bob westphal Posted November 9, 2006 Report Share Posted November 9, 2006 In an earlier thread, Blueskies mentioned having what he thought might be a rod knock. Rod knocks are quite easy to diagnose. With engine running, rev it in short bursts. If it is a rod it will rattle as you drop the revs. To determine which one/ones are bad rev the engine to where the knock is most prominent and hold it steady. Short out each plug and notice if the knock goes away or is reduced. Rod knocks have a sharp sound. To check a main, put the engine under a strain. A main will have a dull sound. Short out the plugs on each side of each main to see if the nock subsides. Wrist pins will rattle more if the plug is shorted. Cam lobes usually don't knock. Quote Link to comment Share on other sites More sharing options...
blueskies Posted November 9, 2006 Report Share Posted November 9, 2006 In an earlier thread, Blueskies mentioned having what he thought might be a rod knock. Rod knocks are quite easy to diagnose. With engine running, rev it in short bursts. If it is a rod it will rattle as you drop the revs. To determine which one/ones are bad rev the engine to where the knock is most prominent and hold it steady. Short out each plug and notice if the knock goes away or is reduced. Rod knocks have a sharp sound. To check a main, put the engine under a strain. A main will have a dull sound. Short out the plugs on each side of each main to see if the nock subsides. Wrist pins will rattle more if the plug is shorted. Cam lobes usually don't knock. Bob- Thanks for the overview... I'm not sure if my engine's noise is a rod bearing or not. The sound isn't rattley when the rev's drop, it diminishes then. It's there when it's under acceleration, but not necessarily load. It is there reving the engine in neutral sitting in the driveway. At about 2000 to 2300 rpm, it's constant and the loudest. The sound is a lower pitch or tone, not "plinky", but more "clacky", if you know what I mean . I tried pulling plugs to hear the difference, but couldn't really hear much change. I'm going to check the timing first, then pull the pan and inspect. Maybe I can get a sound clip with a video camera and post it on the net ... Pete Quote Link to comment Share on other sites More sharing options...
Normspeed Posted November 9, 2006 Report Share Posted November 9, 2006 After my rebuild I got a kind of clacky sound that got louder at higher RPMs, but mine would sort of cycle, louder, then softer, then louder. It was a bad (oversized) valve guide installed by the machine shop. It got a lot louder with the side cover off. Replacing that one bad guide took care of it. Hope yours is a quick, simple and cheap fix. Oh, also take a look at your valve springs. Sometimes a broken spring can make a racket at higher RPMs. Quote Link to comment Share on other sites More sharing options...
martybose Posted November 9, 2006 Report Share Posted November 9, 2006 Oh, also take a look at your valve springs. Sometimes a broken spring can make a racket at higher RPMs. I had the misfortune to assemble my motor the first time with plated springs, which turned out to be embrittled enough from the plating to break occasionally. I replaced one the first time when a ticking noise got my curiousity; the second time I heard the ticking I found two more broken, so I bought a new set of unplated springs and replaced them all. Marty Quote Link to comment Share on other sites More sharing options...
blueskies Posted November 9, 2006 Report Share Posted November 9, 2006 I bought my valve springs from Vintage Power Wagons along with a bunch of other stock rebuild stuff. They were installed with the valves, valve guides, tappets, and cam by the machine shop that did the block work. One of my projects is to adjust the valves, so I'll be checking the springs too. Pete Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.