400ex engine knock

[m36indiana]

engine was running fine during last race. got it home started it up had a real loud knocking noise like a rod bearing going bad. checked valve clearance , its all good,pulled clutch cover off everything there looks good. pulled head and cylinder off no play in rod, only thing left im gonna do is pull stator cover off and look.no metal in oil. its got be baffled now, its not a tick that you get from valves its a loud knocking noise,tranny shifted good, replaced cam chain and piston less than 6 months ago, still had 130 psi compression.any suggestions would be helpful.

[4reeds]

Did you replace the cam chain guides with the chain?A worn out guide will allow the chain to make a knocking sound.

[mlabarca240]

Just out of curiousity, how does the skirt of the piston look? see any chunks missing? Usually when someone bores a sleeve or jug to an aftermarket piston with different clearances and they dont get it right you might get some skirt slap. What about the plug? Any signs of pre-ignition? Any pitting on the top of the cylinder? If you sheared a woodruff key at the race this could cause pre-ignition and sound like a knock.

[m36indiana]

just took the flywheel off, no sheraed key, took the cluch apart no damage. everything i see looks good.no play in crank bearing. gonna put it back together as see what happens, hopefully i have no noise. im out of options, and running low on time.

[4reeds]

Checkout youtube.( 400ex engine noise). Does it sound anything like it.Its how I figured mine out.

[togup]

sounds like a valve to me

[m36indiana]

i checked youtube it sounds just like that, guess ill get a new timing chain while i got it apart and see if it helps.

[m36indiana]

replaced timing chain and a worn out front chain guide, all is good now no more knock

[CJM]

Glad to hear everything is fixed :)