Airhead valve wear anybody else come across this?

Discussion in 'Airheads' started by Rob Farmer, Sep 8, 2010.

  1. Rob Farmer

    Rob Farmer Long timer

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    Whipped the heads off RichC's R90 last night to replace the exhaust valves. The bikes done less than 8k since having the seats, valves and guides done. The engine was noisy so we checked the valves the other day.

    These are two part valves but there's no identification on them so as yet we don't know who made them.

    We had to hacksaw the head of the valve off to get the valves out.

    [​IMG]
    #1
  2. AntonLargiader

    AntonLargiader Long timer

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    I've seen it, but not that bad. Of course the area where the ID is has been damaged so you probably couldn't read it anyway. It is something that happened to Black Diamond valves a long time ago but I've seen it on other valves as well, and you indicate these are not BDs.

    Were the valves replaced as part of the overhaul 8000 miles ago? And were both valves worn that way? What do the tips of the rocker arms look like?
    #2
  3. Rob Farmer

    Rob Farmer Long timer

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    The rocker arms look fine. The engines now fitted with genuine valves and was lovely and quiet when we fired it up again last night.

    Just spoke to the guys who carried out the work and he's suggested the porting work alters the fuelling. If you don't weaken the mixture and run the standard jetting then the valves will stick to the seats causing the valve stems to get a battering. Does that make sense? He thinks they are Intervalve valves.
    #3
  4. AntonLargiader

    AntonLargiader Long timer

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    I've never heard of that as a problem.

    What was the stem-guide clearance?
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  5. Rob Farmer

    Rob Farmer Long timer

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    Neither have I but it seemed very plausable while I was on the phone to him...I think I've been suckered :lol3

    Stem/Guide clearance seemed fine with no sign of any wear on the valve stems.

    [​IMG]
    #5
  6. AntonLargiader

    AntonLargiader Long timer

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    But what was it? If too little, you can get the stem seizing in the guide. You want 0.04 minimum, more like 0.05 on the exhaust. Intakes can run tighter.
    #6
  7. anotherguy

    anotherguy unsympathetic

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    I call your guy out on that bogus explanation.

    Port work does alter fueling. More air=need for more fuel. Maybe a bad port job would cause a loss in flow and corresponding reduction in fuel demand but I've never seen a port job that bad.

    However in my years and literally thousands of valve jobs experience I've NEVER seen valves stick. And I've seen some serious carnage. Like enough heat to make holes in pistons lean and never seen a valve stick to a seat. Extreme heat or substandard parts is the reason for that issue. I've seen many where I had to file a burr from the stem to cleanly remove the valve without guide damage but never as bad as those.

    Sounds like you've got it sorted out. Just don't use those parts or installer again and there will be no repeat.
    #7
  8. mykill

    mykill odd

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    That is really bad. I encountered a slight mushrooming on a set of valves that had receded so badly there was no adjustment left. We ended up filing the ends to get them out. I suspect they were run w/o clearance for a long time. Were the valve springs stock? We had a GS with racing springs that beat the crap out of the cams and followers.
    I think somebody sold you some cheap valves and is covering his ass with stories meant to confuse you.
    #8
  9. Rob Farmer

    Rob Farmer Long timer

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    I was down at Motobins today they've never known a problem with the Intervalve valves before and neither has Steve Scriminger so I agree with you.

    I'm going to contact the previous owner who had the work done to see if he can shed some light on this.
    #9
  10. Bill Harris

    Bill Harris Confirmed Curmudgeon

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    This reminds me of the wear you get with rotating keepers used on valves made with a stem of too-soft material. Like the old Black Diamond valves used to do. What did the keepers and upper valve spring retainer look like? The valve guide clearance might be suspect but with 8K on the clock it might be OK. What did the valve stems in the guide area look like? Scuffing or galling?

    I'd suspect horsepucky from the guy who sold you the valves... :evil
    #10
  11. crampfan

    crampfan Banned

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    I have seen this kind of damage when the tech doing the valve job has issues with stem height due to valve seats being worn. the easy way out is to remove material from the stem, too much will result in removing the hardening in the tip causing this type of damage.
    #11
  12. Rob Farmer

    Rob Farmer Long timer

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    Everything looked fine, if anything the valve guides seemed very loose, no obvious wear or scoring on the valve stems. The valve seats were replaced with unleaded ones during the work.

    The work was paid for by the previous owner. He's a friend and a work colleague. I trust him. I did see the receipt for the work as well and it wasn't cheap.

    These are the guys who carried out the work Cylinder head shop They have a good reputation. They do not apparently supply valves for BMW's but have them sent by the owner with the cylinder heads. I need to speak to Mike and find out where he bought the valves from.

    One of those awkward situations. I sold the bike to Rich and he's had a few issues. Front brakes, Boyer ignition died and now the valve guides. It was great when I had it :D

    Looks pretty though.

    [​IMG]
    #12
  13. wirewrkr

    wirewrkr the thread-killer

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    As Anton indicated (he would know) it seems like the guides were not clearanced correctly.
    Very critical on air head motors, seen it before. More than once when I was an aircooled VW mechanic.
    RV
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  14. Max Headroom

    Max Headroom lost in the '70s

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    Bullshit.

    If they were "sticking" to the seat, there would be clear evidence of damage to the seat and the valve sealing face from micro-welding. The seat would require much more than lapping to match up with a replacement valve, and would probably be the result of poor leadfree seat metallurgy if your guy's explanation was remotely plausible.

    Insufficient valve stem clearance, as has already been suggested, is more likely to be the culprit. There are other possible reasons too, but they are more "fringe", and are the stuff of pure speculation.
    #14
  15. anotherguy

    anotherguy unsympathetic

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    I've seen bad stem tips with inadequate hardening on good quality valves that I never had problems with before. It happens. My issue was with the explanation he got. After looking at the Cylinder Head Shop website they appear to be a top shelf company which makes the explanation even more confusing. Were it my work I'd eat the job going on the info presented here. Without complaint.
    #15
  16. bmwrench

    bmwrench Long timer

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    That valve looks like it has been opened a lot father than stock. I wonder what cam it has in it, and whether the valve spring was in coil-bind.
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  17. Airhead Wrangler

    Airhead Wrangler Long timer

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    There's an interesting possibility. On the same tack, would it be possible to intall the keepers one notch too low on the valve stem, or the wrong keepers, or perhaps maybe the valves are the wrong part and the stems are too short thus compressing the spring too much?
    #17
  18. El Hombre

    El Hombre Banned

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    I've got a set of Motobins, Intervalve exhaust valves, about to go into the 90S. So this got my attention....

    When you think about it, it's either something causing a drag on the stem; like too little clearance. Or the normal drag and something wrong with the valve stem; as in too soft a material. I can't think of anything else that would cause that kind of deformation. But I've had a couple of Canadian Club's, so maybe somebody else is thinking clearer; at least compared to meeeee.:D
    #18
  19. Rob Farmer

    Rob Farmer Long timer

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    Since neither Rich or myself were their customers there's no recourse on the cylinder head shop at all. The call to them yesterday was little more than a fact finding call. The explanation was complete bollox as far as I was concerned but as mentioned above we weren't their customers.
    #19
  20. Rob Farmer

    Rob Farmer Long timer

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    We don't know yet if these were Intervalve valves. Motobins did say they have known a problem with intervalve. I've used them before and have never had an issue.
    #20