Anybody familiar with the hawk 250 to port and polish?

[JerryHawk250]

Pictures as promised. Here is the stock TT250 head before any work.

[JerryHawk250]

Tools and prepping the head. I forgot to take a picture of the Sanding flap disk.

[JerryHawk250]

Results of the porting and polishing. Some of the pictures came out to dark and blurred.

[JerryHawk250]

Next is decking the head. As mentioned earlier you can have it milled or do it old school with lots of elbow grease. Either way the results are the same. With the method I used I started with 80 grit sand paper and finished with 220 grit. I place a piece of 1/4" glass on a piece of plywood and stapled the sandpaper over it. On my Hawk head I did by hand. Using only the weight of the head sand in a back and forth direction rotating the head every 5th or 6th stroke until you removed the material needed.
This time I use my drill which goes much quicker but must do at a low rpm. Before you start I took a measurement using a strait edge placed across the head and the depth gauge on my caliper. I then set the depth gauge 1mm less . As in sanded the head with 80 grit I check every so often until I was close to the depth I needed them I finished it up with 220. I hope this helps other.
Other methods I have used in the past were a larger bench top belt sander for outboard motor heads and bench top disc sander for single cylinder heads.

[Megadan]

Great pictures Jerry!, This is a perfect example of what I would call a good basic port job that almost anybody can do without fear of "screwing up" the head. Call it "stage 1" if you will.

I am going to shamelessly borrow your first picture for some exposition, if you don't mind.

Now, for the OP. If you want to take it even further than what Jerry has shown here, and want to chase as much flow through the ports and in/out the combustion chamber as possible, without taking the head to a machine shop for some more advanced stuff like valve seat work, you can take these next steps.

To start, the Orange arrow points to the roof behind the valve guide, this is the area that Jerry has already knocked down. Follow Jerry's example of how to knock this down and smooth that ramp behind it. I can't explain it any better than his pictures show.

Yellow: This area to the sides of the valve guides is a critical spot to focus on to increase flow through the ports. You want to knock down as much of that area as possible to match up with the rounded part of the bowl and roof, all while keeping transitions smooth. The trick is to not alter the relative diameter of the port. What I do is imagine the cross section of that area as a circle, and work within the confines of that circle. Then I attack it in layers, doing it in increasing stages until I get the shape I am after. Once you get roughly close to what you want, stop short and use a less aggressive method of material removal to give you more control over the final shape.

Blue. This is the valve seat to bowl transition. From these pictures I can already say that the TT250 is still much better than the Hawk head or the one I bought - where the back edge of the seat actually protruded into the port a little in some places. This is an area to be careful at, don't knick the mating surface of the valve seat. Focus on the back edge of the seat and the port material right behind it. The aim is to knock both sections down until that seam is level, and this is easy to check by feel. A small sanding roll can achieve this, just go light, slow, and keep that bit/sanding drum moving. Never stop in one spot (good advice for all porting work in general).

Green: These sharp ridges in the combustion chamber are known as machinist ridges. At a minimum, lightly knock those ridges down and then smooth it out until it is all nice and round. This will reduce hot spots and give a more uniform chamber temp. This will also give a smoother flow transition into the chamber helping to maintain a higher swirl velocity. Combining those aspects together makes for a much more stable and efficient combustion event.

Purple: More or less the same as green, but specifically focused on the outer edge closest to the cylinder walls. This is a great area to try and open up to increase flow in an area that is often the slowest. You don't have to go crazy here, but better flow here is just another thing that adds to the sum total.

[JerryHawk250]

Thanks Dan for putting this into words. You are much better at doing that than I am. Lol I'm more of a here, hold my beer an watch kind of guy. Dan is correct that this is more of a mild porting job. I didn't get as aggressive especially on the bowls. The bowls are thin right around the spark plug hole. My Hawk head had a lot more meat in that area so I was able to take more out.

[Megadan]

I am going to share some links to my own pictures to kind of help with a visual on what I described.

First, this is the intake port of my head in process. Here you can see how I worked around the sides of the valve guide. I slowly knocked this down, always pulling toward the roof/valve guide so as not to alter the width of the port wall. The aim here is to reduce low pressure zones that can decrease velocity and also maintain a more uniform port shape, essentially eliminating a choke point. I spent a lot of time smoothing the short side radius and blending the roof around the guide and sides into the bowl to get a nice uniform transitions, but aside from around the guide, I focused heavily on not removing much material. The intake port is already sufficiently sized for our 230cc engines. Aim to create a smooth gradual funnel shape from the port entrance to the seat.
http://chinariders.net/attachment.ph...1&d=1514533495

This is the intake port before I started any work. http://chinariders.net/attachment.ph...1&d=1511069961


This is what I started with on the exhaust port.
http://chinariders.net/attachment.ph...1&d=1511069186

This is my finished exhaust port. As you can tell, I spent 90% of my efforts focused around that valve guide and the roof of the chamber. The short side radius and floor I just smoothed out with a minimal amount of material removal. One trick with the port exit that I don't have a picture of is to place a new exhaust gasket in the head to act as a guide for the port exit shape if you want to achieve something more port matched to the exhaust header, again trying to make the size increase as gradual as possible. http://chinariders.net/attachment.ph...1&d=1515233940

Here is my combustion chamber. As you can see, I knocked back those machinist ridges a decent amount and smoothed it out. You can also see the rounded edge on the perimeter of the chamber circle as well as just how open the area on the outer edges of the chamber around the valves are. As much as it looks like I have sharp ridges between the two valves, that is just the reflection off of the finished surface. Not a mirror polish by any means, but a light polishing job. http://chinariders.net/attachment.ph...1&d=1515811120

As a final note, don't forget to lap those valves when you are ready to put the head back together! No point in doing all this work if your valves piss it all away. It's also a great idea to go the extra mile to really clean every part of the head before assembly. Go as far as pipe cleaner in the valve guides. Get as much of that grit out as you can.

[Megadan]

Originally Posted by JerryHawk250

Thanks Dan for putting this into words. You are much better at doing that than I am. Lol I'm more of a here, hold my beer an watch kind of guy. Dan is correct that this is more of a mild porting job. I didn't get as aggressive especially on the bowls. The bowls are thin right around the spark plug hole. My Hawk head had a lot more meat in that area so I was able to take more out.

My pleasure! I do agree with you that the Hawk heads, while a much worse casting out of the box, are also somewhat of a better starting point for more aggressive port work thanks to all of that extra material. They are also a lot more work because of that extra material lol.

That being said, the TT250 head also needs a lot less work around the bowl area, such as around the guide, to begin with. Especially the bowl area right under the guide itself.

[roundhouse]

Great informative post here. Thanks guys

[OneLeggedRider]

Dan and Jerry are spot on when it comes to the porting, it's all about transitions, finish and port matching. I took 4 stroke and 2 stroke performance in school and we had a flow bench and a dyno so you could accurately measure increased performance.

The only thing I dont agree with is the homemade decking and valve lapping. Take it to a reputable engine shop and have a millimeter milled off and get a 3 angle valve job. Because if you're gonna put that much time into porting the head (it's not a quick or easy process) then you might as well spend the extra money to be sure the machine work is done properly. Jmo

[Megadan]

Originally Posted by OneLeggedRider

The only thing I dont agree with is the homemade decking and valve lapping. Take it to a reputable engine shop and have a millimeter milled off and get a 3 angle valve job. Because if you're gonna put that much time into porting the head (it's not a quick or easy process) then you might as well spend the extra money to be sure the machine work is done properly. Jmo

Neither of us disagree with you at all.

However, if done properly, the old sandpaper on a true flat surface (glass for example) is an effective and proven method. That being said, if you have to buy everything in order to do so, then it will probably be cheaper to have a machine shop mill it since it is a tiny 1cyl head (not to mention it's a lot less work!). If you already have everything on hand, then it costs nothing.

I actually milled my head at work, but had to finish it on a machined plate with a little sanding to get a consistent finish due to the smaller sized bit I had on hand combined with the old and slightly worn out mill I had permission to use. A straight edge and feeler gauges showed it to have a perfectly level surface when I was done.

The valve seats are already ground from the factory, but not to the greatest standard as you can imagine. Mine had a couple of small spots that weren't the best seal thanks to a quick application of prussian blue. A quick valve lap did the trick. A 3 angle valve job would be better of course, but not essential.

Again, nobody here will disagree with you. If I were building a race engine, then I absolutely would go the many extra miles to get every bit I could out if it, like stainless valves, bronze guides, new/better seats etc. For a bunch of cheap hobbyists with cheap Chinese motorcycles, the mantra is get what you can for as little as possible.

[Allinarush]

This should be on the resource post.

[OneLeggedRider]

Originally Posted by Megadan

Neither of us disagree with you at all.

However, if done properly, the old sandpaper on a true flat surface (glass for example) is an effective and proven method. That being said, if you have to buy everything in order to do so, then it will probably be cheaper to have a machine shop mill it since it is a tiny 1cyl head (not to mention it's a lot less work!). If you already have everything on hand, then it costs nothing.

I actually milled my head at work, but had to finish it on a machined plate with a little sanding to get a consistent finish due to the smaller sized bit I had on hand combined with the old and slightly worn out mill I had permission to use. A straight edge and feeler gauges showed it to have a perfectly level surface when I was done.

The valve seats are already ground from the factory, but not to the greatest standard as you can imagine. Mine had a couple of small spots that weren't the best seal thanks to a quick application of prussian blue. A quick valve lap did the trick. A 3 angle valve job would be better of course, but not essential.

Again, nobody here will disagree with you. If I were building a race engine, then I absolutely would go the many extra miles to get every bit I could out if it, like stainless valves, bronze guides, new/better seats etc. For a bunch of cheap hobbyists with cheap Chinese motorcycles, the mantra is get what you can for as little as possible.

We're on the same page when it comes to money and the cheap Hawk. And I'm extremely impressed at what you guys can do with little or no expense. Years ago I had a 230 QuadSport that I put an XL 350 motor on. We hauled out for a week of camping and riding far from home. 2nd day the timing chain tensioner snapped and bent a valve. With small rivets and a thin piece of metal we patched the tensioner and straightened the valve using a dime and the trailer hitch, then power lapped the valve with a drill. Somehow it worked and I was able to finish out the week with it.

As far as money I've got $6k in my Scrambler and it is insanely fast. But the cheap Hawk isn't getting anything other than a pipe and carb as far as performance goes. If I want a serious dirtbike I'll go Japanese like I did with my XT 500.

[Megadan]

Originally Posted by OneLeggedRider

As far as money I've got $6k in my Scrambler and it is insanely fast. But the cheap Hawk isn't getting anything other than a pipe and carb as far as performance goes. If I want a serious dirtbike I'll go Japanese like I did with my XT 500.

That kind of sums up the reason for the Sandpaper mill work and basic valve lap job.

Assuming you had no tools at all...A Wen rotary tool kit, some cheap double cut carbide burrs for a rotary tool, and a scotch brite buffing kit (again rotary) from Amazon = $50ish. A head gasket set from ebay is another 12 bucks on top of that. So from nothing to even a basic port job for $62. Toss in say another $40 to have the head milled, which wouldn't be too unrealistic. Investment of $100 for quite a decent improvement in power, especially on the top end, is hard to sneeze at.

Combine that head work with an exhaust, which you can also go cheap with if you want, a 30mm PWK carb, intake, and pod filter from Aliexpress totalling a massive $48, and the Hawk goes from "barely adequate" power to being fairly peppy... at least as peppy as a Chinese 230cc air cooled single can be.

[OneLeggedRider]

Combine that head work with an exhaust, which you can also go cheap with if you want, a 30mm PWK carb, intake, and pod filter from Aliexpress totalling a massive $48, and the Hawk goes from "barely adequate" power to being fairly peppy... at least as peppy as a Chinese 230cc air cooled single can be.[/QUOTE]

Well since we're talking about most bang for the buck, and because you have access to machine tools, have you thought about shaving the flywheel?

The reason these 450s are so quick is because they have barely enough flywheel to keep them turning over (they die easily at idle) and less weight means faster engine acceleration and more rpm is possible. My Scrambler is built for dirt drags and for the money shaving the flywheel was the biggest performance increase.