Possible rod knock?

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V8 Sam

V8 Sam

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So a few months ago I posted about possible lifter tick.

This noise hasn't rewlly gone anywhere all though it did quiten down with some additive but I haven't driven the car much. And what with it being summer I wanted to use the car still, but now the winter is here it's time to investigate.

The noise however is loud. Very loud. Even louder when I run the open pipes

So now I'm considering the possibility of rod knock.

How ever a few things that are making me wonder if this is the case:

The noise is not there from cold, and only creeps in after a good 35-40 mins of driving.

Knock/tick slowly fades out and goes completely once I let off the power. And dosnt always come back straight away when I put power back on.

The noise will go away at idle and idle and revving, it won't come back either. (Even more annoying to diagnose) has to be under some form of load.

Noise always matches engine speed

Oil pressure is still good.

I would of said if it had been rod knock it would be present all the time regardless?

Once I have some time off I'll get under the car drain oil, remove pan and have a wiggle of the rod ends see if anything is loose.


What are your guys input? Im still of the idea (hoping) it's lifters. But do they really get that loud?

Or maybe predet?

If I get a chance (weather permitting) I'll try get a sound video.

Thanks guys.
 
if it was a rod i'd expect it to be there all the time once the motor is warmed.


if its pre ignition get out your magnifying glass and go across all plugs
the one with little bits of metal speckles on it is the problem cylinder
you do really need an eye glass or jewelers loupe to see properly

or course you might just have piston slap
how old/ worn is the motor?
this should decrease somewhat when hot because the piston expands slightly. but worn bore and skirt it can be there all the time.

fist things first though check the exhaust manifold gasket this makes a tick when there is a section blown out

Dave
 
PS
pre igntion gets worse under load
gets more aggressive the more the engine lugs.. up hill in wrong gear type lugging
is really a sound and a feeling of dunt dunt dunt....duntdunt...dunt
which is random but aligned with rpm
goes away usually as soon as load is removed.
will eventually result in a big end problem or a cracked piston or damaged rings

Dave
 
In my experience, when a rod bearing goes, it is unmistakable;
get under the car and sound the pan.
DO NOT drive the car with a knocking rod, it will only get more expensive.
I have saved my engines several times, by NOT driving it, and rolling in a new bearing. My oilpan has a reusable gasket on it, lol. Zip-Zip, on a hoist, she's in and out in a few hours.
Isolate which cylinder is making the noise, which is usually a double tap, once at each end of travel. I'm gonna say, tucka-tucka-tucka... then Remove the spark from the suspect cylinder. This will reduce the chamber pressure under compression and reduce the volume.
The sound of a loose rod-bearing, to me, cannot be mistaken for any other engine sound. well except maybe a fuel-pump pushrod on engines that have those, NOT SBMs.
However, there are a couple of sounds that can be a close second.
#1) is crankshaft end-play, which is a random sound, coming and going sometimes with no pattern. and
#2) is a loose flexplate which is almost identical to the rodknock, but without the echo of the pan, and it is usually quieter.
#3) I've only ever had one factory flexplate crack on me. It was to me, not of the same volume or intensity, and was missing the reverb of the pan.

to understand the reverb /echo, just tap the oilpan with a light hammer with the engine off. You'll hear it right away.
Endplay is easy to check from underneath
the Flex-plate is a lil more difficult to check,
but hey, you can take solace in knowing that, the metal cover has to usually come off anyway, to remove the oilpan; lol.
I promised myself the last time, that if my Milodon Roadrace oilpan ever had to come off again, I was either taking the engine out, or dropping the K.
 
The motor is fairly old. Never had an issue though, plenty of power still.

Did 40 odd miles the other day before the sound came back with in the last 5 or so miles

If this was piston related I would expect the noise to be there from cold? to which it is not? This noise is ONLY when warm.

Also sorry should of said Car is also a 4 speed manual
 
Well, I guess we can rule out flex-plate then, lol.
But that then brings crank end-play back, as every time you step on the clutch, the thrust-bearing takes the hit.

This is an easy test,
What I do is climb under the car, and remove the flywheel tin, then stick a prybar up there between the flywheel and the pan, then take a prybar in your other hand and stick it between the balancer and the pan.
Next, pry the crank one way then the other. if you hear the deep thunk-thunk, then you better measure it. IIRC it should be more than zero, but less than .010
If this is your problem, fix it ASAP, cuz eventually the flywheel will grind a groove into the rear cam plug and boss, which is gonna cost you more money to fix, ask me how I know, lol.
 
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BTW, is that a pink 1970 DartSwinger?
I bought a slightly used one back in fall of 1970, 340/4-gear/3.55s similar color, Panther-pink I think they called it; I was just barely 17.
I got a sweetspot in my heart for those
 
Could also be flywheel to crankshaft bolts.
From the description of how it “comes and goes” it isn’t a rod or piston.

Lifter noise can come and go with temp changes, and change with an additive.
Rod and piston noises don’t come and go generally.
They would sound one way cold then change as the engine warms up. You wouldn’t be driving 40 miles without it making noise if you had a rod knock.

Believe it or not, even a belt can make a pretty loud knock type sound.
 
I’m thinking it’s not a rod bearing cause you have oil pressure when warm.
 
We did this last June, - Could be this/that, asked for vid then too .

There are hundreds of moving parts in there Sam, - mosta them we listed then, - just a few seconds of video, pls .
 
If it’s any kind of bearing problem the evidence WILL be in the oil filter. Cut it open and look.
 
Yeah will grab a video etc soon as I can. Just had a spare few moment at work today thought id drop a message in ✌️
 
V8 Sam said:
Yeah will grab a video etc soon as I can. Just had a spare few moment at work today thought id drop a message in ✌️
Click to expand...
"What TT5.9mag said". You want to take the element out into the sunlight and have a good look. Bearing material doesn't always show up in "big pieces." I've seen bearing material look like gray sludge.
 
The noise. Engine idling [ making the noise ], short out each spark plug one at a time. If it makes no difference, problem is unlikely to be individual cyl related. If the noise stopped/reduced, you have found the offending cylinder....
 
I had a weird knock on a new to me 318, it did have low oil pressure though when warmed up. I pulled the oil pan and the pickup was almost completely clogged with broken pieces of umbrella seals. Sadly it had been run long enough and spun a rod bearing. Thats the noise I was hearing. Might want to peek inside the pan.
Good luck.
 
I had a knock that I thought was a rod knock on a 340 once and found out it was a cracked vibration damper hub. It had cracked in the keyway and had opened up just slightly but was enough to make the knocking noise.
 
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Maybe...Exh leak cracked header at flange...
Wrist pin...
Scuffed or cracked piston skirt..
Bad valve spring.. rocker hitting retainers..

Does it sound like a hammer hitting an anvil or is it hollow like a couple 2x4s hitting one another
 
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