Cylinder Head Cutaway

[TwoJugs]

I had these buried in one of my boxes of items I picked up. The PO was racing the XS back in the day. I guess he was doing some port and polish and wanted to see how much and where. Interesting how much and little you have to work with. I have read a bit about this lately and there is lots of good info out there. More important is what not to do.

 

[gggGary]

Great shots, thanks for posting them!

 

[goodgollyjosh]

Thank you for posting these. I was using a Defelsko ultrasonic thickness checker and I detected the thin area in the exhaust step that your pictures reference but sometimes seeing it really helps put it in perspective just how thin certain areas really are. At first I didn't like how RD valve spring's shims wouldn't allow the spring to truly sit on the head like the factory shims will but now after seeing your photos, I am kind of glad since I did remove some material in area photographed while porting. Thanks again.

 

[goodgollyjosh]

Also picked up on a thin area at the oil return passages for the cylinder head. Exhaust side was particularly thin. In the .020" range if I recall correctly.

 

[TwoJugs]

These were very educational and full of warning. As I dig deeper I am learning more about port altering then I thought I needed to know. It occurs to me now that you can do as much detuning as improvements if it is not done with caution. The ultimate conclusion is that you need to have a clear goal of how you will be using the motor before you dive into it.

 

[650performance]

Since the ports are large to begin with, the best race tuners from the '70s concentrated their porting efforts upon keeping the flow velocity up and reducing turbulence. When they got it right (Branch, Lillie, Axtell, etc.) it turned out that the heads provided sufficient flow and linear power characteristics for all forms of competition ranging from TT to road racing.
The tuners changed the cam, exhaust, etc. for a given type of competition, but not the head itself.
A properly ported head also works perfectly for a warmed up road bike (e.g. 700 or 750 kit, Shell #1 cam, free flowing exhaust and well sorted carburetion).
For any 650 just careful removal of the casting flashing and a good valve job will get you 95% of the way there. If you know what you're doing, some work around the valve pockets and the guides will give you the last little bit. The whole thing is to not overdo it.

 

[gggGary]

Hope this hangs around.
A 3D view you can manipulate, add, subtract, parts from the view. Enjoy!
https://grabcad.com/library/yamaha-...6rR3Eoo5tK3bozDzj0lSoVCyk5C4qzs6g9IrJ9J93bMr8
click unclick various parts in the drop down menu to change the view.

 

[YamadudeXS650C]

Cool !

 

[59Tebo]

That's awesome! If I can scale everything right, I can do a "mock-up" without any heavy lifting! I still have some skills with a pencil & paper (huh? what?) so, theoretically, I could "drop" that motor into the (modified) frame of "The Basketcase", add the forks, swing arm, and a few other things, and have a drawing that'll look as close as I can get, without actually bolting things together. (That would be some mean feat, since parts are all over the place right now...)