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MG MGB Technical - Like pinking but not pinking (revisited)

Hello again,

It has been a while since many of you helped me out with advice about the mechanical ticking which seems to be coming from behind me whenever the car is under load/acceleration. Thanks for all your help - I said I would report back to you so here I am again.

The last thing I said was that I was going to fit a new set of CV joints on the prop-shaft and let you know how that went. Unfortunately that all took a lot longer than expected, partly due to someone STEALING ALL MY TOOLS! but also partly due to lack of time.

In the end I threw my arms up and got the garage round the corner to drop the shaft and replace them for me.

The noise is still there unfortunately which left me with a couple of possible conclusions. Firstly I thought that it might be an exhaust leak as Iain mentioned. All the manifold joints seem googd and tight but I haven't looked in great detail yet for holes. However, this problem only happens when the car is in motion. I have even tried putting a small amount of load on the engine by revving it against the hand brake which does not produce the noise.

This seems to point to a drive train problem somewhere. Initially, as the engine was running lumpily I decided to get that running as smoothly as possible to discount the possibility of the drive train being shaken about unnecessarily by a badly running engine.

The engine now runs beautifully with new points, properly gapped, new condenser, timing spot on, mechanical and vacuum advances spot on, mixture good, valve clearances good, idle speed good, new leads and plugs and new distributor cap.

The noise is still there. I suppose I will need to check all bolts, joints, linkages etc. but if you have any more pointers that could be helpful.

How about gear box? It occurs to me I haven't checked the oil level recently. Is the transmission ever guilty of producing these kinds of mechanical tapping noises under load?

Thanks again if anyone has any pointers.

Alec
Alec

Mechanical ticking under load from (apparently) behind could well be a chipped tooth in either the gearbox, OD or axle. Any particular gear or gears? My V8 used to do it in some gears when cold, I say 'used to' but either it stopped a long time ago or I just don't notice it anymore.

I remember years ago seeing a neighbours Land Rover that had a similar problem in reverse, although in that case the 'ticking' occured when the tips of some of the teeth just engaged the result being that progress in reverse was extremely slow and jerky. He drove it that way for years.
Paul Hunt 2

Hi Paul,

Thanks for that suggestion. As I remember it isn't specific to a particular gear but I will check again. If that is the case it might point more towards the dif than the transmission.

I will get the car up on ramps tomorrow and give the back end a good shake to see it that reveals anything loose.

Thanks again,

Alec
Alec

A long shot but worth mentioning, maybe you have something rattling about inside the chassis rails? When I did the floors on my GT I found a piece of broken off drill bit about 3/4 inch long and 1/4 inch diameter loose inside the rails! That would rattle from time to time.
Simon Jansen

Hi Simon,

That's a possibility. About a year ago I did quite a lot of body work and maybe something has just worked itsef into a position where it starts to rattle.

The tapping/ticking seems to be a wheel speed rather than engine speed and happens in all gears under load until about 2500 revs.

It was horrible weather yesterday and I didn't feel like getting under the car but I'll probably have another look over the weekend.

Thanks for the suggestions.

Alec
Alec

If it's at wheel speed I cannot see how this only occurs up to 2500rpm. So the first thing you must do is establish just what affects it. If it is apparent up to this engine speed does it go away at say 10mph 20mph 30 and so on dependent on what gear you are in or can it be heard up to say 55mph when the car could be in either OD4th 4th or 3rd gear and if so is it at the same speed irrespective of the gear when the car is travelling at a constant road speed. On the assumption that the car is travelling at a constant road speed is the noise apparent when accelerating gently and does it remain if you start to gently decellerate ? If you can give us this information I think we can start to pinpoint the noise a little bit better
Iain MacKintosh

Hi again Iain,

Thanks again for your time.

OK. I haven't tried the overdrive yet because I have so far only been pootling round the block. I don't really feel safe enough to take the car onto the open road just yet.

It does seem strange but what happens is that the noise starts as soon as you try to accelerate away from a start in first. When you change up a gear the noise is still there at the same frequency as it had been in the previous gear, unaffected by the engine speed. However, once the revs reach a certain level, i.e. when the load on the engine is reduced by the engine reaching its power band, the noise dies down.

That seems to point me towards suspecting a drive train problem which is somehow compounded by a juddering engine. I am now starting to suspect the fitting of a new cylindrical facet fuel pump I did a few weeks ago. When I fitted it I obviously tried to make sure that all pipes etc. were held clear from the running gear but it occurs to me now that the car was jacked up under the body. Maybe when the weight is back on the wheels the leaf springs or axle or wheel may somehow be interfering with the pipework. I can't see that as likely but still possible and I will check this first. I will also have a look to see if any of the exhaust fittings are loose.

I have to say I don't really like to drive the car too much in this state.

Thanks again for your time,

Alec
Alec

Alec,

I'm still having difficulty in getting to grips with your problem. When you say frequency can you relate this definitely to either wheel speed which will be consistent with drive shaft speed or engine speed. Or is this a vibration which occurs as you load the engine and either it or the transmission or exaust makes contact with something such as the the NS rear shock absorber drop link. Check your modified pipework as well.

Incidentally was all well before you fitted the fuel pump?
Iain MacKintosh

Hello again Iain,

Yes, I am certain that it is related to wheel/prop shaft speed and not engine speed. When I change gear and the revs change the frequency of the tapping/ticking still remains related to the wheel speed. However the odd thing is that even given this fact, once the revs get to a certain point the problem seems to go away. Strange.

As regards your second question, I can't say that all was well before I fitted the fuel pump, in fact there seemed to be a whole series of problems including lumpy running and lack of power at high speeds which a general tune and a new fuel pump cured. It was only once all this was done that I really got to notice this noise so I am unsure whether I induced the problem, whether it just happened of its own accord or whether I simply didn't notice it before.

I will certainly check the pipework though as it is a distinct possibility and is located in the sort of area where the sound seems to come from.
Alec

I think I see where Iain is going with this: could it be the new pump that's ticking as the fuel demand increases? Some pumps are terribly loud. If you accelerate away then knock it into neutral does the noise abate after a few seconds?
Steve Postins

How does taking the battery cover off effect the sound and your view of the direction it comes from.

Have you taken a passenger out with you and asked for their view of where it is coming from?

Have checked the tyre treads for stones? You could also see what happens if you swap your wheels between front and back.

I can't remember if your car is a GT or roadster. If it is a roadster with a folding hood does putting the hood up effect where you think the sound is coming from.

David
David Witham

Pump clicking would normally be related to engine speed, not wheel speed, consumption being constant at a given engine speed and throttle opening irrespective of what gear you were in. And if it is a tick-tick-tick at greater than once per second it is unlikely to be fuel pump. Does it still do it when the cars speed is just balanced by the throttle opening i.e. neither accelerating nor decellerating? If so jack each wheel up in turn and run the engine in gear and see if you can hear the noise then. If so you will have a better idea of where it is coming from, but don't get under the car or in front/behind depending on which gear you select.
Paul Hunt 2

What I was going to say was to take the battery cover off and then go out on the road with someone else driving, crouch in the back and using a listening stick prod all possibilities until you get locate the noise. This shouldn't be too difficult as the stick will be able to access most suspects unless of course you get a few London Buses on your tail.
Iain MacKintosh

Thanks chaps. All good suggestions. As it happens I did drive around a bit with the battery cover off and the noise seems a bit louder but I think I should try getting someone else to drive while I have a listen as Iain suggests.

The idea of jacking the car up and running it in gear terrifies me Paul. Even on axle stands - we've all seen "Ferris Buela's Day Off" haven't we? I'm sure its perfectly safe if you suggest it though.

OK, at the the weekend I got under the car and had a look at the fuel pipework and even with the car's weight on the suspension (using ramps) there is good clearance with the new pump and pipework and everything is secure. The new pump is noisier, especially when dry at startup but the noise is easily distinguishable.

I had a look at the exhaust mounts and although none of the bolts were exactly loose, some allowed a small amount of tightening. Now this slightly improved things. The problem is still there and the nature of the problem is still the same except that the engine now needs to be under a little more load for the ticking to start. (Oh, and by the way, driving on the flat under no acceleration makes the problem go away).

Things seem to be pointing towards the exhaust somewhere. Maybe I'm imagining it but the tone of the exhaust when you tap it sounds similar in pitch to the ticking/tapping noise. Could the problem be due to a pinhole? What is the best way to check? Soapy water?

It's quite frustrating because it is making my otherwise good lttle runner sound like a banger. People stare at me when I drive past shaking their heads.

Bummer.
Alec

Is the sound of the ticking that is making people stare and shake their heads, or you driving flat-out trying to find the ticking, I wonder ...

Running a cold engine will soon find any leaks, they will drip condensation until it warms up, and you should see black patches around any leaks.

Just how frequent is this ticking? Several times a second? Or a couple of seconds between clicks? If tightening the exhaust clamps really has changed it them maybe the exhaust is hitting something under hard acceleration, the engine does twist on the mounts and hence move the exhaust relative to the body during this. Is an engine or gearbox mount breaking up and allowing metal-to-metal contact under acceleration? The axle will twist and wind up the springs under acceleration, is this allowing things to touch which seem to have plenty of clearance when not under load?
Paul Hunt 2

Thanks again Paul,

The ticking is several times per second rather than the other way round.

I'll have a look for condensation and black patches. Supposing I find a leak, is there any temporary quick fix you could recommend pending replacement?

However, the fact that this only happens in motion makes your suggestions about twisting mounts etc. seem more likely. I am fairly sure that the engine mounts were relaced about 3 years ago along with the engine - I don't know about the gearbox mounts.

I really need to get in the back and let a friend drive it like you suggested before.
Alec

I have found that exhaust contact noises tend to be more of a slap than a tick.

When I had a problem with exhaust slap it was where the exhaust passes under the floor cross member. If you have a twin box system the other places worth a look would be above the first box, where it passes the rear axle strap and where is come under the rear valance.

When I had exhaust slap it was at its worst when the engine was cold such as reversing off the drive.

I can understand you being a little reluctant to run your car on axle stands. (Any idea you follow from this site is at your own risk)However, if the car is well seated on good stands the risk is very small and you can always pop the spare wheel under the car as well. I have found it is less frustrating if you remember to remove the spare from under the car before dropping the car off its stands. You can apply the hand brake a little to simulate load while the engine is running.

Good luck

David
David Witham

Hi David,

Yes, "slap" sounds like a good onomatopoeia here. I never thought I'd get to use that word in a sentence. Thanks.

Unfortunately its getting so dark on evenings now that I have to leave my fault finding to weekends. I'll let you know what I find.

Alec
Alec

This thread was discussed between 12/10/2005 and 20/10/2005

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