The Official Head Thread.
 

Since I have seen an increasing number of questions and discussions popping up about cylinder head porting for the OHV CG engines popping up, I figured now is a good time to try and centralize and focus the discussion.

There has been a few members, including myself, that has gone down this path thus far, and we all sing the praises of it.

Silva did a good basic clean up and mild reshaping of his head with a moderate deck shave. http://www.chinariders.net/showthread.php?t=20362

JerryHawk250 with his head porting thread. http://www.chinariders.net/showthread.php?t=20410

My own thread from when I first started, which unfortunately I never really finished/followed up with to this point, but has some good pictures in it here or there to show the ports and chamber. http://www.chinariders.net/showthrea...t=19200&page=9

Another good thread with a lot of detail in a shorter number of pages. http://www.chinariders.net/showthread.php?t=22777

I tried to locate some threads with other pictures to compare the TT250 head in this discussion as well, but I couldn't find them. If you happen to remember what thread it was then feel free to post it up for me.

I will end this post and start the discussion by stating that, YES, it is worth doing.

No, it will not suddenly make your Hawk/Bashan/CSC a fire breathing dragon capable of going 0-60 in 3 seconds.

What it does is open up the mid range and especially the top end enough that you can feel a difference in the higher gears, allowing it to pull much more strongly between 4000 and 7000 RPM especially. I actually stepped my gearing down compared to my last bike to bring the rpm's up a little bit to take advantage of the wider power band in the top end because of this. For me this works the best since the fastest I want/need my own bike to do is cruise at 65mph without having the throttle pegged while also being able to hold that speed up a steeper hill, which it does admirably well now.

Could I aim for a higher top speed? Sure. With 17/43 sprockets I consistently hit 70 on my non ported head Hawk with my very large butt in the saddle, but it struggled to get there, and a couple of times I managed to reach 73-74mph in more or less the most perfect of conditions/ (GPS phone app for all stated speeds). With the ported head and shorter gearing it reaches those speeds with more ease, and I suspect that if I geared it back down I could easily hit 80 maxed out. I don't really want to since the Hawk is a bit too tall and light and "unsteady" feeling for me past 70, and I have no need to go that fast in the first place, so I opted for more torque at the rear wheel.

Anyway, discuss, inquire, or enjoy at your leisure.

I found heads in China a many prices
I’m sure there are many places that make heads etc
Wonder if a ported head n decked etc as a set be a good seller?

anything will sell if the prise is right sport...




..

Good idea Dan. :tup: Keep all the info in one place. Here's another thread that covered P&P. http://www.chinariders.net/showthread.php?t=22777

Dan made a good point about these head. No two are created equal so there may be some variation in the actual combustion chamber volume. Before I did any decking of the head I did measure the volume of the head. I don't remember right off hand the exact volume but have it written down somewhere. Just happened that the two heads I did( Hawk and TT250) were super close in volume and 1mm bumped with compression ratio to 10:1. Here's a calculator that will help. https://davis-motorsports.com/enginecalc.html

Here's video on how to measure the volume of the cylinder head.
https://www.youtube.com/watch?v=-80cwKShjAg

I went ahead and added that to my first post. I forgot all about that thread. Must be me reaching old age :hmm: :p

I think something else worth bringing up would be the tools to use if you want to go down this path.

The simple truth is, you don't need a die grinder and a bunch of burrs that cost $90 each, and in truth would be a little on the large side for such a small head. I tried using my smallest die grinder and had difficulty in the tight spaces around the bowls and valve guide near the seat.

Jerry recommends the Wen rotary tool with a flex shaft, and so far a couple of others have ordered and used this tool and were very happy.

This is the basic Wen kit: https://www.amazon.com/WEN-2305-Rota...ag=googhydr-20

There is also a deluxe kit that comes with some sanding drums, a polishing kit, some grinding stones, etc. for just a bit more. https://www.amazon.com/WEN-2305-Rota...oghydr-20&th=1

If you want to expedite material removal, then nothing does a better job than a rotary burr set. There are two varieties to go with, single cut and double cut. I would personally recommend staying away from single cut if you are new to this sort of thing as they can remove a lot of material quickly. Double cuts are a lot less aggressive and will give a little more control over the shaping when removing larger amounts if material.

Double cut burr kit example: https://www.amazon.com/Tungsten-Wood...s%2C167&sr=8-5

Single Cut: https://www.amazon.com/inch-Carbide-...-2-spons&psc=1

Once you have everything where you want it to be, then if you wish to take it an extra step and really clean things up then it is hard to beat a set of rotary scotch brites. Not entirely necessary, but it sure makes things easy!
https://www.amazon.com/Drill-Warehou...gateway&sr=8-3

Dan, it looks like you hacked into my amazon account. :hehe: But you missed one item. These flap sanding drums work great for cleaning up before I used the scotch brite wheels. https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

Hey guys, thanks for the links on the Wen and sanding drums.

The Wen is what I use on a lot of moto projects. It's a good tool.



This is the one I have.
https://www.amazon.com/WEN-2305-Rota...language=en_US


And I get rotary bits from here.
https://www.sciplus.com/s/?q=rotary+tool

So, an update I wanted to toss out there for the people on here that feel this type of work is beyond you. I bumped into Corey Lansdown on the China Bike N. A. Facebook page. He had some great pictures of a CG head he ported for somebody. Damn good work. This is their facebook page for the business. https://www.facebook.com/LFRPowersport/

Shoot them a.message if you are interested.

Opinions on just doing an even 1.0 mm shave without CC'ing the head? What about gasket considerations? I'm currently holding a brand new single layer metal gasket.

I have a brand new CGP head from Peace Sports and I'm currently talking to Corey from LFR in Missouri.

A thinner head gasket will probably be equal to around .5mm. Be good for about .5 increase on the CR.

I used a dremel with a flex shaft and a combination of stones and sanding drums to get it done. It was a little tricky getting behind the ex valve guide to do the long side of the port, but it was worth it
I ended up with a 120 main due to altitude and heat, my speed run yesterday got me a top of 71mph GPS corrected.

After reading through all of the linked threads twice, and corresponding with some professional head builders, I'm giving careful consideration to the squish band, or the "bevel" as its been referenced. I'll have 2 different gaskets to play with, and I'm going to talk to some more people before I settle on the exact amount I will mill off the head.