CYLINDER HEAD/ CYLINDER/PISTON

Transcription

1 G":nHONDA NU50 NU50M 6. CYLNDER HEAD/ CYLNDER/PSTON SERViCE NFORMATON TROUBLESHOOTNG CYLNOER HEAO CYLNOER/PSTON SERVCE NFORMATON GENERAL All cylinder head, cylinder and piston mainlenance and impection can be done with engine installed, Belore disjssernbly. clean the engine to prevent dirt and dust rorn entering the cylinder and crankcase. Remove i'lil gaske1 material from lhe mating surfaces of the cylinder head. cylinder and crankcase. SPECFCATONS TEM Cylinder head warpage Cylinder bore p. 0 0 (4 mm from bottom of Hon.. piston skirtl Cylinder-e-piston clearance Piston pin hole 1.0. Piston Dm 0.0. PistorHo'p1ston pin cle<lrancc Piston ring end gap (top, second) Connecting rod small end 1.0. STAN DAR 0 mm M::-', 0.10 (0.004) O.OOB , ( ) ( ) ( ) ( ( ) ( ) ( l ( ) ) (1.5709) (0.0039) (0.3949) (0.3925) (0.0016) 0.60 (0.024) ( TORQUE Cylinder bolt: TROUBLESHOOTNG CompreSSion too low, hard starting or poor performance ilt low speed 1. Blown cylinder head gasket 2. Loose spark plug 3. Worn, s1uck or broken pistoll rings 4. Worn or damaged cylinder ilnd piston 5. Faulty feed valve Compression too high, overheating or knocking Abnormal noise piston 1. Worn cylinder and piston 2. Worn piston pin or piston pin hole 3. Worn connecting rod small end bearing Abnormal noise 1. Worn, stuck or broken piston rings 2. Worn or damaged cylinder 1. Excessive carbon buildup in cylinder head or on piston top Date of ssue: Nov., 198t HONDA MOTOR CO.. LTD. 5J 6-1

2 NU50 NU50M CYLNDER HEAD CYLNDER HEAD REMOVAL Remove tile spark plug cap. Remove the bolts attaching the choke control box and remove lhe control box. CHOKE CONTROL BOX SPARK PLUG CAP Remove the four cvlinder head bolts. and the cvlin del head. CYLNDER HEAD BOLTS CYLNDE R HEAD NSPECTON Check the cylinder head for warpage with a straight edge and feeler gauge in the directions shown. SERVCE LMT: 0.10 mm (0.004 in) Date of ssue. Nov., 1981 HONDA MOTOR CO., l TO

3 NU50 NU50M CYLNDER HEAD/CYLNDER/PSTDN CYLNDER HEAD DECARBONZNG Remove the carbon deposits from the combustion chamber. Clean the head gasket surface of any gasket material. AmjJ dajnugillg the combustion chambf!t "'Oil alld guskn surfaces. Remon' corbo" deposits from tile pisloi head. CYLNDERj PSTON CYLNDER REMOVAL Remove the exhaust muffler by removing the attaching bolts and nuts. Remove the cylinder. Do 10f pry bt:\'c('11 {h! cylinder olld crallkcase or strike fhe /ills. CYLNDER Date 01 ssue: Nov., 1981 V HONDA MOTOR CO., l TO_

4 CYLNDER HEAD/CYLNDER/PSTON NU50 NU50M PSTON REMOVAL PSTON Remove lhe piston pin clip using a pair of pliers. Press the piston pin out of the pislon. Do 1101 damage or uralch tilt! piston. Do nat apply side force D the collnectillg md. 1)t) nor lei the fall illfo aallkcl1se. PSTON PN PSTON PN CLP PSTON RNG/EXPANDER REMOVAL Remove the piston rings. NOTE Spread each piston ring and remove by lifting it up at a point just opposite the gap. Remove the expander. SECOND EXPANDER./ / \ \.-11, \ '0 1< :,7 J U TOP RNG CYLNDER/PSTON NSPECTON Check i'll' cylinder and piston for wear or damage. Clean carbon deposits from the exhaust port area. 6-4 Dale of ssue: Nov., 1981 HONDA MOTOR CO.. LTO

5 CYLNDER HEAD/CYLNDER/PSTON nspect the cylinder bore for wear at three levels in X and Y directions. Take the minimum figure measured to determine the cylinder wear. Avoid the pon area. SERViCE L1MT:'40.0S0 mm t in) CAUT,O"N"-c_,- ---, The cylinder has U A or B mark 011 the (:f(l/lk ras,' mating surface as show1l. /hell the cylinell'( is {O b.' r,'placeu Willi (J t'w olle. use (J Cylifldt'f Ul"ilK the sallie //lurk as the uld Ollt!. Mi!asure the piston 0.0. at a point 4 mm from the bottom of the skirt and 90 0 to the piston pin hole. SERVCE LMT: mm ( in) Calcul<ltc the piston-te-cylinder clearance SERVCE LMT: mm ( in) Measure he piston pin hole.d. SERVCE LMT: mm ( in) Measure the piston pin 0.0. SERVCE LMT: mm ( in) PSTON P N HOLE.D. ot PSTON PN 0.0. Dille of S5ue: Nov., 1981 HONDA MOTOR CO. LTD

6 CYLNDER HEAD/CYLNDER/PSTON NU50 NU50M PSTON RNG NSPECTON Measure each piston ring e[lel gap. SERViCE limts: TOP/SECOND: 0.60 mm (Q.024 in) PN PSTON RNG,,\ NOTE Sct each piston ring squarely into the cylinder at a point 30 mm (1 '-:' in) from the bottom using the piston and measure the end gap. CONNECTNG ROD NSPECTON nstall the bearing and piston pin ir. the connecting rod small end and check for excessive play. Measure the connecting rod small end 1.0. \ / / i i SERVCE LMT: mm ( in) PLAY 1.0. PSTON/CYLNDER NSTALLATON Clean the gasket surfaces of the cylinder and crank case Date of ssue: Nov., 1981 HONDA MOTOR CO., LTD"

7 r;;nhonda NU50 NU50M CYLNDER HEAD/CYLNDER/PSTON nstall the ClCO<Jnder in the second fing groove. Align the ring ends with the locating pins in the ring grooves. PSTON nnall the lop and second rings in heir respective ring grooves with the markings facing up. The top ril/g is Q keyslo/l! ring and is 1/01 imercllt1llgeqhle Willi till' U/llure rillg. Check he fit of each ring n lis groove by pre5$ing the ring inlo he groove 10 make sure lhal i is ffum lnlth he p.ston al several points Mound the ring. A flor that Wll not comp'ess means that the rmg groove is dirty and it should be Cleaned. EXPANDEA SECOND RNG Do /Ol replace (m/! ril/g \.-irjlolil rep/acing lht! mill'" EXPANDER,- JR PSTON RNG MARKNGS- H: TOP 2T: SECOND j -,,-J Be sure the ring end gaps 3fC aligned with the piston ring pms in the ring grooves. Date ollnue: Nov., 19B1 () HONDA MOTOR CO., LTO

8 CYLNDER HEAD/CYLNDER/PSTON a HONDA NUSO NUSOM nstall the nm:dle in the r.onnectin9 rod, ilnd the piston with tilt! plslon pin. " pistvl1 with file "Dt''' mark [acing-1 the e;l:halls1 sit/e. Dip the pisw/ pill ill dean uil bcfnre ;lslajoliol1. nstall new piston pin clips. PSTON PN NOTE let the clips tall into Place the cylinder gasket all the nankcase, Lubl'ici11e the piston a,,(j cylinder with 2-stroke oil and install the cylinder over the piston while compressing the piston rings. GASKET CYLNDER CYLNDER HEAD NSTALLATON nstall the cylillder head on the cylinder using a new cylinder head gasket. nstall ilnd lighten the lour cylinder head bolts. TORQUE: 8-12 N m ( kg.rn. 6-9 ft lb) nstall the spark plug and spark plug cap. J f t ' Date of ssue: Nov., 1981 CD HONDA MOTOR CO., LTD.

9 NU50 NU50M CYLNDER HEAD/CYLNDER/PSTON nstall the choke conuol box. ljefoff' installillg rll;' colllrol box, dea" (he (')'linder head //utillg mrla"c' horouithly. CHOKE CONTROL BOX SPARK PLUG CAP nstall the muffler. Perform the following nspections: Compression test (page 3 7) Check; fof abnormal engine noise.. Check for cylinder air leaks. EXHAUST MUFFLER Dale of ssue: Nov., 1981 HONDA MOTOR CO., LTD