Bad engine noise in 2.7 Middie - Detonation?

[NeedSpace]

{FOLLOWUP NOTE-Noise was NOT detonation but a rocker arm that had come loose, skip ahead to see}

OK Pelican braintrust, my 2.7 has taken a bad turn. I was driving it at about 65 and suddenly it started making a very concerning noise. Keep in mind, the engine has been running wonderfully for a few years with no big issues. I pulled over and had it towed home. There was a bad oil leak (not a drip like I usually get but a bit of a stream) that was uncharacteristic of my girl. I had started posting this in my long thread but thought it might me more interesting to get this in a single thread.
1976 911S – from garage find to on the road



Here is the noise it was making. This is the noise before taking anything off the car. At first I thought it was a banging but now I feel pretty confident it is an untimely detonation (or hoping...) {FOLLOWUP-NO, rocker arm NOT detonation}



Since then, I was able to take off my heat exchangers with little fanfare and had a better look. This is what cylinder 4 looks like from underneath.



This is what it looks like when running from underneath. Interested in all ideas...

Notice cylinder 4 doesn't appear to be firing and there is an oil leak very close to that cylinder.

[emac]

That sounds like metal on metal. Bad rod? It doesn't sound good sorry to say
Ernie

[2cam]

As mentioned in the other thread, check the rocker shafts/rockers on that bank.

2cam

[Dan J]

Are both valves opening? Does it perhaps have a broken exhaust rocker?
I've heard a bunch of sick 911's over the past 37 years but that's a new one on me

[Walter_Middie]

NeedSpace,

That is not detonation.

Sounds like timing may have skipped - as in cam timing. The cam timing chain may have skipped a tooth. Pull the timing chain covers and see if the chain tensioner on one side has collapsed. Or you could check cam timing on #1 and #4 - it only takes a few minutes on these old cars with nothing in the way.

While the valve covers are off, check for broken rockers.

[DRACO A5OG]

Yeap, open the valve covers and look at the rocker/shaft.

You Must CHECK the Rocker Shaft Bolts when you DIY Valve Adjust!

Here is the fix:
964 Cams Swap Journey

[NeedSpace]

Holy crap that sounds EXACTLY the same. Once my kid goes to bed, I am headed out to the car. I'll bet that is it. Hopefully, it hasn't done too much damage.

[DRACO A5OG]

I bet it is the lower rocker shaft.

Don't worry, if rocker did not snap, it will just be sitting in the valve cover. Don't worry about oil loss, some will drip out but not much, just be prepared.

[boyt911sc]

Needspace,

What was that fluid coming out from the engine after the engine stopped running? Gasoline? Do you still have the fuel injection system?

Tony

[NeedSpace]

You guys are the best. I took off the valve covers and sure enough, look what I found!



This is exactly what I DRACO reported on in this link, thanks!
You Must CHECK the Rocker Shaft Bolts when you DIY Valve Adjust!

Thanks for the reference, this was perfect.



A quick inspection of the rocker arm and the shaft looks like there is no damage. But shouldn't the shaft have 2 gaskets that this is not showing? If so, it could explain a lot of the extra oil I get on my covers that I haven't been able to resolve.

[DRACO A5OG]

No Brother, stock has no seals, the RSR seals is an update/upgrade.

Take a closer look in day light and inspect that Cam Lobe carefully by hand cranking her. Please disconnect the battery

While you are there check all the shafts for possible movement/looseness per my thread above

[NeedSpace]

Originally Posted by boyt911sc

Needspace,

What was that fluid coming out from the engine after the engine stopped running? Gasoline? Do you still have the fuel injection system?

Tony

Tony,

I am trying to keep my car fairly stock so still using the bosch mechanical fuel injection. That liquid is a whole lot of oil.

[NeedSpace]

Originally Posted by DRACO A5OG

No Brother, stock has no seals, the RSR seals is an update/upgrade.

Take a closer look in day light and inspect that Cam Lobe carefully by hand cranking her. Please disconnect the battery

While you are there check all the shafts for possible movement/looseness per my thread above

DRACO, ah, ok, I'll order the RSR. I am going to check each one and put the seals in while I am in there. I have read through your posting twice already. I don't think it'll be that last time too!

[timmy2]

It happened to me too 4 years ago....
Finally, back in the game!

[boyt911sc]

Originally Posted by NeedSpace

Tony,

I am trying to keep my car fairly stock so still using the bosch mechanical fuel injection. That liquid is a whole lot of oil.

Oil coming from where? BTW, you have a CIS and not the real MFI (mechanical fuel injection) system. CIS is easier to maintain than a MFI. You need to torque the rocker shaft bolts @ 13 ft.lb (156 in.lb) to keep them in place.

Tony

[scarceller]

Few points on detonation:

Detonation at idle and very light loads is really not possible, you don't have enough cylinder pressures during combustion at these light loads. It's very unlikely to cause detonation at idle no matter how lean you make mixture. Even over advancing ignition won't cause detonation either at idle.

These motors are really only detonation prone at loads above 50% to WOT.

Glad you found the problem, rocker arm shaft that walked out.

[Joe Bob]

An RE agent that knows how to wrench, priceless. Hope it goes back together and no problems.

Good luck.

[NeedSpace]

Originally Posted by Joe Bob

An RE agent that knows how to wrench, priceless. Hope it goes back together and no problems.

Good luck.

RE Agent? Actually I am a psychologist...

[Kemo]

this looks like a happy ending!!

[DRACO A5OG]

Originally Posted by NeedSpace

RE Agent? Actually I am a psychologist...

LOL, he is writing about me's :P. I am a better Agent than Mechanic :-)