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Discussion Starter #1
Hi! What would happen if swapping the cylinder on cag engine to a piston port cylinder with 32mm stroke and like 46mm bore?

What would be the best way to do it.
Stick with the reeds and fill the intake port on the cylinder?
Or plug the crankcase intake and use the piston port intake?

Sincerely
 

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honestly it's not worth it because the Reed inducted case is so restricted having to have the fuel mix go between the crankshaft and connecting rod and then the next step of it having to squeeze between the piston and crankshaft counterbalance to get to the transfer ports people have tried completely blocking the Reed cage hole but then all that happens is that crankshaft bearings starving for lubricant and turning blue I have seen success with dual carburetion but this tends to make the tune very unstable I myself have never personally tried it...
 

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Discussion Starter #3
Okay that was some kind of disappointment for me.
I thought of buying a Husqvarna or sthil cylinder with closed ports to get rid of the open ports on the cag engine cylinder.

Too bad it won't work
 

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When I build them I trie to be really frugal and just use what I have on hand
if I were to put a lot of time and money into something I would build a little bit different engine probably something like an SPX 103 or maybe a KTM 50
There is a guy on YouTube his name is 2-stroke stuffing he took one of those 49cc SPX 103 engines and built a 20 horsepower dynoed monster out of one
Anyway no reason to go to big The cag frame won't handle more than 6 HP or everything else around the engine will fall apart including cracks in the frame
 

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It doesn't make any sense to put such a lot money into a cage engine. When you want more power just get a polini, Blata or BZM engine and put it into a cage frame.
 

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Discussion Starter #6
I was thinking of like a cheap Husqvarna 55 cylinder.
46mm bore and 32mm stroke.
If using the stock reed intake it would be possible to jb weld the intake of the cylinder almost all the way and then grind that intake port as a boost port.
Husqvarna 55 cylinder kit cost as much as a stock cag cylinder on eBay

Is it a bad idea?
156788
 

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More then likely you will have to get a crank with the 10 mm pin then keep your fingers crossed that the Piston is not to heavy and it doesn't mess up the balance factor too bad

I tried to hang a saw piston on a 10 mm crank one time and came up with a balance factor of 33% the Reed inducted engine likes a balance factor of about 55% no sense in building an engine where all your added gains are going to go into shaking.

this winter I'll try again I still have the engine I'm going to stuff a bunch of tungsten in the crank counterbalance so I can get the balance factor right
 

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Discussion Starter #8
My balance factor right now is quiet bad. ≈45%
Don't remember the exact numbers rightnow but the conrod is 20 gram.
Piston, pins, rings etc is 68 gram.
So total 88 grams.
Hang weight is ≈20 gram and I can position the crankshaft and it stays.
 

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So you need a lighter piston or add tungsten to the crank and probably add some steal bolt to the flywheel as well to get the balance factor within some kind of reasonable balance
 

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Discussion Starter #10
So you need a lighter piston or add tungsten to the crank and probably add some steal bolt to the flywheel as well to get the balance factor within some kind of reasonable balance
Argh I screwed up.
The 40mm cylinder I took it out to port it some more. Now its broken. No revs and hard idle.
Widen the exhaust too much I think and the boost port a little wider than it was before and now it's runs very very bad and slow as hell.

Will do the 44mm 12mm engine instead I think. The piston though is very heavy.
But right now it's my best choice and later buy a new cylinder or a 44mm 10mm piston
 

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Maximum exhaust port wide is about 60% of the bore diameter. The boost port can be 15-17mm wide. Also it's important that there is an angel on top of the port that aims to the head. The origin cylinders all have 90° and all the load was blow to the exhaust port.
 

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Discussion Starter #12
Maximum exhaust port wide is about 60% of the bore diameter. The boost port can be 15-17mm wide. Also it's important that there is an angel on top of the port that aims to the head. The origin cylinders all have 90° and all the load was blow to the exhaust port.
Which ports do you mean? And what angle should I be?
 

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You have to make sure you have enough back pressure to hold the fuel charge in the cylinder as the Piston comes up the sonic wave is partially responsible for this if you go too big on the exhaust port the engine will literally spit the fuel charge out of it
 

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Discussion Starter #14
You have to make sure you have enough back pressure to hold the fuel charge in the cylinder as the Piston comes up the sonic wave is partially responsible for this if you go too big on the exhaust port the engine will literally spit the fuel charge out of it
Compression feels a bit low.
But when the piston goes down it really sucks and make noises when the reeds open and closes.
Alot more resistance at the downstroke than the upstroke.
I don't think the exhaust port is that big. But what else can explain it? Before I took it out again and Blueprinted to the engine case and widen the exhaust a bit more, did the boost port a bit wider it reved super high but did not have any power down low.
Now it is quite torquee but revs very low
 

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The boost port controls low end torq by sacrificing rpm...

But it sounds to me like you have a vacuum leak somewhere pull off the clutch flywheel and carburetor but leave the Reed block you might have to put some washers on the bolts to keep the Reed block tight against the crankcase.

Put the engine at bottom dead center

Use an air pressure regulator in the spark plug hole about 8 PSI

Spray all around the engine with soapy water to find the vacuum leak
 

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Discussion Starter #16
The boost port controls low end torq by sacrificing rpm...

But it sounds to me like you have a vacuum leak somewhere pull off the clutch flywheel and carburetor but leave the Reed block you might have to put some washers on the bolts to keep the Reed block tight against the crankcase.

Put the engine at bottom dead center

Use an air pressure regulator in the spark plug hole about 8 PSI

Spray all around the engine with soapy water to find the vacuum leak
Unfortunately I don't have the equipment right now to leak test it.
But all gaskets are new.
I do have some permatex aviation form a gasket no. 3.
I can split the cases and use that on every surface, that should make it air tight every where.
 

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Most of the time it's the clutch side crankshaft seal from the heat
 

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Discussion Starter #19
@MrKitty i will work on my 44mm cylinder engine when waiting for seals to arrive.
My current untouched durations are transfers 110 degrees open time and exhaust 160 degrees open time. So blowdown is 25.

If raising the exhaust port to 170 degrees open time leave the transfer ports it would be a blowdown time of 30 degrees. If I also raise the transfer to 115 degrees it would be 27.5 blowdown time.

What blowdown time is needed for those engines?
 

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If you throw away the base gasket that puts the ports about where they should be you need the engine to build compershon as soon as possible I would opt to ramp the piston slightly over raising the ports
 
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