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PostPosted: Sat Apr 12, 2008 10:13 pm 
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Joined: Fri Jan 12, 2007 2:17 pm
Posts: 2854
Location: Wichita ks
more pics.


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Piston crown angle.jpg
Piston crown angle.jpg [ 68.91 KiB | Viewed 968 times ]
Squish angle #1 Exhaust.jpg
Squish angle #1 Exhaust.jpg [ 54.97 KiB | Viewed 968 times ]
Squish angle #2 Exhaust.jpg
Squish angle #2 Exhaust.jpg [ 47.72 KiB | Viewed 968 times ]
Squish angle #1 Intake.jpg
Squish angle #1 Intake.jpg [ 68.19 KiB | Viewed 968 times ]
Squish angle #2 Intake.jpg
Squish angle #2 Intake.jpg [ 66.95 KiB | Viewed 968 times ]
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PostPosted: Sat Apr 12, 2008 10:17 pm 
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Joined: Fri Jan 12, 2007 2:17 pm
Posts: 2854
Location: Wichita ks
more.


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Squish angles on piston refrence for head.jpg
Squish angles on piston refrence for head.jpg [ 69.08 KiB | Viewed 966 times ]
Over view.jpg
Over view.jpg [ 71.07 KiB | Viewed 966 times ]
Piston marking for head work.jpg
Piston marking for head work.jpg [ 68.97 KiB | Viewed 966 times ]
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PostPosted: Sat Apr 12, 2008 10:23 pm 
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Joined: Fri Jan 12, 2007 2:17 pm
Posts: 2854
Location: Wichita ks
few more. I will post barrell measurment tommorow after review with a discussion on #s and how it would relate to clearences and the sweling effect on the piston. I will alos post port maping Base #'s . Time for a cold one.


Attachments:
Old  torgued gasket thickness measurment used for Cr and squish.jpg
Old torgued gasket thickness measurment used for Cr and squish.jpg [ 75.02 KiB | Viewed 964 times ]
New gasket.jpg
New gasket.jpg [ 66.15 KiB | Viewed 964 times ]
Piston barrel measurement tools.jpg
Piston barrel measurement tools.jpg [ 66.97 KiB | Viewed 964 times ]
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PostPosted: Sat Apr 12, 2008 10:29 pm 
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Joined: Mon Dec 15, 2003 2:40 pm
Posts: 22128
Location: Chicago
Hi adnoh , nice work you might try using this type of a stop to find TDC (Top Dead Center) to see if it makes a 2 degrees difference your seeing the timing off by.


Quote:

The basic piston stop. Using this tool you will be able to locate true Top Dead Center (TDC (Top Dead Center)) - even with a flat top piston. It is used with a degree wheel. I had to draw this because I can't find mine - I know it's here somewhere.

Image





http://web.archive.org/web/200404152135 ... r_map4.htm


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PostPosted: Sun Apr 13, 2008 11:26 am 
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Joined: Fri Jan 12, 2007 2:17 pm
Posts: 2854
Location: Wichita ks
Ok. I read the link and so should others when looking over the #s. The pic you showed should have a 1.5" spacer under flat piece. The ploit dome measured .095 above top of cylinder. Second the method I used may have a margin of error based on the link. I will put this to test before posting measurments. The method I used set up wheel on crank at TDC (Top Dead Center) with the T mark on flywheel then set dial indacater on sleves where the mag would hold it. set it to +1" than ran it to the max reading check position of degree wheel. This is how I determined the T mark was off 2 deg. I know will use my cylinder push tool to set up bump stop. I will need to go get jamb nut for shaft. The cylinder push tool I use spans the jug bolted to head bolts than ran down pushing the cylinder up and off. No screw driver there. This may accoount for a one to two degree mis alignment. I did notice the second section in the link stated how I did mine with the exception of reverse run reading. This may have been the mistake. I will set back up and test the way the TDC (Top Dead Center) was set to the ones in the link. One may say one to two degrees no big deal However it really is. One final note on stop it may be more accurate than the eye reading the gauge has a .005 tolerence I will also use a dial that is .0005 as well to test. Should a torgue wrench be used for bump stop method on degree wheel set at 20 in pounds to get accurate reading clock wise to counter clock wise. I will test this theroy and see diff if any. Just in case you where wondering the set up on T on fly wheel I used a laser level in the vertical position. That is why I levled jug before I started. Man I hate it when I screw up. That's why I,am back yard hacker. I will thorw a nother numbe out there. The static F was at 15 degrees BTDC. See why it makes a diff. The down side to this is all the math in note book will need to be adjusted by this margin making the #,s almost usless. Oh well.


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PostPosted: Sun Apr 13, 2008 7:00 pm 
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Joined: Fri Jan 12, 2007 2:17 pm
Posts: 2854
Location: Wichita ks
Could not find nut so I did a little work on exhaust manafold and jug.
Opening at EX manafold on jug
X= 90 degrees from vertical Y= vertical
X Y
New cylinder 44.83 43.10
Modified 46.22 45.99

X Y
Ex manafold 44.94 44.74
Modified jug end 46.25 44.75
Modified pipe end 45.14 45.19


Attachments:
Final cut.jpg
Final cut.jpg [ 54.58 KiB | Viewed 929 times ]
Second cut.jpg
Second cut.jpg [ 49.89 KiB | Viewed 929 times ]
First cut.jpg
First cut.jpg [ 63.21 KiB | Viewed 929 times ]
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PostPosted: Sun Apr 13, 2008 9:22 pm 
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Joined: Wed Dec 17, 2003 8:43 pm
Posts: 1368
Location: Colorado
Wow, you lost me about the second page, but it has still been interesting to watch this thread.


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PostPosted: Sun Apr 13, 2008 10:02 pm 
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Joined: Mon Dec 15, 2003 2:40 pm
Posts: 22128
Location: Chicago
The piston crown and the squish area is actually a radius, you can find this radius pretty easily, to check your math and measurements you can find the radius then draw it on paper and cut it out and see if it fits the piston crown.

I don't have a radius cutter so I have to fake it, a radius cutter is on my shop wish list this year, maybe speedchaser can build one cheaper than buying one? I don't need the whole set just one for Pilot domes.


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PostPosted: Mon Apr 14, 2008 12:53 am 
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Joined: Mon Oct 08, 2007 12:39 am
Posts: 3173
Location: Oklahoma City, OK
Lost me too Drak. I just like to oooh and awww at the pretty pictures.


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PostPosted: Mon Apr 14, 2008 6:52 am 
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Joined: Mon Dec 15, 2003 2:40 pm
Posts: 22128
Location: Chicago
I did some digging this is all I found http://pilotodyssey.com/Tech/Pilothead.htm looks like I found the piston crown radius to be 154.57mm you can draw it in cad and print out or get out the dividers and draw on paper, cut it out and match to the piston to verify.

I think I found the crown height by the difference in height from the edge of the piston to the center of the piston then measured the actual piston OD at the top of the piston (above the top ring) and drew it all up in cad. if you give me the measurements off your actual piston I can draw it for you in cad.


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PostPosted: Mon Apr 14, 2008 2:13 pm 
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Location: Chicago
Combustion Chamber Shapes
http://www.macdizzy.com/ubb/ultimatebb. ... p=1#000000

Fresh post by MacDizzy




There are good and bad combustion chamber shapes for different reasons. If we’re talking about high performance, a good shape will be one that will burn most of its mixture in a small amount of time. That shape will usually be a low and flat dome. With a squish area between 35%-45% of bore area, depending on its displacement and operating rpm.

A bad shape, for high performance applications, is one that is tall. It doesn’t really matter if it’s tall and rounded or tall and squared off. That fact that it is tall means the burn time is going to be longer. That translates into a slower, weaker, rise in cylinder pressure. Some of these designs are good for other reasons, however.

One of the reasons to make a chamber with a slow burn is so that the power delivery will be smoother. With a smoother power delivery, Engine life is enhanced. The piston and bore and main bearings will all last longer.

Chambers with a thick squish area can usually be improved by tightening up the squish thickness. One of the first things that will happen is power will increase due to the increase in compression ratio. If you modify a combustion chamber in this way, be sure to calculate the UCCR before the modification, so you’ll know just how much material to remove without raising the compression ratio too high for the fuel you intend to run.

Fuel mileage will also increase due to more of the fresh mixture being burned – less going out the exhaust port.

There have been engines designed with all kinds of different combustion chamber shapes. Most of them are used to combat some undesirable running condition, or poor Engine design, usually related to an inability to get rid of its heat.

An example of this is if the Engine is shrouded, and must survive on its own cooling fan, blowing air across its cooling fins from one direction only. Or maybe the Engine is placed in such a position as to not receive a cool airstream as it runs. These types of conditions will have engineers doing all kinds of things to get cooling under control.

One of the most popular things to do is to simply lower the compression ratio. Lower compression ratio’s make less heat.

Another popular thing to do is to design a thick squish area. Thick squish areas will usually lower the compression ratio, and provide a decent amount of cool gasses that do not burn. Though the tailpipe will be dirty, it will be cool and dirty.

Still another is to design a deep bowl, or pyramid shape dome. These shapes leave a lot of time for the mixture to burn, so they are more efficient. Their heat rise does not spike quickly, but their burn is more complete. This design is often used on smaller displacement cylinders, in order to take more advantage of as much of the displacement they have.

The offset chamber is another way to calm the effect of too much heat. A design like this puts the combustion chamber on the side of the Engine that runs the coolest, typically the inlet side of the Engine. Medium and large bore engines are sometimes designed this way, particularly if the Engine suffers from some form of shrouding, or if it might, through the course of running, have its cooling fins packed with dirt or mud.

All of these designs may or may not have positive squish. That is, a squish area angle that is greater than that of the piston dome.

Let’s say a typical piston can have its dome averaged out to be 11°, using a protractor. If the squish area is parallel to this, 11° also, less fuel is wasted – more of it becomes part of the power making process. This is a high output design, but tough on pistons and other Engine internals. It’s good for fuel mileage however, in lower compression ratio’s.

In a positive squish condition, the squish area of the combustion chamber should be greater than the piston crown angle. Typically, 1° to 1.5°. When the chamber angle is cut like this, peak power will go down a little, but piston life goes up a lot.

The squish area really needs to be at least 2° to 3° greater than the piston crown angle for better advantage. In this case, 13° to 14°. In extreme cases this angle can be as high as 10° greater than the piston crown angle.

The effect of this is multi-fold. It (may) lowers the compression ratio, burn more slowly, and provide cooler end gasses. In effect, it acts like a huge triangle shaped combustion chamber.

The squish area ratio, that is, the percentage of the combustion chamber that is squish area has a large effect on the performance and heat too.

A 50% squish area ratio (SAR) means that 50% of the combustion chamber is combustion chamber, and 50% of it is squish area – in percentage of area. Ideally, it would be best to have a small SAR, like 40%. But, small SAR’s mean the central, let’s call it, burn area, becomes larger. And a larger burn area only work best on small engines.

The reason this is true is because fuels burn at a relatively constant rate. Whether you pour the fuel in a 500cc single cylinder Engine or a 50cc single cylinder Engine, its fuel is going to burn at the same speed.

With that in mind, consider a running Engine of both of those sizes. To keep it simple, let’s say the spark plug fires at 20° BTDC on both engines.

Twenty one crankshaft degrees after the spark plug fires, when the piston has just passed TDC (Top Dead Center), cylinder pressure should be at its peak in both engines. But, due to the 50cc Engine having a 50 mm bore, and a short fuel burn distance (25 mm in every direction from the central spark), and the 500cc Engine having a 100 mm bore, and a long fuel burn distance (50 mm in every direction from the central spark), the small Engine is much, much, closer to its ideal burn. Its flame front has burned all of the available fuel, its cylinder pressure has risen the most it can. The 500cc Engine will take another (as much as) 15 crankshaft degrees before the cylinder pressure will peak.

That is why smaller engines are more efficient. In the same amount of time, more of their mixture is burned.

Squish areas are less important on small engines, because the flame front is fast enough to burn their mixture well. They will burn more of their mixture, as a percentage of what’s available than a larger Engine will.

The other important dimension to a combustion chamber is the squish area thickness. That is, the distance between the piston, at TDC (Top Dead Center), and the combustion chamber (head), in the area of the squish – the edge of the bore.

The thicker it is, the less efficient it becomes. The thinner it is, the more efficient it becomes. If it is too thin, pre-ignition can become a problem due to creating local hot spots, even if the compression ratio is OK for the fuel it is running.

A local hot spot can be a small piece of carbon that is stuck to the piston crown or dome, becoming superheated. This glowing hot piece, acts like a spark plug, igniting the mixture much sooner than anticipated.

It is important to consider as many things as possible when designing a combustion chamber squish thickness. Another very important thing to consider is the relative condition if its parts.

If the Engine is fresh, with new main bearings and crankshaft and rod bearings, including the piston pin bearing and associated pin, then one could logically assume that minimum squish thickness can be attained.

We consider this because, though seemingly solid, metals are elastic. When the Engine is spinning, these super stiff parts move and stretch and get pulled all out of shape. If the squish area is too thin, the piston will make contact with the combustion chamber at high rpm. This will cause detonation, because the compression ratio will rise to a level higher than anticipated. It can also cause pre-ignition, as well as a severely damaged Engine – usually the crankshaft bearings, piston, bore and dome.

It seems, the major developers of engines have discovered that a single cylinder Engine of about 125cc’s is the closest to ideal. Well, ideal for practical purposes.

In the real world we have 125 cc engines, and 250 cc engines and 500 cc engines, and others. In the interest of keeping things light and simple, a compromise is made. And that compromise is efficiency.

To keep the engines relatively light, their displacement is grown. Their power goes up, but not in a linear fashion to their displacement. What I’m saying is that realistically, a 500 cc single cylinder Engine is not 10 times more powerful or efficient than a 50 cc single cylinder Engine.

Some direct fuel injection two strokes have made their way into the market. Their combustion chamber shape likely has more to do with packaging the injector parts into its combustion chamber than any real attempt to extract maximum efficiency. Given enough time however, I’m sure they will continue to improve.

The fact is that if we want direct injection two stroke engines we must continue to purchase them as they are being developed. As big as the manufacturers are, they can not afford to design the ultimate Engine before bringing a revenue building product to fruition. We must buy their “development”, if you will.

I also want to mention that combustion chamber shapes designed for high fuel mileage and high output are similar, because they waste little fuel.

Engines that turn more constant rpm’s typically use tub shaped chambers, because they do not need to be as responsive but need good torque. Slower burning shaped typically make better torque and fewer rpm’s.

Engines, like ours, on our motorcycles and ATV’s, the kind we want to be really snappy when we blip the throttle, are usually designed around approximately 45% SAR, with the compression ratio relative for the fuel its running.

Smaller engines, like scooters and mopeds will still be relatively snappy with less or no squish area due to their smaller bores.


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PostPosted: Mon Apr 14, 2008 10:53 pm 
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Joined: Fri Jan 12, 2007 2:17 pm
Posts: 2854
Location: Wichita ks
Thanks "H". some really good read I will prnit off and read and see how this can be applied to better enhance preformance of applications. I feel parts need to be broke down and discussed for those who may not follow. I oreders the tool for TDC (Top Dead Center) today I thought the nut on cylinder puller may be to BYH like the new tool was only $10.00 I like new tools. I feel it's the only way to be sure. Iwll put post in word for section break down and discussion as time allows, if that's ok. I forgot to post pre cut pics on exhaust I know stixs could use a UHHH and a AHHH. Stixs I forgot to mentionthe first part to fuel cools. You will get why I mentiond check jetting. "It takes heat to build horse power" I,am not saying build a lot of heat it's just part of the saying. It takes heat to build hp and fuel cools. Axoy moron or what. or what.


Attachments:
new cylinder,un cut window opening.jpg
new cylinder,un cut window opening.jpg [ 30.62 KiB | Viewed 877 times ]
newcylinder, uncut #2 widow opening.jpg
newcylinder, uncut #2 widow opening.jpg [ 33.7 KiB | Viewed 877 times ]
New cylinder, uncut #3 window opening.jpg
New cylinder, uncut #3 window opening.jpg [ 46.43 KiB | Viewed 877 times ]
Final cut.jpg
Final cut.jpg [ 54.58 KiB | Viewed 877 times ]
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