Tapping sound getting louder 2.7

[matty74]

Hi

I get this soft tapping (like my old VW bug) sound that has been getting progressively louder in my 911s 2.7 it sounds like its comming from the cooling fan i n the centre of the motor.

It does not sound like it is coming from either bank, is this the tappets?

I do have a couple of oil leaks from the return tubes that are about to be replace d and oil level is 1/2.

Any clue's?

matty74

[WERK I]

Could be a failing bearing in the alternator. Is it louder when it is warmed up?

[KobaltBlau]

Originally posted by matty74
It does not sound like it is coming from either bank, is this the tappets?

no tappets in the middle like a bug FYI. just crankshaft, intermediate shaft, fan, alternator, not all that much really.

[matty74]

yeah gets louder as the car warms up

[matty74]

and sound a little puffy, but I don't seem to have lost much power

[911pcars]

After a slight warmup, temporarily disconnect the fan belt. If the noise goes away, it's the alternator (bearings). If not, reinstall the belt, then use a hose to engine and ear to see if you can pinpoint the sound source.

Hope all is well.

Sherwood

[matty74]

Disconnected the fan belt still tapping, sound tappet like its noisy but has not got any worse.

Tapping noise comming of the right bank its loud like a vw

[911pcars]

With the alternator bearings dismissed as a noise source, here are some other possibilities:

- Chain tensioner
Usually this noise goes down as the engine speed increases

- Rod bearing
Temporarily disconnect spark plug lead on each cylinder. If noise subsides, it's the con. rod bearing for that cylinder.

- Main bearing
Constant noise

Some other ideas,
Sherwood

[matty74]

Dude, you're awsome thanks for the help

Its coming from underneath, and it does get quieter as I increase revs

[matty74]

- Rod bearing - did this, no different, it really sounds like its in the centre
underneath near the fan, another mechanic reckons it the chain tensioner

sound fades at high RPM, almost disappears, noisy at low RPM

[cgarr]

Piston slap can be very noisy when cold but it usually quiets down when it warms up. A rod bearing will increase in noise if you load it up.

[edbaus]

A failing piston pin bushing will slap,

Also, what about the exhaust. A leaking exhaust at the head will do this and will make more noise after it warms up. Also, it may make less noise (or at least it is drowned out better) at higher rpms.

Thanks

Ed

[afterburn 549]

if your rocker box area has a leak- pull the valve cvr. and check for a rocker shaft that has worked it way out.....it will create a leak and noise.

[matty74]

I'm replacing the return tubes next weekend so I'll remove the heat exchanges and check it out hopefully its not a stud

[cstreit]

What about valves guys?

I know the sound seems like it's coming from the center, but you know how it is with engine noises. I'd check my valve clearences first before tearing into the motor looking for bad rod bearings...

How's your oil pressure?

Rod knock is generally most pronounced under a medium load at about 3000 RPM... Try it with the car in 3rd gear. (less wind noise at this speed)

[matty74]

At 3000 RPM >= the sound fades, oil presure is OK

[911pcars]

Originally posted by matty74
At 3000 RPM >= the sound fades, oil presure is OK

It sounds like a chain tensioner (from your description).

Remove the chain box cover from the noisy side. Try to move the idler arm against the chain tensioner stem. If the tensioner is okay, there should be no slack or clearance. If there is and/or the stem can be compressed into the tensioner body, then you have a bad tensioner.

If this is the case, then you can decide whether to replace this (or both sides) with the latest factory tensioner or go to the oil-fed versions. There's a cost difference of several hundred $$ - more if your tech does it.

If you stay with the self-contained tensioner, you may wish to invest in an inexpensive collar kit that will prevent total collapse of the tensioner next time it happens. As the slippery slope steepens, you should also upgrade with post '81 idler arms (wider bearing surface) and replace the chain ramps (5 black and 1 brown [have I got that color combo right? It's been awhile.])

Much in the archives.

Sherwood

[matty74]

There is no oil being burned, if the guide was worn would'nt oil be getting into the combusion chamber?

[matty74]

I used a stethoscope and the noise is coming from the left side chain housing at the to outer corner near the cam shaft

[afterburn 549]

pull the cover,ez to do, and take alook