piston stroke too much!

triride

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Hi guys,
Had an engine lock up on my China girl 80cc a few weeks ago.
On inspecting the damage,I found that the piston wrist pin/small end brg had collapsed and the piston was damaged although the cylinder bore was ok.
I ordered a replacement piston kit & have just fit.
I have now noticed that piston travel is too much and comes into contact with the head!
On checking the big end brg before & after doing job by checking freeplay with con rod movement,all seems ok?
I think maybe the crankshaft could be bent?
Anyone had a similar issue?

Cheers, Pete.
 
there are 2 different piston designs. I believe you got the type A when you needed the type B. You have an FM80 connecting rod and not a Z-L, unmarked, or ZAE50 rod, correct?
 
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Hi butre,
Super information, did not know there where different variants!
I will duly order the correct "B" type piston.
Thanks, Pete.
 
Hi butre,
Super information, did not know there where different variants!
I will duly order the correct "B" type piston.
Thanks, Pete.
if you had of compared the old piston to the new one before installing the
differences would have been obvious.

The question is how did you miss that the new pistons wrist pin hole was lower?

Also when I assemble my motors I turn them over using the nut on the magneto
to check where the BDC and TDC are and to spread oil to the rings and bore before
the head is installed.
 
Wrong piston!

if you had of compared the old piston to the new one before installing the
differences would have been obvious.

The question is how did you miss that the new pistons wrist pin hole was lower?

Also when I assemble my motors I turn them over using the nut on the magneto
to check where the BDC and TDC are and to spread oil to the rings and bore before
the head is installed.

Yes your right MotorBicycleRacing, I should of checked both pistons before fitting it.
I did not realise there where two different types of piston for the 80cc so "assumed" (something you should never do!) it to be the right one.
No damage done as I turned it over by hand.
Does anyone know where I can buy the correct replacement piston/cylinder body/head ?

Thanks, Pete.
 
Google "motorized bicycle parts"

Thanks for the replies!

I have just purchased a piston & cylinder from MZMiami.
Cylinder is compatible with A or B type piston and piston is for a Skyhawk which I believe has the same piston as mine with higher wrist pin location.
Will let you know how it goes when i've fit the parts :)

Cheers, Pete.
 
that means the new cylinder is high to match a high piston (longer from wrist pin to piston top)
 
Thanks for the replies!

I have just purchased a piston & cylinder from MZMiami.
Cylinder is compatible with A or B type piston and piston is for a Skyhawk which I believe has the same piston as mine with higher wrist pin location.
Will let you know how it goes when i've fit the parts :)

Cheers, Pete.

The piston that I need has it's wrist pin higher up the piston skirt 7mm from bottom of piston to bottom of pin.
The wrong piston that I ordered had it's wrist pin lower down 5mm from bottom of piston to bottom of pin.
Hope this makes sense, i'm enjoying learning about these engines and obviously will make mistakes along the way as we all do when starting out :)

Cheers, Pete.
 
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