Crack in exhaust valve.

[james]

I have a 1980 GS850G that I am in the process of fixing a oil leak. New head and cylinder base gaskets. Problem, there is a crack in one of the exhaust valves. The valve has a split at the sealing edge. What are my options, does anyone know a good machine shop in Chicago.

[james]

is this an option.

There is a 1981 gs 850 head with cams off a 14,000 mile bike on ebay, will this fit my 1980.

[Nessism]

The valve cracked because someone didn't adjust the valves; the valve was held off the seat and couldn't cool itself. You need to remove all the valves and inspect them, along with the valve seats, there could be more damage. GS engines are super durable so there is a fair chance the head will clean up with nothing more than one new valve, and lapping the others. Plus new valve stem seals.

That head on ebay will fit. You should always tear down the head anytime it's removed from the engine so it can be inspected and the valve seals replaced. This is particularly true of unknown engine parts.

Good luck

[james]

Thanks Ed for the quick reply. So I can just lap in a new valve and not have to machine the valve or seat. That would be great.

[TheCafeKid]

Very possibly, but again echo Ed, and drive home the point, if you use your current head and just replace the one valve, you need to carefully inspect ALL of the valves for similar damage. When the valves don't get adjusted at even semi-regular intervals, the clearance becomes so tight the valves won't close. This doesn't allow the valves to cool (particularly exhaust side valves, i would assume, perhaps incorrectly, intake side are somewhat less likely to see as severe damage as they're getting blasts of cooler air on the intake stroke.) against the head (the head acts as a large heat sink) the valves burn, and you see the results of that. The last thing you want is one of them to possibly break and fall into the bore while cruising the highway at 60mph. So if you do plan on using your current head inspect everything before you order your valve(s) for good measure. Lapping them in is easy enough (if you can find lapping compound! I had to go to every autoparts store in the surrounding area to find it and half of them looked at me like I was insane...lapping compound. What's that?? Sheesh) and changing the seals is easy enough. I believe Steve has an excellent little video tutorial on removing the valves, and on making your own valve spring tool with a C-clamp and some galvanized tubing or PvC pipe. ( I recommend the steel as the PVC I have found tends to give and slip and make it more frustrating than it needs to be. Also a dab of bearing grease used as a "glue" to hold the keeper on the end of your dental pick to re-install is handy)

Good luck!

[Nessism]

The valves and head may have to be machined to clean up the surfaces if the neglect was severe. Lapping only removes valve and seat residue, and remove minor deformities between the parts. The only way to know is to pull the valves out of the head and inspect everything carefully.

If the seats in the head are damaged to the point of requiring machine work, I'd just get a low mileage used head and start over. The cost of a "valve job" is about double (or triple) that of purchasing a used head on ebay that will clean up with a simple lap job.

To remove the valves, stuff a rag in the combustion chamber then flip the head over and place it down on a sturdy work bench. Take a deep socket and place it over the valve spring retainer and hold it while wacking the socket with a hammer. The retainer will compress and the valve retainers will jump out of the way. Be careful and don't wack the think like a crazy man or bad things can happen.

Good luck

[TheCafeKid]

Huh, never thought to try that method for removal. Would prolly cut the time in half or thereabouts. Good tip Ed! I'll have to give that a try.

[D-Mac]

The valves and head may have to be machined to clean up the surfaces if the neglect was severe. Lapping only removes valve and seat residue, and remove minor deformities between the parts. The only way to know is to pull the valves out of the head and inspect everything carefully.

If the seats in the head are damaged to the point of requiring machine work, I'd just get a low mileage used head and start over. The cost of a "valve job" is about double (or triple) that of purchasing a used head on ebay that will clean up with a simple lap job.

To remove the valves, stuff a rag in the combustion chamber then flip the head over and place it down on a sturdy work bench. Take a deep socket and place it over the valve spring retainer and hold it while wacking the socket with a hammer. The retainer will compress and the valve retainers will jump out of the way. Be careful and don't wack the think like a crazy man or bad things can happen.

Good luck

Sort of like this...... http://www.youtube.com/watch?v=uOAGx1867sk