Inlet Valves not sealing (84 XR250)

Discussion in 'Technical' started by daewoo, Mar 16, 2008.

  1. My XR250 had a problem in that it would loose all compression, so when you were trying to start it, it was like you were holding the decompression lever.

    The problem was intermittent (of course Mad )

    I rre-ringed the piston, and paid to have the head serviced and the (valves and valve seats re-cut), thinking that it was just old, coked up and worn out...

    Not happy when just after the rebuild the problem came back a couple of weeks later Mad

    Today I pulled the rocker cover off, which means that there is nothing to activate the valves, so they should all be fully closed. The problem was still there...

    So I put compressed air through the spark plug hole, and can hear it at the air box.

    Assuming that the guy who did the head, did actually re-cut the seats and valves (I have no reason to think that he didn't), why wouldn't they be seating??? The only thing that I can think of is a bent valve or a cracked seat...

    Anything else before I pull the head off???

  2. Worn guides would do it.

    Off it comes...

    Get ready for a big argument. Warranty... :roll:
  3. That might explain the intermittent problem, I couldn't understand how sometimes it would be OK, and then sometimes have no compression.

    I was glad when I sort of traced it back to the valves, because until them I was worried that I had dome something stupid like lined all of the piston ring gaps up nicely in a row...

    Of course, I am not sure if the shop is still open, because last time I was there they were selling... :mad:

  4. Actually, I missed the intermittent bit. That's a dead giveaway for worn guides. The valves can move sideways, so sometimes they sit centred and seal, sometimes off-centre and leak.

    They should have checked for that when doing the seats, now they, too, will have to be re-cut.
  5. Sounds reasonable, thanks for that.

    I had a word to the guy at the shop yesterday, now I just have to arrange to get the head to him... see what he says... not sure if he was supposed to replace the guides when he did the head, but I would have thought that was pretty standard.

  6. You only replace the guides if they are worn. It's a big job requiring skill and machinery. So, no, it's not standard.

    But, not checking them is professional misconduct, as all that is required when the valves are out is to stick them into the guides and check for free play. If the guides are worn don't pay more than getting them done, re-doing the rest of the work should be on the shop.
  7. Thanks for the help and advice... I am new to this motorbike spannering caper.


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