Mysterious 4 cyl knock/rattle

[B_man_Al]

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

[32phil]

Remove the side timing cover and you can see the cam gear. Take the plugs out and turn the motor over by hand to see all the teeth. Check the oil tray INSIDE the oil pan they come loose sometimes.......ask me how I know. Might as well check the rods then the main bearings once you have the pan off.

[B_man_Al]

Can the cam plunger & spring be inspected with the side cover off? This was a suggestion from the model A forum. If not, I believe you can get the whole timing cover off without taking off the oil pan can't you?

Al

[Ross F-1]

I went to an aluminum gear on my V8 and started hearing a subdued kind of knock, kind of like a slightly loose tappet but muffled, more frequent, not a sharp knock. It does indeed appear to just be the gear making the noise, combined with a lot less other noise after a rebuild with valve job. No problems in 400 miles or so. I also have an aluminum timing cover which undoubtedly provides less noise damping.

[B_man_Al]

Had a suggestion from the model A forum to reverse the timing pin and push on it at idle. Sure enough the noise went away! Now to find out why....

[DavidG]

Sponsored Links (Register now to hide all advertisements)

Could be a broken or tired spring in the camshaft thrust plunger that seats in the timing gear cover given the result of your timing pin test.

[B_man_Al]

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

[1931 flamingo]

Over the years, many, many have used a cold chisel and a BFH. Ck your nut for signs of this. if not wanting to do that there is a special "wrench" for the odd ball shaped nut (questionable quality I've heard) or a new hex nut is available from the vendors. The above applies to model A and would think the B is no different. There is also a recent thread on the A forum concerning this nut now. Good luck.
Paul in CT

[DavidG]

The camshaft nut on a B is a carryover Model A part.

[B_man_Al]

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!

[Terry,OH]

Al: since you have the 1/4" taped holes in the nut why not install set screws into them.

[B_man_Al]

Why not indeed ! Maybe a cap screw that takes an Allen key. Wonder if the end should be sharpened to bite into the cam?