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valves, adjustment or replacement?

Discussion in 'Maintenance and Servicing' started by dgmeister, Feb 28, 2012.

  1. At what point are the valves replaced rather than adjusted?

    (4 valve single cylinder 250)

    Are they replaced all at once, or do you generally get exhaust valves
    replaced and only adjust the intake valves?
  2. These days, unless you actually bend one or break a cheese wedge out of its head, valves very rarely need replacement.

    However, when they do, it would be the exhaust valves to go first because of the harsher conditions they operate in. There are two major criteria. First is how much sideways wiggle the valve has in the guide (the manual will likely have a spec for this). This is a function of valve stem wear and guide wear. In most cases replacing both is the preferred option, although replacing the valve alone may get you back into spec without the mucking around that valve guide replacement entails. Second indication is the exhaust valve clearance constantly closing up. This means that the valve is stretching and may be about to lose its head. Very common on air-cooled VW engines but I can't think of any bikes where it's a specific issue.

    There is also the possibility of the seating area of the valve being burned and pitted, usually due to running long term with tight valve clearences, in which case, unless you've got something exotic, or a Honda, replacement is likely to be no more expensive than refacing. By the time a valve is in this state, the valve seat may also need work.
  3. Your engines history/ family tree is from an angry valve munching tree hater (i've got one) for the latest incarnation of that donk they decided to make it more docile, and therefore more learner/drongo friendly, and then they replaced the TI valves with Stainless ones.

    Because of such heritage this motor was built to change/ check the valve clearances.. It takes less than 15 min's to check, and about 25mins to change them.

    You only need to get a head job when you run out of shim adjustment. If you need this done let me know and I can point you in the right direction with getting it done at a place that specialises in these (4v single hondas) engine rebuilds.

    I even have quite a collection of shims to suit if you are in need.
  4. "You only need to get a head job when you run out of shim adjustment"
    Yeah i wish i got them more often, gotta work on that. lol :-s

    kwaka mate, not hondy. klx 250. been going 55,000 kms with only one valve adjust, now they're ****ed. i figure the exhaust valves gone coz it won't idle and runs shit. i don't know if i can resist getting the 300 cylinder bunged on at the same time as the valves are done.

    considering the possible displacement upgrade, will probably get the exhaust valves replaced, if not all valves.

    any comments? (yes i want a road bike soon)
  5. Might as well do the upgrade while it's apart as long as you know or anticipate any pitfalls.

    Also, yes, if you're upgrading the engine, there's no point skimping on ancillaries. Might as well start out with all new parts so you get the most benefit you can so definitely replace the exhaust valves. Guides too unless the originals are towards the unworn end of spec. Same with the inlet valves/guides. No point putting an engine back together with stuff that's only got 20% of its useful life left.