Posts
35
Joined
10/26/2016
Location
Seaside, CA
US
Edited Date/Time
8/12/2018 12:10pm
What's up guys, I have a 2001 RM250 that I completely tore down two years ago and restored. When I put it back together, the crank didn't have too much play in it so I left the bottom end alone. I put a new top end in it and ran it for 13 hours. At that time, I had some tapping going on and tore everything down. The crank bearing was on the verge of going so I tore the bike completely down and put a new crank in it. Rebuilt the bike with a new top end... which leads me to now.
I put coolant in the bike and coolant proceeds to go through the carb into the airbox once it fills up enough in the radiator to go over to the other side (near the top). I drained all the coolant and cleaned the carb. Then I pulled the oil drain bolt and there was no coolant in there. I assumed the inner o ring for the top of the cylinder was a bad o ring, because its the only way I can think coolant went into the intake. The piston wasn't at TDC when I put coolant in and I'm assuming it was just below the intake opening, allowing it to drain into the carb and also probably into the exhaust.
Anyways, I just replaced both of the o rings with OEM o-rings and I still have coolant going through the carb into the airbox when I put coolant into the radiator...
Why is this happening? No coolant is leaking around the bottom of the head. No coolant leaks anywhere outside of the head either. I'm kind of at a loss right now for how to fix this thing....What's killing me is the bike ran great (not burning or losing any coolant) before I tore it down. What am I missing here?
Bottom gasket is a cometic (brand new). Top o rings are both OEM suzuki (brand new). Thanks!
-Colton
I put coolant in the bike and coolant proceeds to go through the carb into the airbox once it fills up enough in the radiator to go over to the other side (near the top). I drained all the coolant and cleaned the carb. Then I pulled the oil drain bolt and there was no coolant in there. I assumed the inner o ring for the top of the cylinder was a bad o ring, because its the only way I can think coolant went into the intake. The piston wasn't at TDC when I put coolant in and I'm assuming it was just below the intake opening, allowing it to drain into the carb and also probably into the exhaust.
Anyways, I just replaced both of the o rings with OEM o-rings and I still have coolant going through the carb into the airbox when I put coolant into the radiator...
Why is this happening? No coolant is leaking around the bottom of the head. No coolant leaks anywhere outside of the head either. I'm kind of at a loss right now for how to fix this thing....What's killing me is the bike ran great (not burning or losing any coolant) before I tore it down. What am I missing here?
Bottom gasket is a cometic (brand new). Top o rings are both OEM suzuki (brand new). Thanks!
-Colton
If it was a bad water pump seal, wouldn’t the coolant be in the oil? Not coming through the air box?
What kind of sealing bond did you use?
After further research, I read a thread about a CR250 where the guy had installed the water pump seal backwards. The manual I have is for an 06 (since I can’t find an 01 manual). After comparing the micro fishes Online, it looks like the 01-02 pump seal is installed with the flat side facing the impeller. 03 and up is flat side facing inboard towards the motor. I ordered up a new seal and hope to have it installed by the end of the week. I’ll post the result in a few days. Thanks for the suggestions guys!
The Shop
If you take your subframe including the airbox and filter off ( obviously only in a clean garage environment with a perfectly clean bike for a very brief time) and start it up then put your hand near the entrance to the carb you should feel very brief puffs of air and atomized fuel coming backwards through the carb.
The first time I noticed this I was concerned it was issue with my bike and reeds not sealing etc. but after researching it a bit came to understand its normal on a two stroke due to a very brief moment before all intake type ports.....IE boost, transfer etc. are completely closed off by the piston. If you've got any coolant making its way into the combustion chamber it might be getting blown backwards and into the carb with the rest that i mentioned.
The only other way I could fathom coolant making it into the carb would be something ridiculous like running the overflow vent from your radiator directly into one of the carbs overflow vent openings.
If im not mistaken your water pump seal would only allow coolant into the transmission cavity not the carb and milky oil would be the tell tale sign.
Paw Paw
I don't think the cylinder is cracked because it was never dropped or anything like that during the rebuild. At this point, the only think I can think is that one of the coolant passages in the cases is cracked, the case gasket isn't sealing properly in one area, or there is some internal coolant seal missing that I am unaware of. The rate of the coolant filling up in the bottom is pretty quick, so whatever it is, it is not a small leak point. Any advice would be greatly appreciated.
Edit:
On the Honda I realized it has a weep hole so you’d see it leaking out the bottom. Guessing others would be the same.
The gasket wasn't really sealing in this area. I ditched the cometic gasket for an OEM one. Both the OEM head base gasket and the case gaskets have little, kind of like o rings, embedded in the gasket around the coolant passages. I used a little bit of yamabond with the new gasket as well. Threw the motor in the bike this morning and poured in some coolant and looks like were good! Now just gotta put everything else back together and we'll be in business. Thanks everyone for the help!
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