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Discussion Starter #63
Small update.
Reshaped exhaust port.
Exhaust open duration estimated 175掳
Transfer duration might be to low.
In that case I will raise them a bit or cut some of the piston.

Fuel.
I think I'm gonna try e85 and 2% vegetable oil/ricin oil.

Exhaust is not ready and still thinking about stinger length and diameter.


156851


I also got 2 different cranksets.
Both are for 12mm wrist pin.
One have 1-2mm longer crankshaft, might have been why the engines piston I took it from did hit the top.
The counter weight is heavier on that one so that's the one I will use.
It might have been better to use a crankset with 10mm wrist pin and a 44mm 10mm piston. But I think those are to expensive for now. Cost as much as a 40/10 or a 44/12 cylinder and piston.
Better get a 44/10 cylinder with head.
So I can use a proper combustion chamber and set the squish clearance where I want it.


I also can't stop thinking of putting a chainsaw cylinder with closed bore and ports to get the most out of this engine.

I've got my ballbearing and oilseal, so tonight I will install those.
 

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Discussion Starter #64
I've ordered a complete 47cc engine for 50 dollars.
40mm cylinder complete stock.
No de-compression thing on the exhaust port 馃檪
So I'm hoping I can get this engine to run as good as possible 馃榾
156955
 

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Right on and yes the 40mm has no decompression notch (y) you know what you have to do ;)
 

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Discussion Starter #66
I've got a new cylinder that's going to be ported.
I've raised the cylinder 2.85mm. Didn't have anything thinner to make the spacer

Exhaust duration 170掳
Transfer duration 135掳
So need some porting.
Exhaust will be raised just a little and widen as much as I can.
And blueprinting the cylinder.

I'm currently building 2 exhaust pipes.
One traditional expansionchamber.

One built like a gokart pipe with perforated rear baffle cone, inside a 2.5-3" pipe.
Will be reduced backpressure with that one and I'm hoping that will get this to rev.

I need to machine the top of the cylinder to make the correct squish gap.

Still waiting for the cylinderhead.
Don't know what to use as gasket.
If both the head and cylinder are machined flat wouldn't it be enough to use Permatex?

Anyone used a one ring Husqvarna 44mm 10mm wrist pin piston?
Any good? Weight?

I want this thing to kick some ass.


158946
158947
 

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Don't forget about the cylinder dome squish band matching the shape or curve of the piston that's the part that controls the detonation

 

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I've got a new cylinder that's going to be ported.
I've raised the cylinder 2.85mm. Didn't have anything thinner to make the spacer

Exhaust duration 170掳
Transfer duration 135掳
So need some porting.
Exhaust will be raised just a little and widen as much as I can.
And blueprinting the cylinder.

I'm currently building 2 exhaust pipes.
One traditional expansionchamber.

One built like a gokart pipe with perforated rear baffle cone, inside a 2.5-3" pipe.
Will be reduced backpressure with that one and I'm hoping that will get this to rev.

I need to machine the top of the cylinder to make the correct squish gap.

Still waiting for the cylinderhead.
Don't know what to use as gasket.
If both the head and cylinder are machined flat wouldn't it be enough to use Permatex?

Anyone used a one ring Husqvarna 44mm 10mm wrist pin piston?
Any good? Weight?

I want this thing to kick some ass.


View attachment 158946 View attachment 158947
Haven't tried a Husqvarna piston, have you put it side by side to a stock piston? Yes need more squish. Nice flat surface, glass is nice, and sand it down, 80-120 grit. I like 100.
 

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I've got a new cylinder that's going to be ported.
I've raised the cylinder 2.85mm. Didn't have anything thinner to make the spacer

Exhaust duration 170掳
Transfer duration 135掳
So need some porting.
Exhaust will be raised just a little and widen as much as I can.
And blueprinting the cylinder.

I'm currently building 2 exhaust pipes.
One traditional expansionchamber.

One built like a gokart pipe with perforated rear baffle cone, inside a 2.5-3" pipe.
Will be reduced backpressure with that one and I'm hoping that will get this to rev.

I need to machine the top of the cylinder to make the correct squish gap.

Still waiting for the cylinderhead.
Don't know what to use as gasket.
If both the head and cylinder are machined flat wouldn't it be enough to use Permatex?
Transfer duration is a bit large. Many racing twostrokes use 130 degrees, like some 125ccm with +40hp. Problem with high transfer duration is that it will eat the blowdown area. It means that exhaust port has hard time expelling the burnt gases before transfers already start to open. I would say that 125-128 would be more appropriate for a cag engine. My engine has 133 but I was too lazy to find a thinner base spacer. And exhaust to 190 degrees is good, no more than that.

The cylinder head sealing, I don't use any head gasket in my engine. The surfaces are straight from lathe but would be better to lap them together with some grinding compound. If the surfaces are flat then it will seal. I recommend not to torque the head bolts very tight, otherwise there will be warping and that will cause it to leak. I torqued them to only 8 Nm with a torque wrench and retorque after first warm up.
 

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Discussion Starter #70
Transfer duration is a bit large. Many racing twostrokes use 130 degrees, like some 125ccm with +40hp. Problem with high transfer duration is that it will eat the blowdown area. It means that exhaust port has hard time expelling the burnt gases before transfers already start to open. I would say that 125-128 would be more appropriate for a cag engine. My engine has 133 but I was too lazy to find a thinner base spacer. And exhaust to 190 degrees is good, no more than that.

The cylinder head sealing, I don't use any head gasket in my engine. The surfaces are straight from lathe but would be better to lap them together with some grinding compound. If the surfaces are flat then it will seal. I recommend not to torque the head bolts very tight, otherwise there will be warping and that will cause it to leak. I torqued them to only 8 Nm with a torque wrench and retorque after first warm up.
I will grind the spacer down a bit.
A piece of glass and 800 grit wet sandpaper will work i think.
I i will try to get it down to the suggested numbers.
And yes you are right about the blowdown time.
But what blowdown time in degrees should I aim for?
It depends on the exhaust I'm building too of course.
But around 25-30?
Your's are 28.5 right?
 

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30 blowdown is a minimum for any serious power. Yeah mine is 28.5. More is always better as long as exhaust port does not get too high (over 200 deg exhaust can be considered ruined). It doesn't depend on the exhaust. Blowdown time-area of the exhaust port simply defines the capability of the cylinder to cough out the exhaust gases in given time and more is better and allows the cylinder to reach higher rpm.

There is a catch though, the blowdown comes into play at high revs but the cag engine is overall so bad flowing that I'm pretty sure there are other things that restrict it far before the blowdown area. So...I think 25 would work perfectly well if the cylinder is not otherwise improved(meaning reworking transfer ports).

You will have hard time of sanding the spacer with 800 grit paper :D Start with something as rough as 120, that will remove material quickly. Then finish with 280 and it will be fine.
 

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Discussion Starter #72
Alright. So i must lower the spacer to get correct transfer durations.
But not so much that the piston is above exhaust port at bdc.
So hopefully I can get it to 125-128 by doing that and then widen and raising the exhaust port to a blowdown of around 25.
I have done some porting on the cases and cylinder to make the transfer flow better but not what you can call reshaping.
My cylinder transfers are dual. Not sure if that's better for not.
I think the transfer aims a little bit better when they are dual.
Or shall I just grind away it and make the transfer bigger and grind the cases to fit the bigger transfer?
Oh and my cylinder is 44mm, that don't effect the transfer, blowdown and exhaust durations we discussed?

Exhaust pipe flange will be shaped exactly as the exhaust outlet to make it flow as easy as possible.

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The cylinder diameter does not influence the timings.
Basically the "dual" transfer port design is better and that's why most high performance cylinders use that layout, but with this china wonder cylinder the problem is that all ports are ridiculously small and the dual design is not going to improve anything versus the single port design.
Usually the smaller port nearer the exhaust is called A port(s) and bigger ports nearer the boost port are called B ports. The A ports should be widened hugely, making them closer to the exhaust port and not changing the aim angle. Hard to describe it, I could draw a picture later. The B ports can be widened a lot as well, towards the boost port and preserving the angle. Third thing to do would be to fill the inner corner of the transfer port ends so that it is not a sudden 90* turn, but a smoother curve and pointing about 20 degrees up. It could be filled with epoxy.
 

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Discussion Starter #74
I would really appreciate a picture when you have time.
Thanks for your time and description.
I think I have to do this to the transfers.
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Here is how I did mine it makes good power I removed the bass gasket then you can angle the tops of the ports slightly up towards the spark plug .25mm if you want.
 

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Yeah, you need to make the whole ducts wider all the way to the port exit. And expand slightly outside (make the outside wall thinner) but there is not much material so that's just optional bonus.

Like this. The red area is where you want to cut. Green lines show how you want the ports to "aim". And then I draw with blue the area what you need to fill with epoxy (the corner). If you do the epoxy filling, remember to sand the area with rough paper first to make sure the epoxy can hold. I have heard that loctite "metal" epoxy can withstand. I have used JB weld from ebay and that seems also to work. I plan to also do these modifications at some point.

Also, when you cut the A and B ports, do not cut the inside corner all the way to the end like the stock transfers are, because the sharp 90* turn is bad and this is what you want to fix with the epoxy. So when you cut the widened parts, you can leave the inside corner already smoother and no need to add epoxy there. I hope you got what I mean.

159008



Also, when cutting remember to constantly look out if the wall gets too thin to avoid making a hole. It is not bad to fix it with epoxy but better to avoid making holes. If it's impossible to make the cut without hole, then you just have to compromise and cut less.
 

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Discussion Starter #79
Yeah, you need to make the whole ducts wider all the way to the port exit. And expand slightly outside (make the outside wall thinner) but there is not much material so that's just optional bonus.

Like this. The red area is where you want to cut. Green lines show how you want the ports to "aim". And then I draw with blue the area what you need to fill with epoxy (the corner). If you do the epoxy filling, remember to sand the area with rough paper first to make sure the epoxy can hold. I have heard that loctite "metal" epoxy can withstand. I have used JB weld from ebay and that seems also to work. I plan to also do these modifications at some point.

Also, when you cut the A and B ports, do not cut the inside corner all the way to the end like the stock transfers are, because the sharp 90* turn is bad and this is what you want to fix with the epoxy. So when you cut the widened parts, you can leave the inside corner already smoother and no need to add epoxy there. I hope you got what I mean.

View attachment 159008


Also, when cutting remember to constantly look out if the wall gets too thin to avoid making a hole. It is not bad to fix it with epoxy but better to avoid making holes. If it's impossible to make the cut without hole, then you just have to compromise and cut less.
Thank you very much!
I will order some jb weld.
It should improve the flow pretty much i think with the widen transfer with epoxy to make it a smooth transition.
Very nice of you!
 

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Here is a picture of mine same cylinder the 2019 mini quad engine does not have a decompression notch and is the single most powerful stock Cagllari Daytona engine...

just so you know the cylinders with the decompression notch were designed for the easy start system which is a windup spring system not direct pull.

the fingers actually help the rings not catch the top of the ports and makes the engine last a lot longer!

You can have a look inside this is after break in I know a lot of oil but you can see the height of where my boost Port stops ( porting tips derived from boosted306 ) you can actually see a seat in ring starting to form about 2 mm above the boost port from where compression starts building

In my opinion the biggest two restrictions on these engines are actually where the ports go up in the crankcase and the reed cage if you pay careful attention in these areas your engine will definitely make a lot of power
 

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