Ok, this may sound naive, but in many posts throughout HPISF, is see people talking about engine shims. What is engine shimming? Can someone please explain this to me so I can understand it and start doing whatever it is I'm supposed to be doing? Thanks! :slapped:
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Engine Shimming
- Thread starter thrasher6
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[hs] darkshine
I Keep Breakin $h!t
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- cambridge, england
the shimms people refer to are located under the head button, they allow the mill to have a lower compression ratio (by increasing the area where combustion takes place, comp. ratio is squish volume-the last little bit of area left above the piston at top dead centre, or tdc, to the swept volume, ie the area below the squishey bt, from piston at tdc to bdc, bottom dead centre)
a shim looks like this:
sorry for the marine pic, but you gets the idea...
now, once a mill is broken in, you can remove some shims, increasing the compression ratio-as the squish volume is reduced, see. this basically gives more power, but it can wear an engine out quicker, also it may be harder to start the engine, loosening of the glow plug may be required. And as our engines do not have piston rings, ala normal ic engines, you can expect more 'blow by' if you increase the compression too high (basically the pressure above the piston is too great, the air/fuel mixture 'blows by' the piston, back into the crank case, therefore reducing power.
hope this helps. DS
a shim looks like this:
sorry for the marine pic, but you gets the idea...
now, once a mill is broken in, you can remove some shims, increasing the compression ratio-as the squish volume is reduced, see. this basically gives more power, but it can wear an engine out quicker, also it may be harder to start the engine, loosening of the glow plug may be required. And as our engines do not have piston rings, ala normal ic engines, you can expect more 'blow by' if you increase the compression too high (basically the pressure above the piston is too great, the air/fuel mixture 'blows by' the piston, back into the crank case, therefore reducing power.
hope this helps. DS
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[hs] darkshine
I Keep Breakin $h!t
- Messages
- 879
- Location
- cambridge, england
np. i think i'm in the market for a new mill, my k46 has not a lot of compression when cold...
- Thread starter
- #7
Since I'm already asking "simple" questions, when you say "mill," I have to assume you mean the engine itself? Why does everyone call it a mill? Is that just a European term and that's why I don't get it or is it something else? Thanks!
[hs] darkshine
I Keep Breakin $h!t
- Messages
- 879
- Location
- cambridge, england
to be honest matey i haden't heard an engine called a mill, till i came on here, so i thought it was an americain saying...i used to call engines lumps, till i went to college/uni!!! anyone shed any light on the term 'mill', as i would like to know as well!
Blazer X
Well-Known Member
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- Hoosierland
engine.......mill......?
I believe the two words are often used because of work being done.
I believe the two words are often used because of work being done.
