Worrying noises

[gav]

Hi all
I have at last finished my sprint after much tinkering and took it out for a run today to break in the new pads.
Surprisingly (for me anyway) everything went well - I even had heat out of the heater (eventually).
The thing is, when I got home, there was an ominous knocking coming from the engine at tick over.
Oil pressure was around 25 psi (the engine is dry sumped) and there had been no obvious loss of power when I had been running. When I blipped the throttle or raised the revs, the knocking stopped and the oil pressure rose as usual. no blue smoke and lots of oil in the tank.
I recall seeing chain marks on the inside of the cam cover - I need to check the chain but I'm not sure that matches the symptoms. I'm rather hoping its not the big ends...
I could really do with some pointers as to where to start looking and would be grateful for some suggestions.
Many thanks
Gavin

[gjz30075]

Start with the simple stuff, like a possible exhaust leak.

Greg Z

[jimj]

Probably the engine is running a bit lumpily at tickover and rocking on it`s mountings. The carb. airbox can bang on the flat bulkhead above the pedal box, (in right hand drive cars).
Simples.
Jim

[peterako]

Worn cam follower?

If the cam follower gets slightly holowed out it can knock on rotation when the cam comes into alignment with the worn/hollowed part giving a periodic 'knocking' sound.

This typically will dissappear at higher revs.

Just my 2c worth

Peter

[Frank Howard]

The carb. airbox can bang on the flat bulkhead above the pedal box, (in right hand drive cars).

The bulkhead is there regardless as to whether the car has left or right steering.

[leifanten]

I have had the same symptoms in my Cortina GT for probably ten years. Runs like a champ with no nocking, but has a faint clack-clack sound at idle. My theory is that it is the skirt of one of the pistons that clatters a little, and under load it all "firms up" to run quiet, but on idle things are less "tight" and it is allowed to make this sound. Could be a poor diagnosis, but I only run the car for about 30 miles per year now, so I am not gonna peel it apart to find out what goes.

One way to determine the location of the sound is to buy a $10 mechanics stethoscope and listen to different places on the engine, front, back, top bottom etc. Also if you hook a timing lamp to the car, you can try to reconcile the location of the sound to the frequency of the knocks with the lamp. If the sound is from the top and it knocks at the frequency of the lamp it is probably cam shaft related, if the sound comes from mid engine and it knocks at twice the frequency of the lamp it is piston related, if the sound is from the bottom end and occurs at twice the frequency of the lamp it could be crank/main bearing related.

sorry, nothing magic in here, just trying to point you in one possible direction for diagnosis.

[gav]

Thanks all for your help so far
I have been thinking further on this and I do recall that the inside of the cam cover had marks where the chain had been hitting it. I tightened the chain so I initially discounted it as a possible cause.
The engine was rebuilt about 500 miles ago so I dont think that the wear should be too excessive. I'll lift the cover and check the tightness.
I had a quick look at the clearances and it doesn't look as though anything is hitting but I agree that the tick over needs to be less lumpy so I'll check the carb balance.
If all fails, I could increase the tickover revs..

Thanks so far.
Please feel free to add more if anything occurs.

All the best
Gavin

[Craig Elliott]

A number of people have noted a tapping sound at low revs that disappears at higher revs. Could one possible cause be wear in the collets that hold the valves in place? C

[Carlos A]

This maybe not the source of the noise but I it drove me crazy for two week. It was a tap-tap-tap kind of noise produced by a loose metal Heater Connection (is that the name?) taping the fiberglass at idle and whenever the engine produced enough vibration.

[ElliottN]

A bit left field....

Clutch? See if the noise persists when idling and clutch depressed. If no then it's the clutch (bearings), not the engine.

[bcmc33]

One way to determine the location of the sound is to buy a $10 mechanics stethoscope and listen to different places on the engine, front, back, top bottom etc.

Gavin,

This was my first thought when reading your post. A stethoscope is a very useful piece of kit for your tool box to have.

[alexblack13]

The non return valve in the vac' system which is screwed into the inlet manifold sometimes clatters. Have a feel at it when the noise is there. Can you feel it rattle? If so?.......

Just a thought. I had to throw a very noisy one away once upon a time...

Alex B....

[gordont]

I had been watching this thread. With interest as my s2 has a similar rattle/tap noise at low revs which I had assumed was valve shims but Alex can you advise where the vac return valve is located?
Cheers
Gordon

[bcmc33]

I had been watching this thread. With interest as my s2 has a similar rattle/tap noise at low revs which I had assumed was valve shims but Alex can you advise where the vac return valve is located?
Cheers
Gordon

This is where the non-return valve was on my car:

[alexblack13]

Yep. That's correct. Its a steel ball in the brass tube & they can rattle like hell..

Could be!

Alex...