Coolant leak on CR80 - Losing my mind!!!

[bigboss_an]

Hello Everyone. I'm starting to get desperate. I have rebuilt the top end of this stock 2000 CR80 five times now. With new gaskets (top and bottom) engine runs fine without coolant (obviously just for a little while). As soon as coolant is added, engine sputters, runs terribly and just dies with a coolant soaked spark plug. I also split the cases and replaced the gaskets because I suspected a crank leak at first. Like I said engine runs perfectly without coolant!
I removed the studs and sanded the top of the cylinder, cylinder head, and base of crankcase with 800 sandpaper. I used correct torque specs, even tried coating the head gasket with sealant and still the same thing happens! Is it possible that the cylinder (or even the head) has a hairline crack in a spot that can not be seen?
I know the CR80 has a reputation for finnicky head gaskets, but at this point I find it hard to believe that this is my problem. Your help is highly appreciated because I'm close to the point of pouring gas all over the bike and burning it!

 

[arnego2]

It points to a hairline crack. What kind of gaskets are you using? OEM or aftemarket? New or re-using them?

 

[bigboss_an]

I have used Cometic and another non-OEM that I can't remember the brand. I have not yet tried OEM, but have had very good results with Cometic in the past on many other bikes. I have tried to reuse at first, but when problem persisted I used new every time.

 

[arnego2]

hmm I prefer OEM in gaskets. No good O-rings for my bike over here. All a tat too big or too slim. Can you see any break in the gasket after pulling it? But do you have the chance to borrow head of someone else's bike? It is a bit expensive to replace cylinder heads just by chance.

When running the short time before it dies because of the water did you look into the radiator to see if it throws out bubbles indicating a head gasket leak?

Last can you do a leak down test?

 

[bigboss_an]

It's going to be a tough sell to strip a perfectly good bike to try to solve mine. But do you expect the problem to be in the head or the cylinder? The cylinder makes more sense, the head seems too simple to cause a problem.
I tried to do a leak test, but the frame was too close to the head to allow the meter to attach.
I checked and found the coolant to be circulating in the radiator (as it should) but I did not see excessive bubbling indicating a leaking head gasket.
I'm thinking that I should replace the cylinder. But is this common or even uncommon but possible? Cylinders are not cheap... Thanks for your help arnego2.

 

[SHSPVR]

I take it that your losseing coolant?, there is one other possable that most mechanics forget about checking the transmissions oil fluid so if you have not done that do check it, dose oil color look wrong? well if it dose read on.
If the weep hole drian for water pump is plug up it will push coolant in to transmissions side which in turn get pass your crankcase seal becuases it build just a enough psi for that to happing boom you have in water in crankcase.
If that is the case replace the water pump shalf with new one and new water pump seals and clean out the weep hole on clutch cover with really small drill bit do it by hand not with a power drill.
If do have a hairline crack in the cylinder the best thing to do is have a Steel Slevee install.
But if you do go with a diff jug just so you know you can used 1986 up to 2002 jug that was last year of CR80 then the jug change to 85cc bore which by the way you can also use so long as it 2003/4 jug so long you get that 85cc piston for it, now the cylinder head you do have to watch for the years if bike was made in 1996/2007 you want it get with in thoses years it just that the 1986/1995 are tab diff and you can use any year head from 1986 to 2007 only the radiator hose is diff.
As for the cylinder from 2005/07 CR85 they to can be use but Exhaust Pipe have to be change to that 2005/07 year

My old 1987 CR80 had all kinds years parts in fact the last part I got it was cylinder head from a 2005.

 

[Matt90GT]

take the head and cylinder to a machine shop and have them magnaflux them. If there is a crack, it will show up very quickly.