Engine rebuilt

MinimumVK

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Joined
May 19, 2023
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91
Location
Slovenia
So long story short my second bike blew up at about 2500km:cry:... It first lost compression and i heard pinging coming from the cylinder. Opened it up and saw that both of the rings broke and messed up the cylinder and piston. The right crank bearing was also close to seizing. What caused this i have no idea (i always used 5% mix/ 20:1).
Since im not 18 and cant drive (without a parent in the car) i rely on the bike to go out and stuff i decided to rebuild it right away. Went to buy bearings and crank seals. I already had a piston that had a 10mm wrist pin so i also had to buy a 10mm ID needle bearing. I removed everything, cleaned it up and made my own gaskets out of quality gasket paper (also used a little bit of RTV like i always do to seal up any deep scratches). Changed the crank and clutch shaft bearings, sealed up the cases, installed the piston and closed it up with a used cylinder that was in good condition. Also installed new clutch pads, spark plug, fuel filter and cleaned up the carb. Also i installed 8mm studs for the carb and exhaust because the old threads were stripped. Of course i lubed everything up before the 1st start with 2 stroke oil. When it was all done the compression felt amazing then came the first start! It never started as easy as it did after the rebuild. For the first ride i went around the block and up a hill where i kept the speed low and throttle high to seat the rings (do this to all my engines). Second ride i went farther and power feels great although i crashed while riding during the influence and bruised up my face and burned my leg on the exhaust:ROFLMAO:. Oh well at least the bike runs better then new!
 

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Good going with the rebuild. It’s quite satisfying to rebuild these engines and have them perform well after doing so.

The crash.. thankfully it wasn’t worse. Let the experience be a strong teacher of what can happen.

Never get so preoccupied with the bike or engine that your attention to safety drops. A bad bike crash could be a life changer.

Ride safe!!
 
UPDATE: The engine is now at 2800km. I made sure to torque the cylinder nuts after each heat cycle and yesterday i took off the clutch gear and torqued all of the case bolts and lubed everything up.
It runs nice and has plenty of power on flat ground (tops out at around 60km/h). The biggest upgrades are the 8mm exhaust and carb studs as now they dont start leaking after each ride because i can actually put some torque on them without stripping the threads.
As im building another project and still a student that only works during the summer im thinking of selling it to have a bit more budget. What would be a good price for it? Marketplace isnt nice here in Slovenia as people only buy Tomos mopeds.
 

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UPDATE: The engine is now at 2800km. I made sure to torque the cylinder nuts after each heat cycle and yesterday i took off the clutch gear and torqued all of the case bolts and lubed everything up.
It runs nice and has plenty of power on flat ground (tops out at around 60km/h). The biggest upgrades are the 8mm exhaust and carb studs as now they dont start leaking after each ride because i can actually put some torque on them without stripping the threads.
As im building another project and still a student that only works during the summer im thinking of selling it to have a bit more budget. What would be a good price for it? Marketplace isnt nice here in Slovenia as people only buy Tomos mopeds.
Many here on the forum are in the 🇺🇸 USA 🇺🇸; so we don't know what someone in your country would pay for a self built motorized bicycle.

In the USA, you can generally sell them for double to triple your material investment cost. For example if you had an investment cost of $400; you could probably sell it for $800-1200. The most important thing is selling a safe product. Which it appears you built a reasonably safe bike in the picture you posted.
 
So long story short my second bike blew up at about 2500km:cry:... It first lost compression and i heard pinging coming from the cylinder. Opened it up and saw that both of the rings broke and messed up the cylinder and piston. The right crank bearing was also close to seizing. What caused this i have no idea (i always used 5% mix/ 20:1).
Since im not 18 and cant drive (without a parent in the car) i rely on the bike to go out and stuff i decided to rebuild it right away. Went to buy bearings and crank seals. I already had a piston that had a 10mm wrist pin so i also had to buy a 10mm ID needle bearing. I removed everything, cleaned it up and made my own gaskets out of quality gasket paper (also used a little bit of RTV like i always do to seal up any deep scratches). Changed the crank and clutch shaft bearings, sealed up the cases, installed the piston and closed it up with a used cylinder that was in good condition. Also installed new clutch pads, spark plug, fuel filter and cleaned up the carb. Also i installed 8mm studs for the carb and exhaust because the old threads were stripped. Of course i lubed everything up before the 1st start with 2 stroke oil. When it was all done the compression felt amazing then came the first start! It never started as easy as it did after the rebuild. For the first ride i went around the block and up a hill where i kept the speed low and throttle high to seat the rings (do this to all my engines). Second ride i went farther and power feels great although i crashed while riding during the influence and bruised up my face and burned my leg on the exhaust:ROFLMAO:. Oh well at least the bike runs better then new!
Paragraph your post.


 
Many here on the forum are in the 🇺🇸 USA 🇺🇸; so we don't know what someone in your country would pay for a self built motorized bicycle.

In the USA, you can generally sell them for double to triple your material investment cost. For example if you had an investment cost of $400; you could probably sell it for $800-1200. The most important thing is selling a safe product. Which it appears you built a reasonably safe bike in the picture you posted.
Yeah thats what i meant, just wondered what yall would pay if it was in the states. The bike actually never left me stranded unlike my first build that always kept breaking rims. For this second bike i tensioned each spoke with a spoke tension gauge before installing the sprocket and then trued it on a stand. Still on the same rim since "new"
I did ran out of gas once but i always carry 1L of spare pre-mix in the basket.
 
Yeah thats what i meant, just wondered what yall would pay if it was in the states. The bike actually never left me stranded unlike my first build that always kept breaking rims. For this second bike i tensioned each spoke with a spoke tension gauge before installing the sprocket and then trued it on a stand. Still on the same rim since "new"
I did ran out of gas once but i always carry 1L of spare pre-mix in the basket.
On my bike I have a 4 stroke engine. I also use a see through 5 quart gas tank. With me there isn't any excuse for running out of gas.

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On my bike I have a 4 stroke engine. I also use a 5 quart gas tank. With me there isn't any excuse for running out of gas.
If you ever run out of gas with that see thru 5 quart gas tank of yours and I hear of it, I will NEVER let you live that one down Jerry...lol...lol.
 
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