Piston clearance

[stevieg]

Hi guys,could anyone tell me if the piston should be slightly raised from the block at tdc.i ask as have had the block skimmed and bored and new oversized pistons which I am assured have been skimmed the same amount as the block.i have installed pistons and notice they are slightly proud of the block.many thanks

 

[North Idaho Wolfman]

Did you get a number for the amount they took off the block?
You really need that number because not only do you need it for the head gasket (there are shims) you will need it for under the injection pump, as that sets the timing.

 

[Henro]

Did you get a number for the amount they took off the block?
You really need that number because not only do you need it for the head gasket (there are shims) you will need it for under the injection pump, as that sets the timing.

Assuming the engine is a diesel, since the OP doesn’t say what engine he’s talking about, I do have a question.

If shims are available to make up for the amount that was removed from the block, and are incorporated along with a new head gasket, why would anything have to be done with respect to the injector pump?

Seems like if Shims along with the head gasket would make up the difference for the material that was removed from the block, that that would be all that needed to be done…

…unless the exact thickness of the shim(s) needed were not available.

 

[North Idaho Wolfman]

Assuming the engine is a diesel, since the OP doesn’t say what engine he’s talking about, I do have a question.

If shims are available to make up for the amount that was removed from the block, and are incorporated along with a new head gasket, why would anything have to be done with respect to the injector pump?

Seems like if Shims along with the head gasket would make up the difference for the material that was removed from the block, that that would be all that needed to be done…

…unless the exact thickness of the shim(s) needed were not available.

The shims I'm talking about have nothing to do with the head gasket, they have to do with the injection pump and timing.
If the block is milled you MUST replace the amount that has been milled off, with a shim of that width or the injection timing will be wrong.

 

[lugbolt]

depends on the engine and i didn't see which engine is in question

some engines when the machinest "decks" the block, the pump mounting face is also reduced which affects injection timing. Other engines don't have that issue.

back to original question. IIRC the service manuals show how far out of the hole the pistons should be.

 

[Henro]

depends on the engine and i didn't see which engine is in question

some engines when the machinest "decks" the block, the pump mounting face is also reduced which affects injection timing. Other engines don't have that issue.

back to original question. IIRC the service manuals show how far out of the hole the pistons should be.

Thanks for this insight. I had not envisioned that the surface that the injector pump mounts against might also be milled when the surface the head mounts against was milled.