Mystery noise

[AlanS]

I'm presently doing some work on a BX TZi owned by a family friend (of the female variety - thought I'd mention that to explain what some have described as paranoia) which has done around 157K klms or 90K miles in the old money.
The car has had 2 owners, the first an old codger who managed only 70+K klms in the first 12/13 years all in Sydney stop go traffic, another Sydneysider who only did a few thousand, again in Sinny traffic, and this woman who has done it all in Gold Coast traffic which is probably worse than Sydney these days.
The car is mint as she not only spends money on general maintenance, but seems to be able to talk herself into getting conned by dodgy repairers. As an example, she takes the cover out that fits over the rear of the car under the hatch so she can carry her daughters bike in it. It drums a bit so she takes it to a tyre outlet and promptly gets told they "suspect" she has buckled rear rims (alloys and she hasn't hit anything) so try to sell her a new set of diferent sized wheels and tyres for A$600 a pop and so it goes on.
Current problem is a noise on start up that began after she had a local supposed specialist fit a new cambelt and she has so far had a (second) new pump, idler, (another) cambelt as well as being told it was a loose bolt on a torque converter, big end noise, and piston slap by a variey of repairers. If it had a harmonic balancer on it, I'd say that's what it was; that's the kind of rattle it makes.
The noise seems to eminate from the intake plenum between 1 and 2 and can be felt through the plenum. It isn't constant and it disappears after about 10 seconds as though as soon as it gets slightly warm, it stops. It also seems to stop as the pump cuts out, but even with all belts (except the cambelt of course) removed, it still made the noise.
I had suspicions of possible detonation as the plugs on 1 & 2 were quite grey whilst 3 was normal and 4 was a bit dark and had suspicions of jammed rings, a common problem with the DKZ engine, so I soaked the top end of the engine with a solution and then fed a high grade 2 stroke oil down all of which took about 2 days to achieve. I cleaned the injectors and changed the plugs as it also felt "doughey" performancewise.
Result has been a much crisper feel to the engine and running as quiet as I've ever heard an TZis engine run, but this bloody rattle is still there on start up.
I know I'm grasping at straws, but would it be possible that the butterfly may be slightly worn and is giving this bit of weird rattle and then as it warms, it stiffens in the throttle body and stops doing it? I've run a stethoscope over it and it seems that it's impossible to single it down to just one area inside the engine.
Anybody got any ideas?


Alan S

[jeremy]

I'd have thought that it would take a longish time after starting before the temperature of the inlet butterfly started to increase - as its only sources of heat would be conduction down (air cooled due to flow) inlet manifold - or from the radiator heat when the thermostat has opened.

Noise on cold startup, disappearing soon after would suggest piston slap to me - stopping as soon as the aluminum piston gets slightly warm and expands - I suppose the other possibility in the vicinity would be a little end bearing quietening when some oil was splashed on it but I would have thought that would have materialised as a hard noise when the engine was hot and revved.

I would expect a big end bearing to be quiet when cold and noisy when hot, as well as being accompanied by low oil pressure.

Aluminum engines can be good conductors of noise - which makes detection all the more difficult!

90K miles isn't much when done quickly but over 15 or so years an engine can still wear considerably especially if its been used for lots of short runs - although I do appreciate the the English and Australian experience of cold starts will be rather different.

[stuart_hedges]

mystery noise

Sorry

[AlanS]

What is steering me to the weird and mystical is that it can't be detected with a stethoscope. It's like a noise that's just there in the middle of nowhere.
I would imagine on past experience that if it was any of the mechanical components rattling that you would hear it clearly via a stethoscope. We've even had the car raised and sounded out parts underneath (such as the cat) in case it was there.
Stupid part is, that you have the stethoscope on, you can't hear it. You take it off and it was rattling all the time.
We've even done the "one guy with the scope on whilst another sits it on things they think may be making it" method and again, this hasn't worked.
There's been about 6 or 8 mechanics looked at it and they are all stumped too which is why I'm grasping at straws.


Alan S

[jeremy]

Could I suppose even be the oil pump drive chain - an untensioned single row chain that always looks to me like a candidate for noise but I've never heard of them giving trouble - and the system was used on Jaguar's AJ6 engine to name one other - (its many years since I looked at the diagrams I don't recall it having a tensioner either.)

If you've been using a stethoscope you will have checked the unlikely like manifold/exhaust joint - and disconnecting the ancillaries eliminates them.

Had a valve been bent slightly during the work it would have burnt out by now and you certainly wouldn't be describing the engine as smooth.

I take it there are no mysterious emission control valves in the inlet side and that all the pipes and joints are sound.

On Frenchcarforum there was someone mending his neighbours HDi which had lost its belt - and he found the camshaft drive pulley had slipped and chewed up its key - the thing sounded normal when cranking but just wouldn't fire. Could this have happened?

Happy hunting!

[AlanS]

Jeremy,

Earlier today it appears that I may have found the culprit.
I put a spanner on the crank pulley and gave it a couple of welts with a lump hammer and next time I started it............noise gone.
My suspicions are that our friendly Cit specialist who should wear a blue and white striped apron at times, may have been turning the crank with the pulley off by possibly turning the crankshaft using a shifter or knowing him a pair of stillsons, and may have damaged the edge of the woodruff key.
As she is booked to catch a train up to collect it Monday, I'll possibly have to send her off home and get a mate of mine down there to fit a new key or key and pulley.
Not game to pull it off incase I get her stranded up here as parts are 350 klms at the closest.
I said a cuple of times that if it had a harmonic balancer I'd almost blame it, so decided just on teh offchance to swing off it and looks like I've struck paydirt.

Thanks for the suggestions.


Alan S

[jeremy]

Glad you've found it! - I expect someone simply hasn't tightened the thing up properly when changing the belt - or has failed to use locktite.

I hope it hasn't done too much damage - especially to the crank.

[AlanS]

You're not going to believe it. Went out and started it again and you guessed it........................it's baaaaaaaack!! titanic

Spoke to the last guy who had it off and he had examined it closely and reckons definitely no wear or damage. He uses a gadget to lock it and with a socket and breaker bar he tightened it, so IMO that only leaves the pump sprocket as a likely cause, based on the fact it sounds like a loose pulley/harmonic balance ready to fail and the fact I stopped it so suddenly when I hammered it tighter. Sheesh!!!!!!!!!!


Alan S

[jeremy]

Aren't some of the pump sprockets simply a pinch fit - being compressed between the crank and the pulleys when tightened?

I suppose the pulley securing bolt is the right size - and not a bit too long and bottoming out? (I've never had one apart and don't know how tight the clearance is - or even if its critical as to the use of the correct shims/spacers - I cheated when doing my TD cambelt and found I could get the belt in and out without removing the pulley)

[AlanS]

Pump sprocket's held on with a woodruff key, but I was looking at another pump and noticed when turned by hand it was a bit noisy. Spoken to another guy who is convinced it wouldn't be the pump or its sprocket due to it being a constant pressure, but my thoughts are that a recprocating engine driving it may allow it to backlash slightly, so I'm still not convinced on that argument.


Alan S

[jeremy]

I think getting a chain or belt to run straight is about as easy as achieving straight flow of water without any turbulence - ie virtually impossible at any reasonable speed.

I accept that the chain is under tension when driving the oil pump - on one side only - the other will be slack and I can see no reason why it won't thrash around to some extent like all others of its type.

[tom]

Stops ten seconds after startup? I wonder if the starter motor is rattling as the thing spins down.

[jeremy]

Good thought Tom - could even be solenoid/withdrawal mechanism a bit slow and getting struck by ring gear teeth.

[AlanS]

There's a couple of things against that.
The noise seems to come from the other end of the engine, it can't be heard with a stethoscope on any part of the engine or ancilliary equipment and the noise isn't that "solid"...it sounds too hollow to be associated with the flywheel.


Alan S

[jeremy]

It hasn't actually got a flywheel has it as its an automatic? I don't know how this particular installation works but usually the ring is on a thinnish plate but surprisingly the noise is similar to an engine with a proper flywheel.

I am reminded of a Triumph 1300 I had many years ago - strange beast - front wheel drive, in-line engine, clutch on the back end leading via a transfer gear to a gearbox and then via a shaft running in a tube in the sump - to a diff.

In all this arrangement someone forgot to make provision for a starter - so a flywheel sized ring was fitted to the front of the engine - and an apparently normal starter fitted. It worked well except it made a horrible noise - enough to frighten pedestrians!

Apparently normal starter - well it looked like that but turned the other way! The whole system was rather nice - to change the clutch you took out a panel in the floor, removed a cover, pulled out a small shaft then the clutch could be removed! - No need to move a major component!