ok so i bought a rebuilt 355 from a machine shop back home and put it in my 68 Nova. iv done the break-in and put about 2000 miles on it. recently iv noticed that there is a loud rattling coming from the motor when i floor it on the highway. RPM's are only at 5500 max and there is a slight ticking when cruising only at certain RPMs. The reason i think it might be a spun bearing is because a had a flexplate from a GM 400 (with the big *** counter weight on it) when i first got the motor. There was the heavy vibration but i didnt figure out i had the wrong flexplate until i had put about 500 miles on the motor. stupid mistake. So i think the wrong flexplate damaged the bearings and theyve gotten worse until one spun recently. can anyone cunfurm my suspisions or offer another possible explaination? thanks
How is the oil pressure holding up? A spun main can sometimes give good oil pressure on a cold start but drop drastically on warm up. Rich
I would forget trying to do a diagnosis via the mental awareness process. It's time to pull the engine and do an autopsy. Of course, you could continue to drive it, but carry a tow rope with you, a cell phone and a GOOD friend's number. Noises aren't ever a good sign. Please. let us know what you find.
Seems that if you spun a main bearing you would be cutting off oil to that main and a few rods. One anyway. It dosn't take long to spin a rod bearing without oil. Then the rod siezes, brakes, and you only have to look in through the new window to see whats wrong. Maybe your cam is going flat of something like that.
on a cold startup oil pressure is at around 40 psi and goes down to as low as 20 to 30psi. pressure stays steady at around 60 on the highway.
a spun main is more like a low knock rather than a rattle, when you floor it? sounds like detonation, pressures seem to good for a bad bearing, did you tighten everything up good on the flywheel convertor end??
The wrong balance flex plate should not cause a main to spin. Nobody is going to be able to tell you exactly what is going on by you describing a noise. That's kind of like asking what color Red is this over the phone. If you think something is coming apart do 2 things. Take the filter off and cut it open. If you are making metal frag's take it back to the motor builder in the car and have them check it out. Anything else is just Bench Racing nonsence. The Wizzard
i tightened everything when i replaced the torque converter a couple months ago. but ill go around and make sure everything is tight. ya its not a clunk, its a loud rattling.
what's you'se guys definition of a spun bearing? I spun a bearing once where both halves of the bearing were on the same side of the journal. it didn't make any noise because the motor didn't spin at all.
Since it is loud try running it without the inspection cover under the flywheel. But like other have said what color is red? Wrenchn
What Flatheadguy said. I really think you are playing with fire if you continue to drive it. It will be much more expensive to fix if something lets loose while you are driving it.
After rereading my post I did not mean take the cover off for less noise. I meant it as a check to see if it is rubbing the flywheel. If the noise is still there with the cover off time to teardown and see whats up Wrenchn
Yes I spun a bearing while racing. When I put it in neutral after thr traps the engine immediately died and would not turn over with the starter motor anymore. When I took it apart both parts of the bearing were on the same side of the crank. Locked up tighter than a drum. I don't think you spun a bearing. JMO
well thanks for the input guys. im just gunna baby the car around cause its my daily driver. but im definitly gunna cut the oil filter and check for metal shavings. regardless of what i find wanna get the motor taken apart and maybe even take advantage of the situation and make it into a 383
Could the flex plate have possibly been installed backwards? Check for any cracks in the plate, especially around the crank flange and bolt area. Try running it with no accessory belts to make sure it's not a water pump, alternator, p/s pump noise or something similar.
try retarding timing sounds like detonation. ticking noise could be tappet clearance, or leaking exhaust manifold.
drain the oil into a clean drain pan and do the cut open the filter thing to. i had a 331 stroker built a couple of summers ago. it lasted one summer. it spun 3 rod bearings and wiped the mains out. the engine made a loud tapping noise and then the oil pressure started bouncing around. the tapping turned into knocking at higher rpm. drained the oil and i could see the bearing material floating around in the oil. i was told by the second builder that the tolerances were to tight from the original build.
Check the flex plate if it's an automatic. They are prone to crack and sound like an engine knock when they do. I've seen it more than once.
Try putting the car in reverse while holding the brake, give it a bit of gas. If the flexplate is loose/cracked the clunk will be louder than in forward gears seeing that the power is multiplied more in reverse. Or at least that would rule out the flexplate as the culprit.
When I was a teenager and didn't notice my new torquewrench was inch pounds not foot pounds I put on a flexplate too lose and it sounded like a rod knock at times
Flexplates also tend to make more noise in neutral and quiet down in gear stopped. Again the loading factor. Main bearings as stated tend to be a low rumble and cause oil pressure issues. Don't forget the possibility of a bad torque convertor, they will swell up and wipe out the thrust cheek. You should be able to unbolt it and move it back into the pump like end play. Good luck.
I definately agree with the problem being the flexplate. It has happened to me twice. The second time it was cracked from bolt-yo-bolt sll the way around except for between two bolts. Bad thing is you may not be able to see the crack without pulling the ******. If you're lucky it will only be some loose bolts.
Any cracked flex plates I ever replaced had a very rod like knock at idle in park or neutral, put it in gear with your foot on the brake and load it lightly, if it is flex plate the knock will be reduced or almost gone. Just does not sound like a bearing to me, check your motor mounts and make sure you are not torquing the motor over into the fan shroud when you get on it.
well a retarded the timing and the rattling went away. didnt make any sense to me cause i didnt mess with the timing and it started out of nowhere. thanks for all the input.
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