New here! 50cc build

Atvrunner2

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So, been deciding on a brand new engine, then modifying OR using the parts engines I have. Well, good thing, both used lower engines have 8mm head studs and mounting studs. Allen bolts everywhere as well. So, I believe I would still save if rebuilding, considering I already have the 100cc cylinder. Plus I have the 48/49cc new motor that will go on a bike first. So, I will helicoil both cases, since that seems to be something I would do eventually. I will build one (fingers crossed) bullet proof engine from the start with plenty of power, upgraded cdi/coil, balanced crank, new non Chinese hardware, etc. And I will do a little case/cylinder blueprinting. Money I would spend anyway and save on NOT buying another engine I would modify eventually. I will read through the threads here to figure the best course and learn these engines like I did with the reeded pocket bike engines.
 

Atvrunner2

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Question, the high low pistons. My two lower engines, one has a ZL40 rod and the other has a ZMN80 rod. I believe they are long and then I need the high or taller piston??
 

Greg58

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Do you have a piston? I keep a spare piston for testing, I put the piston on the rod without rings to check deck height, you could do the same to determine which piston you need for each. I add a base gasket and bolt down the cylinder without the head to check port timing and measure for proper squish. In your case the piston would be within 1mm of the deck if correct, above the deck if its wrong.
 

Greg58

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I’m backwards, the piston will be about 3mm low if you have a short rod crank and use a high pin piston.
 

Greg58

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I’m old and it takes me a while to put in to works what I’m thinking, y’all will get here one day!
 

Atvrunner2

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Haha, no, my second engine needs a cylinder and piston. I believe they are the long rods. I was looking to order. It will either be a backup engine or sell it.
 

Greg58

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Maybe someone who knows the rod type/length will jump in and help, both of my larger engines are high pin piston, even though one is a 38mm stroke and the other is 40mm. I’ve got 3 different cylinders and all seem to be better suited for a 40mm stroke crank, I tried all on the 38mm stroke lower and port opening wasn’t near the original cylinder.
 
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