Knocking from engine on medium revs.

[Andyhereford]

Dear All. Sorry but an other query/ advice sought on my daughters Minor…1963, 4 door saloon, standard engine.
Yesterday my daughter, while driving home from work…a journey of about ten miles / engine warmed up…noticed a “ rattle” coming from the engine bay of her car “ as if something was about to fall off.
This morning I went around to see if I could find what might be about to fall off.
Of course there was nothing…but…
the car starts and drives fine.
there is no “rattle” coming from the engine until the car gets warmed up.
the rattle seems to be confined to a “ mid range” band of revs…i.e. it disappears when either the revs are increased or decreased…no rev counter
the “rattle” appears in the same “rev range” when the car is stationary and in neutral
I am finding it hard to locate the exact area in the engine bay that the “rattle is coming from…using the screwdriver in the ear technique.
I thought that it was coming from the Dynamo but changed her Dynamo for mine and it is still there.
Tappets and rocker box are getting oil
While I wouldn’t bet my pension on it it seems to be coming from the front left hand side of the engine.
Any suggestions from anyone please on where I should start to look

[King Kenny]

Is the air filter lid loose? My dad told me he needed a new gearbox on his Robin Reliant many years ago. It would cost him £400n for a new one. I took if for a drive and realised that his filter lid was loose. I said I would fix if for less than £400.

[Bill_qaz]

Perhaps post a youtube video so we can listen very difficult from a description.
Have you tried pulling a plug lead off and try with each cylinder not firing in turn to see if one makes any difference? No harm to rev up on 3 cylinders
Does crank pully seem secure as you mentioned you thought dynamo.

[Andyhereford]

I will try to post a video. This morning I took car for a short run to warm up.
Rattle noice still there.
It seems to be within a fairly narrow mid rev range. I can get rid of it by modifying speed and / or changing gear.
With the engine warm I pulled off each plug lead in turn and reved the engine.
The rattle disappeared completely with lead 1 off but it was present when each of the other leads were off.
I tried with a different alternator cap and leads and then with a different plug in cylinder 1. There was no difference.
Any bright ideas out there please.
Thanks Andy

[mobylette]

Sounds like a big end then

[Bill_qaz]

I will try to post a video. This morning I took car for a short run to warm up.
Rattle noice still there.
It seems to be within a fairly narrow mid rev range. I can get rid of it by modifying speed and / or changing gear.
With the engine warm I pulled off each plug lead in turn and reved the engine.
The rattle disappeared completely with lead 1 off but it was present when each of the other leads were off.
I tried with a different alternator cap and leads and then with a different plug in cylinder 1. There was no difference.
Any bright ideas out there please.
Thanks Andy

Now you know its number one cylinder, by not firing you are taking off the piston load so knock reduced. Unfortunately it's either small end if higher pitched rattle or big end if deeper sound.
Just check rockers as last check but unfortunately it sound like sump off to check big end and head off to remove piston and check small end.

[mowogg]

Have you/are you able to do a compression test?

If one is low it might be worth investigating the top end first

[oliver90owner]

I am just a little surprised of the knock only at certain revs. I would expect a big end to knock under load, particularly while accelerating (not so much off-load). Not saying it’s not a con rod bearing, but just not quite convinced. I might be checking engine mounts or timing chain, but until hearing it, diagnosis is not easy.

[Andyhereford]

Thanks for all the comments. I have not found out how to attach a video to this message…it even stumped my grandson.
Is it permissible to try sending it as an attachment to the private email of someone if they give me permission?
The thing that I find strange given my very limited expertise is that
It only occurs when the engine is warm
It only occurs in a “ mid band “ rev range
It occurs both when the gears are engaged and when in neutral
It does not occur when no. 1 plug is pulled
While hard to locate it seems to come from the front offside corner of the engine
All the engine mounts seem to be in reasonable order
It came on suddenly after a period of regular daily use
The car continues to start and drive fine apart from the knocking at about 40 mph on the flat.
Knocking does not occur below 35 mph or above 45/50mph
I will have to try to find some local garage which has someone who has some knowledge of Minors to at least have a listen and suggest what it might be
I will then have to seek advice on what the best steps are to sort out the problem.
One final question though…do you think the car can still be driven gently keeping the speed and the revs down or would it be best to try to identify the problem first.
Thanks again

[svenedin]

You cannot post a video on here. What you can do is post a video to YouTube and then post a link on here.


Stephen

[MikeNash]

Andy,
Have you checked the clearance between the exhaust pipe and the body work? Modern replacement pipes can get rather close and if the engine mounts are old and sag a bit the pipe can touch the body work when running under load and give a rattle as the engine leans over slightly from the torque it provides.
At last it does on mine, MikeN.

[oliver90owner]

Andy,
Have you checked the clearance between the exhaust pipe and the body work? Modern replacement pipes can get rather close and if the engine mounts are old and sag a bit the pipe can touch the body work when running under load and give a rattle as the engine leans over slightly from the torque it provides.
At last it does on mine, MikeN.

Like… does it still make the noise, at those rpms, when reversing?

Bonnet up as well as down? Does it rattle when slowing from higher revs through that ‘noisy’ engine speed range? Is it the same in all gears while driving? Same driving up-hill and down-grades?

Just that No.1 plug only, and it stops, is a little bemusing.

I might take the risk of it getting worse, if it were my vehicle, but would not advise someone else on that score!

I would still be checking the engine mounts - slightly loose bolts might just be the problem.

[Andyhereford]

This is really an excellent owners group forum…it really feels like there is access to really supportive expert advice and suggestions. I will take it out for a run on Thursday and check the various points raised about when exactly it occurs. I have tried to post a video and the MMOC Facebook page. Not sure if I have succeeded.
Thanks again to everyone.

[Classiccars]

Agreed.

[Guildbass]

I have not got a wealth of experience with the A Series, most of mine is with Vauxhall four cylinders but big end noise is generally most audible at the transition between on and off throttle, when there is the lowest load on the crank.
Number one is also the last big end to be pressurised during a cold start and with thick (20w-50) oil, depending on where in the circuit the oil pressure sensor is, may not be pressurised yet even after the oil pressure light goes out.

One of my elderly Vivas had a noisy big end when I bought it which manifested audibly after about 2-3 miles from cold in the way I described..A 'thrraaap' sound as you come off the throttle.
I put Mobil 1 5w-50 in and drove the car hard for a good year afterwards at high rpms and long distances without any further horrible noises or issues.
Might be worth putting that in pronto. For £50 it has to be a cheaper solution than the alternative...

Just saying.....
Just noticed this post is four years old....D'oh!