Stock 170 knocking(?) under load

Hi guys,

So I recently added AC to my 64 1/2 Mustang, and in doing so had to cut away some of the insulation on the firewall in order to fit the evaporator. After I got the car running, I noticed a big increase in noise when the engine was under load -- specifically a rattling or knocking sound at the same frequency as the engine RPM. Initially I put this down to the reduced acoustic insulation, but I am wondering whether I might actually have a problem with detonation.

Given how pathetic the engine performance is, it's really not hard to put it under enough load to make this noise and I want to make sure I'm not causing any damage. This is happening regardless of whether the AC is running.

Here's a recording. I'm cruising at 50 on a slight uphill, and I put my foot down between 5-10 seconds and 13-18 seconds which causes the noise.

[soundcloud]https://soundcloud.com/cliponmike/knocking-under-load[/soundcloud]

Is this just exhaust noise? Or something I should investigate? The car is due for a change of plugs / cap & rotor, so I also bought a timing light and thought I'd check that. Haven't done that before, and I haven't had to investigate this sort of problem so I'm not really sure where to start. Since it's consistent and happening at the same rate as the RPMs I figured it might be a problem with just one cylinder. Is there something I should be looking for when I change the plugs?

Thanks for your help!

In my OPIN I don't think it's anything internal in the engine such as a Rod or pistion knocking or even caused by detonation. This sounds like a very tinny type rattle, things to check are at the back of the engine block, the tin plate between the bell housing and block, or the flywheel inspection plate are both bolted down tight, bell housing to block mounting bolts are torqued down to spec, flywheel to crankshaft bolts are torqued to spec., clutch pressure plate is bolted down to flywheel to spec. most all of these can be checked without having to take anything apart the exception is for the flywheel and clutch pressure plate. Last check out that the exhaust system is bolted in tight to the manifold, and all the tail pipe hangers, as well as a muffler that's coming apart internally like a losse baffle. To test for that lightly hiting the muffler with a rubber mallet or the palm of your hand to see if you can hear anything rattling inside. Does it feel like the engines is vibrating or miss firing when this is happening? If that's the case then yes you should do a compleate tune up to make sure the carb and Distribitor are in top operating condition. There are also upgrades to give even better than stock engine performance of the ignition system and carb too. Good luck in the hunt.

Y increase/decrease w/throttle? Almost as if the motor rocks w/loose motor mounts - the fan is just beardy tickin the radiator (I have this image w/the sound, not possible w/the real distances involved).

Yeah, I say this every time some 1 hits us up w/a strange sound or asks for assessment on their exhaust note...sounds over the puter (or any speakers) is difficult (analog to digitized, speaker/mic quality, etc, etc).

Back to the ol stethoscope idea on the post 3 day ago. ie 1st step:"Locate sound". U may need 2 ppl for this. U instruct and stay out of driver's seat. There may B several more steps, even way B4 final diagnosis, never mind addressing it (ie moving v stationary, etc)...

Hi, too me, that sounds like something is vibrating and flapping against something. First I would look at all the new AC parts and make sure they are all secure and nothing is rubbing anything. If it never made the noise before it makes sense to assume it has to do with the new AC. Next, If you have an automatic you can put it in gear and have a helper hold tight on the brakes while giving it gas so you can look in the engine bay with the engine under load. The way to check your motor mounts is to power brake the engine in reverse and drive, and lift the back of the tranny to check the rear mount. Good luck

"... If it never made the noise before it makes sense to assume it has to do with the new..."
/AND/
my lill sig quote in reverse: "...Big thing is only make one change at a time. Change 2 or more things at a time it becomes difficult to figure which change helped or hurt..." ie what ya last did.

ahhh the art (& science) of auto diagnosis. The frustrations AND the joys (yeah, right!)
:mrgreen:


"...Back to the ol stethoscope idea on the post 3 day ago..."

starting simple'

... exhaust leaks often can mimic a knocking sound, look for carbon traces at flanges and possible manifold cracks . Howz' oil pressure at idle?...

Welcome & 4 MAINS RULE !

My '63 ' original 170 had a knock when rescued and finally localized to generator - car and Generator had sat and gen. shaft rusted smaller on one side - wobbling in bushing cup.

. .
have fun

i agree with powerband. it sounds exactly like the exhaust leak i have in my 64 falcon 170. i can tell you that mine is due to a few cracks in the exhaust manifold, big enough that you can see them easily in my case.

no thing seen there?
Take a 2 ft piece of garden hose,
place on ear, move around that area...
watch out for fan, the belts and manifold burns (hands, rubber)