Sorry for the lengthy post but I'm pretty stumped with this one. If you don't have time to read the details please just read the bold section and tell me what you think.

About three months ago I was riding my 89 to work and after riding maybe a mile at 35 MPH I heard a very loud and prominent clacking noise coming from the motor. I turned around and went home and tried tightening my cam chain tensioner which did nothing, the noise was louder than cam chain noise usually is, but I tried anyway. I took both side covers off and pulled the clutch out and couldn't see anything unusual. Next I pulled the valve cover off and checked and adjusted all of the clearances, nothing off very much there. While I had everything apart, I went ahead and rebuilt the carbs, put it back together, fired it up and the noise is still there. It makes noise in neutral and every gear and gets faster when I rev it, and it sounded like it was coming from the front, lower section of the motor. My stethoscope made me believe it is loudest around the 2nd cylinder. I pulled the oil pan off to see if there was any broken pieces laying in there but I found nothing. I pulled the motor out and pulled off the head. I found that the tip of the splitfire plug for the #2 cylinder had broken off, which caused a lot more carbon build up than the other 3. I found the tip embedded in the carbon, and it doesn't look like it caused damage to the combustion chamber, piston, of cylinder walls. The number 2 spark plug was a little more backed out than the other 3, but I don't remember if I had started pulling out my plugs 3 months ago to check the valves clearances. Could a loose plug cause such a loud noise? I do know that when I started it up after I did the carbs, air was forced up past the number 2 plug boot, but I thought maybe I hadn't aligned the valve cover gasket properly. I pulled the cylinder block off next and all of the rings look good, and there is no play at all in the rod bearings or around the wrist pin. I haven't checked the cylinder clearances yet, the I can still see hone marks on the cylinder walls. The clacking noise doesn't sound like piston slap and doesn't go away after the bike heats up. Any more suggestions? Thanks

 

Years ago I dropped a very small washer down the intake manifold of a 1954 Buick. It made an incredible amount of noise. Dad had me pull the top end off (intake manifold, exhaust manifolds, heads) and we inspected all eight cylinders with great care. We found nothing. No marks on pistons, valves, cylinders walls, anywhere. I reassembled the engine. We fired it up. Clatters. I tore it apart. we found absolutely nothing. By now the customer (who had come in for a minor tuneup) was tired of waiting, it was after five o'clock, and he went to dinner. I reassembled the engine. More clatters. Dad came over, revved the crap out of the engine, literally. With one finall click the washer found it's way past an exhaust valve and into the mufflere. The customer came back, heard his car purring like a kitten and left. No charge for the tuneup.

Long story to say this: It doesn't take much to make a quite loud clattering noise, and if the object is small there may be no visible damage. It may be what you heard was the piece of your spark plug rattling around. I'd check very closely to make sure nothing made it between the cylinder wall and piston - you'd likely see marks on the cylinder wall if something did - clean your piston crown thorougly, give the valves a close inspection to see that nothing is caught there, and put it back together. Obviously if you find stuff stuck in there you want to do whatever is needed to take it out before reassembly.

As for the loose plug: I've seen engines on which the plugs were finger loose and wiggling with every stroke of the engine and have heard nothing from them. That isn't to say a loose plug couldn't make a popping noise. It might. Check the head for any gas erosion though, and make sure the new plug is in snug.

Good luck.

DRam