Das MZ Forum für MZ Fahrer

Hello,

I made it for Polish MZ riders because of mistakes that were fairly common. It covers simple conversion with using a lathe and for more advanced users I made a complete 3d model in most common dxf format that everyone could use on cnc milling machine. All could be find in movie description

If you find it usefull feel free to use it. Any questions concerning 3d model and concept, feel free to ask.

Youtube video have english subtitles. You have to turn it on.

https://youtu.be/sPmO-do0lhU

Regards
Intr

https://youtu.be/O-mM5Egy0pw

Little upgrade to the topic

The second video looks very professional
But 3 problems :

1. the ring on the top end of the 250 ccm cylinder centers the cylinderhead . Drilling the cylinder to 300 ccm makes the center ring disappear. How do you mange the cylinderhead to be centered on the cylinder ?

2. You use an Almot Piston.This piston is known to expand more than the original piston.Do you have more than 0,05 mm clearance (as it was used on the original piston /cylinder) ?

3. On most of the ETz 250 engines the 300 ccm kit is not "plug and play".Very often, the bottom of the piston comes in contact with the crankshaft or the cankshaft case. How do you eliminiate this problem ?
Some people take off 1 or 2 mm of the bottom of the piston which changes the port durations....

_________________
GüSi

GüSi Motorradteile
http://www.guesi-motorradteile.de

In this simplest solution you haven't got this feature. Head itself is machined to make collision impossible by making it 77 - 77,5 mm wide at the bottom. This dimensions were taken by experience and it is the cheapest way that work. If customer is willing to pay more, of course it is always better to have it. like here for example. There is free 3D model of head for 300 that I made.




Generally, piston clearance is not the case. Couple years ago we took several experiments to figure it out, and after an answer from almot insider we knew, how they make their pistons and what they skip. I assure you 0,05 is more than enough. It's all about cylinder roughness, cross-hatch angle and driver skills If you have seizure at the top of the piston, where it is 0,25 smaller and have 0,3 mm of clearance, then 0,01 from one side to another is really irrelevant. Typical almot seizure is at the top. Almost never on area, where you have this 0,05 of clearance. What I made for prototypes, that have to take extreme treatment from the beginning - I took extra 0,1 mm from piston rings area to make it 0,35 - 0,4 mm smaller than piston, an little angled relief under rings. The piston had enough place to grow but it was very noissy and lasted not more than 8 - 10 kkm.

Unless you make it 0,1 mm which is quite safe, but there's no real power then and the engine is a ringing like bell. There's no sense to make 300 this way in may opinion.


Yes that is true, but almost every aware MZ rider knows that or should know that. Here in poland it is not that typical. I guess we had maybe 2 cases over more than hundred MZ's. But it was years ago, when we found that and right now everyone should be informed by the machinist that this is possible. Crank time at intake is at its extremes even in stock engine if you want to make reasonable economical symmetric motor. Around 160 degrees. Generally it is common here to machine the crankcase. Most aware users make it, when they make general repair.

At the end I have to say - it's not an advert. I was forced to close my shop. It was not profitable enough in polish reality at the end (31.12.2019) despite the amount of work i had and I don't do it anymore. It's just entertainment and while it's about MZ, I thought I'll show you that

Hello

I never saw it as an advertise...
I see it as an interesting information for all MZ drivers...

_________________
GüSi

GüSi Motorradteile
http://www.guesi-motorradteile.de

What does Almot skip, when they make their pistons?

Sorry, but I cannot answer this question with no proof. You can take it by word or don't. All I can tell is that material is 100% a good quality one. They don't mix it themselfs. They buy certified AK20 as far as I know. Generally I have no objections to almot pistons now. Couple years ago every piston was slightly different and despite of simplified production process, you have got random shapes, no consistency at all. You had to machine almost every piece to make it work. But from 2-3 years I think, something changed and from a long time I didn't find one, that is badly made in micro and macro sense . Maybe they feel the breath of guesi's Almets

Have a look at this gps readouts. I took that on a highway road trip to polish mz-klub meeting.



and here you have all-time full throttle from one check point to another on A2 highway in summer time.


and the same data in excell sheet. Better resolution,


There is almot inside and it is 25ps/37Nm modified for touring 300 from 250 ETZ engine. I have no complains,nothing happened... 20 kkm on it till today.

In short words, it is not perfect but it could be forced to work. There is no room for any mistakes like bad ignition timing, carb regulations, bad machining. Oryginal piston forgive many of little mistakes. Almot don't. And that's it. Good luck

ps: here is how the test bike looked. No passenger, only me on board with all that equipment you see.

How much should the tolerance be if you use Almot pistons in a mz engine? 0.05 or more?

Er hat doch weiter oben geschrieben, dass das Einbauspiel bei den Almot-Kolben nicht das Problem ist.
Der Kolben hat von unten bis kurz über den Kolbenbolzen sein eigentliches Maß.
Dann beginnt nach oben hin die Konizität, das heißt der Kolben wird im Durchmesser immer kleiner.
Da die Almots immer im oberen Bereich und nie unten klemmen/fressen, liegt es nicht am Einbauspiel, sondern an einer falschen Konizität/Schleifkurve.
Das Material soll in Ordnung sein, da Almot es nicht selbst mischt und zertifiziert zukauft.
Folglich kann man die Almot-Kolben mit dem von MZ vorgegebenen Einbauspiel fahren.
Man muss aber unbedingt vor der Montage die Konizität des Kolbens messen und ggf. korrigieren.

Hallo zusammen,

Hab mit dem Herrn gesprochen und leider macht er diese Umbauten nicht mehr.
Gibt es hier jemanden der das auch so gut kann ?

VG Daniel

Hallo.

Ich baue sowas recht regelmäßig. Je nachdem wie es gewünscht ist, mit oder ohne Steuerzeitenbearbeitung.
Das Diagramm ist letztens entstanden. Zeigt den Vergleich zwischen der Serien 250er ETZ (Diagramm wurde aus der Reparaturanleitung entnommen) zur bearbeiteten ETZ300. Auspuff ist komplett Serie, als Vergaser kommt ein 34mm Polini mit Gummiflansch zum Einsatz.
Hauptaugenmerk war das Drehzahlband wie Serie zu belassen, dabei aber das Drehmoment zu steigern, da der Zylinder in einem Gespann zum Einsatz kommt.

MfG Lucas

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Hab dir eine PN geschickt.

VG Daniel

Welche Kolben nimmst du? Bearbeitung sieht sehr professionell aus

Hallo.
Habe alles schon genommen. MTK vom Grosche, Schmiedekolben von ORP (nicht lieferbar) und hängengeblieben bin ich jetzt beim HGM von RPT.
Mfg Lucas

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