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Piston Hole - Can I repair it?

Hi guys,

Valve bent, piston got hit, cylinder wall still in specs despite a visible (but not “feelable”) scar. Yes, I used a bore gauge.

See picture:


Can I smooth it out and let it run for another year? Or am I guaranteed hot spots and should replace the piston?

I’m trying to flip this vehicle without spending too much, yet I don’t want to sell a lemon or
something unsafe.

It’s 1-hr of sanding vs 2-days of tear down!

Thanks!

That doesn’t look repairable to me. But then again I’ve never tried such a thing. Common sense says to just replace the piston and be done w/it.

How on earth could you sand that in place? And how can you have two more days of tear down when you already have the head off.

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The piston is damaged, clearly. It has to come out so you can see if a ring land is damaged. If there are no cracks, you might sand the top to smooth it out. It has to come out anyway because you need to run a hone down that bore or the rings will never seal.

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Because this is a motorcycle, not a car, and the cylinders are not removable, to access the piston the crankcase must come apart and be split on this model. Which sucks!

the area with the vertical scratches is about 1.5" wide. not just where the gouge in the piston is. i would want to remove the piston to inspect it for damage. what is causing the vertical scratches?

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Just curious, but what kind of bike? A Gold Wing, Interstate, or what?

Rather than split the block I would try to use a Dremel tool and round the sharp edges of the damage off to prevent hot spots. That’s what I’ve always done with nicked pistons on cars and never had an issue with doing so.Luckily there was never any ring land issues but that Murphy’s law thing always lingers around.

The hole is on the edge of the piston which probably caused the scratch, looking at it closer it could be grind to semi-flat or at least smoothed out. Also, upon removing the head I found the missing piece of the piston, a small ball ! Fortunately the previous owner didn’t run the bike too long for it to scratch everything!

You’re almost right! It’s from a Honda CBR600RR.
Rings are not damaged as the leak down test came perfect with close to 0% leakage (after replacing the bent valve of course!).

I’m just dreading, it’s a 130lbs engine with so many steps to “simply” replace a piston. No buddies to help me.

I see nothing in your original post to indicate that this was a motorcycle. Some times the information you leave out makes replies useless.

I’m sorry it wasn’t my intention. But in all fairness, isn’t a piston a piston? And a cylinder a cylinder? Whatever vehicle, it seems like the same repair process.

Yes, but I was wondering why you had 2 more days of work to pull the piston when the head was off. You also didn’t mention having to split a case. Many things are harder to bo on a motorcycle because of space is so cramped.

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I sympathize with you on wrestling engines in and out of a bike. I’ve done it many times with Harleys and it never gets easier nor does the back get better.

Last time I rode to Sturgis I ran my HD dresser onto the co-op grain scales where I live and it added up to just a shade under 1100 pounds with me on it. Trying to stop a 1/2 ton+ bike on a downgrade was a bear. When the rear brake caliper bleeder blew out heart went to my throat and the runaway truck ramp started looking like an option. :frowning: