Knocking in the engine
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Knocking in the engine
Hey guys, perhaps you can figure out what I have going on here.............I have a '72 351 Windsor with a one year rebuild on it. It runs great except it has recently started making what can be described as a banging knock that keeps time with the engine. It is not in the valve train, it sounds like it is coming from the lower rear, where the engine and trans meet up. I thought it might be the flexplate but that is straight and true and the starter is clear. What could be causing this noise on what is still a newly rebuilt engine with maybe 6,000 miles on it. Any help would be greatly appreciated. Thanx
Roast em' if you got 'em
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From: Rio Rancho, NM
Have you listened to the engine in various places? A long prybar or screwdriver is helpful here, put it up against the engine in various places and then place your ear against it. Alot of time you can narrow it down to a small area that way.
I think it would be worth your while to remove the inspection cover for the bellhousing and physically check the flexplate mounting bolts. Check both the flexplate to torque converter bolts and the crankshaft to flex plate bolts. Sometimes you can get a long skinny wrench inbetween the flexplate and torque converter to check the cranksaft bolts.....sometimes
Good luck, hopefully its not an internal engine knock
Bobby
I think it would be worth your while to remove the inspection cover for the bellhousing and physically check the flexplate mounting bolts. Check both the flexplate to torque converter bolts and the crankshaft to flex plate bolts. Sometimes you can get a long skinny wrench inbetween the flexplate and torque converter to check the cranksaft bolts.....sometimes
Good luck, hopefully its not an internal engine knock
Bobby
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From: Comox Valley, Canada
Hopefully it is a flexplate problem or it is just a loose bolt.........but........sounds a whole lot like a connecting rod/bearing clearance problem 
especially the banging in time with the engine.......does it sound like one bang when piston going down and one bang when piston going up and does the banging increase in speed with increase in engine rpm????
especially the banging in time with the engine.......does it sound like one bang when piston going down and one bang when piston going up and does the banging increase in speed with increase in engine rpm????
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Engine knock
Ok, I checked the bolts to the flexplate and the appear to be in order.I have noticed that the " noise " lessens in intensity and becomes more like a buzz when engine rpm is increased. If the flexplate is cracked I can't tell at this time. Also, the knock is intermitent and not constant, like a rock in a hubcap. Does this help in the possible diagnosis????
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Joined: May 2004
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From: saxton pa.
MD76 it sure sounds like a cracked flywheel. Check for RUST streaks radiating
from the center. Check the spokes for cracks and metal filings all indicate a
broken flywheel.
Have A Good Day----------Hotwrench
from the center. Check the spokes for cracks and metal filings all indicate a
broken flywheel.
Have A Good Day----------Hotwrench
Roast em' if you got 'em
Joined: Mar 2005
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From: Rio Rancho, NM
If it is a broken flywheel you can sometimes change it out without pulling the trans all the way out. Pull all the bellhousing bolts, install a couple of longer bolts, unbolt the torque converter, pull the tanny back an inch or two, replace flywheel.
Bobby
Bobby
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From: NM
Originally Posted by MoonDog76
Ok, I checked the bolts to the flexplate and they appear to be in order.I have noticed that the " noise " lessens in intensity and becomes more like a buzz when engine rpm is increased. If the flexplate is cracked I can't tell at this time. Also, the knock is intermitent and not constant, like a rock in a hubcap. Does this help in the possible diagnosis????
There are two set of bolts on the flexplate that should be checked; those at the perimeter (usually nuts) and the ones at the crankshaft. I assume you only checked the ones at the perimeter?
Those symptoms also sound like a crank with too much end play (thrust bearing sloppy). You can check by prying the front pulley forward and backward, see how much it moves. I'd be inclined to pull the pan and check the crank bearings and rod bearings, tho. Otherwise you'll never trust it. And if it is a bearing, it isn't going to last long before disaster strikes.
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From: Comox Valley, Canada
Originally Posted by MoonDog76
Ok, I checked the bolts to the flexplate and the appear to be in order.I have noticed that the " noise " lessens in intensity and becomes more like a buzz when engine rpm is increased. If the flexplate is cracked I can't tell at this time. Also, the knock is intermitent and not constant, like a rock in a hubcap. Does this help in the possible diagnosis????
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Knocking in the engine
Wow, thanx for all the info guys. There are rust streaks on the flexplate, sorta look like spokes on a wagon wheel. I hope that it is not a bearing as this engine barley has 6,000 miles on the rebuild. I may have to strangle some mechanics if it is. The oil pressure is real good, hovering around 35 psi at a slow idle. I'll pull the pan anyway just to see whats up under there. I like crawling under my truck.By the way it is 1950 F1 that I have been working on for the past 3 years, and I am glad I found this site. I will check check and let ya know what happens.By the way;What would cause the flexplate to crack? I don't drive like a maniac or race. Thanx
Last edited by MoonDog76; Jun 14, 2007 at 10:01 AM. Reason: forgot to add something
Posting Guru
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From: Comox Valley, Canada
Originally Posted by MoonDog76
What would cause the flexplate to crack? I don't drive like a maniac or race. Thanx
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From: Wheatfield, Indiana
I can't say what will happen with all the ignition systems out there but with original ford type ignition systems you will be ok. I guess what Nathan is saying is if a plug wire comes off while you are going down the road you just ruined your ignition system, "not likely". Use a good pair of insulated pliars if you decide to use this method. Mark
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From: NM
Originally Posted by spankys56
I can't say what will happen with all the ignition systems out there but with original ford type ignition systems you will be ok. I guess what Nathan is saying is if a plug wire comes off while you are going down the road you just ruined your ignition system, "not likely". Mark
Moondog, any update?