The Stovebolt Site Forums The Shop Area Engine Shop Slight little knock?

Lately been hearing a slight little knock coming from I believe my 235'.eng. I have been tightening up up motor mounts bell housing, exhaust, etc. etc. The strange thing about it is I only here around say 1700 rpm's and then it goes away. In an earlier thread I had a pinging noise which with a new set of points stopped all that. I don't think it is a rod or main bearing even though it could be. Possibly those 2 lifters I talked about. But when I run the engine up slow no knock, when I run her up a little quicker a knock becomes present, it doesn't seem to get any worse. I change the oil at about every 3000 miles with 6 qts of Valvoline 10W 30.... Need a bailout here Bolters. Thank you..

Some knocks are present only at a "float" condition, neither pulling or coasting like right before a shift to the next higher gear happens. If that describes your noise, it's like being a little bit pregnant- - - - - -things ain't going to get any better! A rod knock can be a light "double-tap" noise at a steady RPM and no load. Worn or loose main bearings make a slower, deeper "thump" noise mostly while accelerating which goes away as the load on the engine decreases.
Jerry

Glad to here your response there Ol buddy, now I feel a little better about my knocking problem. It will even knock a little as you rev up to 1700 rpm's in neutral and in gear also.Now, not to start a Big over rated conversation but are any other of you Bolters have my same cituation? The only thing I ever really changed when I assembled the rod caps was some 3/8" 12 point locking nuts torqued to 45 ft. lbs. I believe the original 3/8" nut had some sort of a safety keeper on it? I guess those were pretty good too? Anyway thanks..........

The small sheet metal nuts were called "Palnuts". They didn't really accomplish anything, and I would find most, if not all of them buried in the sludge at the bottom of the oil pan on a lot of stovebolt engines. A properly-torqued rod nut stays in place three days past forever, and one that's not torqued properly doesn't, no matter what sort of locking device is used. 45 ft/lbs. of torque is exactly right for a 3/8-24 rod bolt, with either locknuts or regular ones. What oil clearance did the bearings have when you assembled the rods?
Jerry

Just checked my book on the rod bearing clearances, and it was showing .002" to .0025",the mains were a little bit more .0025" to .0003". the engine runs normally about 30 lbs. of oil pressure until she gets a little warmed up. , I drive it daily to my work about 20 miles round trip, wished it got better mileage ( 17 MPG ) its worth it to me. Here in California gas is coming up on $4.00 a gallon. Thanks for the advise and help....

How about an exhaust manifold leak? They can sound like a knock.

I can confirm that. A cracked exhaust manifold on my Astro van sounded for all the world like a rod knock.

You're running right at the upper limit of what I'd consider to be acceptable for a new assembly. I prefer clearances in the .0015"-.002" range if possible. You might want to consider going to a slightly thicker oil, maybe a 15W-40, to give a little more cushioning effect between the bearings and the crankshaft. Try at least one oil change using a straight 30 weight oil like Rotella to see if the noise changes or goes away altogether. Unless you're way north in California, running 15-40 or 20-50 shouldn't cause any sluggish cold starts like could happen up in the great frozen yankee reservation.
Jerry