Name That Sound! (Motor Issues)

[chevjayfsd]

Hello all, let's see if we can't figure out what noise my motor is making.

Details:
- Started a week ago
- Fluctuates with RPM
- Sounds like a cross between an exhaust leak (which it's not) and a lifter tapping (impossible) and a pully squeal (impossible, took all belts off and started motor, noise still there)
- Fluids are all good
- Oil pressure is spot on
- Temps are all good
- Gets louder the warmer the motor gets
- Small amount of smoke coming out of the carb (Rochester 4bbl)
- I think it sounds like its coming from towards the rear of the motor, dad thinks more the front.

Motor Specs
350 bored .30, Rochester 4 bbl, XE 262 cam...

Help?

[mario1128]

may be a bad distrubuter i had one once that had the rotor hitting the cap scared the crap out of me . good luck

[mikey531]

"Small amount of smoke coming out of the carb (Rochester 4bbl)"

I agree with mario1128, the smoke in the carb might be caused by a misfire from a bad distributor.

The sounds:

exhaust leak, it could be a slight backfire through the carb

lifter tapping: could be the rotor hitting the dist cap

pulley squeal : a bad bearing in the distributor causing, see above

Just my opinions but I would start there.

[Inked Okie]

Is it a HEI? Check the weights inside the distributor? Had a recent problem with mine would not hold time and the rpms would increase when the engine warmed up.

[pat 70/71]

check to see if the fuel is flowing to your carb. mine did the same thing & poped & farted& it was all about gas brother! good luck, Pat (lean condition) ?

[Bob 68327]

Might check flywheel bolts ..

[68C15]

you sure you don't have a lifter eating away at the cam? I know, I have a knack for bringing up the worst case scenarios.

[GMCMAX]

Mine is the fuel pump arm going tap tap tap; havent pulled it off yet, but it sounds just like a lifter.

[MT1972cheyenne]

I have seen more than one cracked Chevy flex plate make a tick noise like a lifter/exhaust leak, but more squeaky.

[Shaky]

With the engine running, I usually take a length of garden hose or heater hose and hold one end to my ear and move the other end around near the engine. It sometimes helps me isolate where it's coming from...

[71tahoe]

One easy check is to take off valve covers and see if oil is getting to your rocker arms. That can cause the symptoms you describe but it's not the only thing.

[toddtheodd]

Could be the XE cam you have there.
I've read that on some of those, the closing of the valve is so quick that it makes a tapping sound.
I know my XE274 does that.

[Wootdog]

I know it may sound weird, but I had a similar sound once, it was the dipstick coming in contact with the crankshaft. I pulled the dipstick and no noise. Got a different one installed after that.
Kerry

[CSGAS]

Originally Posted by Shaky

With the engine running, I usually take a length of garden hose or heater hose and hold one end to my ear and move the other end around near the engine. It sometimes helps me isolate where it's coming from...

x2 plus read your plugs, make sure they are firing and compare them to a chart to get an idea of how each cylinder is running (keep track of which cylinder is producing good/fouled/detonating plugs or whatever). Charts should be available on major manufacturer's sites (I know Autolite has one)

[idastang]

Man I feel your pain. I just spent many hours chasing a strange sound. I searched many post to try to find the answer. The sound even out witted my best buds that have been doing cars and trucks for years. Here is what I went through. Mind you I could only get the sound under load. To produce the sound in the garage, I had to hold the brake pedal and rev up the engine. I even took a guy for a drive down the street that ran 327's at the track. (thats what is in my truck) He felt very strongly it was a rod bearing. He suggested to drain the oil while hot and filter it through a cloth to catch and shavings that may be in the oil. The result was very fine and very few shavings, so off with the pan to inspect the bearings. Since I would have to pull one by one I went ahead and replaced each rod bearing as I went through the inspection. Never did find one that would produce a rod knock. Next was told the flex plate could be cracked. Was told just to tap it with a wrench and if the sound was a long ringing sound it should be ok. Well I wasn't sure about the sound, and I could only see so far with the inspection plate off, so opt to pull the motor. In doing so the flex plate was fine how ever I had a motor mount drop out, so I thought well there lies the problem since the motor was only bolted down on one side. I put it all back and fired it up and sure enough, that was not my problem. Then someone told me a buddy of his had the same issue and was able to resolve it by changing the timing chain. Ok so long story short, no it was not the timing chain, no it was not the fuel pump rod or the fuel pump, ( yep changed those too) and no it was not the cam or lifters, (yes changed as well) and not the dizzy. Having nothing left to do but pull the motor (for yet a 2nd time) for a complete tear down and inspection, I did just that ( could have saved many hours had I just did that to begin with). The mystery sound was from # 6 piston and wrist pin bind. When I took the block to the machine shop, the machineist said the bore on #6 cylinder was tight. He was able to hone the block for a clean up in all the cylinders and now I have a good runing 327 in my mutt. The piston on # 6 was scored really bad. The machinist speculated this could have happened from a previous hone job not allowing the cylinder too cool before the final hone or the block over heated at one time. Like I say man I feel your pain and hope you find your issue before too much time. Good luck

[BLAZERMAN]

Is it worse at idle? this is hard to desribe but do you hear a fwoosh sound after shutting down the motor? next time its doing this try pulling the PCV valve out while the motor is running.

[Painter D]

Originally Posted by toddtheodd

Could be the XE cam you have there.
I've read that on some of those, the closing of the valve is so quick that it makes a tapping sound.
I know my XE274 does that.

Mine does this too , I hate it. It's definately a possibility for the noise.

[mr48chev]

If it is mechanical you can usually isolate it by doing what Shaky suggested or something similar with a piece of wooden broom handle. Mechanics stethoscopes are easy and not too expensive to find and are a lot of help when checking noises.

As it is happening when the engine warms up I would think that it is either connected to the ignition or fuel system but wouldn't rule out the pcv valve as a possible culprit.
Noises tend to telegraph at times and often aren't exactly where you think they are.

[Jeffs70]

Do you have headers on your truck? are your plug wires clearing your exhaust? check to make sure your plug wires dont have any wear and rubbing against metal, also I would make sure your plug wires are on the distributor correctly in time, this sounds to me as a timing issue with the carb spitting at times also make sure you have your distributor cap on tight and correct, or if your cap has any cracks in it can cause issues also.

[mario1128]

How did you make out with the noise issue ?