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914World.com _ 914World Garage _ Engine knock/tapping noise

Posted by: Hammy Sep 26 2007, 08:19 PM

My carbed 1.7 has a tap tap tap/knock knock knock noise at idle. It seems to disappear with engine speed but I can't tell if it's just the exhaust noise covering it up. I adjusted the valves using the Capn's procedure and set them all at 1 full turn past contact, engine has hydraulic lifters. Still the same knock/tap noise....
What is it? Is it fatal? This engine has been good to me and I just need it to last a little while longer until I get myself a FI engine hopefully soon...

Posted by: Brando Sep 26 2007, 09:26 PM

There are a few things on these engines that make tapping and knocking noises. Sometimes distinct, sometimes not. Valve tapping noises sound different than crank/rod knocking noises.

Injector ticking different than ignition ticking... etc.

First you have to locate where the sound is coming from. I usually use a poor man's stethoscope (long wooden dowel or a long screwdriver with a big plastic handle) and put one end to the engine, the other to my ear. Go around the engine. Heads, case, etc.

Posted by: rjames Sep 26 2007, 09:35 PM

The noises from my car ended up just being a huge exhaust leak. I hope your's is something just as minor.

Posted by: Hammy Sep 28 2007, 06:40 PM

I took a better listen today and it definitely seems to be coming from the passenger side head, and/or in the center of the engine/case...
I really only hear it at idle while sitting in traffic, and sometimes it's worse than at other times.

If I were to get a video/sound clip up, could you guys help me diagnose?

Posted by: Rand Sep 28 2007, 10:01 PM

I hope you get lucky like Robert. A piece of hose is a good way to listen for exhaust leaks... One end on your ear, move the other end around where the pipes bolt to the heads. Fingers crossed....

Posted by: rjames Sep 29 2007, 02:57 PM

You could also quickly just check your exhaust stud bolts to see if they are loose. If I had done this when I first heard the noise I could have saved myself the worry, and been driving the car instead of worrying needlessly about an engine.

Posted by: jaminM3 Sep 29 2007, 03:06 PM

I concur..

Exhaust leak..

Posted by: Hammy Sep 29 2007, 03:12 PM

So an exhaust leak can sound like a knock?

Posted by: Rand Sep 29 2007, 03:32 PM

LOL. Wel, it depends on your ear. But I have to say YES. In MANY cases, what was heard as a "knock" turned out to be an exhaust leak.

Posted by: So.Cal.914 Sep 29 2007, 03:56 PM

Back in the late 70's I built a 1385 (1200 block). The pistons I used were cast,

and at idle the skirt slap sounded like a tap...tap...tap. Not sure what you have in

your engine but...Well you get the point. My .02.

Posted by: jaminM3 Sep 29 2007, 04:15 PM

This has happened to me a couple times with other cars and I always think it is valvetrain ticking or tapping, but when I bring it to the mechanic it ends up being an exhaust leak. And these cars have the exhaust stud issue that make it more common...

Posted by: Hammy Sep 29 2007, 06:38 PM

Ok, so the popular opinion suggests an exhaust leak... I recently put in new copper gaskets, filed the tops of the exhaust manifolds down equally, and used the correct copper plated exhaust nuts...No spinning studs, all is tight. What gives? I know there is a slight leak at the gasket where the manifold meets the muffler, but the sound coming from that is not the sound I am hearing.

Posted by: highways Sep 29 2007, 08:14 PM

I'm going through the same can of worms. Convinced I hear a knock... pin pointed it to the passenger side valve cover.. (I believe it is the forward valve). Mechanic thinks I'm hearing exhaust leaks. He redid the copper washers and copper nuts (I didn't have copper nuts). There definitely was an exhaust leak... but the leak is seperate from the knocking noise.

Still knocking... some people say it's normal valve noise, some say drive it until it blows chunks. I wish I could fix it though. To me it seems like one valve does not hold it's adjusment- you set it, then it get's sloppy.

Posted by: craig downs Sep 30 2007, 04:33 AM

If your engine was built using the aluminum head gaskets one probably burned thru.
These should never be used because of this.

Posted by: LetoAtreides Feb 15 2008, 08:35 PM

I have the EXACT same problem you're having, right down to the irrelevant exhaust leak at the manifold/muffler gasket and new exhaust studs/nuts/washers/rings. I even posted a thread about it. I've gotten suggestions ranging from a missing distributor spring to an exhaust leak.

Posted by: 749142 Feb 15 2008, 09:12 PM

i agree with so cal 914. it maybe a piston skirt slapping in the cylinder. tolerances too lose. if your using aftermarket or used originals if they werent put back just the way the came out during rebuilding you will get that tapping noise from the piston skirt.does the noise quite a little bit when the engine is hotter? i have that noise but only when its cold. it gets warm and goes away. if it is piston skirt slapping one of your pistons is to worn or just wasnt up t o factories tight tolerances. you can start the engine. while running pull each one of the spark plug wires and put it back on. go around all four. if the tapping goes away when you pull one of the wires it is piston skirt slapping on that # piston. if it is this dont be hard on it and just let it try to wear to fit. if it wears to fit even tho that the tolerances maybe too lose it will quiet a little when it wears to fit.like i said mine only taps when the engine is cold. the noise is getting quieter. but its not gone when its cold.
steven

Posted by: 749142 Feb 15 2008, 09:17 PM

also if the noise is a kinda deep knocking you might suspect rod knock. hope i helped
steven

Posted by: LetoAtreides Feb 15 2008, 10:30 PM

If you're hearing the same sound I'm hearing on my engine (and by your description, you seem to be) then you aren't hearing the rattle that is characteristic of a rod knock when revved, correct? Also, by your posts I gather that your engine is carbed? I'm sensing a trend...

Posted by: Twystd1 Feb 16 2008, 12:10 AM

Does the sound get louder with LOAD?

Going uphill or bogging the engine?

C