Maniac's 49cc porting thread

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maniac57

maniac57

Old, Fat, and still faster than you
Oct 8, 2011
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Started grinding on the sweet little 49.
Knife edged the transfer to case joint from this:

To this:

Widened both the intake and exhaust ports without changing timing
Start:

 
maniac57

maniac57

Old, Fat, and still faster than you
Oct 8, 2011
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After porting:




No changes in port timing, just took about 1-1.5mm off each side to widen the port. Have to be careful on the intake not to open it up so far you uncover a ring gap. Ruined cylinder if you do.

Looks are deceiving here as well. All this grinding is perfectly straight with the port contours, not all bell mouthed like the pics look. I work from inside the port to keep a good sharp port edge. Any angle here can ruin the jug. With the 40mm intake and huge port castings on this engine, it was easy to gain a good 2-4mm overall port width with no problem!
 
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maniac57

maniac57

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Oct 8, 2011
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Blended the transfers down as far as I could reach with my bit, smooth gradual blend to match case.


Next I'll install the jug on a case half and blend the transfer joint perfectly smooth from the inside. The crankcase is already nice and tight, so no stuffing is required!

 
maniac57

maniac57

Old, Fat, and still faster than you
Oct 8, 2011
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More pics showing the before and after, as well as a nasty little burr I found on the crank from a poor primary drive gear installation. Had to hand work it to get things right.
Notice how tight the cases are with the bolt on flywheel weights.
No stuffing needed here!




 
maniac57

maniac57

Old, Fat, and still faster than you
Oct 8, 2011
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found this nasty burr on the crank under primary drive gear. Needed a bit of hand filing to get right



 
S

Slogger

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Sep 8, 2014
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Verry Interesting. This piston porting stuff is something I need to learn more about.
Thanks for the pics and drawing, Maniac!
 
maniac57

maniac57

Old, Fat, and still faster than you
Oct 8, 2011
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Love how tight the cases are with the bolt on flywheel weights. Also makes it easy to change balance factor which I might do sometime in the future depending on how she runs.



And finally, here are two shots showing what the transfer ports look like with the jug reversed (Intake in front, exhaust out the rear)
This is what you have to address when building a reversed jug motor. Not rocket science...

 
Greg58

Greg58

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May 1, 2011
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Good work Maniac, are you going to ramp the piston at the transfers? I did on the grubee 48 I did this spring, also notched the piston skirt for full clearance at tdc. That engine revs the best of the three I own right now, you will enjoy the smoothness of a 48 cc engine.
 
Davezilla

Davezilla

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Mar 15, 2014
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Nice job so far... Good job matching up the transfers and the intake port to the manifold.
Looks like doing a reverse jug on that setup would be fairly easy if you got a way to weld aluminum... just build up on the areas that need to be covered and then match port everything, Could probably even build it up with that Alumaloy stuff if you can keep the metal clean and monitor the temperature.
I personally have no desire to reverse jug any of my engines, but it would be a great idea where frame clearance is an issue as well as making the exhaust system a breeze.

That 48 should make good power when you're done with it, maybe a little lower gearing and let her rev, but still possible to build a high torque engine this size too depending on which way you decide to go with it.
 
Dan

Dan

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May 25, 2008
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brian tedesco said:
I have a 80cc 2 stroke i would like to get some mod info any out there
Click to expand...
Howdy Brian. Welcome to the forum. Yeppers, lots of information. The measurement thing is just Western measurement does not include the entire combustion chamber. While most Asian manufactures do. So "80cc" is a correctly stated size/ measurement.

Most searches and information for 80, 69, 66, 50, 49 or 48cc 2 stroke information will be perfectly interchangeable and correct.
 
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Davezilla

Davezilla

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Mar 15, 2014
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Reversing the jug is usually done to overcome clearance issues with the carb or the exhaust system... it's really easy to make an exhaust system when you got the exhaust port facing rearward... Other than that it can be done for it's uniqueness, but if it's done at all it's almost always because of clearance issues in some builds.
 
F

Flyman

Member
Nov 28, 2014
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Vian Oklahoma
Davezilla said:
Reversing the jug is usually done to overcome clearance issues with the carb or the exhaust system... it's really easy to make an exhaust system when you got the exhaust port facing rearward... Other than that it can be done for it's uniqueness, but if it's done at all it's almost always because of clearance issues in some builds.
Click to expand...
Well I kinda thought that was the reason.But something you guys
might think about in doing such.The engine will run hotter with
the exhaust in back out of the air flow.Thats why motor cycle engines mount there exhaust to the front.

Flydrn2
 
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