Posts
206
Joined
6/4/2017
Location
Pinson, AL
US
Edited Date/Time
1/20/2018 6:40pm
about 2 months ago i had just finished building my 2001 honda cr125. I rebuilt the engine and had everything torqued to oem specs. This was my 3rd time rebuilding a 2 stroke engine and i used all the proper tools. It ran fine at first while on the stand but after revving it a few times it got stuck wide open. it was not the throttle getting stuck, it was an air leak. The kill switch wouldnt work and i pulled the spark plug and that didnt work either. I pulled the gas line and let it run wide open until the gas ran out. By this time the water pump seal had busted. I removed the cylinder and the piston was messed up along with minor scarring of the cylinder. Also the crank seal on the flywheel side had a little drops of oil come out of it. I finally got the motivation to try and rebuild it again and just bought an engine rebuild kit. I just need to know what caused the air leak so that I can fix it this time and not destroy my engine a second time. Info on the bike: I recieved it in a box in pieces. Both crankcase surfaces were very scratched up and one was too far gone so I replaced it with a new one. The other is still scratched but i sanded it until smooth (its not perfect but its good enough to use). When i put it together I used a fresh gasket AND some hondabond gasket to make sure it seals perfect. It didnt leak at all so i believe that cant be the problem. What do you guys think the problem is? How can I find the cause of this incident? Im scared to put it back together and have the same thing happen again.
-It's an 2001, so thinking of age what is the condition of the air boots any chance it came from there?
-You mentioned oil coming out the fly wheel crank seal, interesting being there is no oil on that side from the transmission so I would assume it was gas/fuel mixture coming out.
-Did you install new crank seals when you did the rebuild? If so what is/was the condition of the crankshaft mating surface that meets the seal, nice and smooth and no scarring ect?
-Also, the crank bearings themselves. I had a bike that the clutch side bearing went bad and it was sucking in transmission oil and smoking like a steam engine. If that happened on the flywheel side could be a big issue.
Sounds like you had the case halfs themselves sealed properly......
Anyway, that's my 2 cents......
When you replaced the crank seal did you lift on the crank end whit your hand up and down. To check for play. If not its gone make the seal oval again if the crank bearing had play in it
The Shop
Bad air leak.
Bad crank bearing. ( or crank not running true)
Squish set too tight. ( was it checked?)
You did not mention the state of the carb....Dirty pilot jet?
Paw Paw
If set too tight it will create pre-ignition and cause the fuel to ignite even with out a spark.
What did the top edges of the piston look like? Was it pitted? Was the ring stuck in the ring land on the piston.
FYI: Do a google search for two stroke squish....Or look up The two stroke tuning hand book on line.
Paw Paw
You blew an engine up by doing something incorrectly or had bad part(s)... Revisit, revise, retry if you have the $$$. So many variables you put forth to pinpoint where it could have went wrong... 32:1? Fuel type? Post some pics of your efforts. Engine rebuild Kit? From WHERE?
Always take pics during the process to review prior to starting up, even if for your own sake.
Do you have an OEM manual?
One odd bit is driving the crank seals in too far can fuck an 2T engine up as you describe... Sufficient fuel to run, insufficient fuel to lubricate crank bearings. Coupled with an ill-adjusted carb flowing fuel, I guess it COULD happen.
EDIT: Removed troll reference
Quick lesson on gas & compression ratios. Gasoline engines require a spark to run obviously due to low compression ratios. Diesel engines on the other hand rely on compressing the mixture so it ignites on its own. This requires 16:1 compression or higher. So to tie this in with his bike.. if his squish is tight enough to create a 16:1 compression ratio or higher, the mixture will ignite on its own and run as long as its getting fuel.
I would do a leak down pressure test and find exactly where the leak is. Takes rubber plugs for the intake & exhaust and a special hand gaged pump.
Pit Row
The Matco guage I have.
Rubber plug look for intake and exhaust ports.
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