FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1918
1918 - 0967.PDF
AUGUST 29, 1918. Contrary to the usual German practice of building up thewater jackets of sheet steel acetylene-welded at the joints, the water jackets are michined from cylindrical steel forgings,which, as shown in Fig. 8, are screwed on to the flange machined on the cylinder head; the pitch of this thread is 1 mm.This screwed joint is finally sweated in position with soft solder, the whole depth of "the screwed portion having ap-parently been previously tinned; the joint is locked with four 6 mm. grub screws. The whole of the water jacket is machined both on theinside and also on the outer surface to a thickness of 1 mm. The water jackets extend to 104 mm. from the base of thecylinders, or, roughly to two-thirds of the total length of the cylinder barrels; but, as will be noted, the water spaceis exceptionally narrow—i.e.. 7 mm. The only water passages from the cylinder head to theannular water space of the water jackets is through the openings or passages cast in the cylinder heads encirclingthe sparking plug basses, and situated directly below the twin water connections. The formation of these water passages bolted to the inlet and exhaust ports of the cylinder heads to •stiffen up the engine. Pistons.—Very little alteration has been made to thegeneral design of the piston in comparison with the smaller Maybach engines. The pistons are of cast-iron, and weigh12.3 lbs. each, complete with rings. Four rings are fitted all above the gudgeon pin, the lower one being a scraper ring.All the rings are concentric, and are 6.5 mm. wide (vertically) and 5.5. "mm. deep, the depth of the ring grooves being6 mm. The pistons, as will be seen in Fig. io, are quite fiat on boththe top and bottom surfaces of the crown, which is 10.5 mm. in thickness. Eight 4 mm. return oil holes are drilled throughthe piston below the scraper ring in the usual way. The rings are cut diagonally at 450, no locating pegs beingfitted; and the width of the ring gap in the cylinder is 1.39 mm. = .055 in.All the piston rings are machine hammered on their inner, surfaces. This process, which is now extensively used, andis well known, consists gf subjecting the inside face of the ring Fig. 10.—Details of pistons, gudgeon pins, and floating small-end bushes. leading from the head of the jacket is made clear in the per-spective sketch (Fig. 9). The water jacket capacity of one cylinder - 1284 CCS.Fig. 8 shows an enlarged view of the lower joint between the cylinder barrel and the water jacket. This joint consistsof a soft rubber composition packing ring, compressed in position between two steel rings by a large ring which screwson to the bottom of the water jacket by a fine pitch thread in the manner shown in the sketch. This joint is, to a certainextent, flexible, and allows for the relative expansion between the cylinder barrel and the water jacket. Small drain plugs are provided at the bottom of eachcylinder water jacket; these are screwed into bosses welded into the water jackets on the exhaust side. The combustionchamber is circular, but it is slightly recessed below all of the four valve seats, which are all of the same diameter—i.e.,54 mm. «• The area of both the inlet and exhaust ports is 30.15 sq.cm. - 4.66 sq. in. The clearance volume of one cylinder — 778.9 cub. cm. —47.54 cub. in., giving a compression ratio of 5.94 : 1. Short pieces of aluminium tube are fitted over the topends of the lugs in the cylinder heads forming the valve stem guides. These are shown in Fig. 7, and are apparently pro-vided_for lubrication purposes. Thin sheet steel plates are to a series of mechanical hammer blows at gradually increas-ing distances apart. The process shows a large number of small transverse depressions, extending nearly the width of thering on the inner surface. These depressions caused by the hammer are approximately 1 mm. apart at the back portionof the ring—i.e., the part of the ring farthest from the gap— and increase in mathematical progression to about 4 mm. aparttowards the front of the ring up to about 1 in., on either side of the gap. This mechanical hammering of the'inside ringhas the effect of giving the desired uniform pressure to the concentric ring against the cylinder wall. The holes for the gudgeon pin are bored eccentrically in thegudgeon pin bosses, giving a thickness of metal of 14 mm. above and 9 mm. below the gudgeon pin. An oil groove iscut in the piston skirt below the gudgeon pin, evidently to assist the scraper ring and the piston lubrication. The insideof the skirt is machined up as far as the bottom of the gudgeon pin bosses, and a bevelled lip is turned on the' bottom flangeof the skirt. The inside of the piston is also machined flat across -the head, and down as far as the top of the gudgeonpin bosses with 15 mm. radius; an annular rib is cast on the inside of the skirt to reinforce the gudgeon bosses. Other details of the design of the pistons are given in thesection drawing Fig. 10. (To be continued.) 965
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
