Crazy disappearing engine noise. Ideas?
 

My 85 Carrera had what sounded like valve clacking so I had the valves adjusted and the noise is now worse. I also changed from synthetic to regular oil on the advise of the auto repair shop. I mentioned the noise to the mechanic and he said it was most likely exhaust resonance ... I am confused as to what it is and it scares me for sure. Funny thing is now two days after the oil change and valve adjustment the damn noise just disappeared. I am interested to see if it comes back on the drive home today. Anyone have any ideas what could sound like valve clacking that can just stop like that?

Exhaust leak?

loose valve guides.

At first I thought exhaust leak, I am leaning towards something else now. Do the valve guides come loose often?

Timing chain slack (tensioner failure)? Do you have the hydraulic tensioner retrofit?

It is an 85 Carrera so I would assume it does.

the guides don't generally come loose in the head, but they wear in their bore so the valve has a lot of radial movement. in one position it's noisy, another place it's not. usually they have to be pretty sloppy for an off and on ticking. old 2.7s were famous for it. 1/2" slop was common. oil smoke out the tailpipe at all? oil use in X miles?

I have a similar noise that is only there at 2800-3000 rpms. I had the valves adjusted but the noise remained. Being paranoid of tensioner failure, I brought it in and the wrench said the tensioners were fine. I took him out for a drive and he eventually heard it (I must have bionic ears now that I have three young sons) and he said it was...
piston slap.
I've never heard of this so I asked if it was a problem and he says the engine will easily run for another 100,000 miles (22K on it now). It's just a noise that the piston makes inside the bore when the engine's not under load. Comp and leakdown are all excellent and it makes a lot of hp for a 3.0 (nearly 200 at the wheels). So I stopped worrying about it (and started planning for my 3.6 swap)

Im now rebuilding my 3.2 and found a few rockers that had much more wear than others which would seem to make the valve adjustment not very stable

broken valve springs are rather common. the outer breaks and collapses somewhat, and the inner spring and the remains of the outer spring sort of keep things going, but a clatter at 3K or so is often heard, and the valve won't be controlled at higher RPMs, causing a slight power loss/miss.

Interesting ... If I punch it down I hit about 6K and its seems like valve float. Maybe there is an internal rev limmiter? Either way when the weather gets better here I think I may just have to take the valve covers off one by one and do as comprehensive an inspection as I can. Weird that the noise disaapeared this morning tho. The mech also changed my oil from Motul Synth 15W50 to Castrol 20W50 and mentioned that my 85 has seals that were not meant for synthetic oil and that synthetic has smaller molecules thus would only encourage leaking. This along with the valve adjustment were done on Monday.

All the clickety clackety noise went away after I put new guides in my '87.