Tuning kolbe/piston ETZ 250

[MZ_Max]

Are there any tuning pistons for ETZ 250 available and if yes, where could I buy such? The original piston with three rings is heavy and not the best one for my purpose.

[Martin H.]

E. g. from TKM... viewtopic.php?p=971036#p971036

[ea2873]

what do you expect from that piston? your rotation speed (upm) will have to go up, and the torque moment down..... do you want to change other things about the engine? habe a look at http://www.oldtimerracingparts.de

[MZ_Max]

I'd use the piston in a Jawa 579 engine. (Sixdays/motocross). The bike shall be a classic pre'65 motocross machine. I can increase the cylinder diameter with 5 mm, which gives 280 cc cylinder volume, but there are no Jawa pistons for 70 mm bore, but the MZ 250 has. My ETZ 250 piston has the same crown height as the Jawa piston and the skirt is also long enough. The cylinder, exhaust and carb will be tuned /exchanged accordingly to reach about 30 hp at 5500- 6000 rpm. The standard ETZ piston with three rings is heavy and a bit off from my thoughts of piston for this kind of project.
MTK is offering an ETZ tuning piston, but it's total weight was said to be 450 grams, which is 25 grams more than the ETZ 301 standard 75,46 mm piston's weight. I'd expect much less for a 250 tuning piston. (With rings, pin and clips).
There is a coating on their piston, but I got no information about what kind of coating. It would though not last for more than 1000 km, I was told, which I took as a warning. My impression is that it could be some kind of China stuff of unknown quality. The high weight depends likely on low quality aluminium. It doesn't feel that they could offer a real tuning piston and the information from TKM was not good at all.

[Guesi]

Hi

I think it will be difficult to get a piston with less than 450 g.

If someone wants to tune his MZ, it is easier to put in a light clutch.

As the clutch is on the crankshaft, it has the same effect than putting a lghter piston into the cylinder.

Tuning of an MZ is often made by changing the cylinder settings.

I don´t know any supplier who has lighter pistons for ETZ 250.

And by the way: the Almot pistons, which you get from most of the dealers, don´t have a good reputation...

[Dirk P]

Hello Max,

What is the weight of original complete JAWA piston? It shouldnt be so much less then the MZ piston.

It is difficult to find a piston with such an enormous crown high like JAWA or ETZ. Racing pistons normaly are shorter.
But, in my opinion, for your bike, a good original MZ piston made by "Megu" should work fine. The speed range is absolultely OK for them.
In modified MZ-engines the work fine up to 9500rpm (with a shorter stroke).

For racing use in your engine you can modify it a bit,
-use only the top ring in good quality
-use two smaller piston rings in the top groove
-use a thinner or conical pin
-removing material inside the piston

Do you want to use the original cylinder for your project?

regards Dirk

[MZ_Max]

I'll use the original cylinder liner. It can be bored up to 70 mm. The ports will be adjusted. I'm concerned about MZ standard piston's ring width. At high revs there will be ring flutter (ring vibration) and thereby lower compression. Saab cars two stroke engines have pistons that are almost identical with Jawa and Mz pistons, so besides searching an MZ piston, I'm also trying to find a Saab piston model with two rings (Saab Sport had such). They used Mahle pistons, so the quality should be on top. The rings on them are made of stainless steel and thereby unbrokeable. There are Wiseco tuning pistons for Saab, but the piston top is completely flat and it would not work very well together with the Jawa cylinder head. Maybe same problem with MZ cylinder head. The Saab sport pistons have a dome shaped top.