Knocking sound from my Yamaha Fazer: Worn out piston the cause

I measured the camshaft lobes and saw that they were within spec. No surprises there.

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Namaskar to all.

Time for an update.

I got the engine opened by my trusty mechanic. There's good news and there's not-so-good news:

• The timing chain looks fine.
• The exhaust valve and engine head are all coked up. We'll clear out the carbon from there.
• The piston is clearly worn and is past it's prime.
• The block looked OK, nothing major there.
• No excess play observed between the conrod and the crank. This comes as a big relief.
• The intake valve was loose in the valve guide that's in the engine head.
• The worn piston was allowing oil to creep up into the combustion chamber. Even the intake valve stem was coated with oil (you can check the pictures, the whitish coloured valve is the intake valve). The place in the engine head where the intake valve is, also shows oil stains.
• The camshaft rocker pin had above average play. Pictures show wear, too.
• I measured the camshaft lobes and saw that they were within spec. No surprises there.

All said and done, we are replacing the below:

• Valves.
• Carburettor slow and main running jet screws.
• Piston + rings.
• Camshaft rocker pin.

Everything except the piston is ordered through Yamaha direct.

Why not the piston? Well, my mechanic says that the block is fine and Yamaha will only sell you the piston+block as a pair. I told him several times that I didn't mind the expense (it costs only ₹3300 for an entire set) but he said he can bore out the block a little and put in a new piston. So that's what we're doing, it costs ₹800 or so and is "Goetze" brand (Federal Mogul). His word is as good as gold when it comes to this so I don't push.

The Yamaha spares will be here by the first week of April (and I thought only Kawasaki spares took time! I ordered them around the 10th of March).

I'll keep you all posted on what happens next.

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