engine and drivetrain Throttle Blip Causes Engine Screech

[02G]

Hi all,

Thanks for your input in advance.

 

It started a day or two ago.

I blip the throttle and there is a very short

discernible screech/crackle coming from the engine top.

It's definitely not the alternator or belt.

It seems to be just at low rpm when a quick

blip is given, not during slow increase in rpm.

I haven't had time to open the rocker cover yet.

 

I'm wondering if it's perhaps the valve timing...

There is also quite a bit of popping on the overrun, which 

shouldn't be there as I have stock engine with a Weber

36 DCD set for conservative fuel delivery.

 

Any thoughts ?

[Guest_anonymous]

Timing chain tensioner ?

[Hans]

How do you know its definitely not the belt?

[TobyB]

yeah, take the belt off, and try it.

 

Just don't run it very long without the belt- it'll overheat in about 45 seconds without the water pump (if it's already hot)

 

Or just tighten the belt a bit.

 

like everyone else, I think it's the belt...

 

t

[FunkyLaneO]

Water pump could be going out as well.  I just replaced mine because it started making a chirping sound as opposed to the usual worn out bearing sound and when I blipped the throttle it screeched as well.  Grab ahold of your fan and wiggle it, if it wobbles at all then check your water pump.

[TobyB]

Oh, good thought.  Look at the weep hole on the bottom of it- if it's leaking a little, that can rust the bearings.

 

The Alt could do that, too.  (chirp, not rust)

 

So try the belt trick!

 

t

[Hans]

If the alternator mounts are worn - including the end of the support rod at the front cover - the belt won't stay adjusted. lSo the belt may be glazed.

[02G]

Hi guys,

Thanks for all the suggestions.

I was thinking timing chain tensioner, but I checked it out

a few months back after replacing a worn crush washer.

Also replaced bearings in the alternator last year and belt

is quite new.

 

I also suspect the water pump Funkylane.

I gave the fan a wiggle and it has a slight click wobble,

almost like one click on a ratchet spanner although not

as pronounced. I presume this isn't normal ?

Is it possible or worthwhile to rebuild the water pump

or just buy a replacement ?

If I replace it what is the quality of the non-oem replacements like ?

 

G

[Guest_anonymous]

http://www.bmw2002faq.com/topic/140982-play-in-new-water-pump-bearing/

[Hans]

For the price of a new one, I wouldn't fool around trying to rebuild one. As to your symptoms, one would think that screeching with blip - rather than all the time -  would be caused by belt slipping, because it was loose/glazed/unhappy. If either the alt. or pump were seizing, why only with blip? Not saying your pump isn't bad, but seems odd. Does the pump spin freely?

 

I'd be cleaning up the pulleys with some fine emery paper and brake clean. Then making sure the belt stays tensioned. I/2" deflection as I recall.

[02G]

Upon more detailed inspection yesterday I discovered that

the fan blade on the alternator had come loose and was

creating the metallic scratching sound similar to a belt.

So tightened it up and noise is gone.

 

An unlikely source, but there you have it.

 

Thanks for all your inputs guys.

cheers

G

[FunkyLaneO]

If it doesn't appear to be leaking it is probably OK but the slight click warrants that you keep an eye on it, there is a weep hole under the pump, just keep an eye on that and if it looks like coolant is dripping out of there then it is only a matter of time before the pump fails so you can start planning for your replacement.  I wouldn't bother trying to rebuild a water pump, they are cheap (as long as you don't buy them from the BMW dealership) and the quality of the last one I got looked to be very good.