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#1
11-04-2010, 12:33 AM
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How to Lap valves
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#2
11-05-2010, 08:10 AM
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I understand the principle ( I have done this) but when is it permissible to hand lap vs. do the dux deluxe 3-angle valve job that the machine shop wants to do for you? Is there an advantage in using a valve grinder (other than speed?)
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80 300SD (129k mi) 82 240D stick (193k mi)77 240D auto - stick to be (153k mi) 85 380SL (145k mi) 89 BMW 535i 82 Diesel Rabbit Pickup (374k mi) 91 Jetta IDI Diesel (155k mi) 81 VW Rabbit Convertible Diesel 70 Triumph Spitfire Mk III (63kmi)66 Triumph TR4a IRS (90k mi)67 Ford F-100 (??)
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#3
11-05-2010, 07:32 PM
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Lapping the valves is a procedure used for either final seating or as a quick touch-up. When I have a valve job done I request the machine shop to leave the head un assembled.
The machine shop cuts all valves and valve seats to exactly the same dimension/angle. They make no distinction between individual units. Lapping matches the valves precisely to the seat you have chosen for it. It's a bit of "over-kill" but I still do it. Just lapping will not restore the valve/set angles and can in fact make the seal worse if the seats are extremely worn. Look at it as honing a knife. You use the coarse stone to get the edge back (machine shop) and the fine stone to put that little bit extra on the edge (lapping). It would take you forever to bring a blade back using the fine stone and in fact you could never get the original angle back. Small engines do not require the precision of the automotive engine as they do not reach the high pressures. Older American auto engines (up until the early '70's) use a "soft" seat (hence the need for "leaded fuels) and were much more amenable to hand lapping. Sorry, I tend to get carried away on these subjects. Just "lapping" is acceptable when you have a clean, non-pitted "ring" visible on both the seat and valve no more than half way down the seating surfaces. ANY pitting, discolorations, or incomplete ring needs to be machined. The wider the ring, the better condition of the seal. Last edited by Mike D; 11-05-2010 at 07:44 PM.
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#4
11-05-2010, 08:57 PM
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Somewhere I have a hand crank valve lapping tool. It works kind of like an egg beater and gives a "2 steps forward, 1 step back" kind of motion. In essence, it shimmies back and forth while advancing slowly clockwise.
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-Evan Benz Fleet: 1968 UNIMOG 404.114 1998 E300 2008 E63 Non-Benz Fleet: 1992 Aerostar 1993 MR2 2000 F250
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