How much piston damage is too much?

Hi everyone,

I've been taking apart my engine, trying to figure out why I cannot get it started. A compression test shows compression way below spec. The service manual says 138 is the lower limit and I'm getting 100 on two cylinders, 80 on the other two. So, it's either the valve clearance or the piston rings. Once I got the top end of the engine off, I discovered that one of the pistons are scored. A previous owner must have, at some point, installed the wrong size spark plug and damaged the piston head. Luckily it didn't punch through. But how much damage is too much damage? I'm not exactly crazy about the idea of sourcing another piston. Here's a photo. What do you guys think? (That is, aside from the carbon buildup - holy crap!)

Tariq

I would wanna replace it for fear of that causing a hot spot, or detonation. I'm no expert, just my two cents

I would probably consider keeping the piston, but only if I could polish everything out so that there are no signs of the punch, just a smooth dimple. And that there is still sufficient thickness left to retain integrity. But generally, these old pistons were way over-engineered for normal use and can easily tolerate some thinning of the piston crown without much risk of failure.

run as*is

Here's one that shows too much damage to re-use; it makes your piston look pretty good.

Thanks everyone. Any particular recommendations for cleaners/solvents to clean the pistons and valves? A friend recommended carb cleaner....?

Quick Answer,
That's NOT to much if the bike is stock.
Just knock off the high spots and sharp edges,
and it will last forever.

it is a bike and you should try and eliminate all flaws when and as soon as discovered...


it is not a tractor...

sure it will run...sure it is safe but

bore kit and work 1000.00

gaskets and time 2-300


piece of mind

priceless