EXHAUST VALVE

●      Bottom piece seat, grinding angle 29.9 - 30.0

●      Valve spindle seat, grinding angle 30.5 - 30.6

●      Bottom piece seat, max. Grinding, G3 2.3mm

●      Gap of bottom piece seat G2- 1mm

●      Hyd pr - 1500bar

EXH VV CHECKS

●      Vv spindle rotation checl while running, the bar will move by 6mm

●      Spindle drop down test    - shut spring air and release air on the vv, if dropped below 30mins, ohaul. If more than 1hr, then OK.

●      Check of Air spring tightness    - Connect compressed air to the non return (A) valve on the air cylinder.    Disconnect and remove the drain oil pipe from the oil cylinder (C).

●      Check if air is coming out from:

The bore (B): Leakage from spindle stem sealing , change and overhaul.

Hole for drain oil (C): If yes, the leakage comes from the safety valve or the air piston.

Check the safety valve (D). If air still is coming out, the leakage comes from the air piston: change and overhaul.

Ovhaul of EXH VV

●      Open the oil cylinder

●      Release the air from the NR vv, then remove the flange on the top of the air piston, then knock the piston down by a tin hammer to remove the conical locking ring.

●      Then remove the spindle

●      Unscrew and remove the lock screws which retain the bottom piece.

●      Dismount the air piston from the air cylinder using two eye bolts.

●      Mount two eye bolts in the air cylinder and dismount the air cylinder.

●      Inspect the bushing in the spindle guide for wear and measure the top and bottom diameters. If reqd, remove by extracting tool or knock with a mandrel.

●      Check the spindle bushing and dia at the top and bottom.

●      Check the air safety vv of the air cylinder for correct lifting

●      Oil cylinder ohaul- orifice plug under the lifting bracket, flange n oil piston, cylinder, n measurement

BOTTOM INSPECTION

Acceptance criteria

There must be contact around the entire inner circumference of the seat.When the valve heats up in service, the angular difference between the spindle and bottom piece seatings will decrease. At steady, full load, the seatings will be Parallel. Thus, inner contact must be maintained in order to be sure of parallel contact during running.If there is no inner contact, outer contact (Fig. 3) will occur during running, and this will increase the risk of blow-by.

●      Checking the Seat for Gas Leakage

    There must be no blow-by “tracks” across the inner part of the seat. Blowby is shown

marks on the inner circumference. If there are marks, then grinding is reqd

●      Clean the seat with coarse emery cloth.Dent marks, of varying number and size (up to 8-10 mm), will be seen on the seating after a few thousand service hours.In general, dent marks are acceptable and should not necessitate grinding of the seat. If, however, the marks have caused blow-by, then the seat must be ground/reconditioned.

●      Check for cracks and if any, consult MAN

●      High-temperature corrosion on the outer part of the seat may result in a measurable difference in level between the inner and outer seat zones. In that case the spindle must be ground. However, this will not normally happen before 20 – 30,000 hours after the previous grinding.

BOTTOM PIECE SEAT MEASURING

●      Clean the contact faces on which the measuring template is to be applied, and measure:

– the burn-off on the disc underside,

– the total amount the seat has been ground.

●      Bottom piece Measuring

●      Use the bottom piece template and a feeler gauge, take measurements G2(1mm at the bottom) and G3(at the top of 2.3mm). All measurements should be taken at four diametrically opposite points on the circumference of the bottom piece seating.

●      The max grinding angle for bottom seat is 29.9-30 and the max gr angle for vv is 30.5-30.6

●      If the seat or the recess G3 is ground, check data for max grinding for correct grinding angle.

●      IF the template rests on the lower surface in the groove, i.e. G2 = 0, THEN Further grinding or reconditioning is not recommended.

●      Grind the outside sealing face of the exh vv Use carborundum 200 and the special grinding tool.

●      The bottom piece has an U-SEAL at the bottom which has to b heated at 100 degrees for 5min before keeping. Also keep the o-ring at the top.

NIMONIC EXHAUST VALVE SPINDLE

●      Check the stem for dia and also for anhy peeling off of chrome coated/HVOF coating. Check the spindle stem for wear in the area D0815 to D0816 measured from the top of the spindle.

●      Mount the spindle in the grinding machine and, using the dial-gauge positioned just inside the area of inner contact, true-up to within a maximum of 0.05 mm. This is done in order to minimize the amount of material removed during grinding.

●      Grind the seat. After full contact between grindstone and seat is reached at the beginning of the grinding process:

●      Normally limit the grinding to 0.2mm

●      Rare cases - 0.3mm or more

●      If blowby, till they r removed

●      If dents, not necessary to remove

-     Acceptance criteria for grinding:     The ground surface. The grindstone must have removed material from the whole width and the whole circumference of the seat. There must be no signs of blow-by. Max. grinding depth: must not exceed the limit

VALVE SEAT

●      The burnoff F1 of the valve spindle is checked by measuring along the spindle template from point A to point D and in point E.

●      The maximum seat grinding, gap G1 is measured between the spindle template, and the seating of the spindle with a feeler gauge.

Checks before mounting

Before mounting an overhauled exhaust valve in the engine, it is recommended that the valve is checked and prepared as follows: Check the oil level in the bottom of the air cylinder. Unscrew and remove the non-return valve and the safety valve. Fill oil into the non-return valve hole until oil fl ows out from the safety valve hole. Refi t the two valves again. Connect compressed air to the air cylinder to close the valve. Lift up the valve with the engine room Crane. Check that a 1.0 mm feeler gauge can be inserted about 15 mm into gap G3, to ensure that there is a clearance between the outer parts of the seating faces of valve housing and spindle. The valve must be able to stay closed for a minimum of 15 minutes or according to the dropdown test.

NOTE - If the air cylinder is fi tted with new sealing rings, the time the valve is closed may be considerably shorter than 15 minutes. The dropdown test should not be carried out until after a »running-in« period of 500 hours on valves with new sealing rings.