Chilly178
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Exclamation Any idea on what this knocking is 72 C20 350

https://youtu.be/Kn_NCSNnZu4
All help is greatly appreciated. I have no idea if this is a major issue that requires the engine to be removed and rebuilt or it just requires a simple fix. Thanks again.
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Old 09-12-2017, 02:13 PM   #2
geezer#99
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Re: Any idea on what this knocking is 72 C20 350

POp off the valve covers.
You might get lucky and it's only a broken rocker.
Sounds like a push rod rattling.
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Old 09-12-2017, 02:17 PM   #3
AussieinNC
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Re: Any idea on what this knocking is 72 C20 350

Either a rocker stud has pulled out of a head or the rocker has come loose...just pop off the rocker covers and the issue will be obvious...

Doesnt sound deep enough to be a bearing...

Good luck
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Old 09-12-2017, 02:48 PM   #4
Chilly178
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Re: Any idea on what this knocking is 72 C20 350

I did take the valve covers off before and all the rockers were on a few of them had a tad of play and I looked at all the push rods and most of them were good again some of them may have had the slightest amount of play. Is this enough for it to rattle this loud? Should I take the valve covers off again and tighten all the rocker arms? Is there a torque spec on those? I guess I didn't really know what to look for specifically.

EDIT: I just ran the truck again the knocking gets louder and faster the higher the truck revs and it sounds like it is coming from the passenger side possibly towards the rear of the engine if that helps.

Last edited by Chilly178; 09-12-2017 at 03:25 PM.
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Old 09-12-2017, 03:21 PM   #5
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Re: Any idea on what this knocking is 72 C20 350

Sounds almost like an exhaust leak; it's not all that hard a sound. Try using a piece of garden hose like a stethoscope to help locate the source. It's in the top end, for sure, though, from the sound of it, it's at valve train speed.
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Old 09-12-2017, 03:39 PM   #6
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Re: Any idea on what this knocking is 72 C20 350

Well it has what looks to be the original manifolds on it that have been on for who knows how long I would think they would be fine but I guess you never know. I'll try the garden hose trick.

Edit: Tried the garden hose didn't really work that good pretty sure its coming from the passenger side. Does https://i.imgur.com/ShWjLfk.jpg this look like a manifold leak?

Last edited by Chilly178; 09-12-2017 at 03:55 PM.
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Old 09-12-2017, 03:46 PM   #7
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Re: Any idea on what this knocking is 72 C20 350

Sounds like a lifter sticking? Because it's intermittent. Has the motor been sitting up for awhile. Also make sure nothing is hitting the flywheel
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Old 09-12-2017, 03:57 PM   #8
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Re: Any idea on what this knocking is 72 C20 350

Engine has not been sitting. Been running it all summer. Although it did sit for about a week maybe less before I ran it on the day that this started happening. This started last Friday on the highway going about 65-70. I agree with you because sometimes the ticking/knocking misses its not always steady but it does increase speed with RPM. I also did just put some oil treatment in it this morning. Doesn't seem like it did too much. How do I check the flywheel?
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Old 09-12-2017, 04:20 PM   #9
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Re: Any idea on what this knocking is 72 C20 350

Have you tried to pin it down with a mechanic's stethoscope? Works better than a hose imho.

It doesn't sound to me like a cracked flexplate but I guess that's a possibility.... or loose flexplate bolts. As other have said, it sounds more like valvetrain to me.
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Old 09-12-2017, 04:43 PM   #10
Chilly178
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Re: Any idea on what this knocking is 72 C20 350

No I do not have one of those at my disposal. What should I be looking for when I take the valve cover off? Is a little bit of play in a push rod or a rocker arm acceptable?
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Old 09-12-2017, 04:56 PM   #11
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Re: Any idea on what this knocking is 72 C20 350

Remove the passenger side rocker cover.

You need to manually turn the engine so that each passenger side cylinder comes up on compression stroke...you can watch the inlet rocker close off, then turn the engine 1/4 turn...

On that cylinder, check the rocker arm clearance to the valve stem...it should be just touching the stem.

Try and push down on the pushrod end of the rocker arm,,,if it goes down at all, you have a bad lifter.

If the rocker arm has any clearance over 1/16" the adjustment nut on that rocker arm has either backed off...or, worst case, the stud has pulled slightly out of the head. Either way...its not a simple fix...

What is the oil pressure with the engine running?

I have also heard a noise like this when the torque convertor bolts come loose...you can check by removing the flywheel cover plate if it fitted and check each of the three bolts and nuts for tightness...

While you are under there, grab the flew plate and try to move it rotationally back and forth...listen for a clunking sound...

If it clunks it could be a cracked flex plate...
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Old 09-12-2017, 05:42 PM   #12
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Re: Any idea on what this knocking is 72 C20 350

Thanks for all the input! I ran the engine a bit more to give you guys a better idea. https://www.youtube.com/watch?v=4ReGCS4Jkg0

And then I also ran it again with the passenger side valve cover off.
https://www.youtube.com/watch?v=ft2xSmAX-_A

https://i.imgur.com/xuUcwM7.jpg

I'll check the flywheel sometime tomorrow.

Last edited by Chilly178; 09-13-2017 at 08:47 PM.
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Old 09-12-2017, 05:47 PM   #13
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Re: Any idea on what this knocking is 72 C20 350

The rear rocker arm is not moving much at all...it is most likely a bad lifter or cam lobe gone...check the video where you have the rocker cover off...the rear rocker arm is not moving much at all...
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Old 09-12-2017, 05:51 PM   #14
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Re: Any idea on what this knocking is 72 C20 350

I see what you mean.

Last edited by Chilly178; 09-13-2017 at 08:48 PM.
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Old 09-12-2017, 09:22 PM   #15
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Re: Any idea on what this knocking is 72 C20 350

Quote:
Originally Posted by Stocker View Post
Have you tried to pin it down with a mechanic's stethoscope? Works better than a hose imho.

It doesn't sound to me like a cracked flexplate but I guess that's a possibility.... or loose flexplate bolts. As other have said, it sounds more like valvetrain to me.
Sounds deeper and not as high pitched as rockers or pushrods to me. I'm in the line of thinking of the loose or broken flex plate. Also look for the flexplate hitting the torque converter cover (inspection cover). Quick 4 bolt check to rule these out. Good luck
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Old 09-12-2017, 11:28 PM   #16
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Re: Any idea on what this knocking is 72 C20 350

Quote:
Originally Posted by towbar View Post
Sounds deeper and not as high pitched as rockers or pushrods to me. I'm in the line of thinking of the loose or broken flex plate. Also look for the flexplate hitting the torque converter cover (inspection cover). Quick 4 bolt check to rule these out. Good luck
Yup, an easy thing to check. I find it a bit hard to diagnose sounds from a recording. When my flex plate cracked, it made a very deep hard knock and I honestly thought it was a rod bearing about to let go. The OP's video just doesn't have that same sound to me, but I would not bet any money on it either way. It's just too hard for me to tell.
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Old 09-12-2017, 11:40 PM   #17
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Re: Any idea on what this knocking is 72 C20 350

I see. Tomorrow I will check the fly wheel and the bolts and as well as take off the two rockers to compare them for wear. Thanks again everyone, will post back tomorrow.

Last edited by Chilly178; 09-13-2017 at 05:58 PM.
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Old 09-12-2017, 05:30 PM   #18
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Re: Any idea on what this knocking is 72 C20 350

^ good info. To add. If everything checks out you can run the engine with the valve cover off and put a hammer handle or something on the studs of the rockers. You'll be able to feel the tapping or grinding from the bad one. If that's your problem.
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Old 09-12-2017, 05:34 PM   #19
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Re: Any idea on what this knocking is 72 C20 350

Plus there is no torque spec on the rockers. You probably have a hydraulic cam. Tons of reading on google how to set them. But when it's running. Back off the rocker nut until it ticks. Then tighten until it doesn't tick then tighten 1/2 turn. That's for hydraulic only. Not a solid cam which I bet you don't have
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Old 09-12-2017, 05:49 PM   #20
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Re: Any idea on what this knocking is 72 C20 350

the rear rocker on the passenger side isnt moving too much in the last video...DOOOH! i type too slow..
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Old 09-12-2017, 06:57 PM   #21
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Re: Any idea on what this knocking is 72 C20 350

I watched all of your videos and the only possibility is you should have used 50 pounds of Tannerite!

Oh, the engine issue... Look at that last rocker not moving like the rest.

Or as the Muppets sang... One of these things is not like the others.

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Old 09-12-2017, 07:36 PM   #22
AussieinNC
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Re: Any idea on what this knocking is 72 C20 350

Gotta love it "hamjet"...

Either the cam lobe has lost its lift profile or the rocker arm ball has worn thru the rocker arm...

Remove the last two rocker arms on the passenger side and check out the area inside the rocker where the ball sits...compare the two seat areas...if they look the same, you have either a really bad lifter that has collapsed internally or a bad cam lobe...equals engine out in my books...

Post pics of the inside seat area of both arms and their respective pivot balls...

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Old 09-12-2017, 07:54 PM   #23
Chilly178
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Re: Any idea on what this knocking is 72 C20 350

Ok i'll definitely remove the two rocker arms tomorrow and compare them and then post the images. So would a bad lifter or a worn cam lobe make this knocking sound?
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Old 09-12-2017, 07:56 PM   #24
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Re: Any idea on what this knocking is 72 C20 350

Yep...start with the easiest things to access

Then work deeper...

Been doing this for over 50 years now...
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Old 09-13-2017, 06:12 AM   #25
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Re: Any idea on what this knocking is 72 C20 350

Could also be the last lifter stuck in the bore allowing the cam to slap the lifter. a compression test would tell..
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Last edited by hamjet; 09-13-2017 at 06:24 AM.
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