The GMC CCKW

Would like to know the probably reason when I bought my truck and we opened the engine saw a exhaust valve all toast in its head.The truck worked in a brick factory(mud) for long 15 years and its engine was running by butano gas(45 kg).Now the exhaust valve looks like a toast cracker. :roll:Thanks for any help.

That is un-usual as butane is a very clean burning fuel. not nearly as carbon building as gasoline. I really don't have an answer for you but I bet someone will have the solution.

poor air filtration in a very dusty environment could be a suspect,
it would be worse if the dust particles are very small, like clay.

also, if it is the rearmost valve, sometimes there are cooling issues

Exhaust valve seat recession or valves too tight or not adjusted often enough.

Incorrect ignition timing has been known to burn valves as well .
A collection of deposits on the valve itself will heat up and cause them to burn. The deposits could have several sources some of which have been addressed in prior posts.
There are other clues as well that are needed to find the problem
How do all the ex valves look?
How do all the in valves look?
How do the pistons look?
How do the rings look? If you introduce oil into the mix you will quickly build deposits as well.
Do the components in each cyl compare to the others?
And don't forget the valve guides themselves .leakers cause sticking, which somtimes lead to burning.
Hope this helps
John

See Fernando, we have the best on this site when working on these old steel warriors. Good luck on your repairs.

Thanks guys.Yes,my engine already was repaired in april'2005.Now I am only wanting to know the probably reason.I will try to send a pic for you after.