Knock, knock, knock sound

ford-m

ford-m

Senior Member
On Friday afternoon I drove the Roadster a mile into town and she preformed flawlessly. When I was coming home I stopped at a set of lights and suddenly this now sound emerged. No difference in power or response, just a noticible knocking noise. When reving engine it also increases
Went away for weekend and now home troubleshooting the issue.
Took belt off so it's not fan or alternator.
Sound is louder on the exhaust side.

I have only 100 miles on the engine since I rebuilt her.
What do you thinks it is and where do I start? The video is below.

http://http://vid1291.photobucket.com/albums/b558/Ford-m/20170618_140851_zpst12kgeu2.mp4
 
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Ford-m, is it possible that it may be an exhaust leak? I did not watch the video as it had too many pop-ups telling me I am a winner. So I didn't see video, sorry. Jeff
 
Sorry Ford-m, sounds bad. Ground out one spark plug at a time. This might narrow down where the noise is coming from.
 
Yes, short out each spark plug in turn until you find the offending cylinder. It sounds like a rod bearing to me. If it stops when that cylinder is shorted out, odds are it's the rod Babbitt gone South. :(
Marshall
 
That sounds deep, like a main bearing, but not being there in person, I could be wrong. I would drop the pan and check clearances, just to be sure.
 
JDupuis said:
Sorry Ford-m, sounds bad. Ground out one spark plug at a time. This might narrow down where the noise is coming from.
Click to expand...

Hi Jeff,
Just tried grounding each plug with NO difference in sound. Knock was still there. Might be time to drop the pan ?
Regards,
Michael
 
Well, that's GOOD news! That means it may not be a bearing after all. Before you drop the oil pan, pull off the side timing gear cover and pry behind the timing gear in a couple places. If the timing gear nut has worked loose or some gear teeth have stripped, you should feel a wobble. That would be the best of all worlds if all you need to do is change the timing gear. Not fun while still in the car, but a heck of a lot better than dealing with bad bearings!
Marshall
 
ford-m said:
Hi Jeff,
Just tried grounding each plug with NO difference in sound. Knock was still there. Might be time to drop the pan ?
Regards,
Michael
Click to expand...

Yup, drop the pan. It's most likely the center main bearing as they're usually the first to go.
 
Does the sound change at full retard and then at full advance? If the sound lessens at full retard (but doesn't go completely away), "DJ S" may be right about the center main. The knock sounded higher pitched to me in your video than a main bearing, but if a main bearing is going to go, it's usually the center one first.
Marshall
 
I'm probably way off BUT a video is hard to say exactly what...but I had what I thought was a rod knock and it was only a head gasket. Does the sound change with the timing changing and also spray soap around the head and see if you see bubbles. What do you have lose...go simple first.
 
Michael, 3 summers ago I had a freshly rebuilt motor develop a knock after less than 100 mi. The rebuilder took care of it promptly. Turned out to be a center main that had a partially blocked oil supply line.
Good luck, Ian
 
Take a long screw driver to see if you can isolate the noise. If it is the timing gear you will hear it through the screw driver shaft. Or if you have a mechanic's stethoscope that will do the same.
 
I had a knocking sound in my engine, and it turned out to be a bad fiber timing gear. Prior to that, several Model A friend's were not able to diagnose it accurately. Had a new gear installed and all is better now!
 
Marshall V. Daut said:
Does the sound change at full retard and then at full advance? If the sound lessens at full retard (but doesn't go completely away), "DJ S" may be right about the center main. The knock sounded higher pitched to me in your video than a main bearing, but if a main bearing is going to go, it's usually the center one first.
Marshall
Click to expand...

X2, that was my thoughts exactly. :confused:

It'll be interesting to find out what it is.
 
Super hard to diagnose from a video, but to me it sounds more like something from the valve train than a main or rod bearing. Broken valve spring, valve seat insert came loose, adjustable lifter loosened up?
 
Another possibility could be a collapsed spring behind the cam plunger allowing the cam to move back and forth. This happened to me on a 29 model a I owned about 62 years ago.
 
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