Noisy 351 Cleveland

[Jayro]

Hey guys,

So had the car out for a long run yesterday after getting it back from the shop getting the C4 serviced and all the transmission leaks fixed. All good it seems on that front.

Still got what appears to be a tear main seal leak to sort which will get done in the coming weeks.

However my main concern is the engine. Don’t get me wrong, starts and runs fine. Not Smokey or anything. Runs smooth. BUT once I’m doing more than 50 mph and the second my foot hits the accelerator it has a filthy rattling noise. The second I lift my foot that noise stops.

Any suggestions?

Cheers
Jase

 

[71ProjectJunk]

Could it be pinging? You know detonation, knocking...

 

[Jayro]

Could it be pinging? You know detonation, knocking...

I’m not knowledgeable enough to know. It’s certainly not a knocking noise, it’s more of a “tappet” metal fluttering type noise. If I’m making any sense lol

 

[71ProjectJunk]

It is very difficult to describe, but it sounds like a rattling noise, like a can of full of marbles that you are shaking around, that are at a distance from you, like muffled. I found 2 videos on YouTube. There is a motorcycle video where you can clearly hear it, but it seems maybe a bit louder, or closer than what you hear in a car, and then there is a truck video where it is very hard to hear, but you can hear it if you pay attention.

 

[Jayro]

Thanks mate, appreciate that. I might actually take it for a run tomorrow and see if I’m able to record mine making the noise.

 

[Superbond]

71 projeckjunk sounds right
Check your timing and for vacuum leaks

 

[Superbond]

Oh
And buy the high octane gas

 

[AcesArneson]

Hey guys,

So had the car out for a long run yesterday after getting it back from the shop getting the C4 serviced and all the transmission leaks fixed. All good it seems on that front.

Still got what appears to be a tear main seal leak to sort which will get done in the coming weeks.

However my main concern is the engine. Don’t get me wrong, starts and runs fine. Not Smokey or anything. Runs smooth. BUT once I’m doing more than 50 mph and the second my foot hits the accelerator it has a filthy rattling noise. The second I lift my foot that noise stops.

Any suggestions?

Cheers
Jase

Do you have points?

 

[Stanglover]

Can you tell us a bit more about your motor. Has it been rebuilt and if so, do you know what was done to it. Is it a 2V or 4V motor? Is it the original 73? Tell us what you can about it.
Definitely put the highest octane fuel in after depleting the gas in the tank, and see if that improves the noise.
If you're not able, have a trusted mechanic listen to the motor with a stethoscope, for that noise while revving the motor past 2K (stationary of course!!) Maybe have him (or her) test drive it with you. He/she might be able to narrow it down.
Sometimes it's a matter of elimination.
If it is still there with high octane fuel, check the timing and get back to the forum with the results.

 

[will e]

Certainly sounds like pinging from your description.

 

[SteveO_71]

Sounds timing related, so check your timing. See what the initial timing is set for after removing and plugging vacuum advance line. Maybe set it for 6 - 10 BTDC. Then see when the mechanical advance kicks in and when and what the timing maxes out as.

 

[Don C]

Exhaust manifold leaks and loose spark plugs can also sound like engine knock.

 

[73inNH]

Sounds odd that it only happens after 50mph. You can probably induce pinging under 50mph in a higher gear going uphill.

If it's speed dependent, maybe driveshaft out of balance?

Pinging is typical, but seems odd to tie it to speed.

 

[Stanglover]

Sounds odd that it only happens after 50mph. You can probably induce pinging under 50mph in a higher gear going uphill.

If it's speed dependent, maybe driveshaft out of balance?

Pinging is typical, but seems odd to tie it to speed.

I think that is more related to rpm's than speed. 2k is about where my car is at 50 mph. If he jumps on it from that point and it starts pinging or making more of a rattling noise, timing is what I'd look at first.
Unfortunately, I don't think our friend is that mechanically minded and that's ok, but he needs to find someone who is and can set this car up for him.

 

[73inNH]

I think that is more related to rpm's than speed. 2k is about where my car is at 50 mph. If he jumps on it from that point and it starts pinging or making more of a rattling noise, timing is what I'd look at first.
Unfortunately, I don't think our friend is that mechanically minded and that's ok, but he needs to find someone who is and can set this car up for him.

Makes sense.

 

[Jayro]

Thanks for all the replies. Will book in with my mechanic to go over it and certainly check timing etc. get him to go for a drive in it and show him 1st hand the noise.

Ah so the car was imported from the in 2019. Was originally a 6 cyl model before being fitted with the 351 and C4 combo.

I only run 98 fuel in it. Also if say I’m driving on a flat road at 50mph and then accelerate to go UP a hill the car sounds great. Throaty exhaust. But if I was to go down hill under no load and accelerate then she will “rattle”. The second I lift my foot off the accelerator no noise.

 

[71ProjectJunk]

You have 2 wires in the back of the distributor with tape on them? Do you get spark coming off them? You need to take a look at that and see why those wires are like that, maybe you have 2 adjacent wires that are damaged and they are arcing from one to the other. Maybe they were arcing to the air cleaner and someone put the electrical tape on them, but if they are arcing, those wires are probably no good. You can usually fix an issue like that on a wire, by dissembling that part of the wire, and if there is a cut on the wire where the arcing is coming from, you cut that part out and reassemble the wire correctly, correctly being the keyword here. That could have been a universal wire set, and whoever assembled it did not know what they were doing, and you are getting arcing out of them.
Do this simple test. Disconnect the vacuum advance from the distributor and plug the vacuum hose with a screw or something of the sort. take the car for a spin and see what happens. By stating that it does it going down hill under no load, where you have high manifold vacuum which means high vacuum advance, and then you accelerate and it "rattles" it probably means (if what you are hearing is pinging) that you have too much advance at initial tip in, and it will rattle until the vacuum goes down and the vacuum advance goes away. This may be as simple as your timing is too far advanced.

 

[Jayro]

You have 2 wires in the back of the distributor with tape on them? Do you get spark coming off them? You need to take a look at that and see why those wires are like that, maybe you have 2 adjacent wires that are damaged and they are arcing from one to the other. Maybe they were arcing to the air cleaner and someone put the electrical tape on them, but if they are arcing, those wires are probably no good. You can usually fix an issue like that on a wire, by dissembling that part of the wire, and if there is a cut on the wire where the arcing is coming from, you cut that part out and reassemble the wire correctly, correctly being the keyword here. That could have been a universal wire set, and whoever assembled it did not know what they were doing, and you are getting arcing out of them.
Do this simple test. Disconnect the vacuum advance from the distributor and plug the vacuum hose with a screw or something of the sort. take the car for a spin and see what happens. By stating that it does it going down hill under no load, where you have high manifold vacuum which means high vacuum advance, and then you accelerate and it "rattles" it probably means (if what you are hearing is pinging) that you have too much advance at initial tip in, and it will rattle until the vacuum goes down and the vacuum advance goes away. This may be as simple as your timing is too far advanced.

Ok thank you. Going over it now. Apologise for the dumb questions but just checking if there is any issue with these items seemingly being uncapped?

 

[Jayro]

You have 2 wires in the back of the distributor with tape on them? Do you get spark coming off them? You need to take a look at that and see why those wires are like that, maybe you have 2 adjacent wires that are damaged and they are arcing from one to the other. Maybe they were arcing to the air cleaner and someone put the electrical tape on them, but if they are arcing, those wires are probably no good. You can usually fix an issue like that on a wire, by dissembling that part of the wire, and if there is a cut on the wire where the arcing is coming from, you cut that part out and reassemble the wire correctly, correctly being the keyword here. That could have been a universal wire set, and whoever assembled it did not know what they were doing, and you are getting arcing out of them.
Do this simple test. Disconnect the vacuum advance from the distributor and plug the vacuum hose with a screw or something of the sort. take the car for a spin and see what happens. By stating that it does it going down hill under no load, where you have high manifold vacuum which means high vacuum advance, and then you accelerate and it "rattles" it probably means (if what you are hearing is pinging) that you have too much advance at initial tip in, and it will rattle until the vacuum goes down and the vacuum advance goes away. This may be as simple as your timing is too far advanced.

Oh sorry old pic. I’ve replaced the plugs and leads

 

[will e]

That's weird. It does the rattle accelerating down hill and stops as soon as you lift your foot but up hill it sounds normal under acceleration? I am stumped but I will think about it some more.

Those things with the missing vacuum lines were used for emissions controls. Without vacuum lines connected they do nothing. It's not the source of your problem.