Uh Oh !! Bad knocking !!

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dartman59

dartman59

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Something bad happened to my motor on the way into work this morning. I have a 408 stroker LA Small Block, 4-speed manual, relatively mild cam.

I really romped on it getting on the highway, really winding it out in second and third, and just before shifting into fourth it started making a horrible knocking. Shuddering with each knock. Oil pressure remained constant, no change in the air fuel ratios in either header collector. I did notice as I continued down the highway that the temperature rose just a little bit--maybe five degrees. It would run at idle but as soon as I would give it gas, knocking would start really bad. I don't know what has happened! Any clues??

I have MSD ignition with rev limiter set at about 5500 rpm. I hit the ref limit in second before shifting to third, and was about to hit it in third when the knocking started, at about 5400 rpm. It feels to me that the knock is in the top end, but I haven't done anything to try to confirm this. I drove it another ten miles to the parking garage in the city, taking it easy, and that's where it still sits.
 
Oh--one more thing--oil pressure seemed to remain constant through the the whole thing, with about 60 psi at 2500 rpm and 35 at 850 rpm.
 
That's a rod end bearing, my friend.
You may be able to open it up and polish the journal a bit and not have to pull it apart.
If you try this, you MUST baby the motor for a while until that new bearing seats.
 
dartman59 said:
It would run at idle but as soon as I would give it gas, knocking would start really bad. I don't know what has happened! Any clues??
Click to expand...

I would suspect a rod bearing. Irregardless, time to tear it down.
 
It's a really loud knock, and it feels as if one of the cylinders is firing every once in awhile but mostly not. But funny there was no change in A/F ratio in that bank ( I have an O2 in each header collected).
 
With a 10 mile drive with 3.55s say I get nearly 27,000 revolutions; Ima thinking the journal may be beyond hope.

I drove a mile on a barely perceptible squeek. The 340 crank is still in the shed.I had a spare.That was just 1/10th as far
 
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sure sounds like a rod

sucks

time to drain the oil and look for a metallic shine
maybe cut the oil filter and see if there are any shavings in there
 
I had a terrible knock under load but would mellow out under lo-no throttle. I made it home by just barely gassing it in 5th in the slow lane. It was cheap, only a blown head gasket between 2 cylinders, no fluid loss. Good luck.
 
Before you jump on the rod bearing theory. Cut the oil filter open and see if it has metal flacks in it. Pull the valve covers check for rocker arm push rod issue. Look more into it.
 
I'm hoping for Pishta's story, that's for sure. That could explain the 5-deg rise in temperature. I didn't look into the coolant yet (it's still in the parking garage at work--I took an Uber home). Or, something like SGBARRACUDA's suggestion would be nice. I was thinking it might be a rocker arm issue because the sound seems to be coming from the top not the bottom, but that's a big guess.

Well, fellers, I hate to do it to ya, but it's probably going to be a few days before I can give you more information and/or take a closer look. Me and my wife are moving tomorrow (I know--buzzard luck), and I'll be putzing around in the modern sedan for the next week or two. This time of year, the Dart is my daily driver. I hate to see her laid up like this !!
 
It may not be a rod bearing, normally you'd see a drop in oil pressure unless the bearing is friction welded to the journal. Best case scenario may be something in the clutch/flywheel end of it.

Just thought of something real bad--What crankshaft? Eagle cast cranks have been known to break. I have seen many engines with broken cranks still run and run OK but with horrible sounds. Hope you find something in the clutch end of it. J.Rob
 
Darthomas said:
That's a rod end bearing, my friend.
You may be able to open it up and polish the journal a bit and not have to pull it apart.
If you try this, you MUST baby the motor for a while until that new bearing seats.
Click to expand...

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^This right here is false and I feel a need to correct stuff like this when I can. First, bearings don't seat, seating implies contact/rubbing/wearing and if you're bearings are making that much contact you have big problems. Second, polishing a crank journal does not address it's out of round condition--rod knocks creates egg shaped journals, guaranteed. Slamming a new bearing in will ensure that you get to do this job again. J.Rob
 
I had a bad rod bearing and didn't get the oil pressure fluctuation. I think I caught it early.

Run motor and pull plug wires on and off. When one clyinder sounds different than the others, that's the clyinder that is the culprit.

This is what it sounded like for mine. I did pull valve covers and no issues Up there....



 
since were posting clips...here is my 360 with a rod bearing gone

"]20150706


and here is that same engine, rebuild as a 408 with a alternator belt that is too tight



the second video, the noise went away when I loosened the alternator/ac belts
 
dartman59 said:
it started making a horrible knocking. Shuddering with each knock.
Click to expand...


just re-read this
shuddering with each knock

have you checked if it makes a racket in neutral, while to car is standing still ?
because a bad shudder with a knock reminds me of the time I blew a cap out of the driveshafts U joint
 
Well, I sure didn't check my driveshaft, and it would blow my mind if that's what it was. I appreciate the thought, and I will definitely check it. The shudder was related to engine speed, not vehicle speed.

I listened to the videos, and they don't sound exactly like my issue. I won't get back to the car until late next week, but I'll check back in here when I do. I sure do appreciate everyone's two cents, and I sure am hoping it's a head gasket !!! :)
 
not totally grasping at straws, but just thinking out loud

would be nice if it is something simple, but you never know
 
I DID clean-up a rod journal after mild knocking and did sucessfully put in a new Cleavite 77 bearing, and drove the 318 another 15,000 miles with no knocks until I bought a 340 short block.
I know people who used old leather belt sections to replace rod bearings and drove the car another 5 years with no problems, but I'm sure they babied it.
 
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