ETZ 250 Head/Barrel/ Different alloy?

[nice2day]

This post might seem over trivial but surely slightly interesting?
I don't know if you have ever noticed but the aluminum colour of the head is different to the barrel.
The head colour is very slightly more silvery. Most owners might not have noticed but take a close look and you will see. Maybe the barrel requires an alloy that expands less to keep the liner held tightly, whereas the head simply has to expel heat....I wonder if anyone else has noticed and knows why?...By the way.... I am sure it is not dirt or corrosion differences...

head colour.JPG (20.5 KiB) Viewed 4557 times

head colour 2.JPG (23.15 KiB) Viewed 4557 times

Les

[Blurredman]

To a certain extent, I have also noticed this!

I have also noticed that a lot of MZ owners (at least in the UK) have painted barrels/heads in black... Perhaps to stop the unsightly effects of salt on/between the fins!

[Puffs]

I never noticed differences in the alloy, but I never looked carefully either.
The thermal expansion coefficients of the two alloys should be pretty similar though, otherwise you'd get a leaking head gasket.

On the black: black is most efficient in radiating infra red, so it helps in cooling. So if you think that's required, paint it black (as Mr. Jagger says).

[Blurredman]

I wonder if it is the angle/colouring of the pictures:

Here below is my bike (advertising pictures, I hasten to add)... The picture of it outside, you can see a difference.. The picture of it inside- it looks no different..

[Puffs]

Today I did look carefully at my 251, but I cannot see anything significant that suggests a different alloy. Both may actually have the remnants of some coating on them, expected to be original.

If you see differences, could those be caused by coating?

Note I did say 251, and we recently learned there are differences.

[nice2day]

Hi Chaps thanks for taking the time to look for yourselves . I have the barrel and head removed so I can say the colour difference is not caused by a positional effect. So far, I have used phosphoric acid for cleaning them and the barrel always comes out a darker grey colour. Hopefully when I use my Karcher Sand Blasting attachment (Bores and joint faces carefully masked off) they will be back to raw base metal with no oxide layer. I will then be able to judge (as you will when I send in some more photos )...Got to buy the Kiln Dried sand first though.

Les

[Puffs]

Hi Les,
other than the requirement for the thermal expansion coefficient to be pretty similar in head & barrel, the alloys can be quite different. And it is not uncommon to select different alloys, for instance; the Jawa 634 has cast iron barrels below alu alloy heads. But I guess there the required wear & friction properties required the use of steel, while they didn't use the more elegant solution of the steel liner like the MZ has (or more modern hard-chrome / nikasil plating solutions).

So it's quite possible that they used a different alloy, but it's not obvious to see in my 251.