The XZ400

 

The Yamaha XZ400 was developed after the 550 and it was only sold in specific markets. Probably for markets where an “under 400 cc bike” was taxed cheaply or could be insured as a small bike, or, for countries where young or starting riders were limited to small-capacity and/or limited-power motorcycles.

In practice, it was sold in Japan, Australia, New Zealand, and China. But XZ400’s also seem to ride in Argentina, Russia and Philippines and probably many more countries. Some were imported secondhand in European countries.

 

 

XZ400 in Japan. XZ400 have slotted front brake disks and a strap on the seat (see red arrows). Note also the different passenger peg. Also the color scheme of the factory fairing is characteristic.

Photo thanks to Ryuji of the http://xz-style.com site. The side cover says XZ400.

Ryuni informs me that there are two versions of the XZ400 in Japan, the XZ400

(model code14X) that is shown below, and the XZ400D (model code 24R, that is shown above).

 

 

Yamaha made it and importers decided to sell it in their country or not.  

The data below are from a XZ400 brochure in Chinese or Japanese (thanks to Biaggi, who posted it on the ridersofvision.net site), with some additional data from an XZ400 in the UK, a bike obtained by Simcha in the UK.

 

 

I can read the data on this brochure and you find them below: between brackets are the data of an XZ550 from a 1982 550 Euro brochure and/or from the Yamaha 550 Service Manual (1982, Euro models).

 

Model number 14X (11U [Euro550]; 11H [US-RJ & RK 550], 11J [non-US RJ models]).

Later XZ400 models in Japan: the XZ400D had the code 24R.

Length/width/height 214,5/75/109 cm (221/75/109,5 [with factory fairing 132] cm)

Wheel base 144,5 cm (145 cm)

Seat height 78 cm (77,5 cm)

Ground clearance 13,5 cm (14 cm)

Empty weight 189 kg (189 kg [with factory fairing 200 kg])

Gas consumption 43 km/liter @ 60 km/h (not mentioned for 550)

Brake distance 14 m @ 50 km/h (not mentioned for 550)

Construction: 4 valves Double Overhead Camshaft (= 550)

Cubic capacity: 398 cc (552 cc)

Bore x stroke 73 mm x 47,6 mm (80 x 55 mm)

Compression ratio: 10.5 : 1 (10.5 : 1)

Horsepower: 45 @ 10.000 rpm (64.4 @ 9500 rpm)

Torque: 3,4 kg/m @ 9000 rpm  (5.1 @ 8.500 rpm)

Gas tank capacity 17 l of which 3.4 is reserve (17 l of which 2.7 l is reserve)

Battery 12V-14 Ah/YB14L  (= 550)

Gearing: 2.387 (74x31) (For 550 Euro 2.117 [72x34]; for 550 RJ & RK 2.212 [73x33]

Final drive 3.07 (19x18 and 32 x 11) (= 550)

Gear ratios: 2.866 (first) /1.950(second)/1.476(third)/1.185(4th)/1.00 (5th)

(Gear ratios 550: 2.866/1.950/1.476/1.185/0.966)

Rake and trail: 26.20 degrees/116 mm  (26.40 degrees/118 mm)

Tires: 90/90 x 18 51S/ 110/90 x 18 61S (90/90 x 18 / 4.25/85H x 18)

 

XZ400 and children make a beautiful combination! Photo by Ryuji of the http://xz-style.com site

 

On the basis of these figures it is evident that the 400 has the same weight and height as the 550, but it has 70 % of its horsepower at slightly higher rpm. It has a different overall gearing and the above figures suggest that it has a slightly higher 5th gear (closer to fourth than in the 550). After dismantling a 400 gear box that proved to be true (see below).

A good condition 400 will do at 10.000 rpm ca 160 km (100 mph) but that speed will be a theoretical top speed for downwind conditions and a flat-out rider. A top speed of 140-145 (ca 90 mph) will be more realistic in practice.

 

 

The XZ400 imported in the UK. It has a model code 14X. It has a factory fairing; note the color scheme that differs from that of the white and red 550’s.

 

The bike is a 550, but the bore and stroke are both smaller. It is a scaled down 550, but only the engine internals.

However, to judge how it compares one must try both versions for longer periods under different conditions. The 400 brochure indicates a fuel consumption of 43 km pro liter at a steady 60 kph (38 mph) and if this version (developed later than the 550) has better tuned carburetors and lacks the stumble that is so common in the 550, it might have a charm of its own.

 

 

The XZ400 carburetors have a real surprise (see above) : they are Mikunis BD 34 without a fuel pomp! That number is the same as XZ550 1982 carbs! However, the main jets are 107,5 front/110 back, pilots are 60 and air jets are 145 (see below). The photo above shows also that the air box flapper is vacuum operated. Photo and data thanks to Ryuji of the Japanese XZ-site http://xz-style.com.

 

Specifications of the XZ400 carbs:

Pilot Screw (PS) 3-1/2 +/- ½ turns out
Main Jet Front 107.5 Rear 110
Main Air Jet 1.8
Throttle Valve #120
Pilt Jet #60
Pilot Air Jet #145
Valve Seat 1.8
Starter Jet #40
Fuel Level 21 +/- 1mm
Float Height 36 +/- 1mm
Idle Speed 1,300 +_/- 50 rpm
Vacuum pressure at idle > 150mm (5.91 in Hg)
Vacuum Sync Difference < 10mm (0.39 in Hg)

Source: Yamaha Service Manual, supplement for XZ400, # 14X-28197-20,

1st edition, published Sept 1985, data kindly supplied by roro.

 

Why did Yamaha ever make this bike??

It is easy to see if you forget the XZ 550 and look at the total market. If a customer wanted a small-capacity low-maintenance bike in the early 80’s, there was little choice, if that “low-maintenance” meant “a bike with shaft-drive”.

Looking at that market: there is only one bike that is comparable to the XZ400: the Moto Guzzi V35 350 cc V-twin with shaft drive: it had 35 horsepower and weighted in at 155 kg empty.

The first shaft-driver above the XZ400 is a BMW R45 473 cc boxer twin, with 35 horsepower and a dry weight of 205 kg.

So, I would say: in the total market of the 80’s of small-capacity shaft-driven bikes the XZ400 really had a place of its own.

 

 

XZ400 footrests differ from 550 specimens.

 

NB I want to thank Simcha, an XZ400 owner from the UK for helping with information

and photos, and, last but not least, supplying XZ400 parts to me, and of course Ryuji

of the Japanese site http://xz-style.com. I received wonderful photos from him, see

above. 

 

 

 

 

XZ400 discovery tour

 

I obtained the engine of the XZ400, imported secondhand in Britain, from Simcha in August 2006 (the white and red fairing bike shown above), and I took it in the trunk of my car from the UK to Holland.

I made a photograph of the tacho unit, a kilometers unit with a red warning light that comes on at speeds higher than 80 km/h (information thanks to Kiwibum from New Zealand).

 

  

Tacho-unit XZ400 with a warning light for speed over 80 km/h (red arrow).

 

The footrests differ from the Euro 1982 form.

 

 

The aluminum part of the footrest shows well before restoration.

See also picture above for all footrests.

 

 

The engine was dismantled next to a 550 engine.  

 

Engines 550 and 400 on the workbench. The red arrow on the 550 marks the bolt of the

battery earth.

 

The first striking aspect is the engine numbering. The XZ400 sold new in Japan just has the identification combination for the XZ400: 14X, while the XZ550 for the European market has a “complete” engine number that is the same as the framenumber.

 

 

First the flywheel was dismantled. The 400 flywheel is lighter than that of the 550. The 400 flywheel (number FL120-05) weights in at 2654 grams, and the 550 flywheel (number FL120-03) at 3283 gram. Both flywheel are photographed on the same electronic scale. The flywheels seem to be interchangeable.

 

Flywheels of XZ400 and 550. The 550 is weighted with the thin thrust washer. That washer

Influences the total weight only by a few grams.

 

The rest of the parts of the left side of the engine seems to be similar, that is the alternator, the cam wheels behind the flywheel, the starter clutch.

The cylinder and cylinder heads are different from the 550. Fortunately both cylinder and head of the 400 are marked 398 cc3.

 

 

Yamaha marked 400 parts that are different from the 550.

 

Also the 400 head gaskets differ from the 550 specimens, but strictly spoken the 550 gaskets

fit the 400, but they will leave a small gap.

 

 

The crankshaft including connecting rods are slightly lighter for the 400: ca 5.8 kg while the 550 has ca 6.2 kg.

Both carters of both models bear the same number: 11H01. Still the 400 differs from the 550. The opening for the cylinder measures in the 400 ca 80 mm, in the 550 ca 87 mm (see arrows in pictures below). Probably they are made in the same mold, but in the 550 more metal is removed to fit the larger cylinders. So they have the same number (you can see the cast-in number on the pictures below) but they do not fit.

 

 

The 400 has a different bore and stroke compared to the 500. The bore is easy to see: the piston is smaller. The stroke is more of a problem: the total travel of the piston, up and down, is 47,6 mm for the 400 and 55 mm for the 550. The distance the piston of the 400 moves is 7,4 mm less than in a 550. So the piston stays at top end half of the stroke difference lower = 7,4:2 = 3,7 mm.

This difference is compensated in the piston. The total height of the pistons is the same: 71,5 mm, but the piston pen bore is 3,7 mm lower than in a 550. So both piston tops come out the same distance from the carter at top dead end and as a result, cylinder castings and chains for the camshaft drive can be the same between 400 and 550.

 

Pistons of a 400 and a 550 fitted on the same piston pin. Note that the total height

of the pistons is the same but that the piston pin bore is 3,7 mm lower in the 400.

 

 

The top of the 400 and 550 pistons. Note the larger cutouts for the valves of the

400 piston and the central cup. Both pistons are of the rear cylinders.

 

 

Rear cylinders of the 400 and the 550. Note that the water mantle in the 400

cylinders are 11 mm wide and in the 550 8 mm.

 

 

Valve sizes are different between 400 and 550 models.

The 550 has larger valves than the 400: inlet 31 mm (400 27mm), exhaust 26 mm

(400 23 mm). The valves have different imprints too: 550 inlet 11H; 400 14X; 550

exhaust 4U8; the 400 exhaust valves have the “crossed forks” Yamaha logo. 

 

Another difference is the balancer shaft. The 400 shaft has an imprint 14X and weights 973 grams (see picture below), the 550 has no imprint and weights 1100 grams. Except from these differences, the shafts are interchangeable.

 

 

 

There is one more important difference: the wheels of 5th gear. The gear box of the 400 is similar to the 550, except for the wheels of the 5th gear. The 550 has a 30 teeth gear wheel on the main shaft and 29 on the counter shaft resulting in a ratio .96. The 400 has 29 teeth wheels on both shafts resulting in a ratio 1.0 for fifth gear. This implies that 5th gear is nearer to 4th  in a 400 than in a 550. The 400 gear box is slightly more a close ratio gear box than the 550 one. The total is interchangeable. If you want to use the 400 ratio you need both 5th gear wheels of a 400.

 

 

The results

The start of this “discovery tour” was the use of the primary gear wheels of a 400 in a 550 with sidecar, and the observation in a Japanese or Chinese brochure of the XZ400 that all gear ratio’s of the 400 were exactly the same as the 550, except 5th gear. The question was: printing error or reality? After counting the gear wheels it proved to be reality and this might be of use for 550 riders who prefer a 5th gear with more power. Perhaps 550’s used for racing purposes??

Indeed, the 400 primary gear wheels are perfect for 550’s with a sidecar. The 400 gear box could be good for a 550 (with 550 gear wheels) always used for heavy weight transport (passenger and luggage).

 

The flywheel and balancer shaft are 10-20% lighter than the 550 equivalents. I intend to continue my discovery tour by mounting both parts in a 550 “supersport” that I intend to build in the upcoming years.

 

Is it possible for 400 owners to use a 550 “top half” on their 400 bottom part? No, not without some complicated modification work. The carter halves have the same numbers (11H01) but openings to receive the cylinders are smaller in a 400. If you use the cylinders and heads of a 550 with a 400 crankshaft, you get a super-oversquare engine of 80 mm bore and 47,6 mm stroke resulting in ca 478 cc capacity. In theory, this might be attractive if you want to race it in a 500 cc class event. However, the 550 cylinders don’t fit the 400 carters. The 550 pistons fit the 400 connecting rod but your 550 piston will, at Top Dead End, be 3,7 mm too low in the cylinder, resulting in a low compression ratio. So, either you have to modify the cylinders or to use higher pistons.

 

There is a Yamaha Service Manual for the XZ550RJ with a supplement for the XZ400, # 14X-28197-20, 1st edition, published Sept 1985, roro owns this Service Manual and some data above were kindly supplied by him.

 

NB roro mentions one error in this supplement. It mentions as 400 valves sizes 31 mm inlet and 26 exhaust, but these are the sizes of the 550. The 400 has 27 mm inlet and 23 mm exhaust valves.

 

Note also that factory workshop manuals for the 550 mention 70 teeth for the main shaft’s 5th gear wheel (page 8-71 Euro Manual; page 8-23 RJ Manual). Haynes copied this figure on page 84. This must be corrected to 30 teeth.

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