My end cap bolt dislodged from the piston and ended up in the sump, it broke right through the bore at the bottom making a small hole about 0.5cm^2.

I was intent on replacing the piston and bearing but now I see this hole I'm thinking that's the end but maybe not, maybe a hole that far down won't effect anything?

enter image description here

  • Neither the picture or the description is clear. Where is the hole? Is it in the cylinder bore? The bottom of the cylinder block? The bottom of the sump? Jul 19, 2020 at 22:45
  • Zoom in photo and look at the bottom of the cylinder bore. You'll see a triangular hole .
    – Andy S
    Jul 19, 2020 at 23:26
  • You really should add more detail about how valuable this engine is. Also are you wanting an engine to give you a long service, or are you planning on just getting it working so that you can pass the problem onto someone else?
    – HandyHowie
    Jul 20, 2020 at 8:28
  • Is that crank bearing badly scratched?
    – HandyHowie
    Jul 20, 2020 at 8:29
  • Are you sure nothing else has been bent during the collision that broke the block?
    – HandyHowie
    Jul 20, 2020 at 8:43

1 Answer 1


It really depends on how far down the piston travels in the bore as well as if this is the thrust side of the piston or not. If the piston skirt travels lower than where the chip is at, the only option you'd have to reuse the block is to get a new cylinder liner installed into the block. In most cases with small engines, this doesn't make economic sense. You can replace many engines with a used one for a lot less than it would cost in machine shop costs to have this done. At the very least, you could replace the block by itself for far less than what it would cost in machine costs.

Another thing about the chip (hole, whatever you want to call it) is, if it's on the thrust side of the cylinder (the side opposite to the rotation of the crankshaft), there is a distinct possibility of stress risers forming, which means a crack will develop in a short period of time and will lead to engine destruction. If this is not on the thrust side, you possibly could mitigate this by grinding out the chipped area so it is smooth. While you're taking some more material away, you'd removing any sharp edges which is where stress risers start from.

Realistically you've got a busted block, which really should not be put back into service without some serious machine work, which means you should most likely just change it out, anyway.

  • So you'd say it was scrap, there's no way a new piston and bearing would work in that cylinder?
    – Andy S
    Jul 20, 2020 at 7:58
  • @AndyS he is not saying that. He is giving you advice for you to make a decision.
    – HandyHowie
    Jul 20, 2020 at 8:26

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