Clearance Between Valve Head & Piston Measurement


Tools Required

1.      Sliding caliper
2.      Felt pen
3.      Sheet lead strips, width 5mm length 70 mm(appx).
4.      Adhesive tape
Legends

1.      Sealing surface, valve cage/cylinder head
2.      Sealing surface, valve /valve cage
3.      Steel seal ring
4.      Sealing surface , cylinder liner collar/supporting block
5.      Sheet lead strips
6.      Adhesive tape
7.      Valve head(Vlave disc)
8.      Valve cage
9.      M=Marking
10.  S=Clearance between valve head lower edge and piston reacess approx. 5 degree before/after charge exchange cycle TDC.

Clearance between valve and piston
M marking
General

All modifications to timing train, to the crank gear(connecting rid length, piston height), and especially reworking of the valve cage or valve cage seat in cylinder head etc. can have an effect on the clearance S between the opened valve at charge-exchange cycle TDC and the top edge of the piston crown. Whenever reworking is carried out at this points(1-5), or replacements are made, a check must be made on the clearance S.
Starting position

Rocker casing with rocker leaver/swings arm bearig has been removed. Piston has been turned to ignition TDC(valve closed).

Sequence of operation

1.      Release and unscrew all valve fastening nuts and take off all thrusts flanges. (with exhaust valves, shift the coolant plugs to the “ZU-CLOSED ” position).
2.      Make M mark on all vlaves with a felt pen. This marking must be at the outer edge of the valve cage and is an extension of the line drawn fom center of cylinder through the center of the valve.
3.      Proceed with further disassembly in accordance with work cards.

Lead strips
Lead strip attached in valve head
4.      Wind sheet lead strip around a marking tool, or something similar. Wind height about 8-9 mm.
5.      Clean and degrease valve head. Using adhesive tape, tape the prepared sheet-lead strip approx.25mm away from valve head end vertically above the marking M.
6.      Refit valves and rocker casing and tightened to the specified torque loadings.
7.      Turn the engine over once past the charge-exchage TDC, and then remove the rocker casting , remove the vlaves again.
8.      With slider caliper measure the deformed sheet lead strip thickness.
 
Caution:The measured thickness S is note to be less than 3.6mm (MAN B&W 9L 58/64)on any of the valves(engine cold).
As new dimension S-5.2 mm.
Note: Oversize seal ring are available for corrective purpose.

VIEW WHOLE PROCESS IN PHOTOS

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