ETZ 250 - 251 diffrences

[Puffs]

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[Blurredman]

As an aside, I wonder if Guesi has blueprints in regards to the 15 vs 21 hp difference found on different ETZ 250's? The lower hp item being available for certain exports apparently.

[dave47]

@ Puffs, If your number is not on the front, it will be on the LHS of the "neck", in the middle, but it is unlikely to tell you much. It will almost certainly say 29-42.000. On mine there is another number, 710, to the right of that. It may be coincidence that this is 017 backwards.
I say that my barrel has the appearance of a 250 not 251, because it has no frontal number, and what numbers it has are the same as the 1985 barrel.
On the RHS of the neck are two small numbers which almost certainly indicate the month and year of manufacture, eg 89 and 8. They might be upside down.

[Guesi]

As an aside, I wonder if Guesi has blueprints in regards to the 15 vs 21 hp difference found on different ETZ 250's? The lower hp item being available for certain exports apparently.

Hello

In Western germany the hp´s were reduced to 13 kW because of insurance reasons, because we had insurance classes up to 17 HP (13 kW) and 27 HP (20 kW).
So the original 21 hp engine went to the more expensive 27 hp class.
It was reduced by a "longer"downpipe marked with the MZ sign and 13kW.

In the GDR these downpipes were used in the police and military models, because these pipes gave the engine more torque in lower revs.

[Puffs]

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[dave47]

@ Puffs,
The number will be where I said, but may be obscured to a greater or lesser extent by the LH cover which for some reason is higher than the crankcase. It is mostly visible on my early ETZ, ( broken fin makes it even more visible!) but only the top part of the final .000 can be seen on the later bike. It tells you nothing anyway.

All the markings are the same on both of my barrels and on yours, except the date marks. I think it very likely that this is what they are, because apart from anything else they are in circular panels, which suggests they are changeable. This would indicate that your bike, like mine, has a replacement engine/barrel, but whether from a late 250 or early 251 is anybody's guess. I suspect that MZ may have used the same for both for at least part of the period 88/89.

[Puffs]

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[dave47]

I think you are right , it has been dropped by about 2mm, (not 1.2!), which makes it the 251. The data sheet must be wrong about the position of the number. The footnote must only apply to the later 251/301s.
The "datemarks" on my earlier bike read "E" and "85", which I take to mean May 1985. It is consistent with being on a D reg bike (UK), but somebody must know for sure.

[Puffs]

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[Guesi]

29-42.000 is the spare part number

the "0" is only important if the cylinder is new and not rebored.

It says that the cylinder is bored exactly at 69,00 mm, so the piston must be 68,95 mm. Because the clearance on ETZ engines is 0,05 mm.

If the cylinder is marked with 1 then the cylinder is bored 69,01 mm, so you need a piston with 68,96 mm .
If it is marked with 2 then the cylinder is bored 69,02 mm so you need a piston with 68,97 mm.

When the cylinder is rebored, the "0" does not have any importance...

[Puffs]

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[Puffs]

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[dave47]

You have confirmed what we thought was the case. Did you have any other reason to remove the barrel, or was it just to service it before changing to premix?

[Puffs]

Now that the nice weather is over, I wanted to have a look at it's internals: barrel, piston, bearings. Before trying another carb on it.

'we'???

[dave47]

'we'???

I thought that we??? had decided in May that we both had early 251 engines with likely A=13mm, and I also had an ETZ 250 engine with A=15mm, as per Guesi's data sheet. You have confirmed one of them, but I will not be measuring mine in the near future.