Vintage Dirt Bike Q & A

I have a 79 CR 250 thats cylinder head leaks, not a lot just after riding you can see where it weeps out. What are my options for a fix after I have replaced the gasket, used a gasket prep. and retorqued it.
thanks

Get it re-surfaced or replace it....

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Michael Stiles
1979 Honda CR250R Elsinore | 2006 Husqvarna SM510R | 2007 Service Honda CR500R-AF

Hi,
You need to determine whether it's the head surface that's the problem, the mating surface on the cylinder, the gasket, or if something is keeping the cylinder, the gasket, and the head from sandwiching together to for a seal. The head and cylinder surfaces can be eyeballed for flatness using a machinists straight edge. If you see light between the surface that you are inspecting and the straight edge, you have warpage, or distortion.
If you have any scrateches, or gouges anywhere. That's a source for leakage. If you're trying to re-use copper gaskets that are damaged. or haven't been annealed again after previous use, that's a source of leakage. If it's the cylinder surface that's a problem, remove the studs and locating pins and lap the surface using fine emery adhered to a surface plate. Move the cylinder surface on the emery cloth in a figure-eight pattern to avoid any linear surface scratches. Use some light oil on the cloth when finishing the surface. You can do the same thing with the head. Make sure that there is no interference with the studs and locating pins that you are using in your assembly.

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1978 CR250R
1979 CR250R
1980 CR250R
1980 ME360
1986 CR250R

thanks guys for taking the time to answer, sounds like I have a little work to do. The only issue I see is removing the studs without damaging the cylinder.

Removing the studs is uaually easy. Screw a cylinder head nut on the stud to be removed with the flange up. Sctew another nut the normal direction on the stud, flange down. Tighten the two nuts against each other and then unscrew the stud by wrenching on the bottom nut. I often put a couple of drops of Kroil on the stud where it goes into the cylinder to allow the oil to "creep" into the mating thread surfaces. In 25 years, I have never had an issue getting these studs out.
Do not use anything like Vise Grips to remove the stud.

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1978 CR250R
1979 CR250R
1980 CR250R
1980 ME360
1986 CR250R

Whats the process that you use for annealing the gaskets?? Simply heat them with a torch? Will propane get it done??
thanks

I generally use new ones, but I remember you heat it thoroughly and then drop in water....propane torch or gas stove will do.

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Michael Stiles
1979 Honda CR250R Elsinore | 2006 Husqvarna SM510R | 2007 Service Honda CR500R-AF

I use my wife's kitchen stove by suspending the gasket over a flame with wires, working the gasket around the flame for even heating until the copper just begins to turn orange. This is the last phase before becoming molten. I use pliers to hold the wires that suspend the gasket. Once it's reached the orange color, I drop the gasked on it's flat surface into a tub of water so that the whole thing cools evenly. After quenching the gasket I clean the oxidation off with a steel wool pad. You may wish to perform this operation outside with a propane stove to avoid getting yelled at, or possibly starting an indoor fire.

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1978 CR250R
1979 CR250R
1980 CR250R
1980 ME360
1986 CR250R