The in­ner work­ings of the long-lived BMW M10 en­gine.

In­side BMW’s long-serv­ing M10 en­gine which served in the 316 and also as 1100 bhp F1 pow­er­plant.

Classics Monthly - - Workshop - WORDS AN­DREW EVERETT

T he M10’s de­but at the 1961 Frank­furt mo­tor show was in the all-new BMW 1500 ‘Neue Klasse’ (New Class) saloon in­tended to plug the widen­ing hole in BMW sales and save it from bankruptcy. The 1500 was a com­pletely new and very mod­ern car – neat styling, front disc brakes, all in­de­pen­dent sus­pen­sion with rear semi trail­ing arms and un­der the bon­net, the all-new al­loy-head SOHC en­gine.

Named M10, this en­gine took noth­ing from pre­vi­ous BMW en­gines apart from the rig­or­ous qual­ity. The iron block was im­mensely strong – just how strong we’ll see later – but it had large 82mm bores and the five crank main bear­ings set high up into the block for ex­tra rigid­ity. The crank was forged steel with two-inch big ends and de­cent sized coun­ter­weights. Stubby forged steel con­nect­ing rods with studs and nuts for the big ends caps linked onto forged al­loy pis­tons.

The oil pump was bolted to the front base of the block and was run from a sep­a­rate chain from a sprocket on the nose of the crank. A pressed steel sump was used. The cylin­der head was al­loy with hemi­spher­i­cal com­bus­tion cham­bers and large valves, 39mm in­lets and 35mm ex­hausts.

Be­cause of the op­er­at­ing an­gle, BMW needed ei­ther two camshafts or a sin­gle cam with rock­ers ei­ther side and the last op­tion was cho­sen. Long rocker shafts were fit­ted into the head ei­ther side of the cen­tral camshaft with cast al­loy rock­ers that had steel tips where they met the cam lobe and steel ec­cen­tric ad­juster ends that op­er­ated on the valves. Th­ese were se­cured by a 10mm nut and steel bolt and could be slack­ened, the ec­cen­tric turned un­til the cor­rect valve clear­ance ob­tained and retight­ened. The cam was driven by a du­plex tim­ing chain from the crank with a sim­ple chan­nel rail on the in­let side and a ten­sioned sprocket on the ex­haust side.

Cam lu­bri­ca­tion was by a steel tube with suitable oil holes that squirted oil on the area be­tween two cam lobes (it gets onto both lobes) and the oil sup­ply came from two oil gal­leries in the head and a pair of banjo bolts that took the oil sup­ply and di­rected it into the steel tube. A cast al­loy cam cover with studs and nuts was used.

Car­bu­ra­tion was by a sin­gle Solex 36 PDSI sin­gle choke carb and the pump was bolted to the side of the cylin­der head with a pushrod run­ning from an ec­cen­tric cam lobe to op­er­ate it. The dis­trib­u­tor was fit­ted at the back of the head and ran from a gear on the camshaft. The cool­ing sys­tem was slightly un­con­ven­tional be­cause whilst the ra­di­a­tor and wa­ter pump were pretty nor­mal, the ther­mo­stat was a re­mote unit that linked the hoses from the top and bot­tom of the ra­di­a­tor and the wa­ter pump.

Bore and stroke were 82mm by 71mm to give a ca­pac­ity of 1499cc and power was rated at 80bhp – a far cry from the 50-odd bhp of a sin­gle carb BMC 1500 B-Se­ries.

Apart from a few in­stances of con­nect­ing rod break­age of the first batch of 1500s, the M10 was a very tough and re­li­able

en­gine suited to high speed op­er­a­tion on the Au­to­bahn and it was well re­ceived when it went into pro­duc­tion in Fe­bru­ary 1962. The first change was a ca­pac­ity in­crease to 1800cc in Septem­ber 1963. This ex­tra ca­pac­ity was achieved by an in­crease in both the bore size to 84mm and also stroke to 80 mm to give 1773cc. Power was 90bhp with a sin­gle 38 PDSI sin­gle choke Solex carb.

In 1964, to re­duce man­u­fac­tur­ing costs, the 1500 was re­placed by the 1600, and its 1573cc en­gine was ar­rived at by com­bin­ing the 1800 block with the 1500 crankshaft. By this time, the ten­sioner sprocket for the tim­ing chain had been re­placed by a ny­lon coated blade that proved to be very re­li­able. 1964 also saw the launch of two im­por­tant new mod­els, the 1800 Ti and 1800 TiSa. The Ti was a log­i­cal up­grade of the stan­dard 1800, a car beg­ging for more power to ex­ploit its good han­dling.

As well as the sus­pen­sion and tyre up­grades, the en­gine was tweaked with big­ger valves (42 mm in­let, and 38mm ex­hausts on later ver­sions), a new cam pro­file as well as a higher com­pres­sion and the most vis­i­ble dif­fer­ence, a pair of sid­e­draught 40PHH Solex carbs.

With th­ese mods, power shot up to 110bhp but more was to come from the TiSa. The 1800Ti was a com­peti­tor for the Alfa Romeo Gi­u­lia as well as the Lo­tus Cortina but needed some parts ho­molo­gat­ing to be able to com­pete in rac­ing. The com­pres­sion was raised to 10.5:1, the Solex carbs re­placed by 45DCOE We­bers to give 130bhp, im­pres­sive stuff for 1964.

In 1965, the BMW 2000C Coupe ar­rived and with it the big­gest stretch of the M10 to 1990cc. This was achieved by in­creas­ing the bore size to 89mm and re­tain­ing the 80mm stroke of the 1800. Two ver­sions were avail­able – the 2000C

(mostly as an au­to­matic) had a sin­gle 40 PDSI Solex to give 100 bhp on a 8.5:1 com­pres­sion, and as a 2000CS (man­ual only), 120bhp with twin Solex 40 PHH carbs from the 1800Ti and a 9.3:1 com­pres­sion - all 2000 en­gines had the big­ger 42mm and 38mm in­let and ex­haust valves. In 1966. th­ese two 2000 en­gines were used in the 2000 saloon (sin­gle carb) and 2000 Ti (twin carb).

In 1968, the pop­u­lar 1800 en­gine was re­vived with a ca­pac­ity change from 1773cc to 1766cc. That hap­pened be­cause BMW needed to re­duce costs and they did this by com­bin­ing the 2000’s 89 mm bore with the orig­i­nal 71mm crank stroke from the 1500 and 1600. The smaller two-door BMWs ar­rived in 1966 start­ing with the 1600 and joined by a 2 litre ver­sion in 1968 called the 2002 – this was joined by a 120bhp Ti ver­sion at the same time.

1969 saw a new 130bhp fuel in­jec­tion ver­sion of the 2000 en­gine. Fit­ted to the 2002Tii from 1971 and the 1969 2000Tii (the 2000 Coupés had been dis­con­tin­ued in 1968) the new en­gine used me­chan­i­cal Kügelfis­cher in­jec­tion re­quir­ing a new head cast­ing, and the com­pres­sion ra­tio was 10:1.

In 1972, the New Class was re­placed by the new E12 5 Se­ries with 520 and 520i mod­els. The M10 en­gine was re­vised with new ‘triple hemi’ cylin­der head cham­ber and port de­signs from the six cylin­der M30 en­gine, new pis­tons and new car­bu­ret­tors. The 520 used twin Stromberg 175 CDET carbs whilst the 520i used Kügelfis­cher in­jec­tion – the 2002 went to the new E12 units but the carb ver­sion re­tained the sin­gle Solex.

The next change ar­rived in 1975 when the 2002 was re­placed by the new E21 3Series. Again, the head and pis­ton de­signs were re­vised as was the fu­elling. The 316 and 320 (1573cc and 1990cc) used the twin choke Solex 32/32DIDTA carb in­tro­duced on the 2002 in 1972 and the 320i used Bosch K Jetronic in­jec­tion. Th­ese new units were also fit­ted to the BMW 518 (1766cc) and 520 / 520i mod­els from Septem­ber 1975.

In late 1977, the 2 litre M10 was dis­con­tin­ued and re­placed by an all new 1990 cc straight six, the M60/M20 unit and

th­ese new sixes were used in the 320 and 520 mod­els with the in­jec­tion ver­sions dis­con­tin­ued for the time be­ing. The 1600 and 1800 ver­sions con­tin­ued un­til Septem­ber 1980 when a cou­ple of im­por­tant changes were made. The Du­plex tim­ing chain was re­placed by a Sim­plex (sin­gle row) chain, the gear on the back of the cam was changed so that the dis­trib­u­tor now ran the other way and car­bu­ra­tion was changed again with a new Pier­burg twin choke 2B4 carb phased in to re­place the old Solexes.

Elec­tronic ig­ni­tion as also fit­ted. A 1.8 in­jec­tion with K Jetronic ar­rived for the E21 318i and E28 518i mod­els (not for the UK yet) and th­ese en­gines were used in the orig­i­nal E30 316 (1766cc) and 318i mod­els. In Septem­ber 1983, the 316 and 518 re­ceived the Solex Pier­burg 2BE ECU con­trolled carb and the in­jec­tion mod­els re­ceived Bosch LE Jetronic fuel in­jec­tion. Power out­puts were 90 bhp and 105 bhp re­spec­tively.

By this time, the M10 was over 20 years old and a re­place­ment was al­ready in the de­sign stage. In Septem­ber 1987, the facelifted (plas­tic bumper) 318i went over to the all new M40 en­gine, a unit shar­ing de­sign fea­tures with the equally new V12 en­gine and which was lighter, more pow­er­ful and much more eco­nom­i­cal.

Only two cars now used the M10 by then: the carbed 316 and the in­jected 518i E28. Carb and in­jec­tion units used dif­fer­ent heads with port dif­fer­ences that make them non in­ter­change­able. 518i pro­duc­tion ended in De­cem­ber 1987 and the 316 fi­nally ceased pro­duc­tion in July 1988 to be re­placed by a 1600 M40, and that was the end of the M10 en­gine af­ter over 25 years in pro­duc­tion. In a way, it car­ried on a bit longer be­cause the 16-valve S14 unit in the orig­i­nal E30 M3 was based on an M10 type block, and ca­pac­i­ties ranged from 2.0 in the 320iS through to 2.3 and fi­nally 2.5 litres. THE 2002 TURBO The 2002 Turbo was not, as is of­ten claimed, the first tur­bocharged road car - Gen­eral Mo­tors had that years be­fore. But the 2002 Turbo was the first Euro­pean turbo road car and it went into pro­duc­tion in July 1973. Bassed on a 2002 Tii unit, the turbo had a

very low 6.9:1 com­pres­sion, a KKK tur­bocharger and Kügelfisher in­jec­tion but with a slide throt­tle rather than a stan­dard but­ter­fly type. Power was rated at 170bhp at a high 5800rpm with 180 nm of torque. Pro­duc­tion ended in 1974 af­ter only 1672 cars were built.

In the mid eight­ies, BMW built a num­ber of M12 en­gines for For­mula 1. Th­ese were tur­bocharged 1500 cc units and in 1983, Brab­ham us­ing the M12 gave 800bhp in qual­i­fy­ing and 650 bhp for rac­ing – by 1985 the qual­i­fy­ing bhp had risen to 1100 and the en­gine took the 1983 World Cham­pi­onship in a Brab­ham for Nel­son Pi­quet. What has this got to do with the M10 en­gine? The M12 was based on an M10 block, highly mod­i­fied but sec­ond­hand high mileage ones at that due to cast­ing stresses be­ing long gone. STRENGTHS AND WEAK­NESSES Given 6000-mile oil changes, the M10 will do 100,000 miles and we know of a 1987 518i that did over 210,000 and was still run­ning well. The forged steel crank was grad­u­ally phased out on un­der 2-litre en­gines dur­ing the 1970s, not that it made a lot of dif­fer­ence. Valve guide wear was quite com­mon lead­ing to blue smoke and top end clat­ter but again, reg­u­lar oil changes helped pre­vent much of that.

Cam wear was caused again by poor main­te­nance - you need to en­sure the oil spray bar holes are clear ands the ban­jos are tight - the spray bar can be re­moved from its sad­dles and the holes en­larged with a small drill, whilst BMW sell pre-thread­locked ban­jos with a very slightly dif­fer­ent thread

pitch to pre­vent any pos­si­bil­ity of them work­ing loose. Do not thread­lock them your­self as it will con­geal in the cen­tre of the banjo and starve the cam of oil. Be aware the spray bar only fits one way – fit it the wrong way around and it will only lu­bri­cate four of the eight lobes. Cam sprock­ets on the post 1980 en­gines with the sin­gle row chain can wear badly, but they’re eas­ily re­placed. Cylin­der head cor­ro­sion can be a prob­lem if the an­tifreeze is not re­placed on time. Heads can be welded and skimmed but if you want to re­place it, make sure the head is re­placed with the cor­rect type – 121, E12 or E21 – the mark­ings are cast on the side.

Bot­tom end prob­lems are rare, but an oil light that takes a long time to go out can be a worn oil pump or crank bear­ings, but can also be a failed ‘O’ ring on the pipe that sup­plies oil from the pump to the front of the block – you need to re­move the front tim­ing cov­ers to ac­cess it. Reg­u­lar tap­pet ad­just­ment is im­por­tant and you may find you need over­side ec­centrics if the rocker pads are worn. Snapped ex­haust man­i­fold studs are quite com­mon and a pain to drill out and re­place.

Old Pier­burg carbs are gen­er­ally trou­ble and are best re­placed buy ei­ther a new We­ber or a good con­di­tion old DIDTA Solex from an E21. K Jetronic and LE Jetronic are both good and re­li­able – K Jet needs set­ting up prop­erly and the air in­take bowl clean­ing out and the plate re­set­ting if needed, and LE Jet can have trou­ble with the seven pin re­lay for the fuel pump and in­jec­tors – worth car­ry­ing a spare in the car.

The orig­i­nal M10 en­gine (above) and the 2002 Turbo unit (above right).

The 1100 bhp F1 en­gine was based around a For­mula 1 block.

The en­try-level 1502 model of­fered af­ter the launch of the 3-Se­ries.

The 2000CS (above) and Alpina-mod­i­fied M10 en­gine in an early 3-Se­ries (be­low).

First-gen­er­a­tion 320 used the M10 en­gine be­fore gain­ing six-cylin­der power.

Sin­gle cam op­er­ates two sets of rock­ers. Cam drive is by du­plex chain.

The 520 used the M10 en­gine in its first-gen­er­a­tion guise.

Con­ven­tional de­sign makes main­te­nance easy, while the M10 can be highly tuned.

The M10 would con­tinue in pro­duc­tion right into the 1990s.

The ‘S14’ M3 en­gine was loosely based on M10.

High qual­ity con­struc­tion was an M10 fea­ture.

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