# Strange Clack/knock in 68 goat



## jketelsen (Aug 25, 2009)

Ok guys this problem has got me chasing my tail! In March I was out joyriding and on the way home putting through an addition about 20 mph I turned a corner and the heard a loud clacking/knocking noise start. I shut it down immediately and started to push it off the road. I said &*(^ it and went to start it back up to move it and it didn't want to turn over-so I continued pushing. Towed it home and it started to back it into the garage where it sat. Recently I started digging into it and the noise is pretty fast and not quite as deep as a rod or main knock. It speeds up with the rpms and gets louder and faster. Oil pressure at idle is 60 when cold and 30 when warmed up. The engine didn't overheat at idle but at the time the noise started the gauge didn't work. I checked the flexplate-ok and tight, car sat again. A couple days later I pulled the valve covers and found a rocker that was loose and the lifter was weak-#5 exhaust. I got some mystery oil and ran a quart in it and while it was running I noticed some new symptoms. It would idle fine and then start missing and get a deep tone in the exhaust almost like an engine brake and would stall out or if I feathered the gas it would stay running-barely. Then just as quick as it came on it would smooth back out and idle fine-throughout the test the noise is there. So lastnight I went to start taking off the intake and decided to check the lifters again to see if anything changed and I found that the weak lifter had pumped back up and the rocker was fine!. With the covers off I then ran it and felt each rocker to see if I could feel the noise on any of them and I couldn't and they all moved like they should. Lastnight the engine idled like a sewing machine but still had the same noise. Funny thing is is that the noise when idleing will stay constant then double-time it for a bit with a lighter tone, then go back to it's normal pattern. I unhooked the accessory belts and the noise was still there. I even tried the screwdriver/ear trick and I can't find the source. I've also pulled the plug wires one a time and the noise does not quiet down just gets slower. The guys at work said try to unhook the torque converter to rule out the tranny so I'm going to try that tonight but has anyone had a TH400 tranny/converter do that? 67 400 YS with 70 TH400 tranny


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## Eric Animal (Oct 28, 2007)

Prolly not gonna help but, before you pull the tranny, check the crank bolt and the bolts in the balancer that hold the lower pulley on.....just happened to my friend's 67.


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## jetstang (Nov 5, 2008)

When the rocker backed off, did it lose the crimp, oh, they are torque rocker bolts. Did the nut loosen up? Pull the pushrod and check it to see if it's bent, that will give the clearance for a low end tap. I had 2 lifters tapping, ended up being the cam going bad, flat lobes. If you had a dial indicator, you can check a good cylinder cam opening on the rocker, then do the suspect rocker and see if they have the same lift. Odd that the noise would just start all of a sudden. Good luck.


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## Jeff's Classics (Feb 24, 2010)

I know you said you checked the flexplate bolts, but did you also check the condition of the flexplate? I had a 454 Chevy that would crack flexplates, and it would rattle like that sort of strangely. When I check the bolts they were tight, but then I noticed the crack. Changed it out and the problem went away.
Good luck!
Jeff


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## jketelsen (Aug 25, 2009)

Sorry, flexplate didn't have any cracks on it either. The rods all spun freely and didn't rub against the little guide plates in there so I didn't pull any out-nothing obvious anyways. I didn't have a chance to look at it lastnight but here is a clip from the other day. It does run smoother than this now so it might have had some moisture in the fuel causing the idleing issue. Another racer I work with said it sounds like a rod knock what do you all think?


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## Rukee (Feb 8, 2007)

It does kinda sounds like a rod or a wrist pin, maybe a broken piston.


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## jetstang (Nov 5, 2008)

Check for a bent pushrod before you tear it down. I had a rocker nut back off and it sounded terrible, hammering the rocker, and didn't want to idle. If the pushrods have inserts it may have pushed the insert into the pushrod. Pull the valve cover, check for excessive loose rocker, rotate engine quarter turn at a time, check again. If it's a rocker with that much noise it should be obvious when running. It doesn't sound like a rod knock as much as valvetrain, check again. Might be a busted valve spring, measure the spring heights, look for the short one.
Hope it's not bottom end, but may be.


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## jketelsen (Aug 25, 2009)

Thanks guys, I'll take a look at it again this weekend. I wish I could just pull the oil pan off and check the bottom end but there's not enough clearance to get the pan off.


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## mp4life23 (Apr 28, 2010)

Sounds exactly what mine did and i had a spun bearing the oil pump tube a screen fell off and i had the same syntoms oil pressure and everything


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## Eric Animal (Oct 28, 2007)

Hard to tell on sounds on a computer...it does sound sorta like a rod knock, but not deep enough..? Nice looking ride by the way....cool dog too! Good luck and keep us posted....Eric a couple too many trips over 5200RPMs?


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## jketelsen (Aug 25, 2009)

Eric Animal said:


> Hard to tell on sounds on a computer...it does sound sorta like a rod knock, but not deep enough..? Nice looking ride by the way....cool dog too! Good luck and keep us posted....Eric a couple too many trips over 5200RPMs?


Thanks Eric! Not sure what the previous owner did before I got it last year but I only know of one time I took it up there (guessing-no tach). It didn't start rattling until about 3 miles later putting through an addition. I'm thinking if it is a rod I blew more than cobwebs out of it and plugged an oiler or something. :confused


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## 68greengoat (Sep 15, 2005)

Holy cow, sounds like an old farm tractor! I know, I'm not being very helpful. Just wishing you luck from one '68 to another......


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## ALKYGTO (Mar 29, 2010)

Its your wheelwell trim vibrating off the body.

Seriously, have you had any detonation? Could be a cracked piston. Did you pull the plugs and look for any damage?

Good luck, that sure is a pisser, I'm going through a motor pull soon on my Grand Prix GTP.


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## Eric Animal (Oct 28, 2007)

My money is on a connecting rod.........done it 5 or 6 times myself.:willy:


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## jetstang (Nov 5, 2008)

And???
I want to see who is right, hurry up and tear that old beast apart.. If it's a spun bearing, it would still show oil pressure, but the oil would be blocked off by the bearing, correct? So, the oil should read artificially high due to the blockage.


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## jketelsen (Aug 25, 2009)

I know the suspense is killing me too! I'd like to see what I'm dealing with-simple fix or an excuse to start resto. Mama says gotta get some house projects done before I tear into her but I'm goin to try and get it on a stand in the next couple weeks to see what the damage is. I'll let you know who the winner(s) are. Thanks guys! Hey saw an ad on craigslist for a 68 tanked and fluxed YS block with a crank for sale about 40 minutes away, hmm....


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## Rukee (Feb 8, 2007)

Don't be so quick to write off the currant motor. If it IS a rod bearing and the motor has been running good, just pull and take the engine apart, rework the crank, (and the rod if the bearing spun in the rod) install new cam bearings, frost plugs into the block after having it cleaned, a high volume oil pump and new pick up screen, new set of bearings and you'll be good to go. :cheers


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