SECTION 8

MotorBlokken

BESKRIVELSE

Dette kapitel indeholder de nødvendige oplysninger for at servicere motorblokken og de tilhørende komponenter. Der behandles udelukkende mekaniske dele; detaljer om karburatorere og brændstofsystemet behandles i sektion 6, Fuel System; tændingssystemet behandles i sektion 7, Ignition System.
Her bliver det fortalt, hvordan man adskiller motorblokken, hvordan man skal afmontere, reparere og genmontere dens forskellige komponenter, og hvordan man samler den igen. Hvordan man tager motorblokken af motoren og geninstallerer den dækkes i sektion 5, eftersyn Procedures.

SERVICERING AF MOTORBLOKKEN

På Johnsons 2–cylindrede motorer er cylindrene anbragt lodret, den ene over den anden. Forbrændingerne er indstillet således, at hver cylinder giver en forbrænding for hver omdrejning af krumtapakselen. Det frembringer en impuls for hver 180^o af akselens omdrejning.

KRUMTAP og CYLINDRE

Den 2–cylindrede motors krumtaphus er opdelt i 2 ens afdelinger, som er adskilt af det centrale hovedleje. Hver cylinder og dens krumtaphus trækker brændstofblanding gennem hver deres individuelle bladventil, monteret på en fælles ventil–samleplade (se figur 8–2). Krumtaphuset er delt langs krumtappens centerlinie. Den bagerste halvdel er en del af cylinderblokken, mens den forreste indeholder udtagelige bladventiler, indsugningsmanifold og tilslutning til karburatoren.

CYLINDER HOVEDER

STEMPLER

Stemplerne får kraft fra de eksploderende gasser når blandingen af luft og brændstof bliver antændt i cylinderen, og overfører kraften til krumtappen gennem plejlstængerne. For at opnå maximal kraft er stempler, ringe og cylindre tæt tilpassede for at forsegle forbrændingskammeret. Cylindre og stempler skal være perfekt runde og stempelringe anbragt korrekt i deres riller.

PLEJLSTÆNGER, KRUMTAPPE OG LEJER.

Plejlstængerne er forbindelsen mellem stemplerne og krumtappene. Hovedlejer er forskellige på de forskellige modeller. Friction og anti-friction type main lejer are used selectively on the various models. De består af indfældede bronzelejer eller tromler. These consist of cast-in bronze lejer, roller or hall lejer. Indlejrede nåle–lejer bruges i den smalle ende af plejlstangen. Split cage roller or needle lejer are used selectively on crankpins og center hovedleje. Needle or roller type main lejer are locked in place by a dowel pin. Udskiftelige oliepakninger bruges i de øverste og nederste stift, rulle eller kugle type hovedlejer for at kontrollere smøring og forhindre tab af kompression i krumtaphuset.

KØLESYSTEMET

Vand sendes gennem cylinderen og cylinderhovedets vandkappe af en vandpumpe, som er placeret nederst i motorbenet. Thermostater bruges på nogle modeller for opretholde en konstant arbejdstemperatur gennem hele arbejdsområdet. Termostaten bremser vandets cirkulation i motorblokken indtil der opnås en arbejdstemperaturen på 145^o F. (se Figur 8-3). For at undersøge kølesystemet for korrekt temperatur kontrol kan man benytte en »Markal Thermomelt Stik«, en varmefølsom pind i retning af en blyant, som smelter ved kontakt med en overflade med en specifik temperatur.

Der skal bruges 2 »Thermomelt Stiks« – en 125^o F. Stik og en 163^o F. Stik (se Figur 8-4). Det er bedst at undersøge motoren når den arbejder på en båd. Men hvis man afprøver motoren i en tank skal man bruge en test–propel og lade motoren køre i mindst 5 minutter ved en omdrejningshastig på 3000 omdrejninger pr. minut. Afprøv cylinderen med en 125^o F. Stik. Hvis den ikke smelter inden for en rimelig tid er thermostaten permanent åben, og motoren arbejder for koldt. Hvis en 163^o Stik smelter tillader kølesystemet motoren at blive overophedet. Hvis der observeres overophedning bør man se efter om pumpen er slidt, om der er læk i kølevandsystemet, tilstoppet vandindtag, fejlbehæftet termostat, eller om udstødningsgasse siver ind i kølesystemet.

TO-CYLINDER MOTORER

1. Aftag cylinderhovedet og cylinderhovedets pakning.
2. aftag by-pass covers og pakninger, og exhaust covers og pakninger. NOTE: hvis pitting is found on inner or intermediate exhaust cover plate, be certain to install a new plate on samling.
3. Loosen clamps og aftag oil return hose, hvis used, from krumtaphus (see Figure 8-6).
4. Drive taper ping out of krumtaphus og cylinder block assembly (see Figure 8-7). Taper ping must be driven from back of krumtaphus toward front. aftag screws attaching krumtaphus to cylinder block. Tap top end of krumtap with rawhide mallet to break seal between krumtaphus og cylinder. Lift krumtaphus from cylinder block.
5. aftag oil drain valve, hvis used; from krumtaphus for rensning og inspektion (see Figure 8-6).
6. Straighten plejlstang screw lock plate tabs, hvis used. NOTE: hvis tabs break off, they must be found so that in samling they do not remain in engine.
7. aftag plejlstang caps og needle lejer.

   CAUTION!

   stempler, plejlstænger, og caps are matched parts og seat with operation of motoren. Because of this, it is essential to maintain their original positions at samling. Mark each plejlstang og cap, stempel, og bearing component to assure correct mating when they are reassembled. Always replace plejlstang caps on rods before removing rods og stempler from cylinders (see Figure 8-8).
8. aftag krumtap og lejer from cylinder block. aftag stempler og rods from cylinders, marking each stempel og rod to assure correct samling.
9. aftag rings from stempler by prying ends loose enough to grip them with pliers og breaking them away from stempler. DO NOT try to save rings even when they are not stuck. Install a complete set of new rings on every power head eftersyn.
10. aftag wrist pin retaining rings. Press wrist pin through to free stempel from plejlstang.

    CAUTION!

    One side of stempel is marked "L" or "LOOSE" on inside (see Figure 8-9). Loose side of stempel must be up og pressing tool must be applied to loose end when removing wrist pin. Be careful not to distort stempel.
11. Clean, inspect, og reparation or replace power head komponenter as described under "rensning, inspektion, og reparation."

Proceed slowly. Make no forced assemblies unless press fits are called for og make no "dry" assemblies. Be sure all parts to be assembled are clean og free from dirt og grit. Perfectly good cylinder walls, stempler og rings can be ruined in a few minutes of operation unless all forms of grit are removed before assembly. Work in clean surroundings og with reasonably clean hands. Coat all bearing surfaces, cylinder walls etc. with clean oil before assembly. Always use new pakninger throughout when reassembling the power head.

1. The relative positions of stempler, plejlstænger, og cylinders must be considered when assembling stempler to rods. stempler must be installed in cylinders with intake side of deflector toward intake port s (see Figure 8-31). Oil hole in plejlstang must be toward top of motor (see Figure 8-32).
2. Apply coat of oil to wrist pin, making sure surface is clean. Place a drop or two of oil in each pin hole in stempel. Oil wrist pin bearing in plejlstang.
3. Insert wrist pin through slip tit side of stempel. Place plejlstang, with bearing (hvis used), in position og install wrist pin. This can be accomplished more easily hvis stempel is heated slightly, causing it to expand.

   CAUTION!

   One of the stempel bosses is bored for a slip fit on the wrist pin og the other for a press fit. When installing the wrist pin, press from the side marked "L" or "LOOSE". Use an appropriate fixture to guard against distortion or damage during the operation.
4. Install wrist pin retaining rings, making certain they come to rest in the grooves provided for this purpose.
5. Check stempel with micrometer to determine whether stempel has been distorted during assembly (see Figure 8-33). hvis slightly out-of-round, tap high side with light mallet (DO NOT use hammer) to restore original roundness (see Figure 8-34). Proceed carefully og caliper frequently until stempel is rounded out.
6. Install stempel rings. Spread each ring with a ring expander just enough to clear stempel head (see Figure 8-35). Be sure rings fit freely in stempel ring grooves, og that ring gaps are aligned with dowel ping in ring grooves.

1. Coat stempler og cylinder bores with oil og install stempel og plejlstang assemblies in cylinders, being sure to install each stempel in cylinder from which it was removed. Intake (straight) side of stempel deflector must be placed toward intake port. Make certain that rings are correctly positioned in grooves with respect to groove ping. Damaged stempler og broken stempel rings may result from imperfect alignment of ring gaps og stempel dowel pins. stempel rings must be compressed before stempler can be installed in cylinders. Use a stempel ring compressor (see Section 15, Special Tools), or compress the rings by band.
2. aftag caps from plejlstange. Place plejlstang liner (hvis used) on plejlstang og cap, making certain that dovetail ends match.
3. Place retainer (hvis used) og half of bearing needles on each plejlstang, using OMC Needle Bearing Grease to retain needles during assembly. NOTE: See Needle Bearing Chart at the end of this Section for the number of needles used in each needle bearing.
4. Place krumtap og lejer into position on cylinder block. Install retainer half (hvis used) og remaining needles on crankpins, using OMC Needle Bearing Grease. Make certain that journal lejer are aligned with dowel pine (hvis used).
5. Attach plejlstang caps, using new lock plates. plejlstang caps are not interchangeable with those of other rods, neither may caps of the same rod be turned end for end. To assist correct assembly, small embossings are provided on matching sides of rod og cap. Check cap alignment by drawing a pencil over edge surface on both sides of rod (see Figure 8 - 36). hvis not aligned, offset edge can be felt with pencil point. Check whether all needles are in place (5 HP, 6 HP, 9-1/2 HP only) by inserting a small rod or wire through oil hole in cap. It will not be possible to touch wire to crankpin hvis all needles have been assembled.
6. Tighten plejlstang screws to torque specified in Section 5, eftersyn. Check movement of plejlstænger on crankpins. Rods must float freely over full length of crankpins after tightening screws. Bend lock plate tabs up to prevent screws from loosening og backing out. NOTE: DO NOT adjust position of screw hvis tab does not fit against flat on screw. Lock plate tab MUST be made to conform to screw.

1. Make certain that all krumtap journal lejer og pakninger are in position. Apply a fine bead of Sealer 1000 to krumtaphus face. DO NOT over-cement; excess will squeeze over to foul oil channels, etc. There should be a thin line of cement between screw holes on inside edge of machined surface.
2. Install a new krumtaphus seat (hvis used). Cut the new seat somewhat longer than necessary to obtain a good butt seal at both ends. Run a fine bead of Sealer 1000 in seal groove to secure seal in position while trimming. After cement has set, trim ends of seal for 1/32 inch overhang.
3. Position krumtaphus half og install krumtaphus taper ping, driving in carefully with a hammer. Install attaching screws og lighter to torque specified in Section 5, eftersyn.
4. Install intake by-pass covers (hvis used), using new pakninger. øverste by-page cover has tapped holes for mounting of fuel pump.
5. Install exhaust covers, using new pakninger. Install all screws finger tight before tightening screws to torque specified in Section 5, eftersyn.
6. Install cylinderhoved, cylinderhoved cover (40 HP), og pakning. Tighten cylinderhoved screws to specified torque, following correct sequence. NOTE: Re-torque cylinderhoved screws after motor test has been completed og motor has cooled off.
7. Install oil drain valve (hvis used) og check for proper clearance under leaf stop (.023 to .039 inch). Install oil return hose (hvis used), og tighten clamps with pliers. Install new øverste hovedleje oil seal, using seal seater (see Section 15, Special Tools).
8. Assemble power head to motor as described in Section 5, Eftersyn.