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Sportster Motorcycle Air intake, Carburetor, EFI, Fuel, and Exhaust Problems, advice and/or how tos for Sporster and Buell motorcycle carburators, Electronic Fuel Injection (EFI), Air Intake, Fuel and Exhaust.

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  #21  
Old 4th November 2016
photobiker photobiker is offline
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Quote:
Originally Posted by aswracing View Post
Just to add another piece of data ... back when we were using straight wound springs, we had huge, huge problems getting people to clearance rocker boxes correctly. The larger springs would hit the rocker boxes, which made the valves land sideways on the seats, which caused seat recession and leaking. I can imagine that given enough time, it would also cause a seat to fall out.

...

But if we're talking about a set of stage 2 heads that was done ten years ago, man, I'd sure look at the spring to rocker box clearance. If not properly done, it could definitely have contributed to this failure, and in our experience, it was a very common mistake.
This is an excellent point and one that I discussed with the guy who did the tear down and rebuild this last time. He looked and thought I had clearanced them sufficiently, but it would be a good idea for me to double check them and wouldn't be that hard to do. This always seemed like one of the more plausible explanations for the seat failure. Thanks for bringing it up!
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  #22  
Old 4th November 2016
John Harper John Harper is offline
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I had a valve seat come out on an old VW I owned. Did not break the valve off, but traveled up and down with it without further damage. It happens.

Also dropped a valve on my 1971 van one time, that was a bit more involved. The valve head embedded in the #4 piston was a cool memento.

John
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  #23  
Old 4th November 2016
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