Cylinder head milling

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2/18/2019 10:10 AM
Edited Date/Time: 2/18/2019 10:13 AM

As a street bike i have got a Husqvarna SMR 510 (2008).
When i disassembled the motor to change the piston, i unfortunately scratched the sealing surface of the cylinder head.

So i wanted to take it to a shop to have them mill
/ resurface the head while taking away as little as possible, so that the compression does not increase too much and the valves dont hit the piston.

My question is, how much do you think i can take away max.? Would 0,5mm be too much?

And is there a rule of thumb on how much increasement in compression that would be?

Thanks in advance!

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2/18/2019 10:28 AM
Edited Date/Time: 2/18/2019 10:29 AM

mnomis484 wrote:

As a street bike i have got a Husqvarna SMR 510 (2008).
When i disassembled the motor to change the piston, i unfortunately scratched the sealing surface of the cylinder head.

So i wanted to take it to a shop to have them mill
/ resurface the head while taking away as little as possible, so that the compression does not increase too much and the valves dont hit the piston.

My question is, how much do you think i can take away max.? Would 0,5mm be too much?

And is there a rule of thumb on how much increasement in compression that would be?

Thanks in advance!

If you’re really worried have a thicker base gasket made by the same increment you remove from the head... at ,5mm. Or roughly .020” I wouldn’t think would provide a problem with interference, definitely would see an increase in compression... but I would check how much piston to valve before hand to see how much actual clearance you have... depending how deep the scratch is you shouldn’t have to come anywhere near .020” to remove it and square the head surface...

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2/18/2019 1:16 PM

Youre going to remove the amount of material equal to the depth of the scratch. The depth is what you need to measure and report back that number. We have no idea if you have a .030” deep gouge or a scratch that you can barely feel with a fingernail.

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2/19/2019 4:45 AM

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2/19/2019 4:49 AM

This is the scratch. Looks like about 0,1- 0,2 mm to me
Photo

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2/19/2019 5:37 AM

Holy hell how did you do that lmao.

Just tell the machinist to take off just enough to get rid of that. He will make very light passes.

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2/19/2019 7:05 AM

I bet .005(.13mm) would clean that up. Any competent machinist would be able to fix that.Chamber might be .25cc smaller.

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Race Bike: 2018 KTM 350SXF

Other Bikes: 1985 CR80R, 1990 CR250R, 1998 PW80, Specialized Fuse Comp 29.

Sold: 2016 YZ250F, 2012 CRF250R