Knocking when warm

[LordAnthony]

Hello, today when the engine got warm (Smthis temp gauge over the half way mark) after about 15 minutes there was a worrying knocking noise from the engine somewhere. Oil pressure gauge shows about 30psi when warm at idle.
The only thing that's different today is the weather is warmer and I fitted some electronic points yesterday. Could this be anything to do with the points?
You can feel the knock through the pedal when your foot is on the clutch and it only seems to be there at idle. It's not noticeable once motoring along.
Any ideas?????

[hotrodder13]

could be the fuel pump mine does it when idleing in traffic

its not getting enought fuel becuase its evaporating before getting to it, its just the hot weather and the hot manifold

does it sound like a wood pecker

tom

[LordAnthony]

It's not the fuel pump - or would fuel starvation cause another type of knocking.
This is a bigger knock than the pump - it can be felt through the clutch pedal.

[MarkyB]

What does the exhaust note sound like at tick-over?
Does the sound only occur with the clutch down?

[LordAnthony]

It runs a bit lumpy, but it's not too bad. I don't think I've ever been able to get the mixture set up properly.
The noise is there whether the clutch is down or not.

[bmcecosse]

Definitely firing on all 4 ? You haven't mixed up the firing ordr - although it would hardly run at all if you had! Have you optimised the ignition timing since fitting the electronic gubbins ? 30 psi at idling is excellent - what is it when running along at 50 mph in top ?

[MarkyB]

How does the engine look at tickover?
Is it just sitting there, or is it shaking about.

Have you located the lifting pin on the carb?
If so, you are at least half the way to getting the carb set up.
When you lift it up does the engine run faster, or cut out?
Just faster means the mixture is too rich and you need to tighten up the big nut on the bottom of the carb a bit.
If it cuts out, you need to loosen it.

The ideal is when it speeds up a bit then drops back.
Anywhere close to this and the carb is fine.

The thread on the jet is the same as on a tube of toothpaste, or any other threaded thing you come across.

There isn't much that can be felt through the clutch pedal that isn't obvious to your other senses.

[LordAnthony]

I haven't mixed up the firing order but I have noticed that it looks a bit wet around plug no2. I haven't altered the timing - I've read about the different methods but have yet to do it.

Pressure gets just over 50psi when going about 60mph.

The engine does have a little shudder every few seconds but it doesn't seem to happen at the same time as the knock.
I'm not sure that I have a lifting pin on my carb - could this be correct? There is something where the pin should be but it appears to be fixed in place. Perhaps it's just jammed - I'll have a better look tomorrow.

I have tried taking the filter off and lifting the piston with a screwdriver blade and tried to get it as you describe but I'm not convinced I've done it very well. How far are you supposed to lift it and for how long? Whatever I try it just seems to want to cut out if I lift it much more than 5mm.

Could the knocking be related to the timing? I considered altering it in my lunchtime today at work but decided against it as I didn't want to be stranded if it all went wrong...

[MarkyB]

Richer is safer than weaker, undo the jet half a turn then try again.

I doubt it's just the mixture, if you can feel something through the clutch unless you have very sensitive feet.

[bmcecosse]

Just lift the piston ~ 3mm. Use a very small/thin screwdriver. To diagnose properly - check/set the valve gaps - and then you need to get a compression test reading from each cylinder. Without that we are shooting into the dark!

[chickenjohn]

Yes, could be anything from a big end to a burnt valve!

Do a compression test, check the mixture and timing.

[LordAnthony]

Compression tests:

dry: 125 120 110 120
wet: 125 125 115 122

Exhaust doesn't give off any visible smoke but there is a bit of plume from the filler cap.
I don't think the results look good but the question is how bad are they and what does it mean?
Could this indicate the cause of the knock? I had the car idling for 20 minutes or so and no knocking occurred. It's only after it gets hot after a run.

[PSL184]

Compressions are not disaterous - not ideal but nothing to give you the knock.
As it only does it hot after a run I would start to suspect main bearings are worn out which will mean engine out and a crank regrind with new shells.....

[chickenjohn]

Compressions are not disaterous - not ideal but nothing to give you the knock.
As it only does it hot after a run I would start to suspect main bearings are worn out which will mean engine out and a crank regrind with new shells.....

Does the knock occur when you rev the engine on the over run?? In which case it is big ends. Could also be mains as said above or even both!

[LordAnthony]

Would there be any other symptoms of worn bearings that may be going on that I may have overlooked?
I also just realised that I didn't have the throttle open when I did the compression test....
Does having the throttle open make the results higher or lower or either?

[PSL184]

Throttle open will raise the results slightly - Don't worry about compressions - That's NOT your problem.

[LordAnthony]

It doesn't seem to be affected by revving. I'll have to take it out for a spin later to check though as I can't remember 100%.

[PSL184]

If it's crank erlated you'll hear a rapid knocking on overrun....

[bmcecosse]

The compressions are pretty desperate....... as low as I have seen them on an engine that's still running! The throttle should be held open - but I suspect would only add maybe 5 psi or so. You said earlier the oil pressure was ok - so I doubt it's bearings. To be honest - I would just run the engine - but not thrash it - and it's likely to last for ages!

[MarkyB]

It could be the head gasket or a valve.
A blown head gasket can produce a terrible knock.
Time to take the head off methinks.