Tapping sound from the front of the motor *Think I fixed it*

[k20]

Ok, on my 496, internally balanced, I have this tapping sound coming from the front of the motor. I took off the clutch fan, to see if that was the prob, still does it, then I took a piece of vacuum hose, and made a stethoscope. I cant find the noise anywhere. Probed all around the oil pan, the water pump, timing chain cover, manifold, heads, valve covers, everywhere I can think of. I swear it sounds like its coming from the crankshaft pulley/balancer.

I checked the bolts on the front pulley and they are all tight. Anyone have any ideas? The tap seems to be most evident at idle, it doesnt always do it, but when it does it, if you tap the gas, it does increase its speed, with rpm. But like I said, it isnt always doing it. I usually notice it when the engine is warm, cant recall hearing it when the engine is cold.

Help.

 

[dirtwarrior17]

torque converter????

 

[surpip]

thats on the back of the motor, close though

 

[RingMaster4x4]

fuel pump? but I bet you are electrice.

 

[kyser_soze]

Does your motor run rough? The last tapping sound I heard on my truck was an arcing plug wire, intermitantly.

 

[k20]

Fuel pump is electric, and truck doesnt run rough. With it warmed up, I hit all the header pipes with a spritz of water to see if they all evaporated at the same speed, they all did. That tells me all the cylinders are firing. Also, none are glowing red like if an exhaust valve was burned letting raw fuel into the header pipe and it igniting there.

 

[73k5blazer]

Loner tap, or like multiple things tapping at once? How's your oil pressure?

 

[Smitty]

I'd check the end play on the crank. Had the same thing and it turned out to be a wasted thrust bearing and the crank counterweights were just starting to hit the block.

 

[k20]

Oil pressure is 45 at hot idle, 60 the rest of the time.

Also when it does it, it might be a single tap, or it might be 3 or 4 in a row, then quiet, then it might do it again in 10 secs or 10mins.

 

[k20]

Anyway to check endplay without dropping the oil pan?

 

[garlicbreath]

Cam walking and tapping timing cover?

 

[k20]

It is a hydr roller cam w/ cam button, but, I did the sounding probe to the timing cover and couldnt hear it, even though it was tapping at that time. In my left ear I could hear tap tap tap, and my right(piece of vacuum hose) I couldnt.

It sounds like its centered on the motor. Somewhere around the crank pulley, balancer, waterpump, timing chain area. Waterpump shaft doesnt have any discernable movement, though I did notice alot of 'trash' floating in the coolant recovery tank. None in the radiator, but some in the recovery tank, dont know if it got in last time I went muddin or what.

 

[garlicbreath]

Only reason I asked is I too have a roller cam motor, but mine is a 355. The rebuild shop forgot to tighten the cam retainer plate, which allowed the cam to walk forward and tap the timing cover. Mine was also consistent with RPM, and I also couldn't tell where it was coming from, just knew it was from the front of the motor.

 

[grindkings]

Got a blown exhaust manifold gasket?

 

[k20]

I have Copper header gaskets, checked all the bolts, all tight.

I just went outside and fired it up, if I look REALLLLLLYYYYY close, you can see a little movement in the crank pulley. Like its out of round. All the bolts on it are tight though. Dont see it makin a tapping sound, but figured Id throw it out there, see if it matches some symtom from somewhere.

 

[grindkings]

lifter knocking?

 

[dirtwarrior17]

thats on the back of the motor, close though

serious?????



You've never heard of loose torque converter bolts causing a knock? you must not have much experience with torque converters...

dude, i have done alot more than you think... pulled the tranny atleast 3 times...

you don't have to tell me where a torque converter goes...

K20: If can do it easily might want to snug up the tc bolts... i know when they come loose it can cause a knock.

 

[k20]

Alright, Ill check em this aftn and Ill update this then.

 

[k20]

Ok, torque converter bolts are tight. Its definately coming from the front of the motor. I did the vacuum hose stuck in my ear(neighbors are probably like wtf), and probed the oil pan. Its quiet. Probed the top of the timing chain cover(cant get square on the front w/ the fan and waterpump there) and its quiet. Probed the waterpump, hear coolant flowing, but no banging sounds.

Now however, I am thinking. It looks like my crank pulley 'wobbles' a little, but the balancer doesnt appear to be. I have an 88 suburban pulley setup, 2 v-belts and a flatbelt. Does anyone know if this pulley is a 2pc pulley? Is it 2 halves welded together? For some reason, I remember when I powdercoated all my pulleys, there was a little 'slot' where it looked like 2 pieces joined, but now crossmembers are in the way of being able to see that. I am thinking, perhaps my pulley has separated a little and is tapping around. Anyway to check this theory short of swapping pulleys(which I dont have another one)?

Thanks guys, this has me semi-worried(have to rebuild the motor) and semi-perplexed(I dont know wtf the sound is).

 

[diesel4me]

did you take the belts off??

Did you try removing all the fan belts and running it for a minite or two,to make sure its not the water pump,altenator or air pump(if you have one!)/??

That will help narrow it down some...I have seen harmonic balancers "wobble" and make a weird knock,usually happens after someody honed the I.D. of it with a brake hone to make it slide on easier,or if they crack during installation,sometimes the woodruff key in the crank will make the balancer crack--I've seen the crankshaft timing gear crack when installed too,and they will knock for awhile until it breaks in half,and you can imagine what the 2 chunks of gear will do to the rest of the rotating parts..

Also seen mechanical fuel pumps with loose rocker arms make clacking noises,that sound like a loose timing chain hitting the cover--the pushrod that runs that pump can knock if the cam lobe that runs it goes flat,and allows it to slap against it--seen a few bent ones too!...

Did you try pulling any plug wires off and see if it makes the knock go away or increase??--it could be a wrist pin,they can sound horrible at times,then fade away and almost dissapear at other times--usually loudest when its hot,as opposed to piston slap,which gets quieter as it warms up,and is loudest when first started cold....it can be quite difficult to locate the noise source at times--hopefully you'll find it before whatever it is fails completely and takes out the rest of the motor....good luck!..