Cranks con rods and pistons

Jaycee604

Jaycee604

Member
Hey guys, new user. I need some help. Getting confused. I used amazon and i got a crank that says zae50 on the con rod. All three bikes i have say af80 on them. The zae50 is the slightest bit shorter. So my question is, can i install the zae50 crank into the case and use the same cylinder as i would with the af80 crank? I have a type A and a type B piston. But i think with the shorter rod i need the low hole piston. Can i install the low hole and short rod into the case and use the same jug? Is there a downside, what should i do
 
Welcome to the forum, since there are only two piston types one should work with that crankshaft. Port timing is what you need to check. Before you remove the old crank remove the head and measure from the deck to the piston at bdc. Also measure or take pictures of the transfer openings so you can compare them to what you have with the new crank.
 
You can add a second base gasket to raise the ports but will need to sand the deck of the cylinder to raise the compression back up. I like to bolt the cylinder down without the head to compress the gasket to get accurate measurements.
 
You don’t have to bolt the cases together, I use one side and slide the crankshaft in the bearing. I add a piston without rings and put the cylinder on to check piston height at TDC. I just did this on what is called a hybrid, mine is 38mm stroke but uses a high pin piston. Be sure to add a base gasket when doing this.
 
Greg58 said:
You can add a second base gasket to raise the ports but will need to sand the deck of the cylinder to raise the compression back up. I like to bolt the cylinder down without the head to compress the gasket to get accurate measurements.
Click to expand...

as i suspected, so basically make sure piston clears ports at bdc and tdc, using gaskets and sanding
 
Here’s a 48cc with the cylinder compressing the base gasket for measuring.
 

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Jaycee604 said:
as i suspected, so basically make sure piston clears ports at bdc and tdc, using gaskets and sanding
Click to expand...


The cranks marked ZAE50 are cranks for what we call half breed engines, dyou will need to use the Type A low hole piston and then just as Greg suggested, check and see what your transfer ports and exhaust port looks ljke when piston in at BDC then remove intake from cylinder and also look to see if or how much of the piston is still seen in port when piston is at TDC.

With the ZAE50 crank wnd a Type A piston one issue that you will likely find is that at TDC piston will be downnin the cyl. aprox. .060" which will drastically lower your compression if the deck height of the cyl. isn't sanded or machined down to get poston height back up around flush or slightly above flush.

The reason for teying to make sure all of this is right is because all these things that Greg mentioned wlong with what I hwve said here will have a noticable impact on the performance of the engine.

Port timing being at a good place and having good compression and or squish if you have a head with squish band machined into it is very important to have beat performance with these little engines, jist one of these being way off will have a huge impact and could determine if ypu have an engine that will struggle to push your bike to 25mph or let it perform well enough to get ypu zipping down the road at 30-35+mph

Stay plugged in here on this forum, take pics and dont be afraid to ask questions, lots of experience on here and secwral people who are more th an willing to give you solid advice which we have learned over many years of playing with these little engines through trial and error.

Best wishes and if you decide not to use the ZAE50 crank there are other choices out there that will give you a 40mm stroke engine with either the Low hole Type A piston or the High hole Type B piston.
 
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