Gearbox noise (with video)

[IslipMinor]

Presumably when knocking it into neutral, the engine revs drop to idle? From everything that you have said the noise is engine speed related, so if the revs drop the noise stops??

Have you tried driving beyond the initial onset of the noise in each gear?

What happens if just slowly increase the engine revs to ~4,000 rpm at a standstill? Does the noise come in at around 3,400 rpm?

[Phil-1954]

All,
An update to this is that increasing the speed in an attempt to drive out of the noise, as 'IsLipMinor' suggested, only causes it to get louder and more intense.
I also tried running the car in 4th whilst it's up on axle stands, the intention of this rather dangerous escapade, was for my son, who was outside the car, to try and work out the source. He was unable to be specific though, as for some odd reason he declined to actually be under the car at the time so as to listen better - kids nowadays, all H&S,
As 'IsLipMinor' suggests the engine revs work out (using maths) to be around 3400rpm and over in the affected gears, so I'm confidant that it's engine speed related, but notwithstanding that I have also checked the prop for missing balance weights and worn U/J's and even the tyres for lumps (which apparently revolve at 12+ times per second at 50mph!). Engine has 40psi of oil @ tickover with 6000 miles on it, so ruling that out.
I'm now thinking something, the exhaust maybe, has developed a resonant vibration at a fixed rpm, but I am leaving things as they are for now until spring arrives with some warmer weather!

[IslipMinor]

Phil,

If you simply rev the engine to at least 3400 rpm whilst stationery in neutral, does the noise occur?

[oliver90owner]

And the next logical step (depending on the result of Islip Minor’s request) might be to check again, but with the gearbox input shaft stationary.

[Phil-1954]

All,
I fully see the logic behind Oliver' & Islip' request, but no, I have not built the engine revs up into the mid 3k's in neutral and held it a couple of seconds, simply because I'm reluctant to do so without any load on what is a 50+ year old engine. It's very easy when unloaded to exceed a safe rpm limit. True the engine was reconditioned about 6k ago, but the crank, rods & valve gear etc, are all still 50+ year old parts. My fear is because I know from personal experience what can happen to over revving an engine without a load from many years ago, and I'm not taking the chance again (broken crank web on my 1st car, a Volkswagen 1200 Beetle). There is also the chance that being unloaded may not cause it to happen anyway (that's partly a cowards excuse as well.
I'm replacing the clutch next year, if it lasts that long, so that gives a chance to inspect gearbox input / spigot / clutch.

[oliver90owner]

So what does the engine do every time you take your foot off the accelerator and change from ‘loaded’ to ‘driven’ on overrun? Never used a rev counter? Admittedly engines are more modern, but the MOT test for diesels require the engine to be revved to governed speed for emissions testing.

But your choice.

[Phil-1954]

WATCH THIS SPACE.
I've just ordered a handheld Laser tacho. I just wondered on other peoples thoughts regarding running an engine up to 4000rpm without a load on it, while stationary and in neutral.
No Liability will be attached for anyone who's brave enough to reply

[philthehill]

If your 'A' Series engine is in good working order and it appears to be so then it will happily run at 4000rpm without a load being imposed on it.

We are not talking here about continuous running but short bursts of 4000rpm.

There is more than one reason for a crankshaft breaking and I would discount high revs as a sole reason.

[paul 300358]

As mentioned earlier, I have the same noise at the same speeds but a bit quieter. So this morning I placed a straight edge across the alternator pully to see how it lined up with the crankshaft pully and the water pump. (straight edge on the crankshaft pully, all is in line). The indication was that the alternator pully was slightly out of line. Apart from welding and re-drilling the alternator bracket the only way that I could line it up was by placing a washer on each bolt between the block and alternator bracket. This has altered the angle of the alternator and stopped the noise.

Its got to be worth a try.

[Phil-1954]

Paul,
That's an interesting thought. The vibration caused by non-alignment possibly causing a resonance of the belt I suppose. I'm not doing anything until spring most likely [no garage and only vehicle] so keeping below 50mph for now until the birds start building their nests But I'll certainly check next time I check the oil.