Mysterious Knock/Rattle

B_man_Al

B_man_Al

Senior Member
My model B 4 cylinder has developed a mysterious knock/rattle at idle or during deceleration but is not there when the engine is rev'd. Its more like a loud rattle rather than a knock, and appears to be coming from the valve or timing gear area, but not sure. The engine runs fine, so I don't think its the distributor drive or a broken valve spring.

The noise doesn't change as each spark plug is sequentially shorted out so I don't think its a connecting rod or wrist pin.

I put an aluminum cam gear in it a few years ago, wonder if one or more of the teeth got screwed up?

Any thoughts before I rip it all apart ? What order to check these things?

Thanks Al
 
I have been chasing this sort of thing for 6 years. I finally changed the engine {for other reasons} and the noise is still there. So if you find something let me know. Jack
 
An 'easy' way to check if the noise is being caused by a lose timing gear is to reverse the timing pin and apply hand pressure (push the timing pin against the timing gear) while the engine idles. Noise caused by a loose timing gear should diminish or cease while the timing pin is being pushed in and return when not. This is the way I isolated a "knocking sound" to a loose 2-piece aluminum-hub-and-fiber timing gear.

As an aside, stay away from two-piece timing gears.

And stay away from the fan blades while diagnosing a loose timing gear with this method.
 
Jack, if you changed the engine and it's still there, maybe it's in the transmission. Sounds migrate all over the place. The cluster gear is alway in motion while the clutch is engaged, even when idling in neutral. Maybe it's a bearing in the ****** that's making noise?
 
Skip got it! ... pushing on the timing pin makes the noise go away . PS right hand is still in tact.

Thanks Al
 
I had a mysterious knock,rattle also, so I dropped the pan to ck. the rod bearings & found them O.K. But when I lowered the pan I found this shroud around the oil pump. Put the pan back up without the shroud & rattle, knock went away. Found out later it was added to the 31 model.
 
Problem solved .... The big cam gear nut came loose! . Anyone know how to tighten it to make sure it doesn't happen again? Locktite perhaps? If so which type?

Thanks Al
 
Cam gear nut loose ? This is a place for the special cam nut socket with a big-*** bar. Toss a rag between the gears and tighten away. The torque spec is around 100#, but, tight is tight. Have you checked to see if you have a 2 piece gear ? If you do, tightening won't help. That gear should probably be replaced.
 
Last year I replaced the fiber timing gear.The nut has come loose & while the teeth were good,the 2 dowels had worn the holes in the gear.When I put the new alum gear on,I cleaned the threads on cam & nut with brake cleaner & put green Loctite on the threads & tightened it up.I never use a T-wrench on an A except for the cyl head.I didn't have red Loctite at the time.If you use red Loctite.you will have to heat the nut to about 400 degrees to get it off.
 
According to my notes, the cam gear nut should be spot torqued.

For those not fortunate enough to be mechanical engineers, allow me to explain the cam nut 'spot torquing' procedure:

1. Install the cam gear and run the cam nut down by hand until finger tight;

2. Obtain a cam nut adapter/socket (depending on which cam nut you have) and place it on the cam nut;

3. Engage the largest, longest, heaviest extension you can find onto the adapter/socket;

4. Get a firm stance and pull on the extension until you see spots in front of your eyes.

The cam nut is now properly 'spot' torqued.
 
OK so here's what I did. Drilled two holes in the cam nut, half way between the IS and OS diameter of the nut. Tapped these holes with a 1/4 in. coarse thread tap. Made a small plate out of 1/4 in steel with corresponding holes for two 1/4 in bolts. Welded an old lug nut (13/16) to the center of the plate to get a torque wrench on. Screwed the two together ( loosely as the cam sticks out past the end of the gear when fully seated) Added "blue" locktite and torqued to 110 ft lbs. Got my fingers crossed that that’s enough!
 
Hi Al,

Humble opinion:

With or without fingers crossed, that should hold until Global Warming melts the Blue Locktite -- don't hold your breath!
 
A friend's wife was able to hold the engine with the CRANK, while hubby torqued the cam nut to a true 110 Ft Lbs!!!!
DON'T CROSS THAT LADY!!!!!! Bill W.
 
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