250f valve job?

Question

what all is done? for yz250f? doing a valve job like what do you do to the valves?

Answer 1

Take the head to a machine shop

Unless you have a few thousand dollars worth of equipment to grind the valves and seats ,then replace the guides and reset the valves

Answer 2

You can replace the valves but it isn't an easy job. If you're going to all this trouble its worth replacing everything for brand new rather than reusing old valves etc. Remove the cylinder head, use a valve extractor (like a large G-clamp with attachments) to compress the valve springs and remove all the valves from the head. Have an engineer replace all the valve guides. This can only be done by heating the cylinder head to a specific temperature as the guides are an extemely tight fit in the head. You will want to have the head skimmed while the engineer has it as well. When you get the head back, use a valve grinding stick, which is a wooden shaft with a rubber sucker on each end (high tech huh?) to grind in the new valves. Use a small amount of valve grinding paste (coarse) between the lip of the valve and the valve seat and grind the valve into the seat with the grinding stick. Repeat this process with the fine valve grinding paste. Apply this process to each valve in turn. Remembering which valve you ground into which seat is vital here. At this stage you can check whether the valves are seating properly by pouring a little petrol (gas) into the outlet/inlet in turn. With the valve fully in, no petrol should seep from round the valve seat. Be careful when using petrol though for obvious reasons. If you see even the slightest amount of seepage then repeat the grinding process until it's sealed. Now replace all the valve stem seals. Then, finally, you can install the new valves, using the valve extractor to compress the valve springs. Remember which valve was ground into which seat. This can be quite fiddly. You will still need to adjust the valve clearances/change valve shims to correct clearance.

In short, it's not an easy job and will cost you if you can't do it yourself. Good luck.