Loud tapping noise coming from otherwise good running engine

[jackofalltrades]

Hello all,

I managed to get everything hooked up on the 69 mustang to get it started and even do a little test drive up and down the driveway, but the problem is that when the engine is running it makes this loud tapping noise that almost sounds like someone tapping on metal with a hammer. You could stand 50 ft away from the car with the hood down and the tapping echoes out from the car. I checked the valve train to see if there was something out of place that may make such a loud noise but all was well. The engine runs good with no misses or backfires or anything that may imply that the valves are stuck open. To my best knowledge these weren't interference engines like the foreign counterparts where the pistons destroy the valve train when the timing belt/chain breaks. The oil pressure is also way up there and gets to the top end very well, so well that when I had the valve cover off to observe the valve train, it sprayed oil all over like a sprinkler. The car takes the throttle well and accelerates just fine. The engine runs good overall, with the exception of that stinking noise! The exhaust pipe is slightly crooked where it goes into the manifold and I can feel vapor coming from the apparent gaps but could a leaky exhaust right at the head cause this much noise? Any help anyone can lend on this one would be greatly appreciated.

MP

 

[Mercury Mike]

If it sounds at all like an exhaust leak, then yeah, definitely!

Where does the sound come from? Listen around with a long extension to your ear, use it like a stethoscope.

 

[rbohm]

8) yes an exhaust noise is actually quite loud.

 

[Lazy JW]

.... I can feel vapor coming from the apparent gaps but could a leaky exhaust right at the head cause this much noise? ...

Oh, yes it can and will make LOTS of racket. If you can feel the leak you have found the problem.
Joe

 

[jackofalltrades]

From what I could gather, the noise was coming from the right side; I had my head in the engine compartment with my ear literally turned towards the engine to try and pinpoint the noise but all I could conclude was that it was coming from the right side. With the hood closed I can hear the tapping clearly when standing some 30 ft away in front of the car. I have to do a couple of tests the first chance I get, one will be to pull the exhaust pipe from the manifold and run it to see if the tapping is still there and the other will be to manually turn the engine over while underneath and listen around the oil pan and the flywheel to see if anything may be scraping or hitting in any way to see if I can find the problem, more to come....

 

['68falconohio]

Like others have said, an exhaust leak can be pretty loud. That donut gasket on the header pipe is probably leaking, like mine is. Stupid rusted up bolts, I'm afraid to break them off.

When my water pump went out, it made a knocking/hammering noise that I initially thought was one of the front cylinder's rod bearings/wrist pins. I'd never had a rod knock/hammer before so I didn't know what it sounded like and assumed the worst.
I pulled the water pump belt off and ran the engine for just long enough to determine that it had to be one of the accessories that was making the horrid noise. Play in the waterpump's bearings helped narrow it down from there.

Stephen

 

[jackofalltrades]

I didnt think about the water pump, Im going to have to check that out just as well to eliminate and/or find the problem. Im pretty optimistic that it isnt a rod knock, Ive heard engines with rod knocks and they're nowhere near as loud, and if by chance they were that loud, the engine probably wouldnt have lasted much longer as the thing shot the piston through the head...My engine was left idling for a good 30 min, only generated 180 degrees temp the whole time. Well tomorrow Ill be digging into the car to mop up with the build so I can get it on the road, as well as find that stinking noise.

 

[jahearne]

I wouldn't wish this on anybody, but my last '66 Ranchero 200 cu in. had a loud knocking noise at first was random then all the time. Turns out somebody sabotaged the motor by pouring a few ball bearings down the carb. Most had made it past the valves, but one would get caught between the piston and quench area on the "D" shaped combustion chamber on #6 cylinder. That hardened ball bearing wouldn't give, so the softer piston took a severe beating. Similar dents/marks on #4 and #5 but #6 was hammered. It sounded like a somebody took a ball peen as hard as you can hit it only from the inside if you can imagine that.

 

[Quick 8]

I recently had a problem that sounds EXACTLY like you are describing. I hate to tell you this, but mine turned out to be bad rod and crank bearings. I am now building my new engine, but to buy some time until the new engine is ready, I installed new bearings. The sound is now significantly less. I am just hoping it lasts until I am ready to install the new engine.

I sure hope your problem turns out to be somthing different. You can check the bearings while the engine is still in the car by draining the oil, dropping the pan, and pulling a few caps.

I hope this helps.

-Jim

 

[jackofalltrades]

I went under the car yesterday (Monday) to listen around while it was running. I tried checking the water pump by running the engine w/o the fan belt, the tapping was still there. While under the running engine, the tapping was VERY loud. I checked around the tranny to see if maybe a warped flywheel may be causing the noise (I had this happen before). It didn't appear to be that. Then I put my hand on the oil pan towards the rear and besides feeling a sizable dent in the pan, I also felt the tapping in the dent area. Apparently the pan was dented enough that its being hit by a crank lobe or connecting rod cap. Either way, the pan's gonna be coming down to have the dent tapped out. We'll then see what happens after that.

 

[69.5Mav]

jackofalltrades

Do your self a favor and check your rod bearings while the pan is off. I got a used Sentra engine once that had sat for a long time and all the rod bearings were pitted like from corrosion. One had just started to knock but after replacement (no apparent damage to the crank) it runs fine.

Quick8

You might try one more rod bearing replacement. Use Plasti Gage to check clearances.

 

[jackofalltrades]

I pulled the oil pan yesterday and found out just what I suspected, the dent in the oil pan was deep enough that one of the connecting rods or crank lobes was scraping on the inside of the pan. In fact the scraping was deep enough that after I pounded the dent out, it opend up a hairline crack that for now I temporarily patched with some JB stick weld but will end up replacing the pan with another one (when I can find one). The rods all appeared solid, no play/movement.

 

[rbohm]

I pulled the oil pan yesterday and found out just what I suspected, the dent in the oil pan was deep enough that one of the connecting rods or crank lobes was scraping on the inside of the pan. In fact the scraping was deep enough that after I pounded the dent out, it opend up a hairline crack that for now I temporarily patched with some JB stick weld but will end up replacing the pan with another one (when I can find one). The rods all appeared solid, no play/movement.

8) you might not have to replace the oil pan. many years ago(1979 in fact) i had an oil pan that had a hole in it where a rod bolt went through when the engine broke. i flattened out the metal, cleaned it thoroughly, and epoxyed a piece of sheet metal to each side of the hole. i held the two pieces in place with a C clamp. that pan has never had an issue since as far as i know. the last time i saw the pan was three years ago when i sold it to a guy in west virginia because he needed an oil pan.