HuldlAses yeys 190ueTeg Hurury OOPZ PIesemey«Workshop -43 Balancer shaft service Stripping and reassembling engines with balance shaft arrangements involves certain procedures particular to their type. Here we show how to tackle a bottom end overhaul on the relevant models made by the big. four Japanese manufacturers. Honda 360 vertical twin Balance shafts are used in some engines in order to make the motor smoother by damping out vibration and so provide the rider with a more comfortable ride. Most single cylinder and parallel twin engines counterbalance the reciprocat- ting mass of the piston and upper cor necting rod assembly with a weight in the crankshat (see pages 56 59). How. ever this alone is only partly successful in reducing vibration and manufactur- ers have to resort to other means to reduce its effect further. Engine mount- ing arrangements such as Norwon’s Isolastic mountings, and other vibration damping details, such as rubber mount- ed handlebars, are some examples. One solution to this problem is the use of counterbalancing shafts, fitted in the crankease and driven from the crankshaft. The shafis are fitted with out-of-balance weights which generate their own forces when rotated to act in 1324 Chain driving front and rearbalance shafts Balance shaft 1. ‘The CB400T has balance shafts placed fore and aft of the crankshaft, ‘They are chain driven opposition to those set up by the crank- shaft. Thus the two forces effectively cancel each other out, Of course the forces still exist so the crankcase must be rigid enough to contain them and let them act against one another. In practice there are two means of arranging balance shafts in an engine, depending on its design. In the first case there is the single and the 360 degree parallel twin cylinder engine which both share the same balancing problems. Such twins are more likely to suffer from vibration because they run at a higher crankshaft speed, usually have a larger capacity and probably a less rigid crank- case structure, However, the even firing of the twin may be an asset. For these types of engine two balancing shafis are necessary, both rotating in the opposite direction to the crankshaft. In the second case, where a 180 degree crankshaft layout is used for a parallel twin, the design problem is ifferent, and the reduction in vibration can be obtained with a single shat, with two balance weights on it, running in either direction. On a 4-stroke engine the 180 degree layout gives an uneven firing interval but this is acceptable and common practice on many twins whether they are fitted with balaneer shafis or not (fig. 2). Counterbalance shafts are always fitted in the erankease of the engine and when two are used they are situated in front and behind the crankshaft, The shafis may not be in a direct line with each other, and usually one lies on the horizontal crankshaft axis and theother is offset: this layout assists further cancelling out the minor out-of-balance forces. In most cases access to the balance shafis is obtained by splitting the crankease in the normal manner so that if work needs to be carried out on items such as the crankshaft or bearings, the balance shafi(s) can be dealt with at the same time. In some cases the balance shafis have to come out before the crankshaft can be removed, but ifnot it makes sense to remove and inspect the balance assembly parts anyway, having already carried out so much of the dis- mantling work. It may also be neces- sary to strip the balance shafts or their drive because of faults in them, and, of course, if this happens the opportunity should be taken to inspect all the other items which have to be dismantled at the same time, Balance weights run on bearings and these can wear after high mileages, and the shock absorber mechanism, which usually incorporates springs or rubber blocks, can also deteriorate and thus need renewing. In most cases the shafts are chain driven and some form of ad- juster is built in to enable the chain free play to be set. Although the chains operate under ideal conditions and should have a very long life, it is always possible thata fault has arisen requiring the chain to be renewed. Splitting the crankeases All the Japanese engines currently using balancer shafts have crankcases which splithorizontally. Splitting horizontally is dealt with on pages 1079-1083, and rebuilding is detailed on pages 1110Suzuki 180 vertical twin wp 2. ‘The Suzuki GS425 has a single gear-driven balance shaft in front of the crankshaft 3. On the Honda X1250 removal of the 4, To gain further access, remove the clutch cover reveals the balance ‘clutch unit and the primary drive ‘weight at the top right hand corner drive gear from the casing 1115. In nearly every case you must drain off the oil and remove the engine unit from the frame (see pages 618-624 and 647-652). The exception is the Yamaha XS500 whose balance shaft can be removed with the engine in the frame. Check whether the top half of the engine requires to be disturbed because on many engines the balancer shafts and their drives can be removed without touching the head or the barrel. Take the plugs out so that the engine can be turned over more easily and remove the side covers from both sides. Only dismantle any items which will prevent the lower half of the crankcase coming away. Thus the clutch, primary drive, generator and gearchange mechanism can in most cases be left in place. ismantling the shaft mechanism The simplest balance shaft to dismantle isthat on the Yamaha XSS00 which can be removed while the engine is still in the frame. To do this first remove the rotor, starter chain and the outer brac- ket from the left side of the engine and the clutch from the right side. This will allow access to the single balance shaft drivechair, Access to every other balance mech- anism requires a crankcase split. In all cases, however, there is no need to dis- turb the upper engine assembly. First remove the lower crankcase half. At this stage it is necessary to make a note of the position of the balance shafts id_weights in relation to the crank- This is vital as they must be placed in exaetly the right position on or the engine timing will be thrown out Now remove the oil pump drive gear and the intermediate gear followed by the oil pump unit Continued 13256. Removal of the generator cover 7. A special extractor is needed to 8. Turn the engine over to check that all reveals the generator fiywheel. The dislodge the flywheel. Do not try to the timing marks are located on the stator remains in the cover tap it free with a hammer chain and sprockets Kawasaki Z400 ‘aance weight bot —— > component parts i tas ‘ence weight <4 tatace shay 4 chan Sorocet ——— Pnge pin a ri wight ring Bearing Hock 9. Very few of the components in the [-- & balance shaft assembly are stressed ‘Bot ——4] and this ensures reliability. , 1326The details of chain removal vary from bike to bike. On the Yamaha XS$500 the drive chain runs over four sprockets: a driveanda driven sprocket arranged in pairs. The sprockets have alignment dots and you must make a note of their position, On the Suzuk GS400 and GS425 the single balance shaft runs across the front of the engine on the split line and is gear driven by the crankshait. Itisaligned by dot markings on the balance shaft driven gear and the crankshaft driving gear. Honda and Kawasaki employ two balancer shafts fitted either side of the crankshafis on some of their models, notably Honda's le cylindered XL250, XLS00, XR- 250 and XRS500, the 360 degree parallel twin CB250T and CB400T and the Kawasaki 2400. On the Kawasaki make note that the balanceshaftsare aligned when the two bright links in the drive chain align with the punch dots on the drive sprockets when the webs on the balance weights and the crankshaft point downwards (fig. 20). In this posi tion the pistons are at TDC and the oil holesin the main journal are just visible. On the Honda twins you must align the “TC” line on the front weight and the ‘TH’ on the rear weight with the hori zontal line of the crankcase split while the weights are horizontal and the “B' mark on the crankshaft is also aligned with the case split line (fig. 19). Once you have noted the con balance shaft alignment you can pro- ceed to dismantle the shaft(s) and weights. On the Suzuki GS400 and GS425 the balance shaft lifts straight out of the crankease. Once the whole assembly is out of the crankcase simply pull the tivo ball races off the end of the balancer shaft and pull off the driven gear which incorporates the torsion damper. On the Yamaha X$500 first pull out the upper jockey sprocket shaft. This will release the now you can remove the free sprocket. Undo the retaining nut and lock washer and remove the balance shaftsprocket which, asin the Kawasaki system, contains a damping mechan. ism, Next remove the circlip which retains the shaft bearing on the right side of the crankcase, pull the bi out, and then push the whole bala shaft out through the right side. You can then pull out the bearing behind the drive sprocket. On the Honda twins you must first remove the oil strainer. This frees the rear balancer shaft which thea simply pull out. Next ng retaining chain and anning loosen the support cas bolts evenly to avoid distorting the casting, and remove the casting. Lift out therear balance weight and label it along with the rear shaftto avoid confusion on Extracting the balance weights 10. To split the eases, remove the retaining serews and tap the ca: apart. Take care of any dowels 12. To remove the front shaft extract the circlip that retains the drive gear in place 14. The gearbox layshaft and the front shaft drive sprocket can now be removed as one unit reassembly. The front balance weight is mounted on an eccentric shaft whic is used to adjust the chain tension. The chain tension adjusting mechanism comprises a spring which is keyed into the shaft. Pressure on the chain can be adjusted by looseninga clamping nut on 11. The balance assembly remains in the upper half. This engine has a second weight on the gearbox layshatt 13. Hold the gear in one hand and pull the shaft out of the casing from the the right. Take note of any shims The shaft can now be pulled out of. holder, Note the location of the bearings and shi the adjusting quadrant which i fixed to an arm splined to the front balance shaft. Remove the clamping nut and take off the spring on the other end of the ft. Make a note of exactly how the spring fits to the-crankcase and the shaft. Then simply withdraw the bal-16. The shaft and its component parts are now ready for inspection. This varies according to the model ance shaft from the crankcase. This will free the front balance weight and the drive chain. Remove these from the crankcase and label them both to avoid any confusion The Kawasaki 2400 and the larger 2750 feature two chain driven balance shafts running in a pair of blocks either side of the crankshaft, First pull away the centre main bearing to allow ace to the balance chain and its guide. Pull off the four support blocks and then 17, Examine the bearings for excessive rattle. If the shims or location washers show wear, replace them carefully lift away the whole assembly. ‘You should remove each balance weight in turn toavoid mixing up the parts. Pull away the balance blocks and removethe shims and thrust washers carefully noting their position. Next tap the drive sprocket off the balance shaft. There is no need to unbolt the balance weight from the shaft untess the shaft is worn. ‘Once you have dismantled the bal- ance assembly you can continue by examining it for wear or damage. Honda CB 400T balance weight timing [— Crankease spit tne Front balance shaft tiring mark 19, Line up the front weight TC mark and the crankweight mark with the crankcase split line. The TH mark on the rear weight must also line up with the bearing holder shoulder 1328 Flywheel pcinting in same direction as balance weighs 18. Check the splines in the weights and on the shafts for cracks oF wear. Replacement is the only cure Examining the balance shafts The main areas for attention on the balance shaft assemblies are the shaft bearings, the drive chain and the damper ‘assemblies. To check a ball race for wear first clean it in paraffin then, holding the centre between your thumb and forefinger, spin it while listening for a rattling noise. Renew the bearings if they are worn, Shake the sprocket and the spring damping mech- anism on the Suzuki GSs, Yamaha X$500 and Kawasaki's 2650 and 2750. Ifthe springs rattle dismantle the dam- per and renew the springs. On the Hon- da twins you must remove the balance ‘weights from the shaft to gain access to the damper mechanism. Make @ note of the position of the balance weight in relation to the drive sprocket. Punch markson both components show align- ment. Remove the circlip which secures the parts together and inspect therubber damping blocks. Renew them if they are damaged in any way. If the drive chain has streiched to the end of its adjustment you must renew it Reassembly In most case reassembly is a straight- forward reversal of the dismantling process. If you have taken the drive sprocket off the balance shafi(s) note that it is keyed on. Also take care to locate the balance shaft bearings pro- perly ~ in most cases there are locating pins which fit into the crankease. ‘On Honda twins first refit the front balancer together with the shaft tension spring, To tension this wind the shaft three quarters of a turn in an anti- clockwise direction. Next lay the rear balance weight in the drive chain and assemble it" into the support casting. ‘Then insert the rear shaft and check the balance shaft timing. Fit the oil strainer noting that one of the securing boltsKar i ‘imi On the Yamaha XS500 take care to wasaki 2400 timing Ineate the bearing pin correctly and do Lighter link not forget to refit the right side bearing circlip. The balanee shaft sprocket only fits in one position and the correct tim- Teyog mark ing is achieved by positioning te érive qn bance chain. Refit the two idler sprockets and > weranisprorket then recheck the timing. With the balance shaft assemblies refitted you can continue to rebuild the engine and refit it into the frame. Lighter link Flywheel Timing mark In all cases except for the Yamaha XS500 you must refit the engine in the frame: for details of this see pages 677 680. When reassembling the parts always oil them generously, especially bearings, which can suffer serious dam- age if left without oil even for just a few moments. Before you start the engine turn it over by hand and see if it turns freely with no strange noises. 20. Align the bright links in the ehain with the marks on the sprockets when the flywheels point upwards locks the rear balance shaft On the Kawasaki Z400 first fit the balance weight assemblies together with the bearing blocks and then mesh the chain so that the two bright links align with the dotson the sprockets. Hold the drivechain taut and lay it into th ease so that it meshes with the shaft. Check the timing of the balance assemblies once more, and if correct, bolt down the bearing blocks and the bearing cap once the chain guide is in place (fig. 23) On the Suzuki GS400 simply place [}21. Refit the weight to its shaft and 22, The drive sprocket on the crank the balance shaft in place, meking sure J ensure that the timing marks on the must have its timing mark aligning that the timing marks on the balance |) shaft and the weight align with the cutaway on the crank shaft sprocket and the crankshaft align. Continued 23. For final timing each bright link 24. A this point the cutaway on the 25. The slightly hidden rear weight must ‘must align with all three timing marks front weight must align with the mark also align with a similar mark at the ‘on the sprockets in the crankcase back of the crankcase 1329