409 Knock

[DonSSDD]

I have a knock in my 409. It doesn’t seem to be there when you first start it up, but starts after it starts to warm up. With a broom stick against the block you can feel it in your hands and I also can hear it when I had it running with the fan belt off- no water pump or generator running.

It is a 63 340HP 409, just rebuilt, 10 over on the crank, line bored, 30 over on the pistons, stock cam, stock oil pump, just fired it up for the first time. It has about 30lbs oil pressure at idle, starts well, and the knock wasn’t there until now. I may have run it a total of 2 or 3 hours before the knock appeared. I am not an experienced mechanic, but it sounds like a knock, not a tick like if it was a lifter/valve issue.

It runs normal temp wise, plugs, oil, and anti-freeze are normal as well.

The engine work was done by a very reputable shop- they put the bottom end together, plus installed the heads and set the valves. I did the rest of the install.

It has a stock oil pan, distributor, exhaust manifolds, the bell housing, block mounted starter, clutch, PP, and transmission from the 59. I removed the pans from the bell housing due to the upper one rubbing on the end of the crank.

What can knock other than something inside the block?

Brings back memories of George Carlin- the seven words you can’t say on TV have come to mind several times.

Thanks,
Don

 

[Ronnie Russell]

Don, I will take a guess. The beginning of a rod knock. Easily dianosed. Keep driving and if that is so, it will get louder and louder. What I believe is probably the real cause is piston pin knock. Faint but steady. Not an issue. Will run for years. Just my opinion.

 

[skipxt4]

Don: If this isn't stressful, I don't know what is. You're kind of lucky, in a sense. Your machinist assembled your engine. Guess who has to make it right. That's right. I hope you get it straightened out, soon. Skip

 

[Old School]

Don, that makes even my stomach turn…

I experienced a similar knock after startup of a new rebuilt 409. Turned out to be one of the camshaft gear hold down bolts hitting the timing gear cover. Got lucky, it was an easy fix.

You might take a listen up front to rule that possiblity out first.

 

[pg409]

Try checking the fuel pump push rod. I have seen many
sbc and bbc engines pulled for a very small, simple item.

If memory serves me right, the rod is the same as 283 Chevy
however I assembled my 340 horse about 6 years back.

 

[Tom Kochtanek]

Oil pan?

I had a rod bolt that felt it needed to nestle up against the oil pan every cycle, made a reciprocating sound (but not a knock, more of a scraping sound) that was clearly a "rotating" sound, if you know what I mean.

Perhaps the engine builder needs to come over to your house (or wherever the vehicle resides) and put his ear to the test?

Good luck, I hope you sleep well and don't get overly stressed about your new engine build .

Best,
TomK

 

[mac1]

Sorry to hear that. Try removing the spark plug wires one at a time and see if the sound goes away. Could be what Ronnie said or piston slap. Either way, this test could help isolate where it's coming from. I had a similar noise on a 327. I started using Mobil one full synthetic and the sound eventually went away.

 

[bubbletop1961]

All good sugestions. I would talk to the shop that did it. No reason to make it worse unless the shop will warantee it. But even then, Do you have an extra 409 around just in case it is something important. Its coming on winter and plenty of time to fix something now.

 

[Fathead Racing]

Did you pre lube the engine before breakin?

 

[petepedlar]

Check the harmonic balancer & make sure it's tight !! ....... I had a small block years ago that drove me nuts trying to figure out what was making a knock...... the engine was about 6 months old......... the balancer was loose.

Dave

 

[bubbletop1961]

Check the harmonic balancer & make sure it's tight !! ....... I had a small block years ago that drove me nuts trying to figure out what was making a knock...... the engine was about 6 months old......... the balancer was loose.

Dave

And torque convertor bolts. They can sound like something really bad if they loosen up. And the sound will change with rpm.

 

[walkerheaders]

let me toss some more into the mix...........

a cracked flexplate will sound real bad.

and once a friend had a baffle spotweld break in his oilpan sounded like hell. easy fix.

 

[DonSSDD]

Thanks for all the replies- I'll make my way through the list and see if it is anything easy.

Don

 

[DonSSDD]

Knock is on the driver side, checked for noise on the fuel pump, timing chain cover, nothing and the harmonic balancer bolt was tight.

You can feel the knock in your hands when holding the broom stick, disconnected the 4 plug wires on the driver side, no change in the knock until I removed #1. It got louder with the wire off.

A bearing?

Don

 

[models916]

Is it a 409 pan?

You say everything from the 59. 348 pan needs work with a hammer up front to clear everything. Still, pulling a plug one at a time is easy to do and may show what cylinder is suspect. Exhaust leaks sound serious sometimes.

 

[vin 58]

This sounds like a problem I once had with a 350. The thing sounded like a diesel. Come to find out it was a piston slap. The engine was rebuilt at onetime and all that was done was a cylinder hone with oversize rings. The funny thing is I drove it then sold it. The last time I saw it someone was delivering pizza with it. vin

 

[mac1]

Knock is on the driver side, checked for noise on the fuel pump, timing chain cover, nothing and the harmonic balancer bolt was tight.

You can feel the knock in your hands when holding the broom stick, disconnected the 4 plug wires on the driver side, no change in the knock until I removed #1. It got louder with the wire off.

A bearing?

Don

I believe piston slap happens on the power stroke. Sound should go away with no ignition, right? Do you have an automotive stethoscope?

 

[DonSSDD]

No stethoscope Mac.

I guess I should drop the pan.

Don

 

[Ronnie Russell]

Don, Maybe you addressed this earlier and I missed it. Is there a way to drive or trailer the car to the engine builder?

 

[DonSSDD]

Ronnie, it is about 20 miles, so a drive would be hard on my nerves. I will see if I can get him to come listen to it. His shop is not large enough for the car- and it has been snowing here as well.

Don