Exhaust sounds like machine gun when I accelerate

[mweist]

Porsche 911SC, 1981

All,

Next drama. when I accelerate and apply a large amount of accelerator (like passing a car), I get a tatatatatatatatatat. Sounds like an M60A1.

Anyway, when I take my foot off the accelerator or slow acceleration the noise goes away. It is easy to control - just don't gun it!

Any opinions?

Thank you.

MikeW

P.S. love the spell check feature!

[DRACO A5OG]

Chain Tensioner?

Have a friend video tape it and post here

[techman1]

Head slap, due to broken head studs?

[Josh D]

Originally Posted by techman1

Head slap, due to broken head studs?

This would be my guess as well.

Pull lower valve covers and see if anything falls out.

[Peter Zimmermann]

Might be an exhaust leak, but the symptom is classic for escaping exhaust gasses from a cylinder head/cylinder that has become loose as the result of broken head studs.

FYI; At this point, if the cause is failed head studs (highly likely) every time that the car is driven more damage will result.

[mweist]

Thank you all!

[steenkamp]

Originally Posted by mweist

Porsche 911SC, 1981
Next drama. when I accelerate and apply a large amount of accelerator (like passing a car), I get a tatatatatatatatatat. Sounds like an M60A1.

That's not ok. It is supposed to sound like a MG 42.

[Joe Bob]

If it sounds like playing cards in the bicycle spokes, it's head studs.

Pull the lower valve covers and look for bolts with snapped head studs.

[TJJSC]

funny, history is repeating itself?..

Engine Flapping Noise 911sc

[cabmandone]

My brother had his distributor go bad and I think it caused all kinds of popping.
The best suggestion I saw here was to take the valve covers off and look for broken studs.

[mweist]

tell me the truth, do I have to remove the engine to ultimately fix this?

[timmy2]

If the head studs are the problem, yes pull engine and tear it down.

[cabmandone]

Originally Posted by mweist

tell me the truth, do I have to remove the engine to ultimately fix this?

If the head studs are shot, yep. Don't panic, find out what it is and move forward from there. My brother drove his 3.0 for a few years with broken studs knowing he was going to be transplanting a 3.2 in later. If you check around I don't think the distributor wearing out is all that uncommon but neither are broken head studs. Plan for the worst and hope for the best.

Does it only do this under load are will it pop setting still in neutral?

[TCracingCA]

Well actually second thought after reading the other responses and that first thought actually would be no comment!

I would think it is severely leaning out and the problem is how the timing is firing off a bad mixture at the higher rpms!

The head studs would be a different sound than you described and you would probably pick that up in the lower rpms also!

[don gilbert]

sound like head to jug seal has expired..this is the end result if you keep driving it. Lots of expensive machine work,,

[DRACO A5OG]

Originally Posted by TCracingCA

Well actually second thought after reading the other responses and that first thought actually would be no comment!

I would think it is severely leaning out and the problem is how the timing is firing off a bad mixture at the higher rpms!

The head studs would be a different sound than you described and you would probably pick that up in the lower rpms also!

Hmmm? Was it hot when the "machine gun" sound occurred? HI Engine Temps plus Too Lean situation could sound like a "rat tat tat..." when accelerating.

[Dan J]

Maybe you got: https://www.youtube.com/watch?v=0TIZb8d87AI

[mweist]

The engine noise only appears in gear and in acceleration. At idle, it will not pop, though it almost sounds like it could if under stress.

[mweist]

It's definitely not Phil Avlin and his 'One bad Stud'!!

[Dan J]

Maybe it's 2 bad studs?