Chrome plating peeling off? Too much oil?

Joined
Sep 26, 2018
Messages
130
So I recently hauled off my old, beaten bike and I started disassembling the engine to check everything before I blow something, and I'm noticing things I wasn't expecting.

Firstly, the piston was covered in a layer of carbon. It will flake off with solvent easily but I think some polishing is in order. To help prevent build up and hot spots.

Secondly, there is alot of blowby being shown on the first piston ring though the ring gap and it seems it blows into the intake. But, for some reason, there is a ring of bronzing along the top of the cylinder. Possibly too much oil just being squished out?

Thirdly, gouges in the walls that are otherwise mirror finished and seems to be thin spots or weak spots in the galvanizing. Is it time for a top end rebuild? Bad cylinder? I made sure everything was immaculately clean when I assembled it and broke her in well.

Also, I'm getting some piston slap near the bottom of the cylinder. Any remedies?
86249
86250
86251
 


Lukesky36

Active Member
Joined
Oct 3, 2018
Messages
311
You need a top end kit just replace all the parts. if you 4 stroke alot you might want to lean the carb one notch 32 to 1 seems to work really well
 

Will'smotobikes19

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Joined
Apr 9, 2018
Messages
1,356
If anything it’s too little oil. If there’s proper oil on the cylinder walls it shouldn’t do that. You’re either revving the crap out of it or there was a previous defect in the plating (no quality control). Those jugs are crap though and that’s normal. One of the many reasons I’m not using crap girls anymore and switched to rackmount with auto clutch from now on. That was my remedy. If you’re into mods you can get a velocity stack straightpipe and some other mods. There are many different options of 76mm clutch motors both 2 stroke and 4 stroke. People complain about price but would you like to have 50k on your bike with nothing but a tune up or 3k and have to replace or rebuild your motor?
 

JerboaJohn

Active Member
Joined
Jul 29, 2018
Messages
674
time for a new jug kit,, good news and bad news lol. good news they are $25 cyl piston rings n pin sometimes too. bad news is the whole engine can be replaced for like $75-80
 
Joined
Sep 26, 2018
Messages
130
If anything it’s too little oil. If there’s proper oil on the cylinder walls it shouldn’t do that. You’re either revving the crap out of it or there was a previous defect in the plating (no quality control). Those jugs are crap though and that’s normal. One of the many reasons I’m not using crap girls anymore and switched to rackmount with auto clutch from now on. That was my remedy. If you’re into mods you can get a velocity stack straightpipe and some other mods. There are many different options of 76mm clutch motors both 2 stroke and 4 stroke. People complain about price but would you like to have 50k on your bike with nothing but a tune up or 3k and have to replace or rebuild your motor?
I did drive the heck out of it. It would top out at 7500rpm off the yz85 pipe and I've pushed it to 9000rpm. Could running it faster than the tuning of the pipe do that? I always run my bike on excess of oil. 8:1, 12:1, maybe a tad more or less...

I personally prefer the 2 stroke for the thrill of it. Eventually, I'm just going to switch over to a cbr250 or similar if I decide to want to go 4 stroke. For now, I'll deal with it and learn.
 
Joined
Sep 26, 2018
Messages
130
time for a new jug kit,, good news and bad news lol. good news they are $25 cyl piston rings n pin sometimes too. bad news is the whole engine can be replaced for like $75-80
Well, I have a gt5 bottom end from CR Machine, CDH Power head, Dio reed, 21mm oko, and yz85 pipe. So if my bottom end blows, I'm not going to bother getting a new one from China. It's just going to blow up after a month anyway.
 

MotorBicycleRacing

Well-Known Member
Joined
Jul 3, 2008
Messages
2,260
I did drive the heck out of it. It would top out at 7500rpm off the yz85 pipe and I've pushed it to 9000rpm. Could running it faster than the tuning of the pipe do that?
I always run my bike on excess of oil. 8:1, 12:1, maybe a tad more or less...
Really???
How many ounces of oil are you adding to a gallon of gas?
7500 rpm is a good running stock motor. 9000 rpm is not pushing it.
 
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