Actually you can go for HQ9 razor head.Its a perfect replacement for your unit Philips-Norelco model # 8140XL shaver
The procedure to replace the head is as follows:--
Turn the razor off, remove the plug from the outlet and cord from the razor.
Press the razor head release button. Open the razor head assembly.
Turn the wheel counterclockwise and remove the retaining frame .
Remove used cutters and combs and insert new ones. Remember: Each new cutter and comb is a matched set and should not be interchanged. Make sure that the 2 pointy edges of the razor heads fit exactly into the recesses.
Replace frame on the razor unit by pressing down the wheel of the retaining frame and turning it clockwise .
Replace the razor head assembly back on razor. Place the protective razor head cap on razor to protect heads.
Important: If you accidentally interchange the cutters and combs, it could take several weeks before optimal shaving performance is restored. Replace damaged or worn razor heads with Norelco HQ9 Speed-XL razor heads only.
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Click the link below for Hq9 head
http://www.epinions.com/search/?submitted_form=searchbar&search_string=Philips+Norelco+HQ9+Replacement+Heads+For+Shaver+Model+8140XLhttp:&no_results_vertical=all&no_results_vertical_name=