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Thread: Apparent valve or seat recession?

  1. #1
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    Question Apparent valve or seat recession?

    '77 R100S Roughly 80,000 miles, recent 10K service by PO Feb.'12, no comment by service folks about valve seat recession.

    While doing pushrod seals I noticed left side exhaust adjusting screw is nearly backed all the way out, about .250" higher than any others. Also the left side is 120# while the right is 130#.

    Rechecked adjustment after less than 1,000 mi. and exhaust in question was at least .003" closed up.

    The big question: I'm sure I'll tear it down this Winter to see what's actually happening but should I or could I run it for another month or so?

    Bike is running very good getting up to 54 mpg. Hate to jeopardize some very expensive components!

    My thoughts are that if it closes up the full .008" it shouldn't drop the valve as it will held in place by the rocker and pushrod. Naturely I'll experience loss of compression, etc.
    Tom

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    Administrator 20774's Avatar
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    How many miles do you anticipate putting on in the next month? I wouldn't worry too much about it in the short term. The first indication that the valves have closed up is that it won't idle very well. If you sense that is happening, get it home quickly and check things out.
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

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    Thanks Kurt, possibly just a few hundred since Ohio weather will go downhill pretty fast!

    Does anyone have any recommendations on valves, I see BMW's are $150 each. I already read Snowbums article and know his opinion.

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    Moto bins sells valves, guides, seats, etc. at good prices. I am rebuilding a head bought off ebay and intent to put new guides and seats from Moto bins - it's a hobby. Supporting your local BMW parts supplier is always admirable.
    Stan

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  5. #5
    advrider.com
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    If it looks like this on the outside:



    Then it looks like this on the inside:



    Why risk it?

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    My /7 heads are going to Ted Porter this year. What he uses, that's what I would use.
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  7. #7
    Registered User richardak's Avatar
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    Quote Originally Posted by rolyak View Post
    The big question: I'm sure I'll tear it down this Winter to see what's actually happening but should I or could I run it for another month or so?
    When I was wondering about my valves, I ended up pulling of the exhaust header giving you a pretty good view of the exhaust valve.
    1983 R100RT hacked w/Cozy Rocket My blog
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    Airhead #10576

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    crazydrummerdude, very good point! As a retired mechanic and engineer I don't need much of an excuse to dig into my boxer.

    Stan
    , I have seen Moto-Bins and noticed their kits Use AE valves. AE once partnered with Clevite and McCord so I am somewhat familiar with their quality. I did failure analysis.

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    Great pix!

    CDD - you may be Crazy, but you know how to illustrate your knowledge with excellent photos. Yeah, I'd say all those threads a-showing would indicate some kind of problem! And the internal shot: THIS, boys and girls is a recessed valve.

    Hope you're enjoying Oklahoma -- some fantastic riding over in the east -- Cookson Hills, where Pretty Boy Floyd hung out. . . (He was crazy, too.)

    Walking Eagle

  10. #10
    Registered User ebeeby's Avatar
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    Quote Originally Posted by 20774 View Post
    My /7 heads are going to Ted Porter this year. What he uses, that's what I would use.
    +1 on Porter's recipe. He does enough of them to know.

    And yes, you've got valve recession.

  11. #11
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    Quote Originally Posted by rolyak View Post
    crazydrummerdude, very good point! As a retired mechanic and engineer I don't need much of an excuse to dig into my boxer.

    Stan
    , I have seen Moto-Bins and noticed their kits Use AE valves. AE once partnered with Clevite and McCord so I am somewhat familiar with their quality. I did failure analysis.
    After reading Ted Porters description of the (BMW) valve construction, I am reluctant to use aftermarket valves. Certainly, BMW does not make their own valves but specifies a valve with the needed requirements. So, some aftermarket valves may be identical or as good. Some talk about the official BMW valve guides indicate they may not be superior to others, but I plan to go with them. Going OEM is always a safe bet - especially with BMW engine parts IMO.
    Stan

    AH# 13238

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