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You're welcome FutureWorld.

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
I think that worst restriction are the transfer ports as a whole, and then the reed inlet at the back of the cases. Cannot say which one is worse, but the transfers are definitely poor.

Look at this 40mm Bidalot cylinder for a 50cc Derbi moped ( I suppose this is a performance cylinder with approx 10hp out of the box):

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See how the transfer ports occupy almost the full circumference of the cylinder. Then see the cag engine 44mm "bigbore" cylinder. I think the bidalot cylinder has easily double the transfer port area!
It is obvious that you are not going to gain much by just porting the crankcase mouth and start of the transfer passages. You can maybe gain some, but the cag cylinder will still be utterly limited by the ridiculously small transfer ports. Then other thing is the shape of the ducts. The cag cylinder is forced to have narrow passages and the sharp 90* turn which you can fix a little bit. Much better would be to have these large and smoothly curved ducts.

The cag cylinder has only so much(little) material to work with so there is not much to improve. But I'm sure there is a pretty substantial gain to be had from widening the transfer ducts.
 

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Awesome information thank you for sharing this with us 馃檪 I feel the same way and at bottom dead center is where things go really bad when the Piston is blocking the feed ramps at the worst possible time when you want as much fuel charge to go up the transfer ports as possible and it's like squeezing out the last bit of toothpaste out of a empty tube...

I have started to modify the piston to aid in this problem I originally saw this modification on a really good piston kit produced by pocket bikes unlimited back in the day before they went out of business it was called the yellow jacket kit I personally never owned one but it looked really really cool it came with a pre-ported and boosted cylinder that was powder coated yellow and a piston that had been modified and windowed it's been pretty evident that China copied it but they got a few things wrong the Chinese version that we all know they've got the window triangles in upside down? And no modification to the Piston skirt. the triangles upside down are really bad because that allows blow by...

Anyway here is a picture of my piston after modification.

I feel that if you get a piston that has the triangle windows in it that it should be replaced with a 44mm stock piston and then drill round holes to help with the blow by problem.
 

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Discussion Starter #83
Cylinder modified with wider transfers and epoxy filled bottom to make a better angle.

If then add a cnc machined engine case with reed port above instead of original position.
That should make it more willing to rev high and make good power?

Like these cases, there are no threaded holes for a reed basket. But that's easy to drill and thread.

Cost as much as a new cag engine.
This design would also benefit a full circle crank?
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Edit. It getting more and more expensive
 

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I like the idea but then at what price do I just go with a BZM and get that crispy clean 14hp

Honestly I run a CAG and it won't fit to well those cases work really good for standing scooters but well I'm sticking with the Robin NB 411 clone for now
 

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Discussion Starter #85
Started grinding a bit on my test cylinder.
Just using a flat file.
A bench drill would work much better i think.
It tapers down to the exit of the transfer.
Not sure if that's right but can grind away and make it straight if needed.
Just started grinding a bit, not done yet.

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Here you can see it tapers down.
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Untouched side
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I can see the angle is a bit off so i need to correct that.
I will also try to use the dremel tool cause it takes a bit of time to do it manually
 

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Right on!!! What I do is I use needle files to clean everything up then I hot glue little bits of sandpaper to the end of the needle files for finish sanding 馃榿
 

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Discussion Starter #89
Just need to do the opposite side.
Then clean it up a bit.
The other side is the difficult one.
Making them exactly the same.
Probably will be okay.
Need to get a lot of material grinded of from the engine cases.

Then get the exhausts ready for welding.
 

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Discussion Starter #90
Some more pictures of the port in progress.
I can't make the transfer equally in shape.
I will smooth some up but I can not make them look exactly the same.
I'm not good enough for that.

Hopefully it's good enough though.
Or what do you think.
Sorry for dirty cylinder and bad pictures

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That's looking pretty good 馃槂 you have made huge improvements you're definitely going to notice the power increase
 

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Discussion Starter #92
That's looking pretty good 馃槂 you have made huge improvements you're definitely going to notice the power increase
I hope so.
This is done on my 1 piece test cylinder.
So i will try it out when it's done and then will do the port work to the 3 piece cylinder/cylinderhead.

Much to do and little time.
I've haven't got any further on my exhaust pipes.

I've ordered some jb weld so i can fix the 90掳 angles to be not 90掳 馃槈

I also ordered a Husqvarna 44mm one ring flat top piston.

Will see how this turns out 馃槉
 

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Discussion Starter #95
Gy6 50cc springs.
They are way to short so I just pulled them in a vise to the right length.
I ordered wrong springs.
I was supposed to order gy6 125cc/150cc springs, those are longer on the 125cc/150cc.
I ordered them from banggood.
So if these 50cc springs won't work i will try the 125/150cc springs.
 

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The cylinder looks quite good. I'm sure that will give much better transfer flow. I think the A ports could still be ground a lot more closer to the exhaust port, but maybe a little less deep to avoid puncturing the outside. But that's already good. You can smooth out the grinding with some 180 grit sandpaper attached to a round stick, that will also improve flow.

Good idea the 125cc gy6 springs. Would be interesting to know the length of those.
On my clutch the second piaggio tuning spring snapped. Seems that they cannot take it if they are stretched too much.
One possibility would be to make some spring adapters from around 2mm thick stainless sheet. It would have 2 holes and it would act as an elongation for the spring so they don't have to be stretched as much.
 

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Discussion Starter #98
The cylinder looks quite good. I'm sure that will give much better transfer flow. I think the A ports could still be ground a lot more closer to the exhaust port, but maybe a little less deep to avoid puncturing the outside. But that's already good. You can smooth out the grinding with some 180 grit sandpaper attached to a round stick, that will also improve flow.

Good idea the 125cc gy6 springs. Would be interesting to know the length of those.
On my clutch the second piaggio tuning spring snapped. Seems that they cannot take it if they are stretched too much.
One possibility would be to make some spring adapters from around 2mm thick stainless sheet. It would have 2 holes and it would act as an elongation for the spring so they don't have to be stretched as much.
I can make the A ports bigger.
I'm just worried i will screw up the angles.
Yes I will need to smooth the grinding quite a bit i think.

I am very keen to get the engine up and running but have much things to fix before start up.
And this is my test cylinder so i have to put a engine together and matching the case to the cylinder and getting some oil seals for the crank.
And getting the two exhausts ready.
Then i will start working on the engine with separate cylinderhead again.


And you need to figure out how to get the cag engine to rev past 11 000 when hot 馃槈
Have you thought of getting the squish band 1-2掳 greater?
I'm thinking if the velocity is to high it might help to change it to 1-2 greater angle.
And keep the piston cooler.
Also how big squish band area does your head has?
 

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I have also thought the same that squish velocity might be too high on my engine. The squish area is around 60% I think. Actually the squish velocity is a bit unknown subject to me. I have never calculated it. I read from one source that too tight squish gap made a (very) high power engine to stop running, I guess it would happen on high rpm. I just don't understand why. Maybe there is so violent turbulence in the combustion chamber that the spark somehow blows out.

In my engine there is an issue with the crank bearings. They are so worn that the squish gap almost closes at high rpm because the piston inertia. If the squish velocity theory is correct, that would explain the difficulties the engine has at high rpms. Definitely going to investigate that.
 

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Discussion Starter #100
I've now got my single ring piston flat top.
Also the cylinderhead.
So the squish not line up with the flat piston so need to wet sand it flat.

And i assembled a engine with the test cylinder. Put it in the small cagllari clone or i think it is that anyway.
Now waiting for an exhaust for that pocket bike so I can try the port work.



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