CR80 coolant in exhaust - new head gasket

[bigboss_an]

Hello Everyone,
I have been working on my kids' bike (2000 CR80) for a while now and can't find a solution so your help is needed.
Even after sanding down cylinder head and top of cylinder on a mirror with 800 and then 1000 sandpaper and installing three new head gaskets (with correct torque on cylinder and head) I still get coolant in the exhaust and excessive pressure in radiator. Bike is also very hard to start. It will only start when pushed down a hill and jump starting it. When it finally starts it runs terrible, especially at higher RPM's.
Is it possible for coolant to leak into the exhaust by means of a (hairline) crack in the head or the cylinder?
I'm now considering new studs and a fourth set of gaskets, but maybe I should be looking at the head or cylinder for leaks? I know that the older CR's are very finnicky with head gaskets, but I can't believe the problem is a leaking head gasket anymore. Is the coolant being forced into the exhaust because of exhaust gases leaking into the cooling system (which makes no sense, I know) or is it being forced out by the temperature and pressure in the cooling system itself? I must say that this happens before the engine even warms up so I can't believe it's an overheating issue either.
BTW; Crankcase oil is perfectly clean.
My son is desperate so your help is really appreciated. Thanks.
'Confused' Marc

 

[RM_guy]

Sounds like a crack someplace. You'll need to do a leak down test to see where it's at...or at least get an idea where it's at. Are you seeing bubbles in the radiator? That's a good sign you're dealing with a bad gasket (which it sounds like you eliminated that possibility) or a cracked head or cylinder.

Start with the leakdown test. A fealer can do it or you can buy a kit to do it yourself. Google leak down tester and you'll get a bunch of info on them. You need one that blocks off the intake and exhaust ports.

 

[whenfoxforks-ruled]

By all means replace the studs and nuts. They fatigue and do not take torque properly. I do see you are getting way over board with the sand paper, 400~600 is fine enough. Too fine of grit seals worse. Get a can of gold permatex high temp gasket spray. Hang the head gasket and coat both sides, dry and install. The spray is an absolute last ditch effort, and I have sprayed the head and top of cylinder. Keeping it out of the rings and combustion chamber is important! The dowel pins are installed? When installing the head to frame stays, if there is a gap, install washers. Torque applied to close the gap will cause a head leak. I do not remember if that bike has one, but? Vintage Bob

 

[bigboss_an]

Thanks for the ideas guys. I will be working on those and update if I'm succesful or not. I will be looking for the leak down test and the gasket spray. Can I use the spray on a used gasket? Dowel pins are ok and this model does not use a head bracket. But definitely good ideas. Thanks again.

 

[helio lucas]

for the unit price is better to not re-use old head gaskets (you might get away with it but i didn´t said so, nor i ever have done it ;) ).
if you have the cylinder out you can visually inspect it. you have to do it anyway after the leak down test.

if the leak is in the gasket you will see some discoloration at the head or cylinder face, darker grey, maybe slightly brown.
if there is no leak search the head, most of the cracks happens around the studs.
next, the cylinder. the crack could not be at the exhaust duct, maybe on the bore.

------one thing i almost forget, the base gasket seals not only the cylinder and crankcase but a water duct from the pump as well. if the gasket or the surface leaks the water enters the cylinder and goes out on exhaust. (the engine is a air pump right?)------
--edit-- after posting i start to get some doubts and confirmed that the cr80 had no duct but a external pipe instead. i apologise for being dumb :cool: ---

 

[whenfoxforks-ruled]

The metal stamped gasket, junk after 1 use.

 

[Patman]

If the sealing surface of a part (say the head) is not perfectly parallel to the sealing surface of the mating part ( say the cylinder) all the sanding (on a hopefully flat piece of glass) in the work won't fix it.