Would this compressor be sufficient to keep valves elevated in a 103 engine for valve stem seal replacement?

http://www.partsamerica.com/ProductDetail.aspx?categorycode=3483A&mfrcode=ALT&mfrpartnumber=835183

Yes. BTDT, just don't let the connection slip off. BTDT, too.

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Norm in NJ
Next oil change at 230,000miles

Most any compressor will do that job since it takes pressure not volume. As nglitz said, if the valve slips down and looses seal, it's gone. For this reason, make sure the piston is at the top on the cylinder you are working on. If the piston is at the top you will be able to lift the valve with your fingers to reseal. For that matter, some guys just roll the piston to the top and change the seal, at least on a diesel. I don't know if the chamber is tight enough for this to work on your engine.

Good luck,

I did valve seals on my 560sl w/o compressed air; just turned each cylinder to TDC.

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as ever
Paul

1989 560SL
1987 300SDL
1987 300TD
1983 BMW 633CSi
1972 280SE 4.5