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Discussion in 'Airheads' started by Rob Farmer, Sep 8, 2010.
If the "porting" involved cutting off the bottom of the valve stems then the valves may have been getting poor support`and rocking in the guides. This can beat up the tip as it is not square to the rocker.
A good shop will measure the spring force and shim the springs to get equal force on all ANd the force required for the riding you do. Too much shimming = too much spring force = more wear on the tips and cam---but the cam gets better librication.
Check the rocker assembly to make sure all the lube holes are lined up correctly.
The keeper ribs match the valve stem. They only go one way.
"sticking" valves was an issue when unleaded gas was phased out. The lead lubricated the vale seats. It was also a marketing thing from Waaaaay back IIRC. Should not be an issue with a modern valve and seat. But if the concentricity of the valve was not set correctly then it may have leaked and partially burned. That can cause some sticking. Again, a non-issue for a good shop.
A valve that is too tight in the guide can stick open. Happens with badly burned oil too. The noise is unmistakable.
My call would be a lube issue or a bad valve. If the rocker is good, a lube issue.
The suggestion about grinding too much off the top of the stm is interesting. Never thought of that one. But you would really need to over cut the seat or valve.
That wear pattern in the keeper ribs is odd. The first groove (top) is moderately worn, the second groove is very worn and the thrid (bottom) groove is minimally worn. Wear occurs at the top edge of the groove. And the top of the valve stem is mushroomed. Very strange.
My money's on a poorly hardened valve. I think that too-tight clearance on the stem might make it stick open, but I can't see it causing mushrooming of the valve stem.
Just my thoughts.
Hello everyone. I am new here. I have been lurking for a bit. Great pics!
I have seen a lot of non BMW valve keeper grooves wear like that. I have seen a few BMW valves do that to a much lesser degree. What I have seen like that had nothing to do with running the guide/stem too tight. Usually the reason was crappy valves.
I suspect the mushroomed tip is because someone ground the tip through the hardening. Or it wasn't hardened for some reason.
When people say they had unleaded seats installed, I hope they mean just the exhaust seats. You can't get any better than those stock cast iron intake seats. They never changed. They never needed to. They are just about perfect.
Those guides in the photos look like they have been in there a lot longer than 8k miles to me.
The baked on oil looks like 100k miles without an oil change. There is a lot more to this story.
Just the exhaust seats were replaced.
It's a bit of a complicated story.
A friend bought the bike a few years ago with 105k on it. because of the mileage he did the right thing and sent the heads off for a valve job paying top dollar for the work. Another friend bought the bike from him and then subsequently came down with cancer and died. He left the bike to me (along with a couple of other bikes). I rebuilt the bike in Feb 2009 (ADV link here I changed the oil twice and set the valves before selling it to Rich. When I set the valves there was no sign of any mushrooming. Rich has only covered a 1000 or so miles on it and has changed the oil so the bikes had plenty of oil changes.
It's always possible that I missed something when I set the valves before selling it but I'm sure I'd have noticed if it wasn't right and certainly wouldn't have sold the bike to Rich if there was an issue.
Rich is looking for a metallurgist to take a look at the valves to see if it's just a hardening issue.
Make sense? The bottom line is whatever has happened before is irrelevant. The main thing is the bikes running sweetly with it's new valves in. It would have been nice to know why the valves suddenly mushroomed.
If it's mushroom, then it must be bullshite (especially as valves are also kept in the dark). As you said earlier
Who rattled your cage?
Shouldn't you be heading for Derbyshire by now. I'll buy you a pint if you are.
One quick-and-dirty way to tell is to try to scratch it with a file. If it scratches, it's not hardened. If it is impervious, it's hardened. Usually.
You cut the valve head off with a hacksaw to remove the valve. That doesn't mena hardened or not-- a two-piece valve has a softer and less brittle metal in the haed and a harder, better-wearing metal in the stem. As "official" BMW valves are done.