Engine knock again.

Fred K-OR

Fred K-OR

Well-known member
Last weekend we went to a car show about 15 miles away on a freeway that was mostly flat (no big hills, just some rolling little ones).

On the way back, my engine started to knock when I was traveling about 40 to 45 MPH. This is about the speed I maintained all the way home and the knock started after traveling about 13 miles or so. I pulled over to the side of the road, pushed on the gas slightly and the knock was there. I then decided to continue on my way home. After getting back on the road, the knock stopped and I have not heard it since. I had a similar problem when I went to another car show a few weeks ago and was pulling up a rather long grade. What could this be?

The engine was rebuilt and it has about 350 miles on the rebuild. Any ideas what this might be??

Thanks for any ideas you may have
 
Sounds like your pistons are to tight. I would try driving a little slower until it is broken. You may have scored a piston, if so you will get a lot of blow by in the oil filler tube.
 
Fred, did it sound like it was in the lower end? Any change when you advanced the spark? Have you put a broom handle (or some other sound post) to the engine while running to see if you can isolate the noise? A knock is never good news, but sometimes it isn't terrible news. With 350 miles, you could go back to your engine builder and have him explain it to you.
 
i doubt if you will get a knock from to tight pistons, if they are loose in the bore, yes you will get a knock, grab the fan blade (with the engine off) lol and pull it up and down to see if there is any play in the crank pully, a worn keyway will make that sound, next time it happens with the engine ideling short out each plug one at a time, if the knock stops you have found the cylinder that is making the noise, i would drain the oil and look for babbit in it, and i think 40 to 45 miles an hour is to fast on a new engine i would hold the speed to 30 to 35 mph for a thousand miles at least
 
You didn't state how it ran while it was knocking. If it ran badly during the knock, it was likely sticking valves. A very pronounced knock that totally disappears and returns is probably a benign one. My fresh rebuild did that after running it too slow for too long at idle. After a tear down and cleaning of the valve assemblies, it disappeared.
 
I did not get a chance to do any detail checking because after taking off after I pulled off the road to see what was happening, the knock stopped. When I was stopped along the road, the engine was running and seemed to have no problems (except for the knock) running.

Guess I will have to take it easy, going slower and see how things develope. I may change the oil like ford 1 suggested and check it. I do have a two piece crankshaft pulley. I may also check this to be sure it is tight.

Thanks again guys.
 
Are you running the "keyed" two piece pulley or the threaded one? I hear the keyed one can cause the problem you describe.
 
I had a similar experience.. New Engine, new alternator, etc..
Developed a terrible knock like the center main was rattling around.. Got her about 1/2 way torn down before the issue was discovered.

The Alternator bracket was put on incorrectly, and when the engine would spin up to speed, the belt would pull the alternator over and start tapping on the side of the motor..

Hopefully it's something simple like this.. It never did it until the engine got good rpm, which made the belt pull on the alternator.

Good Luck!

- Dave in Boise
 
Russ/40 said:
Are you running the "keyed" two piece pulley or the threaded one? I hear the keyed one can cause the problem you describe.
Click to expand...

I think it is a treaded one because when I put the pulley on, I had to screw in the crank end.

Thanks again guys. I will have to do some more checking on things. Maybe load it on the trailer and take it down to the rebuilder and see what he thinks.
 
before you go to far make sure its not the pully is not moving back and forth on the crank because of a warn key way on crank or pully make sure the pully is tight against the crank when the bolt is tight,
 
I had a 30 Roadster in reciently and it had a (NEW) engine, but noisy. Moving the fan back and forth you saw the Two piece pulley moving. Had to remove the Rad for some work anyway, so I removed the front section of the pulley, cause the crank stuck out past the pulley by .020 at least. Started the engine and took my small grinder and removed about .025 of the crank (looked very machine shopee) and tightened her up. All is well and the engine went from a trashy to a very sweet sounding A. Iceman
 
Get your stethoscope out and go fine the offending knock, if you can. Consider piston slap or the shims in the bearings on the mains. Since your down there look~see the con rods and check for the crank end play. And timing gear. R.U. running adjustable or non adjustable tappits? One of them might be rotating to the 'sloppy' end and then rotate back to the 'tight' end. Ground on a slope and no longer flat to the cam?

skip.

 
skip said:
Get your stethoscope out and go fine the offending knock, if you can. Consider piston slap or the shims in the bearings on the mains. Since your down there look~see the con rods and check for the crank end play. And timing gear. R.U. running adjustable or non adjustable tappits? One of them might be rotating to the 'sloppy' end and then rotate back to the 'tight' end. Ground on a slope and no longer flat to the cam?

skip.
Click to expand...

Am running adjustable tappits.
 
Grinding off the front of the crank....

Ice man said:
I had a 30 Roadster in reciently and it had a (NEW) engine, but noisy. Moving the fan back and forth you saw the Two piece pulley moving. Had to remove the Rad for some work anyway, so I removed the front section of the pulley, cause the crank stuck out past the pulley by .020 at least. Started the engine and took my small grinder and removed about .025 of the crank (looked very machine shopee) and tightened her up. All is well and the engine went from a trashy to a very sweet sounding A. Iceman
Click to expand...

Is it possible the front oil slinger is missing. I have only seen the condition you describe once and that was the cause. The front pulley fits up tight to the oil slinger and retains it in position along with the key.
Dave in MN
 
I found it!!!

After all these months, I got together with the fellow that rebuilt my engine and we worked on finding the "engine knock". Well we found it. It was the generator pulley. We took the fan belt off, started the engine and no knock. Took the generator off and found that the pulley was one that had four rivets to hold the front and back together. These rivets were loose and the front and back parts of the pulley produced a "clicking" sound. Hammered the rivets tight and the noise went away. The fellow working with me said this was an aftermarket pulley (eventhough it was 50 or 60 years old).

I put is an order with this fellow to get me an original pulley. Should fix the problem.

Thanks for all your help and hope this helps someone else.
 
Up until the 90"s engines had problems with carbon building up in the combustion chamber and on the backside of the valves, mostly the intake. This called for a "carbon" job. If not serviced, sometimes a chunk would come loose and sit on top of a piston, causing the piston to slam it into the head causing a very loud knock, sounds like a bad rod bearing. After a while the carbon breaks up and everythings ok. I had one so bad once it wouldnt turn. There are products to clean carbon by feeding it to the intake while running but I dont know if the babbit can take it. If thats what it is and it happens again I would pull it apart and clean it manually.
 
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