So, I'm rolling down the road, and I get the urge, You know the urge,I roll the Olds down to about 10 mph,(engine is warmed up) pull first and nail it. Not the hardest ever, just 5,000, push the Zgate onto second, roll out of it. I hear this tapping noise, around 2,300 easy load, but its there. It still runs, But I'm thinking wrist pin or spun rod bearing. It also cranks over slower than usual, which really sounds like a rod bearing. Dammit,
Get yourself a inexpensive automotive stethoscope, and try and isolate the problem. A screwdriver or solid steel bar works well also. Once you isolate the top end from the bottom end, you can save yourself some time and money.
Yank the valve covers and see if anything looks out of the ordinary. If it's a tapping noise, often times that comes from the top end, usually a damaged lifter or rocker arm. If it's a knocking sound, it's usually the bottom end. If it's a spun bearing, you'll see a drop in oil pressure and possibly metal shavings in the oil. A wrist pin will knock, but not as loudly (or deeper sounding) as a bearing. I learned this method for identifying a wrist pin issue: Either advance or retard the timing and see if the noise quiets down. If it does, it's a wrist pin. The issue with it cranking over slowly could very well be a main bearing.
check your distributor and see if it moved, if it rotated , your timing is off, you could be hearing spark knock at that rpm, it will also make it cranks slow if its out of time
If you spun a bearing you would know it for sure. It gets no oil to the bearing and will make a loud screeching sound, just before it locks up.
A spun bearing would have a rod knock sound. I would check your oil pressure first then inspect your valvetrain.
Piston knocks at idle, and on cold start. Rods, when you rock the throttle. Just as you let the revs level off at about 2000 RPM, BRRRT! Valve train is at any speed and "tinnier". Also slower frequency, valve train operates at half crank speed.
been there, mine made a funny knocking sound then the oil pressure started bouncing around. the noise went away for the most part at idle but knocked slightly off idle. pulled pan and found spun bearings.
a spun bearing would create much heat ! take it apart so as not to break a rod . spun bearings make big heat & sieze the motor . ............. steve
Try pulling your sparkplug wires one at a time and see which one lessens the noise, when removed. That's the cylinder you need to look at. If nothing changes, it's most likely a main bearing.
Others know far more, but FWIW the spun rod bearings I've heard there was *zero* doubt what the problem was. My experience with my last motor that was hard to start when warm, actually, was the distributor hold down clamp was bad! Who knew?!? Tightened up good, but it would loosen up and the car started good if it was cold, but run it for a while and it didn't want to start, it'd turn slower. Put a new clamp on, set the timing, problem solved. Good luck man, I'm betting on(hoping for) a lifter!
i have a 350 here that has a spun bearing, a friend came here with it for me to figure out what the noise was, at idle and just moving around the yard you couldn't really hear it, but give a little more gas and there was no trouble hearing it, so i pulled the pan and sure enough it had spun the bearing, the crank was scored up and the rod was beat out, both shells were on top of one another, i have seen bearing spin and not hurt the crank, but the rods have always been messed up.
thought I spun a bearing in a chevy van once(350) but turned out to be a cracked flex plate. also had a ford ranger with a v-6 that spun a bearing, it deadheaded the pump and blew OFF the oil filter.
The mains will cut off the oil pressure... the rods might or might not affect the oil pressure erratically but will get louder with the rpm's. I just changed out a set of Rod Bearings on my OT hodge podge Dodge Increpid! With some difficulty I was able to do this while in the car and caught the crank damage before it got too bad. The crank needed a 1,500 grit emery clothe polish job.
OK the last rod bearing was toast, so I have been putting together another engine and its almost done! Another 455, keith black pistons, polished rods, rod bolts, fresh "C" heads, same intake carb and Distributor. we'll see what happens tomorrow.
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