15 yz250f GYTR head

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Mad_scientist_MBP
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15 yz250f GYTR head

Post by Mad_scientist_MBP » Tue May 02, 2017 7:22 pm

This is a GYTR head I did for a 15 yz250f. Cnc porting was cleaned up and improved as well as the dome being reshaped and polished. Previously had a 270 kit and u4.4, it's now stock bore, stock cams, stock piston, and pump gas. Racer is happier now than he was with the big bore. My personal opinion is that, built correctly a stock bore and stroke engine will make the vast majority of people happier than getting big bores done. This is another build that proves that.
Attachments
IMG_20170418_223102_831.jpg
Better pictures of the hand porting
IMG_20170418_223102_831.jpg (649.92 KiB) Viewed 333 times
IMG_20170418_164258_615.jpg
Before and after reshaping the dome
IMG_20170418_164258_615.jpg (750.9 KiB) Viewed 333 times

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Sandblaster
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Re: 15 yz250f GYTR head

Post by Sandblaster » Sun May 14, 2017 4:16 pm

Post pics of your other work.
I've seen some other nice work you have done.
If bikes are for kids I'll never grow up.

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Sandblaster
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Re: 15 yz250f GYTR head

Post by Sandblaster » Sun May 14, 2017 4:31 pm

As most of you know I am not a big 4 stroke guy.
However, it does not mean that I don't work on and mess with the valve slingers :lol:
Below is a pic of Michael's head work that he posted.
Here is my notes that I can see what has been done.
IMG_20170418_164258_615.jpg
IMG_20170418_164258_615.jpg (144.63 KiB) Viewed 302 times
A. The valve seat to head edges have been blended and polished.
B. The machined edge of the valve seat area to combustion chamber have been blended and polished.
C. The exhaust ports have been blended and polished.
D. The transition from the plug to the combustion chamber has been blended and polished.
E. All the casting flash on the intakes have been removed but no polish.
F. The combustion area has been blended and polished.
G. The head to cylinder surface has been cleaned up.. likely on a surface plate of some sort.

What I wonder is, what else has been done that you can't see?
Also, what has been done to the exhaust port 8-)
Are you CCing the head after your work so that you can compensate for the increased head volume?
What are some of the hidden pitfalls of porting a 4T head that is easy to overlook?
Nice work..
If bikes are for kids I'll never grow up.

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Sandblaster
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Re: 15 yz250f GYTR head

Post by Sandblaster » Sun May 14, 2017 4:39 pm

Here is a head that has had some port work done to the exhaust.
While it looks better then stock I still see some room for improvement :o
example 1.JPG
example 1.JPG (19.16 KiB) Viewed 298 times
If bikes are for kids I'll never grow up.

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Sandblaster
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Re: 15 yz250f GYTR head

Post by Sandblaster » Sun May 14, 2017 4:49 pm

Here is another head that has been worked over.
The work looks good although I like my cylinder polished to a higher luster.
I know that the more you polish you get less and less returns for your effort.
But in this game, every little bit helps.
I know there is a lot of theory on polish vs. just smooth.
Here is what I do know.
All imperfections cause turbulence.
The smoother the surface (Less grooves) the less heat transfer takes place.
But how smooth is smooth enough?
I don't know, so I polish to a high sheen and don't worry about it :D
example 2.JPG
example 2.JPG (74.58 KiB) Viewed 297 times
If bikes are for kids I'll never grow up.

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