Pinking/detonation

[ndevans]

Here is a video taken a couple of weeks ago, the noise is evident as I charge gear and accelerate several times.

https://drive.google.com/file/d/1rj8Z4_ ... p=drivesdk

[svenedin]

I can certainly hear the noise in your video. It is louder and different to what I thought was pinking in my engine.

It sounds like an ordinary rattle to me. I'm sure you've been round the car over and again but have you checked methodically, everywhere? Are the ashtrays rattling (if fitted), is there something rattling behind the dashboard, is it the heater loose or something loose inside the heater? Another rattle point is the bonnet release rod which should have a rubber bush where the metal rod passes through the bulkhead (with a clamp to stop the bush popping out), the bonnet release rod anti-rattle spring can also rattle badly. if not tensioned properly (ironic). Once I was driving from Edinburgh to London on my own through the dead of night. I became obsessed with a rattle until I realised it was my metal watch strap!

Stephen

[Edward1949]

I'd say it's an ordinary rattle, not pre-ignition pinking. Could be lots of reasons. If you really want to discount the pre-ignition theory you could try massively retarding the ignition to see if the noise disappears.

[myoldjalopy]

It does not sound like pinking to me either. I might be investigating exhaust clearance, or even loose baffles in the silencer....

[Bill_qaz]

Hard to tell on audio on video but it only seems to come at higher rpm?
Or is this just a trick of the recording.
Sounds suspiciously like a small end rattle but hope not

[geoberni]

I'm with everyone else; it is always hard to hear 'noises' on a recording, but yours sounds like a rattle rather than engine pinking.

[ndevans]

I've had the ignition retarded to TDC and that hasn't helped. I thought it was the bonnet release but I'm happy it's not, and I'm happy it's not dashboard or ashtrays, they are not loose.
It only happens under specific conditions, wide open throttle when accelerating, present in all gears but most noticeable in 3rd accelerating from about 30 to about 45mph. It does not happen at steady speed, nor if I floor it in 4th when climbing a hill.

[MikeNash]

" . .nor if I floor it in 4th when climbing a hill". Now that's precisely when I'd expect the pinking to be heard at its clearest.

I suppose you've the usual ribbed gearbox behind your 1275cc engine, in which case you've a straight drive through the 'box in top gear with the all geary bits then whirling around enjoying themselves. In the intermediate gears, they are all working hard, and any minor imperfections, etc will show themselves by noises and vibrations, either directly from the 'box or elsewhere from bits the 'box excites. So I'm with the others who strongly suspect you've not got pinking.

However, that said, pinking is a very serious condition to be avoided at all costs, and you need to assure yourself that it isn't there. I suggest you drive your Minor hard up, say, a long motorway grade in top gear so you can have an extended time for a test. If it begins, I'd first suggest a cooler grade of plug and thicker oil in the dash pot. (In answer to your question, jack oil's about the same hydraulic oil so is too thin. Your damper oil might do if you've gone down the recommended thicker oil path!) Perhaps Phil will be along to comment shortly.
Regards from MikeN.
PS You've magnet in your gearbox drain plug, haven't you?

[Bill_qaz]

Or could it be you are not reaching the same rpm under load it top gear that you do in lower gears.
Could you hook up a temporary rev counter to see if the noise is rpm specific?

[svenedin]

Or could it be you are not reaching the same rpm under load it top gear that you do in lower gears.
Could you hook up a temporary rev counter to see if the noise is rpm specific?

Good idea. When I first had my Minor in 1989 it had some nasty resonance/vibration issues. At certain speeds in top gear there would be a lot of vibration which would pass as the speed increased. As teenagers we used to call this "breaking the sound barrier" (after the 1952 David Lean film). As I recall it was around 45-50mph and then it was as if nothing happened. The trouble is, it is so long ago I can't remember what was wrong. My car hasn't done this for decades.

Stephen

[ndevans]

That could have been worn cardan shaft u/js. This is definitely related to engine or gearbox speed.

To answer questions above, I don't have a magnetic gearbox filler plug, and I haven't rigged up a temporary rpm counter, though I suppose I could see if I can get the strobe rigged up under the dashboard.

I'm not able to identify where it is coming from, I can't isolate whether it is from the gearbox or the engine. Holding the gear lever when accelerating (tricky, not always possible) does seem to modulate it somewhat but does not eliminate it. It could be transmission related but I feel I need to rule out pinking first.

[mobylette]

Put some octane booster in the tank, if it still rattles, it is almost certainly not pinking.

https://www.amazon.co.uk/Redex-RADD0063 ... A1OLE&th=1

[ndevans]

Well swapping to a BDL needle has definitely improved things. At first it didn't, as I just dropped the new needle straight in without adjusting the mixture. It ran really roughly, almost feeling like the head gasket had gone. A compression test established that all was well, so I adjusted the mixture but it still wasn't right. Since I had been using a BFY needle with a yellow spring, i swapped back to the original red spring, which is weaker than the yellow. That improved things immediately, and the car is now running well.
The "pinking" noise that I was hearing is now gone, though there is still some rattle that is definitely related to the gear lever. It's now only really noticeable in 3rd, not in all gears as it was previously.
One good thing has come out of it - I am now happy that compression is good in all 4 pots, and my spare compression tester (£5 from the Beaulieu autojumble a couple of years ag) works perfectly well and gives comparable readings to the ex-AA set that I have.