A two-stroke engine stuffing box (gland box) is fitted around the piston rod where the rod passes through the diaphragm or the bottom of the scavenge air space, to separate the crankcase/oil space from the scavenge space and to prevent:

• blow-by of scavenge air into the crankcase;
• lubricating oil from the crankcase splashing up into the scavenge space;
• gas and oil from contaminating each other.

Principal components of a stuffing box:

1. Outer and inner brass (bronze) box housings/two halves forming the gland body, bolted together on the rod.
2. Upper (scavenge-side) sealing rings: typically two to three rings (often metallic, such as hardened steel or bronze) which prevent scavenge air passing down; these may be arranged as one set above and one below.
3. Lower (crankcase-side) rings that prevent oil passing up; there are usually a series of sealing rings in the lower part (oil scraper rings).
4. The space between the upper and lower ring sets is connected by drain passages to scavenge space and crankcase space, with a drain to a spill tank/drain tray so that oil and condensate can drain away.
5. In some designs the box has a small groove fed with oil (lubricating the rod) or relies on the low-level oil splash.

The piston rod sealing rings are split and held against the rod by their own elasticity or by a spring, and are located in grooves. The rings are numbered/oriented so that the split remains tight; the ring gaps are staggered.

Procedure to overhaul a stuffing box without removing the piston:

1. Isolate and secure the engine (stop engine, turn gear engaged or the unit locked), make it impossible to start, and isolate starting air and turning gear as per permit-to-work. Place warning notices on the bridge and in the ECR. Never rely on automatic systems alone.
2. Remove the crankcase/scavenge space door(s) in the vicinity of the piston rod.
3. Purge the scavenge space of any gas which could be flammable; ensure adequate ventilation and gas monitor.
4. Drain the oil from the scavenge space drain and any oil in the gland area, collecting spill in a drip tray. Keep the work area clean, wear oil and hazard protection, and have rags/fire precautions.
5. Half-turn or lock the piston rod in a defined position so the box is accessible. Loosen and remove the two halves (bolts) of the stuffing box housing. Care: the box is heavy; support it with suitable lifting gear. Withdraw the upper half first, then the lower.
6. Mark the parts and record the order and orientation of rings so they can be returned the same way. Remove the sealing/scraper rings.
7. Clean all parts, inspect the rod for wear, scoring, taper and cracks, and measure the ring/interior clearances and the clearances in the grooves.
8. Replace worn, broken or fatigued rings with new ones of the correct size and ring gap. Check ring gap and side clearance in grooves; stagger the gaps of the fitted rings so joints do not line up.
9. Reassemble in the reverse order, tightening the housing bolts evenly to the correct torque. On reinstallation, ensure the box is correctly clocked/aligned so the ring halves match.
10. Restore drain connections and re-fit the doors, then reinstate the permit-to-work, remove the locks and turning gear interlock, and test the engine on turning gear and subsequently at low speed, checking for leaks and correct oil level.

Tools required: ring spanners/socket set with correct torque wrench, drift/punches, brass or soft-faced hammer, seal/screwdrivers, feeler gauges and micrometer, ring expander tool, appropriate lifting gear/sling and eye-bolts, cleaning rags and solvent, drip trays, and personal protective equipment (overalls, safety footwear, gloves, goggles). Always comply with the confined space entry and permit-to-work procedures.