SBC Mystery Knock

bilodeaulynn · Sep 29, 2014

How about some more history.
When was the first time you noticed it?
Had anything been changed?

Get a real mechanics stethoscope. They are not expensive.
Try the oil pan, the front timing cover, the valve covers, then the intake, the side of the block, and finally the bell housing.

Almost sounds a little random, like something flying around in the bell housing getting pounded by the pressure plate or the flywheel.

I would pinpoint the location first, then start thinking about exploring.

cv2065 · Sep 29, 2014

Thanks for the explanation Don. Makes sense.

Lynn - the noise has been coming and going for some time. Very hard to detect for the most part, with other times being able to hear it from inside the car. I'll pick up a 'real' stethoscope tomorrow and do some more probing. I've changed a few things over the past two years (dizzy, pumps, balancer, etc), but the noise would come and go. Not sure I noticed it in the first few months of ownership.

Let me do a little more investigating and I'll get back to you guys. Thanks again.

bygblok · Sep 29, 2014

Flexplate or a converter failing internally?

zdld17 · Sep 29, 2014

bygblok said:
Flexplate or a converter failing internally?

What I first suspected but he has 4 on the floor and fifth under seat.

NH69Z28RS · Sep 29, 2014

Just throwing this out there seeing as it's a manual transmission car, the noise seems to be emanating from the lower rear of the engine and the following is an easy check; when the noise is present, have you tried depressing the clutch pedal to see/hear if the noise changes at all?

zdld17 · Sep 29, 2014

Chad, I think someone mentioned this, if you run an inspection cover on the bell housing, have you checked to see if this may be rubbing somewhere?

Someone else mentioned clearance on cam lobes to rods, You are not running a stroker are you? Some aftermarket rods come very close to some cam lobes.

cv2065 · Sep 29, 2014

Hey guys. I bought a 'real' stethescope today, and big improvement over the broom stick. Fired her up, waited from cold to operating temp, and could not get it to do it. I listened to everything from the block, fuel pump, oil pan, valve covers, manifold, exhaust, transmission...and nothing. I thought I heard a small glimpse of it, but nada.

In answer to your questions:

Scott - I don't believe that the clutch has any effect on the sound, but I'll check again when it does it. I recall pulling into the garage and the sound was there the whole time.

Don - I'll check the bellhousing tomorrow. No stroker here. Maybe next year.

Not sure about the flexplate Bill. I'll see if I can get a flashlight up in there, but don't expect to see much.

I'll try again tomorrow and see if I can persuade her to knock. Thanks again for all of the ideas!

zdld17 · Sep 30, 2014

cv2065 said:
Hey guys. I bought a 'real' stethescope today, and big improvement over the broom stick. Fired her up, waited from cold to operating temp, and could not get it to do it. I listened to everything from the block, fuel pump, oil pan, valve covers, manifold, exhaust, transmission...and nothing. I thought I heard a small glimpse of it, but nada.

In answer to your questions:

Scott - I don't believe that the clutch has any effect on the sound, but I'll check again when it does it. I recall pulling into the garage and the sound was there the whole time.

Don - I'll check the bellhousing tomorrow. No stroker here. Maybe next year.

Not sure about the flexplate Bill. I'll see if I can get a flashlight up in there, but don't expect to see much.

I'll try again tomorrow and see if I can persuade her to knock. Thanks again for all of the ideas!

Chad, only automatics have a flex plate, your signature says car is a 4speed? If you have a four speed, scratch looking for a flex plate, don't think you will ever find one.

SBC Mystery Knock

bilodeaulynn

cv2065

bygblok

zdld17

NH69Z28RS

zdld17

cv2065

zdld17

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