CG250 Head - A Closer Look.
 

Yes, I have nothing else to do with my money, so I buy bike parts. To be fair, this was 50 bucks to my door, so not a huge investment lol.

I bought this head as a port and polish project for my Hawk (which arrives Thursday thanks to the Holiday and weekend combined with my work schedule).

Before I get into a lengthy report, let's just get on with the pictures.

Intake port and combustion chamber side first.

Exhaust port.

So right away, these images alone give a great idea as to why we only get a massive 14hp from a 230cc engine.

The intake side of things really isn't too bad, but there are a few things I observed right away with just my eyes. The intake port is smaller than 30mm. Without going and digging out my calipers to measure, I would estimate it to be around 27-28mm. The casting around the valve guide is rather obtrusive into the port, but surprisingly, there is very little in the way of flow restriction from the short side radius. There is a little bit there, but way less than many other heads I have worked with. On the right side of the port is also a slight intrusion into the port that causes a small narrowing of the ports cross section about halfway down the port. It's nothing big, but another flow restriction.

The exhaust side of things is by far the worst. The pictures really don't do it justice. There has to be at least a 30% reduction in cross sectional area at the valve guides greatest protrusion into the port as compared to the exhaust valve area and port size. The exhaust is literally leaving the valve to slam into a huge bottleneck halfway out of the head.

I would honestly not be surprised that proper porting to simply even out and open up the restrictions in the ports, as well as a port match with a tapered reduction through the port could easily pick up a 20-25% increase in power without altering the lovely powerband this engine possesses. I may not even bother decking the head at all.

Oddly, I have never been more excited to do head porting in my life. Now I just need to find the time lol.

There's a lot of room for reshaping and improvement in those ports. It may flow enough to be able to step up to a 34mm or 36mm carb.

That was the plan. I want to use a PWK/KOSO style 34mm flat slide carb with this head. The trick will be reshaping the ports without killing velocity off, which is where the tapering of the port "bore" from the opening down to the valve is crucial. I want to improve flow without killing charge velocity so it maintains a good swirl and atomization at low engine speeds.

One thing this head does have going for it is the limited amount of short side radius bending and valve shrouding. The angle of the valves is fairly wide, so it does have that going for it.

Do you plan to polish the exhaust side?

Mega... Many have threatened to go thru with this but never reported back here. I Guess you are one of the few of us that are not so tight fisted. This looks interesting.

I plan to port both intske and exhaust and polish the exhaust side, yes. I also plan to smooth the edges of the quench ring and polish the combustion chamber,.

I have been accused of having more dollars than sense... but yes, I plan to follow through with this. Having 2 bikes affords me the luxury of being able to do this kind of work while still being able to ride. Plus, I like to tinker.

Well so far, your toy signature seems pretty sensible.

It only appears that way. :)

I'll be following with great interest. :tup: I've often considered polishing the surface of the piston as well. I've noticed that stock pistons are typically quite a rough casting on the combustion surface, whereas the rest of the piston is nicely machined. I've also noticed that aftermarket pistons are generally machined on the combustion surface as well as the skirt, etc. This leads me to wonder if there might be two benefits to polishing the combustion surface; one is the theoretical efficiency increase in moving fuel/air and exhaust, and the other is resistance to carbon build-up. What do you think?

From my personal experience, polishing does help resist large carbon deposits forming, but you will still get a thin layer no matter what you do, because even the best polishing job possible still has microscopic grooves for carbon to cling to and build up on. I did consider pulling the piston and doing that kind of work, but that may be for a later date. I will do what I can with the head, and put on a new head gasket.

That said, it would be kind of fun to go all out on one of these motors, but even I have my limits on how much I want to spend. What I would personally do is send the piston and head off to Swaintech, have their ceramic coating applied to the piston top, combustion chamber, valves, and exhaust port, and their low friction skirt coating done as well. Since it's a one cylinder engine, the cost wouldn't be too horrible. This does amazing things for keeping aircooled motors run a little bit cooler, since more heat is retained in the chamber during the combustion process. Current prices for that treatment would be $52.50 for the piston, and $54.50 to do everything to the head. So...$107 bucks.

I did consider seeing if I can find some undercut stainless steel valves that would work with this motor and have a shop install and hone some bronze guides for it. Again, not entirely necessary, but an idea. I would definitely consider this more if I were to bump the compression up a point to around 10:1. I really don't want to do that personally, at least not without some way to control the ignition timing.

With a full P-N-P, valve work, larger carb, better exhaust, and higher comp, I think the cam will start to be the limiting factor. I'm not sure if it would be possible to run a different ratio rocker arm on these engines. You could always try degreeing the OE cam.

It's tough with only one cam lobe; neither event is optimized. That said, you could get a cam grinder to shave a little off of the base circle for a little more lift. :D

Personally, for my goals I don't believe a camshaft is necessary. I just want to get an honest 20-22hp out of one of these engines. No doubt it would help, but when you start changing cam profiles, you start to effect the powerband of the engine more, and I want to keep it happy in it's current operating range.

How about this ?
http://www.ebay.com/itm/MOTORCYCLE-Q...-/401311496266

Don't tempt me lol

I've been looking at them for a while. They are proud of those little turbos. I have bought full size turbos for less. So being here in south Louisiana there are lots of jet ski parts at the outboard repair shops. I'll find a good use one eventually to experiment with.

I'm eager to watch this play out! And yeah, that exhaust port is nasty.. makes me want to tear mine down just to do it myself. The intake port doesn't look too bad to me, until you hit the valve guide area. This could make an interesting winter project if you get the results we're all drooling over! :lmao:

Take lots of pics as you go! We're all going to want every detail.

I will do the best I can to take pictures, but I tend to have a hard time stopping once I start working to snap a shot unless I deem it worthy lol.

While I was assembling my bike I went ahead and checked my stock ports, and they are more or less the same. I was wondering if maybe it was just this particular casting that was kind of crap, but it wasn't.

This most likely will be a winter project for me, but I want to try and get started sooner rather than later. My biggest problem is, I have other obligations through the year that require my attention more, so if I do get any work done it will either be in spurts, or all at once.

Yes, I'm very interested in this as well. I have, in the past, recommended leaving the ports alone, because it is way too easy to screw the job up if you don't know what your doing. Not the case here. Megadan has a well thought out process in mind. I particularly like the ceramic coating idea. Should reduce oil temperature....ARH

:lmao: Coated piston (<$5) is the standard item in workhorse trike...
http://gd1.alicdn.com/imgextra/i1/18...1864097574.jpg

^I wouldn't trust that coating to do much of anything that I am talking about. If you want to try it go ahead. I have my limits on things I would cheap out on.


Speaking of coatings. As much as I would love to do so, I am not going to dive that far into this. This exercise is literally just a matter of porting the head to see the results. I intentionally bought a second head for this so I can not only enjoy the bike while doing this on the side, but also have the factory head to switch back to if I discover I don't like the nature of the bike after doing said work.

The whole ceramic coating idea was part of a "if I were to go all out" discussion. I wanted to keep this as pure as possible and not introduce anything to skew the results of what just simple port work can do with a more "high performance" carb.

I just looked at the head again. It has a hemispherical combustion camber, so your bike will have a hemi in it. :tup:

They should all be hemis. Not uncommon on old Japanese engine designs.

I don't know what high performance carb you have in mind, but in a round slide carb, Mikuni makes ANOTHER VM26, costs about 80 bucks, but has an enriching circuit instead of a butterfly choke with shaft hanging in the air stream...ARH

Looking at a 32 or 34mm flat slide style carb with an enrichment circuit similar to what you just mentioned. I am open to, and welcome all ideas.

Wow. Bigger than 1 1/4 inch on a 250? Other than an Italian single cylinder road racer? My 22 hp AJS 250 CSR only had a 1 1/8 inch carb on it, for what ever that's worth...ARH

As I said, just considering at this point. There are a lot of variables to consider,

Dan, have you made any "head way" on this?

Nah, I don't have my head in the game yet. I am too busy trying to get ahead in other projects, and I just can't get enough flow at the moment.

I will be starting on it here soon though if time permits.

Boo. :lol:

I see where this is heading. Please don't lash out at my post.

I need to stop reading this stuff. Its got me thinking about getting another head to start playing around with. Besides the port and polishing I'm thinking about decking the head to get the compression ratio up o about 9.5:1. this should gain at least 2 hp minimum. My oldest brother runs a machine shop so the machine work to deck the head isn't a problem. He's a motor head too so won't take much to convince him to get it done for free. lol

Do it! With resources like that, what's stopping you?

Anyone want to donate a head for the sake of valuable research? Anyone? Anyone? Lol. Cheapest I have found is about $55 and not as easy to find as piston and cylinders.

I feel the same way! I start watching the videos and reading the posts, next thing you know, I’m buying levers, exhaust, carbs and now tires!:)

If you do plan on buying a head, then make sure to measure the distance between the Head/Cylinder bolts. Supposedly there are minor variations in this pattern between some manufacturers of this engine, so not all of them will match up. I managed to do mine with calipers and the valve cover removed. Was a little annoying trying to get an accurate set of numbers, but doable.

Since you done all the dirty work would you be willing to share those dimensions or post a link to the one you got. This is the one I found. http://www.motopartsmax.com/index.ph.../2/cPath/21_85
http://www.motopartsmax.com/images/C...999011/2-l.jpg
http://www.motopartsmax.com/images/C...999011/500.jpg