GTV6 Idle Knocking

[Luke L]

My 2.5L GTV6 has been developing a louder & louder knocking noise at idle.

I have been trying to work out where it is coming from ie. valves/tappets or big ends!

My best guess is that it might be related to the driveshaft/doughnuts/engine mounts as
1) the noise goes away off idle (driveshaft rpms change)
2) the noise changes with the clutch in/out & trans in neutral (due to trans. drag torque & idle rattle masks noise?)
3) the noise seems ok cold & gets worse with increasing engine temps (as rubber doughnuts/mounts soften)
4) I had also noticed a slight squeak noise which also seems related to the driveshaft (only occured warm)

Has anyone out there had a similar experience/can point in the right direction as to what to look for on the mounts/doughnuts??

thanks 

[shane wescott]

Not an expert, not a mechanic, but check the level and grade of oil.

It may be that a heavier oil will quieten the knock, but if this IS the case then that would suggest to me early signs of worn out bearings or some such engine internal component.

At ilde you would have less oil pressure (i assume) and this could mean less oil around the worn components and more knock. The tappets on my engine have made some small ticking sounds since I have had the car and I have been told if the engine doenst make some sort of tick sound then start worrying :-)

But that's not a knock.

As for it being mounts or drive shaft, bery careful positioning of your head should give you some indication of where the noise is from. I work in IT and years ago, back in the dark ages we used to use a large screwdriver with the pointy end touching metal, and the blunt end to your earto listen to what was going on inside disk drives.

I have had people tell me they do the same thing to "listen" to the inside of motors.

Just a thought.

Good luck and I hope what ever it is it turns out to be the cheapest option.

Catch ya

Shane

[Luke L]

Hi All,

thanks for replies so far

the noise does sound like it is coming from the engine rear/driveshaft front
(have just been too lazy to get under there with the engine running for a closer look!)

I have also noticed more driveshaft vibrations than before ....off idle & transitioning from + to -ive torque.
-> may suggest mounts/doughnuts getting soft/worn?

I am also due for an oil change so i will check that out also ...low oil pressure @ idle is a valid pt!
(what oil is recommended...I have heard Penrite HPR30 20w-60 mineral oil is this correct??)

Just hoping someone has seen a similar problem & can point me in the right direction?
eg. what to look out for on doughnuts/driveshaft mounts??

otherwise I can plan a night lying under the car with a torch/srcewdriver.

thx
LL

[MD]

Luke L,
You sort of have to know a little of what sound you are looking for to identify the problem internally to engines and gearboxes etc but a mechanic's stethoscope I find is useful tool to have. About $20 on Ebay.

You will hear lots of noises when you use it but there will be clearly a dominant one which you can than approximate its location and thereby identify more accurately (but not certainly) what it may be. eg gudgeon pins.

[shane wescott]

Penrite HPR 30 is what I have been using for over 3 years in mine and happy with it.

[Luke L]

Oil & filter change completed (with HPR30)
- oil pressure when cold looks higher (as expected if old oil had thinned out)
- but idle knock is still there!

The noise is intermittant, sounds like a metallic "click click" noise & appears to be coming from just behind the rear of the engine.

Couldn't see anything obvious under the car but need to have another look when it is making the noise ...maybe time to invest in the stethescope?

Just wondering if it might be an exhaust or engine mount that had worn & is possibly grounding out?? & if anyone else has had the same experience???

[Sheldon McIntosh]

Choder's advice seems pretty sound to me.

If it was the engine mounts/exhaust hangers/donuts it would be pretty easy to spot with an hour under the car, have you done this yet?

What is the frequency of the knocking?

-is the knocking constant, or random?
-what does it sound like? Hollow or solid?

[MD]

LukeL.
Always a pleasure to help out any Alfa owner and especially a transaxle owner and most of us that have tried to diagnose your problem are pretty savvy with them but can't conclusively give you an exact diagnosis and not much will change as describing noises is one thing, hearig them is another.

You seem keen to do the job yourself, if that is the case, here is my final tip.

Find an outlet that is willing to hire a hoist say for half an hour. Get under the car and examine it end to end.Get a friend to sit in the cabin and change gears and rev the engine a little here and there. See if it will generate the noise that concerns you. If you still cannot work out what is causing the noise, well frankly, give up and learn from the mechanic as suggested by others.

You may or may not encounter problems hiring a hoist as there are workplace health and safety issues that could be a concern for some operators. No harm in trying.

[Luke L]

all sorted! (finally)

in case anyone else ever finds a similar noise....read on

- had a closer look/listen on a hoist (Hugh @ Monza was kind enough to help)
- diagnosis was centre driveshaft joint noise/rattle (possibly due to worn centre bearing/donut bolts not as tight as they should have been/centre bearing rubber sagged slightly)
- have now replaced centre mount/bearing assebly...idle knock is gone, trailing throttle shimmy gone!....phew....car & I are much happier!

advice - first check all the driveshaft bolts are tight, including bolt at front joint which clamps spline at front of driveshaft!

[MD]

Well done. Nothing like getting the job done yourself and learning something along the way.