LOUD tapping noise coming from valve train...

[c.moser]

Last night on my way home from work something broke in my engine. I have a 98 GT. It sounds like it's coming from the top of the passenger side cylinder head. The sound is like a really, REALLY loud tapping sound. The car runs but the idle is really low and when it happened, the rpms would hang around 1800-2000 when I pulled in to my drive way. It happened when I was 2 blocks from my house. I heard a faint snap/pop sound and then the constant loud tapping sound.

The car came with a limited power-train warranty so I'm going to have the dealer look at it but does anyone have any suggestions what it could be? I know the 5.0 engines pretty well but the 4.6 is all new to me. I haven't really worked on them before. I tried the search function but nothing helpful came up. Thanks for any input

 

[bhuff30]

Hard to say without seeing the engine... but it is somewhat common for the 4.6 to blow spark plugs out. You may have popped one out. If not, then something could have broken in the valve train... lifter, rocker arm, whatever.

Sounds lucky if you still have some sort of warranty.

 

[trinity_gt]

I'm guessing a rod bearing even if it sounds like it's coming from the top. What were you doing when this happened? Any high-RPM shenanigans? Does the car have a dead cylinder now?

 

[c.moser]

That's the most irritating part. This car has 53,xxx miles on it and I seriously drive this thing so easy and slow. I was gently pulling away from a stop sign when it happened. The rpms were around 1600-1800. I don"t beat on my cars at all anymore, it's just not worth it. Of course I did when I was 16, 17, 18, ect.. but I grew out of that. I'd rather take a nice cruise and keep the car looking and driving nice than beat the piss out of it

I'll check the spark plugs, but I'm guessing it's something much worse due to how loud the tapping sound is. It doesn't feel or sound like it has a dead cylinder...

 

[ItsStock02]

Sound like this?

YouTube - mustang 4.6 2v spark plug blow out

 

[trinity_gt]

If the tapping varies in loudness/intensity with engine load and/or RPM, it's probably a rod. If the tapping is pretty constant no matter the load and happens at roughly half the engine speed, think valvetrain.

I'd expect anything in the valvetrain causing such a loud tap or a plug blow-out to cause a dead cylinder. If you're not feeling that then this again suggests a reciprocating assembly failure of some sort. It may be a piston has cracked (and the noise is a wrist-pin knock as a result) but again, the conditions when it occured make this unlikely.

It's unusual to have a breakage occur under the conditions you mention. I've read of 4.6s spinning a rod bearing at high RPM and it's usually due to oil starvation. But if you were just puttering around with a low-miles engine that's pretty strange.

You might invest in an automotive stethoscope to try to isolate where the noise is coming from. If it's at the top of the engine and near the front, perhaps you've got a timing chain issue of some sort. If it's loud near the oil pan think rod bearing. You might also disconnect the each spark plug on that bank to see if you can change the intensity by killing a cylinder. (If you remove a plug wire, be sure to stick an old plug in the end and lay it on the cylinder head during this test to protect the coil). If the noise abates when a given cylinder is killed you're definitely looking at a piston or rod issue.

 

[c.moser]

ItsStock02,

That sounds very much like it! This is probably a very dumb question but is it just a matter of putting the spark plug back in or would the thread be messed up on the head? In the replies on that youtube video, people mentioned having to replace the head?

 

[bhuff30]

Sounds very likely it is a blown out spark plug. The threads in the head will be gone, so it won't be so simple as throwing in a new spark plug unfortunately. You can search the forums for fixes, and there are many different routes to take with varying cost and reliability. Pretty much anything from a simple thread insert to replacing the entire head. Just depends on how permanently you want it fixed and how much you want to spend, and you'll have to weight that out for yourself.

I am pretty confident it isn't a rod bearing. Normally, rod bearings will start making noise very faintly and get louder and louder over a period of time. You described this noise as a sudden event which made me think it was a plug blowout (or broken valve train). Also, a rod bearing is most noticible around 1500-2000rpm at light loads, and the noise can go away completely at high loads and high rpm.

 

[trinity_gt]

I hope it's a simple as simple as a plug (though if it were, I suspect that cylinder would be dead and the OP said "...doesn't feel or sound like it has a dead cylinder...")

Fingers crossed...

 

[Rejekt]

Mine did that. It blew the COP apart and broke the plug in half.

It sounded like **** when it went. A loud POP and then it kept making a terrible noise with the RPM's going nuts and it sounding like it wanted to die out. My CEL came on too.

I replaced the plug and COP and it has been perfect ever since.

Autozone for the COP and it was like $35 bucks


Hope it's an easy fix man.

 

[c.moser]

I looked really quick last night and sure enough one of the spark plugs popped out. It was raining out and dark so I didn't attempt anything yet. Hopefully this afternoon I'll get to see what's going on a little better.

Rejekt, your threads on the cylinder head didn't get messed up when it happened to you?

 

[ItsStock02]

When one of my plugs blew the threads were fubared. I tried putting a new plug in and it would just keep spinning and never tighten up. Ended up paying my aunts mechanic $100 to put an insert in. I think he used a heli-coil, but I havent taken the new plug out yet to check.

 

[c.moser]

What is a heli-coil?

 

[trinity_gt]

What is a heli-coil?

Heli-Coil | HeliCoil Inserts | Helicoils Screw Thread Inserts | Emhart Teknologies

 

[ItsStock02]

Yep thats its. I bought the timesert kit, but gave up on trying to do it myself. Called him up and he told me he has his own inserts. Either way its held up since January. I did an oil change in August and made to re-torque all the plugs down again.

 

[Rejekt]

I looked really quick last night and sure enough one of the spark plugs popped out. It was raining out and dark so I didn't attempt anything yet. Hopefully this afternoon I'll get to see what's going on a little better.

Rejekt, your threads on the cylinder head didn't get messed up when it happened to you?

Nope, put a new plug in and it threaded perfectly. No problem since.

 

[c.moser]

What brand spark plugs are you guys using? Are autolite's ok? I found out these are Bosch Platinums and I read they aren't good to use?

 

[N8Dogg98]

IIRC, the autolites don't have many threads and people have had troubles with them blowing out of the heads (thought I heard this somewhere ) If it were me, I'd stick with the Ford motorcraft replacements. Get copper's if you don't mind changing them every 10-15K miles and like having a more powerful spark, or get the platinum's if you don't want to change them for 100K miles at the expense of slightly less powerful spark

 

[joshjwc9]

Actually, I've heard the Autolites are made by Motorcraft, or vice versa. But, I've had one spark thread blowout and it was a Bosch platinum or double platinum ICR though. Happened to me twice so I just had a reman head put on. Lesson learned, I make sure that mine are torqued to the correct rating 13-15 ft lbs.

 

[ItsStock02]

I have autolite 103s. They're copper and 1 degree cooler than oem ones. Before them I had Motorcraft platinum ones.

And the threads on the sparkplug wont really matter. They can be fully threaded, but only the bottom half of the threads will be threaded into the head since the head only has 4 or so threads.