Slight 'growl' under acceleration

[Owlsman]

I'm probably fretting over nothing (as per usual) but on the way to and from the National, my ''62 1098cc saloon covered more high-speed long miles than it has ever done before - certainly in my tender care.

The car went far better than I could have expected really, baring in mind that it was fully laden with all the kit 'n caboodle necessary for the DPR stand. The needles on the extra dials, all stayed within the parameters that I hoped they would do BUT there was a slight 'growl' when under hard(ish) acceleration.

'Hard acceleration' is of course a relative term when referring to a standard Moggy set up.......but I'm sure you know what I mean! The car reacted positively to increased right foot pressure, by picking up speed and it was very easy to stop the growling by easing back a tad on the accelerator, so that my foot was just 'feathering' the pedal but at the same time maintaining a good speed. I suppose I was cruising around 50mph or a bit more and it seemed as though I could nearly always find a 'sweet spot' when any noise from under the bonnet was almost non-existent - until I depressed my right foot again.

Noises are notoriously difficult to describe in words. A gentle growl is the best I can come up with. It certainly didn't sound like anything sinister, like a bottom-end rumble I once had on an MGB. With the car back home and static, I was unable to replicate the growl simply by revving the engine.

This is not the first time I've noticed this noise but most of my driving, up to this point, has been local tootling about in traffic. It seemed more noticeable this last weekend during long sustained periods of mainly 'A' road cruising.

Perhaps surprisingly, I have never ever travelled in anyone else's Minor (even round the block) so I've nothing to compare the driving experience/sounds with. Any thoughts anybody? Or am I fretting unnecessarily?

Thanks,
Alan

[liammonty]

It's always difficult to tell without hearing, but what you're describing sounds like a bottom end rumble from the crankshaft bearings under load, indicating a bit of wear. If you covered a lot of high(er) speed miles than you have done before, chances are that the oil warmed up and thinned out more than usual which will have exacerbated the 'growl'. Does it do it when the engine is less hot (i.e. hasn't been on a long high speed run)? One of my 1098 cars used to do exactly the same but it ran for years like it without any problem.

If this is the problem, the first thing I would do is make sure that the oil in the engine is at least 20W50 and not thinner.

[simmitc]

Have a look at the air filter. Has the intake silencer tube either come loose or fallen off completely? They tend to crack around the joint, and then you get a throaty roar under acceleration.

[Nickol]

Whether it is the same noise or not....but the growl that my 1098 engine exhibited for a while disappeared once I had reset the static timing which was slightly out. It was too far advanced or retarded, I do not know. In comparison, the before and after performance gave no noticable difference.

[Guildbass]

I know exactly the 'growl' you refer too.
I have literally JUST fitted new mains and big ends to mine, so it isn't that, but I have noticed it is somewhat timing related, and is more pronounced as timing advances. I'm not sure, but 50 ish may well be where the mechanical advance (or perhaps the vacuum advance) has reached its maximum 'full' point.
When I got my car, its ignition was intentionally retarded, and I think that was to mask a noisy bottom end. it was quite noisy starting at 50 mph once the timing had been set correctly and a bottom end refresh sorted all the excess out, but there is still a little there.
I might be imagining things, but mine seemed a little more evident after I fitted a new air cleaner filter too, so it might be induction noise in response to full advance.
You will of course have more induction noise when carrying a load anyway.

I doubt its oil pressure related. While most old mineral 20W-50s don't hold up well to high operating temps and their working viscosity is pretty close to that of the 30 weight the engine was built around, on my car at least, the 'growl' is there irrespective of how hot the engine is and stays constant whether I've been belting along at 70 mph plus before slowing, or pottering about.

[Davemate]

I have the same, I’ve fitted a new engine as the ends did start knocking and the growl is still there,so in my case I’m guessing it’s gearbox bearings, as I’d be very surprised if the same sound at the same revs would be found on two different engines.
Backing off the throttle does make a difference as well so basically the same as your growl.
In my case I know it’s not induction roar,pinking or shells on their way out

[Guildbass]

I have the same, I’ve fitted a new engine as the ends did start knocking and the growl is still there,so in my case I’m guessing it’s gearbox bearings, as I’d be very surprised if the same sound at the same revs would be found on two different engines.
Backing off the throttle does make a difference as well so basically the same as your growl.
In my case I know it’s not induction roar,pinking or shells on their way out

when I got my car, the ignition was 10 degrees retarded and the points gap was around 25 thou. it sounded 'busy' at 50 mph ish, but not 'growly'.
As soon as I set the timing according to the book at 8ish before TDC you could hear the 'growl as you got over 50 mph and the noise eases of if you throttle back which is why I think it might simply be what they sound like under load at full advance. My big ends and mains are less than 1000 miles old so like you, I know it isn't ends.

[olonas]

I experience the same "growl" which seems to be related to speed and accelerating at that speed - just under 50 m.p.h..
The dynamic ignition timing is set to 6 deg. b.t.d.c. at under 600 rev/min. with vac. disconnected and plugged. Stroboscopic timing light. Dwell is 60 deg. with c.b. at 15 thou.
I know the mechanical advance is correct, it should be because the distributor has been refurbished by Distributor Doc. and an advance curve graph provided.
I know that my timing chain is very "slack" and I'm in the process of working up the enthusiasm to fit a duplex chain set.

[Guildbass]

I experience the same "growl" which seems to be related to speed and accelerating at that speed - just under 50 m.p.h..

I know the mechanical advance is correct, it should be because the distributor has been refurbished by Distributor Doc. and an advance curve graph provided.
I know that my timing chain is very "slack" and I'm in the process of working up the enthusiasm to fit a duplex chain set.

My timing chain is a brand new duplex one, and to be honest, the old one was in great condition. If I hadn't cracked the lip of the cam sprocket while removing it, the old timing set would have gone back on!
Perhaps someone will chime in, but I 'feel' at around 45-50 mph the distributor has been through its curve and is fully open, or close to it.
I tend to blat along at about 60-70 mph, but at those speeds, wind noise drowns out most engine noises. 50 is perhaps the point where it is at full advance, yet wind noise is still low enough to make that change in engine note audible.
Whatever. My car made the 'growl' before the rebuild once I timed it correctly, and with new mains, big ends, timing chain, cam followers, electronic ignition with a new vacuum advance, all timed on a strobe to the right point on the marks, although significantly quieter in itself, still makes the same growl...So, i don't think it is anything but 'the noise they make!'

[olonas]

"So, i don't think it is anything but 'the noise they make!'"

Possibly the point at which that blistering power is unleashed?

[myoldjalopy]

Very possibly! I had an 803cc engine in my car once and the 'growl' used to sound like spitfire coming in on the attack on acceleration!

[Owlsman]

Firstly, many thanks gentlemen for all your helpful suggestions and responses. I apologise for not responding myself sooner........but life seems to have got in the way! To be fair, only today, have I had the chance to take the car for a spin.

There is a 70mph dual carriageway about 3 miles from my house and to get to the start of the by-pass, is typical suburban traffic. I gave the car a bit of a 'blast' (briefly at 60mph plus) and there was no detectable 'growl' on the outward journey but a bit of one on the return run. This does seem to suggest that any noise might be oil temperature/viscosity related. The growl today was nowhere near as noticeable as on the return run from Gaydon but the car was not carrying anything like the load today and without a passenger.

By the time I had reached the start of the by-pass, the water temp had reached its normal operating temperature. Needless to say, I don't have an oil temp gauge but I assume that there must be at least a correlation between water and oil temperature. I'm guessing though, that depending on external weather temps and driving speeds/duration etc, oil temperature can vary considerably whilst water temperature will remain more or less constant. I assume also, that most engines will sound a bit quieter when setting off from cold, as whatever engine oil is used, it will be a bit thicker.

My car does have 20w/50 oil, which is probably in most engines. Are there any alternatives to consider?

I do recognise an induction roar, when driving, say, without an air filter but I don't think my 'growl' is anything to do with that. Everything on the air filter box is as it should be.

The suggestions re incorrect timing are certainly worth investigating. I do have Accuspark electronic ignition fitted (the complete distributor replacement version), so I don't know if that would make any difference. I freely confess that whilst I've heard of terms such as 'dwell angle' and 'advance curve' etc. I might as well be reading about nuclear physics!!

All in all, I'm not overly concerned but noises/sounds that I can't quite explain do niggle me a bit. If there is something fairly simply that can be done to eliminate or reduce it or if I'm assured that it's 'normal', then so much the better.

Thanks again all, for your input.

[Myrtles Man]

Here you go:-

"Dwell angle is the amount of time, measured as degrees of rotation, that contact breakers remain closed in a distributor."
(To allow the coil to re-build its charge for the next spark.)


"What is advance curve?
The rate at which ignition timing advances as plotted on a graph; the line rises from some initial amount of advance and levels off at the maximum advance."

[Guildbass]

My car does have 20w/50 oil, which is probably in most engines. Are there any alternatives to consider?

Generally an extremely contentious topic!

I'm running a synthetic 10W-40 with a good ZDDP package for the first 1000 miles as I replaced cam followers along with the bottom end bearings. I'm changing to Mobil 1 5w-50 after that as it holds up extremely well at temperature and gets round the engine quickly on first start yet has a decent ZDDP package critical for our type of cam followers.
The 1969 handbook includes 5W-30 amongst the older 'legacy' oils from earlier decades and the engine was originally designed to be happy with a hot SAE 30 with the caveat that even then SAE 30 was not good cold. Back then they recommended SAE 20 for winter use, because it was the 'least thick' they dared recommend for cold starts but still OKish hot.
Things have moved on a bit in 70 years though! Today,
a 5W for the cold start with an optimum 30 weight rating when hot is pretty much on the ball with most engines more than 20 years old and listed as 'all temperatures' by manufacturers who list it. Newest spec Oils with 'SP' rather than 'SL' 'SM' or 'SN' may have less ZDDP than our engines like, so bear that in mind!