There is a noise in the engine which bothers me. It has been there for almost 4K miles, and has not gotten any worse. It is a mid range frequency. That is not as high pitched as a loose valve and not as low as a rod knock. There is not block vibration associated with it. You can not feel it when you lay your hand on the block. It is at the RPM of a valve, but does not sound like a valve. It cycles in and out of phase on about a 10 second phase cycle. That is, it is loudest for awhile and then fades completely away in about 5-10 seconds, and then in the same time period grows back to full volume. Those who have not had it pointed out to them do not hear it. Only after concentration, and focus do you hear it. But it is there. And it bothers me. I already adjusted the valves while it was running, as is my custom, to make sure it was not simply a loose valve.

Here is my theory. I think the noise is a from the sideways play in the rocker arms. I think this is the sound of one rocker bumping up against the spacer tube on the shaft. As the spacers shift left and right the noise comes and goes. That is my theory, but I have no way of proving this. The theory is based on the fact that when I set the valves I thought I could make the same noise with the sideways turning force of the wrench I was using to set the valves.

The question is: has anybody experienced this kind of noise, and is there a way to make it go away? Or more importantly, does anyone suspect there is something more serious going on here.? I have forged pistons in the engine, and wondered if this is the sound of piston slap. The engine is still actually pretty tight. When I shut it off, it stops instantly with no coast down. Thanks in advance for any thoughts you have on this.

Sam

_________________

Sam
have you tried using a piece of hose (heater hose works well) and a funnel as an ear piece to zero in on where the noise is coming from,,
be careful around the fan and belts..

Not yet. That is a good idea. Thanks.
Sam

_________________

Never heard of that. Long screw driver. (handle on the ear!!)

_________________
'72 Duster 198 stock cam, 3:23's Hookers on jack stands for 8 years in the driveway
'79 Maxivan 360 Offy Qjet Comp RV cam/rusting in the driveway.
93 D350 160HP Cummins Auto Dually Clubcab needs a injector pump
2005 Golden Couch Buick

want to hear some interesting buzzes,,
get a post card to 8.5 x 11 sized, piece of paper and balance it lightly on the the tranny gear shift nob while motoring down the road,,

Perhaps the radio isn't loud enough????



- Mac

[quote]Perhaps the radio isn't loud enough???? [quote]

I'm pretty sure it is the muffler that is not loud enough!!

Rick

_________________
2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

From your description my first guess would be (mechanical) fuel pump noise, but I don't think you're running a mechanical fuel pump so that's out!

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

You cannot hear this noise at all driving down the road. In fact, I am pretty sure it goes away above 1500 rpm listening from under the hood.
Dan I know the sound you are talking about. This is harder sounding, but no louder.

Sam

_________________

Remove the fan belt(s) to rule out the water pump and alternator.

_________________
Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

The sound you hear is your own paranoia......

Check the oil pressure and level, shrug your shoulders ,,,,,,,

_________________
Yeah....Im the one who destroyed this rare, vintage automobile.....

Sandy, you are right. But, being paranoid is not proof they are not out to get you. The concern is it is time to get this EFI dyno tuned. But my dyno guy is reluctant to put the engine on a dyno if there are any concerns about the integrity of the engine.

I am not concerned about the engine in normal driving. It is a slant, after all. I was hoping some slant guru here would recognize the sound from my description and have some insight.

Sam

_________________

Sam,

Yes......I hear this sound same sound with my old stock 79 motor and the brand new rebuilt motor.

I have always wondered what it was but no mechanic admits to it......I am not sure most folks can really detect it. I did buy a automotive stethoscope which really amplifies the sound. I just can't pin point it. It sounds pretty uniform all over the block then disappears then cycles back......
I have heard the fuel pump knock, but can't believe it would create this intensive and uniform sound all over the block.

So your not going looney. My muffler system is super quiet so it is very obvious to me when idling only.

Good question! Maybe Doc can explain the engine harmonics at idle. My oil pressure is well over 45 lbs. at idle, hot or cold.

_________________
Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

Hate to say it but...
I tend to use the: "wait until it breaks, then you will know exactly where the sound was coming from" point-of-view.

I have "chased" engine "harmonics" before... with little success.
One area to look at is the flex plate / torque converter. I have see "wobble" in that area at low RPMs.
DD

Doc,

So your saying to pull the cover and look for a slight wobble in the flex plate? That will be kind of hard to see with an automatic.
Do you run a pointer or stick of chalk from the bottom of the block to the flex plate and listen for a tick????

Please describe how you have done this process. All my bolts are super tight and per the torque spec.

Thanks,

_________________
Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG