I brought a 2003 Trail Boss 330 not running to fix up. I now have it running it runs good and plenty of power but the valve tappets are noisy at idle when you speed up the motor it goes away. I set the valves .006 did'nt help. I toke cover off top of head and looked at cam and rocker arms did'nt see any abnormal wear. The timing chain is tight and the sprocket on the crank is not loose.

 

Engines are a little on the noisy side,but check that the noise may be worn drive clutch spider buttons. The clutch can clatter at an idle and decreases as engine rpms rise if these are worn. A plain old engine stethoscope can pin point whether it may be an engine or clutch related noise you're hearing.

 

It is'nt the clutch, i have ran motor with clutch removed, noise still there. I have done the stethoscope thing but with me the noise seems to carry though out the entire motor on these small aluminum cases. I would say the noise is slightly louder around the valve cover and the starter bendix. Have you seen cases of the bendix boncing around and hitting ring gear? Is there a way to confirm piston slap with out tearing the motor apart?

 

If the bendix was to hang up or the garter spring broke around it you'd know it fairly quick,plus the bushings in the recoil housing and the case are what keep the bendix aligned. No really good way to tell unless you do tear it down if the noise is excessive.Could be piston slap as you mentioned or rod slap. The 325/330 engines were the only ones to use plain rod bearings and car type engine rods. Had several early 325 engines fail because of soft bearings but the 330 should have addressed that years ago,but since you bought it not running who knows how the previous owner treated it.Plus had a couple that the lower crank sprocket nut backed off,but you mentioned that it was tight. Parts break down shows the rod and piston.Dirt Cheap Yamaha, Polaris, Suzuki & Kawasaki OEM Parts & Accessories – Cycle Parts Warehouse

 

I have noticed that i think the valve springs are installed backward. the manual states coils close together go to the top of head. What would be the effect of the valve springs being installed backwards? Or if the springs are weak could the rocker arms be floating a little coming off the back side of the cam lobe and slamming down on the cam?

 

325/330 engines were plain noisy to begin with.Even if valves are adjusted to spec (.006) rocker arm tapping is normal in this engine,but if it's a loud slapping noise I'd check into the engine. Here's a noisy old Magnum 330 for reference.