Transfer Port Modification- Pictures and results here.

[europorsche914]

I know that the head kit to have (according to most) is the ada head kit and they run 13:1 for 91 octane; 15:1 for 105 octane; 17:1 for 116 octane or alcohol.
Pocket Bike 44mm Head Kit 21-1530 - ADA Racing
Maybe we can look to their design for some recommendations... I would love a better piston and head for my motor -Justin

 

[runslikeapenguin]

Whoa! Hold on there killer....a normal two stroke engine will have a compression of 9:1 or a little higher, but certainly not 15-17:1 or higher.

Ours are closer to 6:1 which is a little low.

im talking about the dynamic measurement of UCR which is around 9.2:1 and should be around 15:1

the 6:1 is the corrected ratio which is measured from the closing of the exhaust port when the engine is static.

most "factory" 2 strokes have a CR of around 9:1 but wheres the fun in that??

 

[Bikeguy Joe]

Yes, got it. I am clearly out of my league here....carry on.

 

[europorsche914]

I found some more info about designing a cyl head w/ a squish band that i wanted to share:

CYLINDER HEAD

Cylinder heads can be reshaped to change the power band. Generally speaking, a cylinder head with a small diameter and deep combustion chamber, and a wide squish band (60% of the bore area). Combined with a compression ratio of 9 to 1 is ideally suited for low to mid range power. A cylinder head with a wide shallow chamber and a narrow squish band (35-45% of bore area) and a compression ratio of 8 to 1, is ideally suited for high rpm power.

There are many reasons why a particular head design works for certain types of racing. For example; a head with a wide squish band and a high compression ratio will generate high turbulence in the combustion chamber. This turbulence is termed Maximum Squish Velocity, MSV is rated in meters per second (m/s). A cylinder head designed for supercross should have an MSV rating of 28m/s. Computer design software is used to calculate the MSV for head designs. In the model tuning tips chapters of this book, all the head specs quoted have MSV ratings designed for the intended power band changes.

BASIC TWO-STROKE TUNING

another site states something similar:

Heads and MSV

MSV - Maximum Squish Velocity rates the maximum velocity of the fuel air traveling across the squishband just before the piston reaches TDC. If MSV is to low the flame front will not burn the fuel air mixture effectively. If MSV is to high, detonation will occur and cause engine damage. The TSR programs calculate MSV for various types of heads.

Tub Head - Shape of the combustion chamber - like a tub or hat.

Hemi Head - Hemispherical shape for the combustion chamber.

Squish Band - Outer area of head that forces the unburned fuel air mix into the center chamber for combustion. The squish band angle is usually 1-2 degrees greater than the angle of the piston dome. Verticle clearance and squishband width affect MSV.

Squish - Verticle distance between top of piston and head. By measuring the step in the head and subtracting this number from the squish clearance you will have the distance the piston is below deck (negative deck). The negative deck measurement is needed to calculate port timing.

Squish Band Area - Varies from 30% - 60% of Bore area.

Step or Step Cut - The step cut in the head at the bore diameter. The squish band angle starts at the bottom of the step cut in the head. Measure the depth at the very edge of the step cut.

Note: Some heads have the step cut diameter 0.020"-0.030" thou more than the bore diameter. This allows the head to be offset to the piston. This creates less verticle clearance on one side. By moving head back and forth, leave extra clearance over exhaust port side. Then, center the head, by doing a squish test, on each side of the piston, over the wrist pin. Try to get the variation to within 0.001" thou. This is important if you are running near the mechanical limit for verticle (Squish) clearance.

2-stroke-porting.com - Terminology

if we reach a consensus on how to design this head hopefully we can make some real power.

here's a vid about what squish band is:

YouTube - CYLINDER SQUISH BAND CLEARANCE CHECK

I do not know a whole lot about this stuff, just tryin to learn as much as i can -Justin

 

[runslikeapenguin]

Justin that pretty much covered it.

our heads don't have any squish let alone a tuned amount for our type of riding. its something that needs to be looked into.

 

[europorsche914]

as we speak im playin around with a 3d model in ProE. I will need more precise measurements before i can play with it too much more. The final design of the head depends on if we plan to stick with the original piston or create a new one. I know the basic idea but before it is ever produced i want to look to people that are more knowledgable (such as you (runslikeapenguin) and other 2 stroke tuners (creativeengineering's neighbor)). I am able to offer 3d modeling to help this project if anyone else is committed to this as much as i am. -Justin

PS another great site:
Getting A Head

 

[Creative Engineering]

Excellent posts guys!!!

I've worked through different chamber designs for the Nitro motor in the B.R.E. Dragster. The way nitro lights off, (It basically explodes under pressure), the chamber area and piston, shape, make a huge difference in the life of the engine! Nitro is not forgiving at all!!! The dual plugs per cylinder just keep the engine running until the blower spins up and the fuel injection pressurizes...then the nitro explodes like a hammer atop the pistons.

I had no Idea that the cylinder head chamber on a 2-cycle was THAT critical to performance.

I think I need to build another small engine Dyno for testing purposes. I built one about 20 years ago to test twin cylinder mower engines. Guys were modifying riding lawn mowers to use in mini tractor pull events in NC. I was able to get 65H.P. out of a horizontal crankshaft base 22H.P. V-twin.

Brendan will be over tomorrow, and I will post his thoughts tomorrow evening. I plan on offering remanufactured engines that will include his recommendations as well as a proper crank and many other fixes. I may increase the stroke, and we'll have the first 80cc engine. I'm not going to rework these to be unreliable high horsepower bicycle mutilators. I just want to be able to offer a smooth, reliable, relatively maintenace free alternative. 5 H.P. is plenty for a bicycle...these engines will easily achieve that; reliably.

Jim

 

[lennyharp]

I am working on mine and my buddy who has 55 years working on motorcycles says this is a common performance mod to make the engine breathe better. I'll take some photos and see if it works at all.

 

[runslikeapenguin]

just for reference here's a pic of where our squish is.

yeah i know, your thinking to yourself.
"where is it?"

also if anyone is planning on machining a head make sure that you allow for a much better cooling system than what they have now. at least double the size of the fins they come with now, if not bigger.

 

[BrettMavriK]

my new word for the day: Squeeshband =-]'

I believe mild adjustments in head and flow would make nice changes.
I think the big thing would be if the motor was balanced.
Keep up the research guys...

I want to do wheelies !!!
'BrettMavriK

 

[Creative Engineering]

Hey guys,

I had a long meeting with Brendan Power this afternoon about our little Chinese engines. He confirmed that the cylinder head geometry is all wrong. I also showed him what was done to the jug in the "boost porting" thread, the hacksaw blade thing!...and he said NO,NO,NO!

Here's a line item list of what needs to be done:

1) Re-machine the cylinder head to create a proper Squish. He says this will be good for a 10-15% increase in power. It's a 15 minute fix in the CNC. The cylinder head also needs to be dowel pinned to the jug so that the combustion chamber will always be perfectly aligned to the cylinder.

2) The crankshaft is too heavy for the size of the engine. He said they probably did that so that the engine would idle based on the many other flaws.

I set the crank up on the surface plate and showed him the out-of-concentric way the weights had been attached. He recommended leaving the weights on for now and chucking the crank in the lathe to true everything up.

There has been no attempt to balance the assembly at the factory...and as I already knew balancing a single cylinder engine is a best situation compromise through the entire range of crank rotation. As he pointed out; the out-of-concentric condition is causing 90% of the vibration. This is why some engines vibrate terribly and others don't.

As far as balancing goes, I will model the crank and rod assembly with the piston in SolidWorks...from there I can rotate the crank in 5 degree increments and the computer will show me the centroid of the assembly. After a few hours I will have the ideal location and amount of material to remove to get a "best situation" balance of the assembly.

3) The cylinder needs to be dowel pinned to the engine block, for the same reason that the head needs to be dowel pinned to the cylinder. Once pinned the transfer ports can be blended and radiused knowing that when it is disassembled it will go back together perfectly.

4) The port timing is all wrong...I'll set up degree wheel and give him exact numbers so that he can recommend what to do. He did say the jug needs to be spaced from the block in order to correct the worst of the timing problem. Removing the base gasket in an effort to increase compression actually decreases perfomance because the port timing is pushed even further out of phase.

5) The intake and exhaust ports are too small...they need to be opened up. Width not height. Tapered side to side.

6) The crooked intake is a performance killer...I explained that it was necessary in order to keep the carb level for many installations. I've got a new Schwinn Jaguar in the shop to develope an installation kit, so I'll see if the engine can be mounted at a more level attitude so that a straight intake can be used. The straight intake worked out fine on the last bike I did.

7) All mating surfaces should be "O-ringed" for a perfect seal. He was tellig me they would pressurize their go-cart engines before leaving the shop in the evening, and expected zero leak down in the morning...NOW THAT'S SEALED!!!

8) He didn't like the block register at all and recommended using dowel pins. If the two block halves are not perfectly aligned the crank bearings and countershaft bearings will fail prematurely.

There's more...but this is enough for now! Everything he described is easily done...It's the little things that can make an engine sooooo mch better.

Brendan learned on Dirt bikes and 2-cycle racing go-carts in Australia. He is VERY knowlegeable and always offers no nonsense advice down to the detail. I will remanufacture an engine based on his recommendations and report back.

We will have a few more Q&A sessions as I go along...It was simply too much info to digest in one session.

I explained that about 5HP was plenty, as a bicycle will not handle excessive HP. I'm after smooth reliabilty, easy starting, and a power/torque band that is complimentary on a bicycle.

Jim

 

[runslikeapenguin]

a few of those things sound like they might be a little bit overkill for our cheap ass engines but its good to know about everything else.

the pro that i have been bouncing questions off of as well told me that he could see just by looking at the engine the port timing was off and that he would get back to me on some number amounts. it will be interesting to compare the numbers i end up getting from him with yours.

also when your talking about fixing the head in a CNC are you talking about making a whole new head? because short of that i don't see how you could fix the head as it sits.

the intake is something ive been thinking a lot about. see if your guy can offer any insight to a good length.

 

[robin]

If there is someone who would do this for me i would gladly hire it out

 

[POPS]

Hey guys,

I had a long meeting with Brendan Power this afternoon about our little Chinese engines. He confirmed that the cylinder head geometry is all wrong. I also showed him what was done to the jug in the "boost porting" thread, the hacksaw blade thing!...and he said NO,NO,NO!

Here's a line item list of what needs to be done:

1) Re-machine the cylinder head to create a proper Squish. He says this will be good for a 10-15% increase in power. It's a 15 minute fix in the CNC. The cylinder head also needs to be dowel pinned to the jug so that the combustion chamber will always be perfectly aligned to the cylinder.

2) The crankshaft is too heavy for the size of the engine. He said they probably did that so that the engine would idle based on the many other flaws.

I set the crank up on the surface plate and showed him the out-of-concentric way the weights had been attached. He recommended leaving the weights on for now and chucking the crank in the lathe to true everything up.

There has been no attempt to balance the assembly at the factory...and as I already knew balancing a single cylinder engine is a best situation compromise through the entire range of crank rotation. As he pointed out; the out-of-concentric condition is causing 90% of the vibration. This is why some engines vibrate terribly and others don't.

As far as balancing goes, I will model the crank and rod assembly with the piston in SolidWorks...from there I can rotate the crank in 5 degree increments and the computer will show me the centroid of the assembly. After a few hours I will have the ideal location and amount of material to remove to get a "best situation" balance of the assembly.

3) The cylinder needs to be dowel pinned to the engine block, for the same reason that the head needs to be dowel pinned to the cylinder. Once pinned the transfer ports can be blended and radiused knowing that when it is disassembled it will go back together perfectly.

4) The port timing is all wrong...I'll set up degree wheel and give him exact numbers so that he can recommend what to do. He did say the jug needs to be spaced from the block in order to correct the worst of the timing problem. Removing the base gasket in an effort to increase compression actually decreases perfomance because the port timing is pushed even further out of phase.

5) The intake and exhaust ports are too small...they need to be opened up. Width not height. Tapered side to side.

6) The crooked intake is a performance killer...I explained that it was necessary in order to keep the carb level for many installations. I've got a new Schwinn Jaguar in the shop to develope an installation kit, so I'll see if the engine can be mounted at a more level attitude so that a straight intake can be used. The straight intake worked out fine on the last bike I did.

7) All mating surfaces should be "O-ringed" for a perfect seal. He was tellig me they would pressurize their go-cart engines before leaving the shop in the evening, and expected zero leak down in the morning...NOW THAT'S SEALED!!!

8) He didn't like the block register at all and recommended using dowel pins. If the two block halves are not perfectly aligned the crank bearings and countershaft bearings will fail prematurely.

There's more...but this is enough for now! Everything he described is easily done...It's the little things that can make an engine sooooo mch better.

Brendan learned on Dirt bikes and 2-cycle racing go-carts in Australia. He is VERY knowlegeable and always offers no nonsense advice down to the detail. I will remanufacture an engine based on his recommendations and report back.

We will have a few more Q&A sessions as I go along...It was simply too much info to digest in one session.

I explained that about 5HP was plenty, as a bicycle will not handle excessive HP. I'm after smooth reliabilty, easy starting, and a power/torque band that is complimentary on a bicycle.

Jim

WOW Jim
What a wealth of info. I was going to modify a frame tommorow to install a motor (80cc=69er or ?). I was going to have a VERY sharp angle on the motor and mod. the intake to bring carb. back to level. Should I mod the frame to have a straight intake instead ? Also does the same apply like drag raceing cars that the long intake(tunnel ram) gives power in upr.RPM and short gives torque and throttle response ? Thanks for the reply and keep up the good work. You the MAN Jim...POPS (Rick)

 

[Creative Engineering]

WOW Jim
What a wealth of info. I was going to modify a frame tommorow to install a motor (80cc=69er or ?). I was going to have a VERY sharp angle on the motor and mod. the intake to bring carb. back to level. Should I mod the frame to have a straight intake instead ? Also does the same apply like drag raceing cars that the long intake(tunnel ram) gives power in upr.RPM and short gives torque and throttle response ? Thanks for the reply and keep up the good work. You the MAN Jim...POPS (Rick)

Thanks Rick,

If you can set the engine level, or near level I can supply a straight through intake. I'm not sure if the tunnel ram effect is the same for a two stroke. I'll ask Brendan Monday...good question! The 2stroke motorcycles I've had, had a short intake.

I've got a bunch of engines in-stock to modify. I'm planning on doing the first one based on Brendan's recommendations...If it's a night and day difference I will offer them for sale.

Jim

 

[NEAT TIMES]

Bless This Forum And Jim And The Rest Of The Talents On Here!!

 

[NEAT TIMES]

Jim, I Will Take 4 Of Each, Just Put Them On A Ticket!!

 

[Creative Engineering]

Bless This Forum And Jim And The Rest Of The Talents On Here!!

Thanks Ron...This is a great forum!!! And these bikes are just too much fun.

Jim

 

[europorsche914]

hey jim if your plannin to stock and sell high perf motors then i would definitely switch out the bearings for skf 6202-2rs and from what i have heard from others i would want the wristpin end of the connecting rod to be a bushing rather than a roller bearing (it be nice if the large end of the connecting rod was also a replaced with a bushing (not sure how committed you want to eliminate china made bearings... since you obviously gotta tear the crank apart to achieve this...)). Another way to improve perf at high rpms would be to create a new cyl design that incorporates another transfer port or two (49cc pocket bike perf cyl kits have four transfers). Some engines incorporate boost ports and 4 transfers to achieve a 5 port motor. By creating a new cyl you could use a steel lining so the engine would be rebuilable with oversized pistons. Maybe im getting carried away lol. Glad to here you learned some interesting mods to improve the china junk. -Justin

 

[POPS]

Jim... Thanks for the reply. I would like to hear about the intake thing after you talk to your bud. I looked at my build today and I have no choice with this one. It's going to have to be a real radical angle with the motor mounting. Because I'm going automatic I don't have the clutch cable and stuff in the way and I'm going to make an intake,3/4" in dia. but it can be real short as I will have a lot of room. At least it will be 1 smooth bend as opposed to the stock junk. I guess I'm going to have to sacrifice a bit on this one but I should make it up with the 3/4" intake and smooth flow...RICK