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Coolant leak

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May 23, 2002
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#1
I started taking my 91 CR 125 apart today to pull out the engine.

Earlier I had posted a thread about a super rich condition i this bike (there was black gunk coming out of every orifice in the exhaust system and it would not start anymore) So we concluded it was the right side crank seal allowing motor oil into the combustion chamber, which is the reason I'm taking the bike apart.

When I drained the coolant out of the drain hole on the pump cover I only got about six ounces out (I think it holds about 1 liter of coolant). I immediatley knew where I was going to find the rest of it and I was right. It was in the tranny oil. My first thought was that it was leaking around the head gasket and into the cylander then into the oil but I don't know if that makes any sense. I'll be finished taking the engine out of the bike in the next few days. What is the most likely place it could be leaking from and is there any sure fire way to know for sure? I just need some ideas.
 
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May 23, 2002
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#3
Wouldn't there be oil in the coolant too? Is there anyway to tell if it's bad or do I just have to replace it and see if that works?

Thanks for the reply.
 

jmics19067

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#4
The oil is incidental contact in that area while the water is getting pumped thru so the action of the water pump pushes the water thru the seal.Also since the cooling system is a closed system it will build pressure as it gets hot, the transmission is vented so it will not build pressure. If the seal is bad the pressure from the cooling system will push the water thru it. Plus the fact that the coolant is stored up higher in the radiators, any way you look at the coolant has more pressure helping it make it a one way scenerio.

a bad head gasket on a four stroke could easily have oil in the water because the oil pressure would be greater than the coolant pressure.

The easiest way to check would be too drain the oil, fill up the coolant, using a pressure tester pump up the radiator to whatever the pressure rating is on the cap and see if water comes out your oil drain hole. It will be either the water pump seal,the gasket for the clutch side case cover if the water passes thru it, or the side covers themselves leaking the water.

On your two stroke the engine is separated from the transmision oil.which you know because you suspected the rights side engine seal causing the smoke. If the condition of your engine was so bad that enough water went thru the engine,head /base gasket and thru the right side seal in that direction I highly doubt that the bike would run. Where as if the water pump seal went bad contaminated your oil, raised its level up with something that isn't a good quality oil, ruining the seal and passing into the engine a more likely direction. Either way I would replace the water pump seal , right side engine seal and inspect the bearings in the engine and the piston closely because wherever the water was oil wasn't. The transmision should survive the water better than the engine.
 
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#5
I had a pretty big brain fart about the head gasket. I'm not exactly sure what you mean by side case cover seals. Does replacing any of these seals require splitting the cases. I've done some engine work on my bike but splitting the cases freaks me out. I have a clymer manual and eric's book but there both at my brothers house along with my bike.

Thanks again for the help.
 

jmics19067

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#6
I meant the clutch cover that houses the water pump, if that was cracked it could leak water.
 
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Sep 1, 2003
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#7
no you dont need to split the case just remove the cover u would take off to replace the crank seel the water pump is in it your water pump should have two seels one on the inside to seel the tranny and one on the out side to seel the water system. there is a little hole under the water pump and when the seels blow water willl drip out of it this hole is between the two seels and is to tell you when the seels have blowen any way the water pump shaft will probley need replacing as well due to deep wear from the seels and when you put it all back together make sure you get the thing the opens the exaust valves in the right place nothing worse than riding round with your exaust valves wide open all the time
 
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Oct 28, 2003
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#9
I had a '85 cr 125 that the previous owner ran water for years. It ate a hole through the water pump housing and got into the crankcase. Not good!
Ive heard that '85-'89 cr's had this problem, so maybe yours is similar
 
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#11
I tried to patch the holes with marine-tex (used for repairing boat hulls) but after two trips they opened up and i think the crank seized. I dont know. I sold it for $300 because I didn't want to deal with it. The bike was trashed anyway.