2 stroke engines with a design flaw

Toby woodman

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Mar 4, 2023
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this will be a longer post. In the span of about 8 months, I have had 4, two stroke engines fail on me, and I have had two engines that have run perfectly. my friends and I ride these bikes all across the uk and take good care of them all, they have all seen semi-synthetic oil mixed at 25:1 and have never been pushed too hard (tachometer has never exceeded 7800). 4 of our engines were bought from amazon for £89 (I'm in the UK) and two came from aliexpress for about £91. all of these bikes and engines have seen equal care and maintenance. the four engines ordered from amazon used a one-peice cylinder and head design. this is easy to see without taking the cylinder head off as the cylinder studs are visible through the side of the cylinder as the pass through the cooling fins (i will attach photos below). these engines have all run well and started easily, but every single engine after only about 10-15 hours of break in running have seized, causing the bottom end to be destroyed by ground away bearings and bent con-rods. these engines were ordered at different times with about 6 months between the first and most recent purchases of the engines off amazon. these engines have seized running alongside at the same speed as the engines with a two piece design off aliexpress. this leads me to believe that there is a design flaw with the one peice cylinder head engines. has anyone else had any experiences like this. btw I'm only but i have lots of experience with engines and have maintained all of mine well. my freinds are also capable mechanics and look after their engines. I have also built my own bike from scratch using a honda gx160 as I can weld. so maintenance doesn't seem to be problem if you ask me.
 

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Did you have to put the cylinder and piston on the rod? Or, were those engines preassembled?

I always pull the jugs off ready made engines and rinse the cases out with some premix fuel. The fuel I use is 16:1 to give all the internals a good coating of oil.
 
Supposedly synthetic two stroke oil cant be used for breakin but I couldn't tell you why. I want to say its something about polymerization of the oil into a protective varnish like on cast iron cookware.
 
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