Anyone use a Zeiss Jena 2.5cc diesel?
 

I recenlty picked up a nice Zeiss Jena 2.5 and was wondering what they were used for. It has rear intake so I'm wondering if it was considered a performance engine.

It's RRV with ball bearings, fairly compact and weighs 6.4 ounces. The only thing I don't like is the large prop driver which forces you to drill your props oversize.

Anyone have any info?

RE: Anyone use a Zeiss Jena 2.5cc diesel?
 

:) Hi Dan You have a Zeiss Jena 2.5 cc DK. Although rear rotor, it is a sport, not a performance engine. In order to assess the quality and characteristics of this, and other Zeiss engines, one should consider how things were done in the DDR (East Germany). In that planned economy commercial enterprises were state owned or had state participation. Full employment of the population was mandatory, and a bloated production staff tended not to be highly motivated with respect to quality. So Jena engines tend to be good but not great. Fits tend to be too tight. Access to raw materials was not consistent and a great deal of scrounging (now "recycling") )was necessary. One consequence is that ball bearings are not good quality-and they tend to be fitted too tightly, altogether resulting in a rough feel. At the Jena model airplane plant, response to official directives also led to constant development of new models, which differed cosmetically but did not produce better performance. This makes Jena collecting interesting because of the variety of engines available.

I am interested in engines made by companies that are well known for some other primary type of product so that model airplane engines come as a bit of surprise. E.g., Citizen Watch Company making G-Mark engines and Karl Zeiss, famous for high-quality optical goods, making the Jenas (Jena, DDR, was the city).

I have five Zeiss Jenas, and their portraits are attached below. The wee 1cc engine with the red cylinder muff has piston-port induction, but with the venturi pointing forward, parallel with the crankshaft, making it quite distinctive. It has two races of ball bearings, which seems to be standard for all Jenas, and dates from about 1960. The 2 cc with the blue muff (Jena's head colors indicate capacity) is a Model D RC from about 1961. The two with the smaller diameter black head muffs are 2.5 cc, perhaps from about 1961. One has reed- valve induction , identified as a Model MK and the rotary-valve induction engine, like yours, is a DK. These 2.0 and 2.5 cc models have a long crankcase, whereas the earlier equivalent engines have a shorter crankcase but the same-length crankshaft. The difference is taken up by a black-anodized aluminum spacer between the case and the prop driver. This arrangement is illustrated by the rotary-valved Model DN, below, which has a larger diameter black head muff and dates from about 1960. Note the milled-off bosses below the exhaust ports, which on the Aktivist III (1959) and earlier models were drilled and threaded to receive three head bolts, as on PAWs and Ollies. Note that the box is incorrectly labeled-it says Jena 2,5 DK but this is how it came to me.

These are only a few of the many models of Jena engines from that period. Note how compressed the time line is-lotsa variations in a few short years!

Most of this information is from Selbstzuenderkleinstmotoren und Gluehzuenderkleinstmotoren aus Jena, a self-published book by Eberhard Stenzel, 2007. To my knowledge, it is available only in German.

Now, have I run any of my little Jenas? No, I have not! I always have great intentions to run each new acquisition. But mostly they collect in the cabinet as hanger queens!

As a final item of interest, check out eBay Item No. 300357862286, if you have not already done so. Or if you have, go back and drool over it some more. These boxer-style diesel twins were produced by Rolf Roehner in Western Germany using Zeiss Jena piston-cylinder-head muff sets and sold by the firm Robbe.

Regards. -Gary

RE: Anyone use a Zeiss Jena 2.5cc diesel?
 

Um-RCU lost the pics. I'll try again. -Gary

RE: Anyone use a Zeiss Jena 2.5cc diesel?
 

Gary,

Thanks for all the useful info.

This .15 seems to have great compression and the bearings feel smooth. If I ever get some free time I plan to run it.

I just sold two of those cute little 1.0cc Jenas and then came into another one last week, along with the 2.5cc.

The exhaust port fitting on your 1.0cc interests me. Is it a factory option or something you made. I like anything that gets diesel exhaust residue off the model.

Here are pictures of the two Jena 1.0cc engines I just sold. One has a thick top fin like yours and the other has thinner top fins, as does the one I picked up last week.

The 1.0cc engines are real conversation pieces.

RE: Anyone use a Zeiss Jena 2.5cc diesel?
 

:) Hi Dan! You are lucky if your Jena 2.5 DK has smooth bearings. Most of my Jenas have a cogging feel owing to action of the ballbearings.

Your two Jena 1cc engines are a version 1 (thick, hemispherical top of head muff) and version 2 (one more fin, flatter head top), according to the book I already quoted. Both listed as about 1960. The sheet metal exhaust stacks were a factory option; the next page of my book shows a Jena 1W (marine with water jacket) with the exhaust stacks.

Indeed the Jena I's are cute and have loads of character!

I like Jenas because there are many versions that show rapid evolution (though mostly cosmetic...) and because of the connection with Karl Zeiss Optik. And because of insight into manufacturing in the DDR. Another point the book makes is that individual Jena parts are quite good, but assembly of the engines degrades the quality somewhat.

A German friend says that nowadays, if one wants to see new roads and other public works, one needs to go to the former East Germany. There they are, paid for mostly by the western Germans, who do not have such nice new roads and other public stuff.

I do not have any Russian engines. Do you? My impression is that only the high-end, contest-grade (expensive!) engines are really good. Is this true? Or an overstatement?

Regards. -Gary

RE: Anyone use a Zeiss Jena 2.5cc diesel?
 

Gary,

The one Russian engine that I know is good is the MK-17 diesel. I would recommend that one to anybody wanting to get their feet wet in diesels.

It has good power, easy starting, pretty quiet and is fairly inexpensive.

I have several MK-16 and MK-17 engines as they had an interesting progression of models over the years.

RE: Anyone use a Zeiss Jena 2.5cc diesel?
 

Thanks, Dan! I shall start looking for one, new-in-box with propeller, other stuff, and papers. Altogether, makes an interesting piece. -Gary

RE: Anyone use a Zeiss Jena 2.5cc diesel?
 

Gary,
Edd Carlson has the Mk17 NIB for US$40 ( http://carlsonengineimports.net/index.shtml ) so dont pay over this from another source, Ive seen some ridiculouse prices payed on the austion site as of late.
Other reasonable priced diesel's are the "Sharma " a sorta PAW copy , a bit agricultural on the outside, but fits and finnish inside -were it counts, are good and they perform as well as a PAW, Edd also has these.
Stewart

RE: Anyone use a Zeiss Jena 2.5cc diesel?
 

:)Hi Dan & Stewart- Thanks, guys. Yes, indeed, I have ordered a Mk 17 from Ed. His $40 special beats likely eBay deals, with which one takes the chance of getting less than what seems promised... Ed and Eric Clutton supplied me with my first diesels some years ago.

I forgot to say earlier that your little engine boxes and labels are really neat, Dan! I may bid on one of your eBay engines, but you better hope I don't win. I am cheap, and I bid low!

Regards. -Gary

RE: Anyone use a Zeiss Jena 2.5cc diesel?
 

Gary,

Thanks, my wife suggested I make boxes for some of my Ebay engines and it sees to work out pretty well so far. I have some Oliver Tiger Cubs on there this week that have over 80 people watching them.

The clear display boxes work out well for collectors because you can view the engines easily without exposing them to air, fingerprints and abuse.

RE: Anyone use a Zeiss Jena 2.5cc diesel?
 

Please can you help to tell me if there is something missing from my engine ....check pics in my gallery...
I have a marine version of diesel 2,5 cc ( I think)
Greetings from Split Croatia.

i got the engine from a friend. I think it has been opened before me...

RE: Anyone use a Zeiss Jena 2.5cc diesel?
 

It looks like you are missing the pin on the end of the crankpin to extend out to fit the rotary valve so that it rotates.
There usually was a short extension to the crankpin to connect with a hole in the rotary valve. But with some engines, the pin was part of the crankpin, on other engines it was separate, and some engines even had a spring loaded pin. if I remember correctly, a few engines used a left hand threaded screw with the head of the screw being machined to fit into the hole on the rotary valve too.

You can see the short pin extension on the crankpin on this crankshaft here. it is a different engine than yours, but there ought to be something like this for your engine too.
http://i248.photobucket.com/albums/g...sembled_05.jpg

RE: Anyone use a Zeiss Jena 2.5cc diesel?
 

That's just what I thought, now I have to see if it is possible to make one or order one or something like that. you can also see on the rotary valve it self a letter R and L probable for "left" or "right" spin of the prop i.e. engine direction...
Hope that someone else will see this and give me more info .
Thanks for your quick reply.
Greetings from Split Croatia.

RE: Anyone use a Zeiss Jena 2.5cc diesel?
 

yes that is correct. Some engines with a rear rotary valve had a Left or Right rotation direction, depending on which hole you used.
If the hole in the crankpin is threaded, check to see if it is a left hand thread, so that the screw won't unscrew when the engine is running. Otherwise one could take a decent piece of steel alloy rod, chuck it up in a drill press, and using some files carefully file in the two different sizes to fit.  Of course using a lathe would be even better.

Yeah maybe someone who has worked with the engines will notice the thread and tell us more about it.

RE: Anyone use a Zeiss Jena 2.5cc diesel?
 

Here is some info about the marine engine butr not much more than pics though. I sorta like the bulbous water cooled head/jacket on it:
http://www.radiocontrolmodels.co.uk/...os/EG3707A.jpg

http://www.radiocontrolmodels.co.uk/...os/EG3707B.jpg

RE: Anyone use a Zeiss Jena 2.5cc diesel?
 

Be careful running that MK 17. They are superb little engines but the crankshaft is like a long toothpick. They break easily if over compressed. I have two of them and really like them.

Max

RE: Anyone use a Zeiss Jena 2.5cc diesel?
 

Were you referring to my Marz engine or the Zeiss engine?

RE: Anyone use a Zeiss Jena 2.5cc diesel?
 

I think this is the Mk. 17 being discussed.

George

RE: Anyone use a Zeiss Jena 2.5cc diesel?
 

Gary, I see you have some engines verry like mine, is it possible for you to take off the back and send me pics of the little rod inbetween the rotary valve and crank shaft, p l e a s e .....
Greetings from Europe Croatia. I think I'm the only person with this old Diesel engine im my region.... I would like to see it run...
It is very difficult to get fuel for it as well, so I'm trying to mix stuff.....(kero, caster oil, and some starter spray....) I saw on Youtube ;)

RE: Anyone use a Zeiss Jena 2.5cc diesel?
 

Hi,
You could log onto this site (http://modelenginenews.org/) and go to 'Engines" on the left hand column, the 'finder' and go to the entry for the Marz 2.5 - this engine's crank take off point is very similar to yours.

And once again I will shamelessly provide the line drawing from that site (kudos to Diesel Die hard for this .)

RE: Anyone use a Zeiss Jena 2.5cc diesel?
 

neet little rod inbetween valve and crank shaft, I have to check if there is thred ore spring mounted..

thanks mate, take care, it's getting cold down there now...:)

Zvonko (Bruse)

RE: Anyone use a Zeiss Jena 2.5cc diesel?
 

:) Hi Kiwi2 - Please disregard the personal response I sent you. I found your post and see which Jena you have and what the issue is.

My 2.5 has the pin. Small diameter portion fits into hole in crank pin. Large diameter end into one hole or the other in the rotor. Easy part to make if one has a lathe or knows someone who does. I will make you one if you don't have a local friend to help out.

Chances are the dimensions of my pin would be correct for you. But not necessarily. There are MANY variations among Jenas! You would have to accurately measure the two holes in your engine. Metric or English. Either one...

Regards. -Gary

RE: Anyone use a Zeiss Jena 2.5cc diesel?
 

AHA Yess, That is it, I don't have that pin!!
I would be ever so pleased, happy, and all other sorts of excitement that you can imageine... sorry for my spelling. I haven't been writing English for a verry long time.

Here is my Adress..:

Zvonko Gudelj
Lovrinacka 21
21000, Split
Croatia..

Also since you are in Diesel, can you please tell me a simple formular to make home made fuel....Can't buy the stuff here.

Thanks once again.

RE: Anyone use a Zeiss Jena 2.5cc diesel?
 

I can send you the messurements of the valve pin on Monday, I have to bring the engine to a guy who has a shubler ruler.

Thanks again Gary.

RE: Anyone use a Zeiss Jena 2.5cc diesel?
 

Do you recone this will work , the new head the previous owner made?
And how do I check it out to see if its a 2,0 or 2,5cc,? how large opening e.i. diameter of cylinder should it be?
I will mesure my engine and you will know for shure.