Second hand advice Honda CB 750 K-F

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Second-hand advice Honda CB 750 K / F

Second-hand advice Honda CB 750 K / F

The second generation of the Honda CB 750 series is already a classic today. But with its bare look, the four-cylinder is currently back in fashion. Well cared for, it purrs lively from high mileage.

Peter Limmert


Honda CB 750? There was something? Right. With the simple name, Honda redefined the term motorcycling in 1969. The first large-scale four-cylinder motorcycle engine was only replaced ten years later by a more modern double-cam engine with four valves per cylinder. The two four-valve valves CB 750 K (Z) and F with the factory abbreviations RC 01 and RC 04 are characterized by their durability. Today around 7500 copies are still registered in this country.
The touring model K (Z), built from 1979 to 1982, and the sportier F (1980 to 1983) differ only in a few details. The most striking feature of the K are the classic four exhaust bags. With this exhaust system, however, the engine only produces 77 hp instead of the 79 of the otherwise identical F-engine, which only adorns two silencers. On the chassis side, the spring struts differ, those of the K (Z) are only adjustable in the spring base, the F dampers can be varied in rebound and compression stages and have 15 millimeters more spring travel. In addition, the F characterizes a slimmer line with the bol d’Or design of the CB 900 F, the second generation of the bolted ComStar rims and a disc brake instead of a drum brake in the rear wheel. In the front double disc systems, the F double-piston instead of the single-piston calipers are fitted with the K. In addition, the rear swing arm of the F is mounted in needle bearings, while the K model had to get along with primitive plastic bushings until the end of 1980.
Both chassis designs cannot deny their great age. If the directional stability is still satisfactory, unrest quickly arises in fast bends on the country road. The telescopic fork is underdimensioned at 35 millimeters and has no adjustment option for the damping. The braking systems also require foresighted driving – especially with the K: The manual force is high, the pressure point imprecise.
There is good news and bad news for those interested in the CB 750 K and F. The good: Since the two models do not yet have the classic car status of the first CB 750, the prices are still relatively low. The guideline value for the F is between 3,000 and 3,500 marks with mileage around 25,000 to 40,000, the mostly older K models are rather lower.
The bad news: Those who do not like to do the work themselves often should not be shortlisted for the youngtimers. New parts are unusually expensive, and being able to find what you are looking for at a used parts dealer requires not only time but also some knowledge. Many parts of the CB 900 and 1100 F fit the two 750s.
What is broken most often? If the machine has been idle for more than a year, the oil pan should be removed and the oil strainer inspected for traces of rubber particles. The shock absorbers on the primary drive shaft may have become porous over time and block the oil circulation. But then you have to take the entire engine apart. The screw of the timing chain tensioner of the exhaust camshaft may only be tightened slightly, otherwise the wedge will be damaged. The stator and rotor of the alternator are also susceptible; used prices range from 150 to 250 marks. Often all that helps is welding the broken wires to the anchor plate (30 marks).
The four-pipe exhaust system of the K model rusts through between the manifold and the pots over the years, the new price completely over 3000 marks. An EU system from the accessories only costs around a third of that. The hydraulic brake lines are also often porous, so steel braided lines (for example from Spiegler, phone 0761/611340) are ideal for a better pressure point. With the brake pads you should definitely stick to the original.
Returning the oil ventilation hoses to the air filter box is environmentally friendly, but the filter clogs up pretty quickly. A collecting container under the battery while retaining the opening that has now been created in the air filter box so that the engine does not run too rich is the better solution. The starting difficulties after a long period of standstill are also known; Draining the old gasoline from the float chambers and changing the candles provide the necessary tinder.

Reader experiences – Honda CB 750 K / F

Kilometer marathon with the Honda CB 750 K (Z) and F: From 100,000 kilometers, the oil consumption increases. But that’s far from the end. Who offers 300,000 kilometers?

In May 1981 I bought my new Honda CB 750 F Bol d? Or. I drove between 18,000 and 36,000 kilometers per season. Apart from the usual wear parts, nothing was replaced. After the first 100,000 kilometers, I wanted to know exactly how long the Honda would run without an engine overhaul. In 14 years the total was 293,800 kilometers. The reliability of the four-cylinder engine convinced me. Ruedi Barmettler, Buochs, Switzerland When I bought my CB 750 K (A), built in 1981, gray import, I was 17 years old. In 1982 I paid 4,200 marks for the 8000 kilometer machine. Today there are 240,000 kilometers on the clock. I carried out the inspections every 8000 kilometers, always with an oil filter change. Between 40,000 and 110,000 kilometers I didn’t have to readjust a valve. Then I milled the seats of the intake valves, and only reground those of the exhaust valves. New pistons, replacement of the timing chain – the tensioner was broken in the middle – the primary chain as well as the crankshaft main and connecting rod bearings were in place. Material and labor costs (cylinder grinding) for the overhaul amounted to almost 2000 marks. Since then the engine has run 130,000 kilometers again and is slowly getting tired again. Klaus Kiene, Herzogenaurach My Honda CB 750 K is now almost 16 years old and has run 203,000 kilometers. It was acquired in 1982 as an accident vehicle and restored. At 72,000 kilometers there were new valve stem seals and piston rings, at 114,000 kilometers there was a new clutch. At 155,000 kilometers, the long timing chain, the primary chain and all crankshaft bearings were replaced. When the odometer reading was 197,000, the upper timing chain was due. The extremely expensive exhaust system is not very durable; the first pots were rusted through after just two and a half years. After problems with the starter, it helped to dismantle the magnetic switch with the help of a soldering iron and to smooth the contact surfaces. Heiko Fromm, Hamburg, Germany, has covered a total of over 100,000 kilometers with four machines of the type CB 750 K (Z). In the front I drive the Metzeler ME 11 (grooved tires) with air pressure 2.6 bar, in the rear ME 77. It is essential to install a fork stabilizer, best experience with the inexpensive Tarozzi (HG). Result: The fork swallows everything and is absolutely stable. Synthetic oil recommended, engine running and shiftability of the transmission significantly improved. The oil consumption, which can otherwise be up to two liters (1000 kilometers) even in intact specimens, gradually decreases to no longer measurable. It is important to readjust the timing chain tension every 2000 kilometers: engage fifth gear, loosen the timing chain tensioner screw at the front, turn the engine a few times on the rear wheel, carefully tighten the screw. Rear (inlet): Loosen the two screws, for the lower one you need a slightly cranked, long 10 mm key, turn the engine again, tighten. The starter freewheel is the weak point: it tends to slip over time. The three springs that ensure the frictional connection are available individually for less than 50 marks. So you don’t need a new freewheel or even a complete starter. Blumer, Havixbeck

Technical data – Honda CB 750 K / F

Honda CB 750 K (Z) Technical data Engine Air-cooled four-cylinder four-stroke in-line engine, two overhead camshafts driven by toothed chains, four valves per cylinder actuated via bucket tappets, crankshaft with slide bearings, contactless transistor ignition, four Keihin constant pressure carburetors, 0 30 mm, three-phase alternator 260 watts, 12V battery / 14Ah, electric starter. Bore x stroke 62 x 62 mm, displacement 749 cm3, compression ratio 9: 1, rated output 77 PS (57 kW) at 9,000 rpm, max. Torque 6.7 kpm (66 Nm) at 7000 rpm power transmission Primary drive via toothed chain, multi-plate clutch in an oil bath, claw-shifted five-speed gearbox, secondary drive via roller chain. Chassis Double-loop frame made of round steel tube, screwed right down beam, telescopic fork, steering head with tapered roller bearings, standpipe diameter 35 mm, rear wheel diameter 35 mm (from 1981 in needle bearings), two spring struts at the rear, spring base five-way adjustable, double disc brake with single-piston calipers at the front, O 275 mm, drum brake at the rear, O 180 mm, ComStar aluminum wheels, spring travel front / rear 160/112 mm, rim size front 2.15 x 19 rear 2.15 x 18 Tire size front 3.25 H 19 or 100/90 V 19 TL rear 4.00 H 18 or 120/90 V18 TL dimensions and weights steering head angle 62.5 degrees caster 117 mm length 2330 mm wheelbase 1520 mm seat height 780 mm handlebar width 730 mm tank capacity / reserve 19.6 / 5.1 liters weight fully fueled 256 kg Total weight 430 kgService dataService intervals every 6000kmOil change with filter every 6000kmMotor oil SAE 10 W 40Fill quantity with filter change 4.5 liter spark plugs NGK DR 8 ES-LTelegabelol ATF -AutomaticFill quantity per spar 172.5 to 177.5 cm3Valve clearance cold inlet 0.06 to 0.013 mm outlet 0 .06 to 0.13 mm test valuesMaximum speed solo / with pillion 200/179 km / hAcceleration 0-100 km / h solo / with pillion 4.5 / 5.5 secondsConsumption 7.3 litersFuel Normal unleaded Spare part pricesCarpet partsCoupling armature Mark handlebar MarkRear-view mirror MarkBinker front MarkTachometer MarkFork standpipe MarkFront mudguard MarkFront wheel MarkExhaust MarkTank, painted MarkFrame complete MarkCladding: Upper shell MarkEach side cover MarkDisk MarkWear partsChain kit MarkBrake pads front, one set of MarkCouplings, one set of Marks, front brake disks, MarkowThrottle locks, engine oil filter e Seating position (also for pillion rider) Lower used price Weaknesses Chassis unstable Weak brakes Expensive original parts Test in MOTORRAD1 test (KZ) 24/1978Comparison test (KZ) 18/1979Long distance test (KZ) 21/1979Test (F) 15/1980Comparison test (F) Tire released 24, 25/1981 RC 01 front rear 3.25 H 19 TL 4.00 H 18 TLDunlop Gold Seal F11 Dunlop Gold SealBridgestone Mag.Mopus S703 Bridgestone Mag.Mopus S710Metzeler ME 11 Metzeler ME 77Alternative tires100 / 90-19 57H TL 120 / 90-18 65H TLMetzeler ME 33 Metzeler ME 99A1Pirelli MT 29 Pirelli MT 28 Dunlop K 825 A Dunlop K 825 Footnotes: 1Tests can be ordered from the publisher, telephone see box on page xxx.

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