ETZ 250 - 251 diffrences

[akirasan]

Is there a list of the differences between the ETZ250 and 251?

Tank
side panels
rear wheel
seat
exhaust
centre stand
side stand
rear light
indicators
gear change (read on another post)
rear shock springs??

[Blurredman]

As someone who owns both, I can confirm some of those on your list:


- Tank - Yes, different tanks- Though I'm not entirely sure if you could fit a 250 tank on a 251 and vice versa- For although I know the 251 is shorter, I always presumed that was due to the rear subframe being shorter.

- side panels - Yes, different shape, but fixings are the same. I have done this.

- rear wheel - the 251 has a 16" rear wheel, the 250 an 18".

- seat - the 251's seat is of different design but is also shorter too. A 251 seat will not fit on a 250. I have measured in the past.

- exhaust - the 251's silencer/expansion is shorter, but internally pretty much the same- Will inter-change. I have done this.

- centre stand - the 251's centre stand is made of aluminium. They will not interchange- the pivot hole is of different size. I have checked and measured this in the past.

- side stand - all mz's side stands take place of the rear wheel spacer. They interchange.

- rear light - the 251's rear lamp takes use of a bilux bulb. Whereas the 250 makes use of two seperate bulbs for illumination and brake. However, the bodies of the lamps themselves can be interchanged. You'd just need to feed an extra earth if you put a 250 lamp on a 251 (which I have done). Indeed, the ETZ125 uses the same two bulb round lamp from the earlier 250's (trying to get rid of backstock? - however the indicators also seemed to sometimes be round or square on the 125.. The 125 seems like a mixed bag type of bike regarding spares)

- indicators - the 251's indicators are squarish, and seemingly supposed to look more up to date. At least the fixings tubes for them are a lot thicker and bigger.. However the indicator units as a whole can be interchanged with the 250- I have done this.

- gear change (read on another post) - The gear change lever itself is shorter on the 251. Though obviously interchangable.

- rear shock springs?? - I don't believe they are different between the 250's. It's a possibility the ETZ 125's however had less stiff springs.


Hope this clarifies your query?

[Puffs]

I believe the choice for a different rear wheel impacts many parts, particularly frame, swingarm & shocks.
The 250 shocks are 2cm longer (both in Lmax & Lmin) to accommodate the larger wheel (1" more in R), and consequently so are the springs.
The swingarm is longer for the same reason.
And again, the frame geometry too: the swingarm axle has to be in a different place, hence also the engine. Distance to the steering head might also be slightly longer on the 250.
Quite a few other/smaller frame parts differ too.

However, engine, forks & entire front section are the same, allegedly (headlight?). I didn't know the exhausts were different, but it looks like they are, at least the down pipe. I hear the carb is different too, though interchangeable.

[Guesi]

Also different

Cylinder
Frame
rear mudguard
rear brake light switch
Carburetor (30N3-1 on ETZ 251, 30N2-5 on ETZ 250)
Speedo and rev. counter have plastic "arrows", ETZ 250 has metal
rear brake lever (the big black one) it is shorter

[akirasan]

thanks good replies


ok cylinder diff? how please?
i can see the springs look diff i will have to measure the length
carb is there a huge difference?

I have parts from a 251 i dont need but keeping parts that will fir my ETZ 250

[Guesi]

[akirasan]

ok so inlet and exhaust angle is diff and crank angle but how does that equate
to performance?

i do not know the technical reasons

[Guesi]

Because the frame is shorter than the ETZ 250 frame, they had to install a shorter exhaust.

To correspond with the shorter exhaust they had to change the measurements inside the cylinder (especially the intake side from 15 to 13 mm).
So the best performance is to connect the 251 cylinder with the 251 exhaust...

Also due to the shorter frame they had to change the exhaust pipe and the exhaust holding nut. With the ETZ 250 echaust pipe the front mudguard came in contact with the exhaust pipe when the front brake is used hard.

[Puffs]

Excellent, thanks Guesi. I didn't know there were timing differences between the two barrels.

But I presume the pistons are the same then, having made the timing differences in the barrel = cylinder?

[Guesi]

Yes, pistons are the same.

[Blurredman]

Interesting, and yet I've swapped 250/251 barrels around with eachother and not felt any performance difference...

[Puffs]

Well, as always, things are more complicated then you'd hope for.

Look at the timings, given in degrees crankshaft angle (Steuerzeiten in Grad Kurbelwinkel) in Guesi's 'Zylinder ETZ 250-251.jpg'; there are generations of barrels, varying both by model & by year. The biggest difference came right with the introduction of the 251, so between the latest 250 & the first ('89) 251. Then, from end '90 onwards, the timings are roughly half-way between those 2 extremes.

The timings of the first, '89 251 suggest more high RPM focus, and apparently they didn't like that too much and went half-way back. It is possible that yours, being an export model, is just one of the first of the latest generation, which has less difference with the 250. Quite possibly those differences are so small that they are difficult to perceive, and might be masked by other effects. You should however have the ~10mm difference in how far the exhaust port protrudes, and 1mm in squish band. So say these data.

These timing differences could also explain differences in how you & me perceive the character of our bikes.

PS/edit: I just had a look for the indicated markings on mine, a '89 251 UK export model, and I cannot see any markings / Kennzeichnung at all at the indicated place. Yet I am quite certain it is an original barrel, of the first 251's.

[Puffs]

Actually a pretty crude thing they did there; simply taking a bit from the base & thereby reducing the exhaust & overflow opening period (by resp. 6° & 9°), while at the same time increasing the inlet opening period (by 6°). That will increase the blow-back (through the carb) yet reduce the breathing ability above the piston. Maybe a longer piston skirt would have been in order, and it does explain why I felt the need for a reed valve (to which it responded very well).

Also, I suppose the bit they took off the base was added to the top of the barrel, in order to retain the volume of the combustion chamber & the size of the squish band, but I don't see mention of that.

[dave47]

PS/edit: I just had a look for the indicated markings on mine, a '89 251 UK export model, and I cannot see any markings / Kennzeichnung at all at the indicated place. Yet I am quite certain it is an original barrel, of the first 251's.

I have two ETZ barrels, one made in 1985 which must be an "alt 250", and one made in 1989 which looks like a "neu 250". According to the official data, kindly supplied by Guesi, they should both have the same timing, but, in fact, all the ports in the later barrel are approx 1.25mm lower. They otherwise appear to be the same size and shape. So my 1989 barrel does not really match any of those in the data chart; it has the appearance of a "neu 250" but the timing of a 251.
The exhaust outlet also looks a mess. Instead of being circular and central in the pipe seating, it is irregular in shape and wildly off centre.
@ Puffs
It may be that your barrel is the same. In fact my rather rough and ready measurements fit quite well with the paper transfer that you have posted elsewhere on this website, except that your exhaust port is 2mm bigger than either of mine. Has it been enlarged?

[alexxx]

What effect would the longer exhaust have on an ETZ251?
Just thinking of the chances of ever getting the correct 251 length of a pattern exhaust.
Another small difference is the speedo and rev counter, my 91 bike has the electronic tacho and the instruments are the square type, there is also a headlight surround/wind deflector, makes the front look more like an off road machine.