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Motor knocking

Alex Ayala

Alex Ayala

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Joined
Apr 1, 2007
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Location
FT Worth TX
A little help here guys, I have a stock '78 350 with all of the smog equipment removed. The truck has well over 100,000 miles and since i bought it last year has always had a small knock in it. I use it for a daily driver about 16 miles a day round trip.
A couple of days ago I was going down the freeway about 70mph which is about how fast I normally drive it on the freeway, and I noticed the knocking started getting louder.
I got it home and oil level was normal motor was not overheating. I haven't driven it since. it starts and idles fine except for the knocking.

Someone told me that I might have a spun bearing. how can I check this?

Can I replaces them from underneath without pulling the motor?

Is there anything else that could cause this knocking?

Thanks I advance for the help.
 
You'll probably need to pull the motor. To check for a spun bearing, you need to remove the connecting rod caps or main caps and inspect the insert bearings for damage. Check the crank for any grooves. If theres any grooves, you'll need to take it to a machine shop. If you don't see any grooves, carefully measure the bearing with a micrometer. Your gonna want to check for taper and out of round. To check for taper measure one end of the bearing, then measure the other end and compare readings. Measuring for out of round is similar. After you get your measurements, compare the readings. As long as the measurements are about the same, you'll be good with new bearings. I would recommend that you put the smog equipment back on or at least clean out the EGR system and reinstall the EGR valve. Without an EGR system, the combustion camber can reach higher temperatures and will damage will pistons.
 
I hope my tips weren't too confusing. I didn't realize it until now, but I must have been half asleep when I posted my last reply. The tips are still useful but somewhat vague
 
here is an old trick for ya !!!! with it running ideling get a broom handle or shop broom handle put your ear close to the stick and then put it close to engine you'll be able to hear where its knocking !!! keep it away from the fan ? it maybe the fuel pump also check oil pressure with a manual gauge ? :D the noise travels up the stick !!!!!!
 
If the noise sounds like tic,tic,tic,tic(high pitched) it is mostlikely valvetrain noise. If it sounds like knock,knock,knock(low pitch) it is lower end.
 
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