The invention thus relates to a guide means that finds use when fitting or removing a piston to or from a crosshead engine. There can occur in boats engines a fault that makes it necessary to remove a piston and then refit or replace the piston after having carried out any repair work required. In some instances, it may be beneficial to repair or clear a fault immediately, therewith requiring a malfunctioning piston to be removed and fitted whilst the boat or vessel is in motion. In the case of a piston change, the cylinder head of the engine is removed first, whereafter the piston can be lifted up with the aid of a winch.

When the engine is a crosshead engine, the piston will have a piston rod which is firmly connected to the piston and extends coaxially therewith. Before the piston can be lifted out, it is necessary to release the piston rod from the crank arrangement of the engine. The piston will often have cooling ducts with inlet and outlet ducts that extend down adjacent the piston rod.

The piston is liable to start to swing immediately after having been lifted from the cylinder barrel, for instance when the boat or vessel is moving through rough water. Such pendular movement of the piston is hazardous to any person in its vicinity, by virtue of the fact that the arms, hands, fingers of this person may become pinched, particularly between the upper part of the cylinder head and the piston rod. Such pendular movement of the piston rod may also result in damage to the cylinder lining. Personal injuries and material damage can also occur between cooling ducts and cylinder lining, in those instances when the engine includes cooling ducts. Furthermore, any cooling ducts that may be present can be damaged by direct contact with the cylinder as the piston swings whilst hanging from the winch.

The object of the present invention is to provide a new technique which reduces said risks and/or enables a piston change to be effected in a crosshead engine in difficult weather conditions.

This object is achieved with a guide means according to Claim 1.

In one preferred embodiment of the invention, a guide is fitted to the free end of the piston rod. This guide has a small clearance relative to the cylinder wall and restricts the possibility of pendular movement of the piston rod/piston after the piston/piston skirt has been lifted out of the cylinder barrel. When the support plate is lifted up over the cylinder barrel, any cooling ducts present will also have essentially left the cylinder barrel.

Although it is true that the piston/piston rod are free to swing, the important fact is that the wall of the cylinder barrel will not form an anvil for the pendulous piston rod and that in this stage of the proceedings lateral movement of the piston is controlled with the aid of a stop abutment.

It will be noted that any cooling ducts present will be protected from contact with the wall of the cylinder barrel. The guide is suitably mounted on the piston rod beneath any cooling ducts present in the scavenging air space beneath the cylinder.

Further embodiments of the invention will be apparent from the accompanying dependent Claims.

The invention will now be described in more detail by way of example, with reference to the accompanying schematic drawings.

Fig. 1 is a partially sectioned view of a crosshead engine fitted with a guide means in accordance with the invention.

Fig. 2 is a side view of the guide means fitted to the piston rod.

Fig. 3 is a plan view of the guide means taken on the line 111-111 in Fig. 2.

Shown in Fig. 1 is a cylinder I that belongs to a two-stroke diesel engine of crosshead design. Mounted in the cylinder 1 is a piston 2 to which there is affixed a piston rod 4 whose bottom end b is a crosshead 5 which is guided in a guide 6 that extends coaxially with the cylinder 1, the piston 2 and the piston rod 4. The crosshead 5 carries a bearing 7.

The engine 2 includes a crank shaft that has a crank 8 which rotates about the shaft 9. A link arm 10 connects between the crank 8 and the crosshead bearing 7.

It can be assumed that the cylinder head 12 shown in chain lines has been removed and that a hook 20 belonging to a winch 21 has been hooked firmly to the piston 2 with said piston in its upper end position.

An operator is able to enter the scavenger air space 30 located beneath the cylinder 1 under the piston 2 through an opening 31 in the cylinder, with the aid of a trunk line, not shown.

Fig. I also shows two conduits 41, 42 which extend down from the piston 2 and which function respectively as a supply conduit and an exhaust conduit for coolant transported through the piston 2 for cooling the piston during running of the engine. An operator is able to fit a guide means 50 to the bottom end part of the piston rod 4, beneath the ends of the conduits 41, 42. The scavenger air space 30 is conventionally terminated downwards by a bottom diaphragm or membrane 48, to prevent sparks, etc., from landing in the crank housing.

As will be seen from Fig. 1, the guide means 50 of a preferred embodiment is formed by a disc whose periphery lies in the proximity of the inner wall surface 11 of the cylinder 1. If the piston 2 is now lifted up by the winch 21 as the vessel is in motion, interaction between the peripheral edge of the guide means 50 and the inner wall 11 of the cylinder will ensure that the piston rod 4 remains generally coaxial to the cylinder 1 even when the piston 2 (i. e. the piston skirt) has been lifted above the top edge of the cylinder 1. This prevents the piston 2 from swinging dangerously as it is lifted up and therewith avoids damage to the conduits 41, 42 as a result of being struck against the cylinder 1. Contact between the piston rod 4 and the cylinder wall 1 above the guide means 50 is also prevented. When the piston 2 has been lifted to a height at which the guide means 50 lies in the proximity of the upper edge of the cylinder 1, the piston rod 4 will be exposed above the cylinder 1 therewith enabling the operator to prevent pendulous movement of the piston rod.

Interaction between piston 2 and cylinder 1 can no longer take place, when the piston rod 4 is completely free from the cylinder 1.

In the illustrated case, the guide means 50 has the shape of a disc 52 which is divided diametrically into two equal parts 51. The guide means 50 has a circular peripheral edge 54 whose diameter is slightly smaller than the free diameter of the cylinder 1. The disc-shaped guide means 50 also includes a central hub 55 and radially extending stiffening ribs 53

which stabilise the disc 52 and the hub ring 55 and extend out from the hub to the peripheral edge 54 of the disc.

As evident from Figs. 2 and 3, each disc half 51 includes stiffening ribs 53 that terminate at the joining plane of the disc parts 51. This enables the edge ribs 53 of the disc parts 51 to function as mounting flanges. These flanges will include mutually aligned holes that receive bolt joints 60. The hub is dimensioned to be clamped firmly on the piston rod 4 as the bolt joints 60 are tightened.

The primary purpose of the guide means 50 is to keep the bottom end of the piston rod 4 centred in the cylinder 1. This means that the guide means may have many different forms.

The important thing is that the guide means can be fitted to and removed from the piston rod easily and that it restricts possible pendulous movement of the piston rod in the cylinder 1. The guide means may also comprise a number of support arms that extend from the hub so as to support against the cylinder wall 11. In an extreme case, it may suffice with generally diametrically opposed radial arms whose supportive ends terminate in the close vicinity of the surface 11 of the cylinder wall. In practice, embodiments are preferred in which the support means has the form of a disc whose circular peripheral edge has a diameter that is slightly smaller than the diameter of the cylinder wall 11.