would you replace this piston?

Had some engine trouble recently. Broke a rocker arm which lead to the valve spring coming apart and dropping a valve. It's a hand built Mast motor so I'm letting them call the shots. They want both heads back for inspect/repair. After pulling the heads, we found there the piston smacked the valve. Mast is saying just buff it out with sandpaper and/or die grinder. I'm no motor guy so I typically just do what they tell me. Would you guys be ok with that "fix" for the piston?

Oh man that sucks !
That said it's not looking bad at all and I wouldn't be too worried about running that after proper care has been applied.

Bebop said:

Oh man that sucks !
That said it's not looking bad at all and I wouldn't be too worried about running that after proper care has been applied.

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Yea, I meant to tell you. Turns out our electrical problem was mechanical. Doh!

Smooth it up like they said. It is fine. :****:

I'd knock off the bur/ raised damage and rock out.

Ive ran much worse than that on old race motors

Run it

Your good. Rock out

hell yeah ive got valve kisses all over my #2 piston

Ok thanks guys

May have found the problem, not that it helps anything now. That look like a casting defect to anyone?

Nope, looks lightened for race applications. Or at least that's what they'll say. Lol

Oh hell yeah, knock off the bur and rock it! Pistons take a hell of a beating. Your valve train is where your issues are. But looks like you found that.

It will be fine as long as it doesn't have any burrs, burrs turn into holes!!

Here is what I use to knock the sharp edges of pistons with, they work great.

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Will they warranty the damaged piston?

I would replace the rod bearing on that cylinder.

Unless it has ARP hardware, the rod bolts will need changed as well. This begins to be a snowball effect at that point. I would think since the valve was free floating the bearings wouldn't be affected. I would leave the bottom end alone unless you have to pull the piston to replace it. As far as the piston goes, be gentle but knock down the high spots and rock out. You just don't want to get crazy with it for rotating weight purposes.

Did it bend the valve?

pholmann said:

Unless it has ARP hardware, the rod bolts will need changed as well. This begins to be a snowball effect at that point. I would think since the valve was free floating the bearings wouldn't be affected. I would leave the bottom end alone unless you have to pull the piston to replace it. As far as the piston goes, be gentle but knock down the high spots and rock out. You just don't want to get crazy with it for rotating weight purposes.

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It is all ARP. Motor is a handbuilt unit from Mast with the best of everything.

al1tonyota said:

Did it bend the valve?

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Valve is ****ed but not bad, it was relatively straight. Luckily it stuck straight up in the head as soon as everything let go so it wasn't in there bouncing around. Both heads went back to Mast today. The passenger side head is fine but they wanted both back.

redneckengineered said:

It is all ARP. Motor is a handbuilt unit from Mast with the best of everything.


Valve is ****ed but not bad, it was relatively straight. Luckily it stuck straight up in the head as soon as everything let go so it wasn't in there bouncing around. Both heads went back to Mast today. The passenger side head is fine but they wanted both back.

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It sucks more when you go for the best/nicest things and it still doesn't hold up.

All up to the owner but the piston hit atleast once metal contact, maybe it didn't hurt the bearing at all but changing out a $5 part is cheap to ease my mind.