Two into One

[AlanJ]

Hi Puffs,
Thanks for the translation, and looking at the pics, really great, but there is no way that I would build a twin that way, far too much involvement in
machining, and because of it, high cost. As I said earlier there is a way to join the 2 cranks at a reasonable cost without having to machine a special window
to tighten and adjust them, for a start. I actually have the ability to design this twin on cad and then send the change of parts out to an engineering workshop
to do that would be extremely high on cost. No, my whole idea is to take 2 engines that were probably not going anywhere and make them into something
a little different, without breaking mind and bank, before I pop me clogs or go nuts with this pandemic.
Stay safe Alan.

[Puffs]

Yes, you mentioned the BoWex M-32 earlier, a curved-tooth gear coupling involving nylon parts:
How you're going to fixate that to the crankshaft of an ETZ?

I guess you'd still be pressing & making parts.

A serious concern is that this coupling is rated to just 100°C, and rated for a load range of up to 180 Nm ( https://www.ktr.com//catalog/index.php? ... gy#page_92 ). Are you sure this is suitable? My fear would be that both the temperature range and the load range will be exceeded. I know that the torque specified for these engines is only about 27.4Nm (ETZ251), but that's an average value, point loads will be much higher. If you use a coupling like that, you would certainly have to use a 0° orientation, with combustion cycles in unison, but even so, I have my doubts if that joint will last long. Also because under full load those main bearings are likely to generate heat. But I'm not a mechanical engineer, so maybe I'm completely out of order. I hope you don't find me looking into this intrusive, otherwise just ignore me.

[AlanJ]

Hi Puffs,
Thanks again for your input. I had not looked at the values for that coupling, the reason being that a Thomas Scott is actually using one on his running
twin. The only reservations I had prior to your post was the size of the coupling, I thought it a bit bulky. I want to have a chat with the 2 engineers that
would be able to cover any machining problems I might have, but as you know with the lockown problem I can't do that yet, and sadly it's still too cold
in my garage to work reasonably, the other thing of course, it would be nice if I could purchase the other ETZ 251 engine. Something which is nothing to do
with looking at producing a twin is, I have managed to acquire an ETZ 150 for my brother, which requires quite a lot of refurb, the trouble is he is not computer
literate, so as we all know in this day and age one is definitely up against it, thank goodness it's an MZ, even though it's not one I know well. You have to keep
the flag flying, don't you,
Stay safe Alan.

[Puffs]

On bulky: the M32 has a length L=84mm, and an overall diameter DH=75mm (other info in the earlier link). With all the adapters, the coupling, bearings & seals in between, I suppose the big ends will be a fair distance apart. On the up side: then you don't have to take much off the cooling fins.

Would you mind saying a bit more about that working twin that Thomas Scott made? Is this the Scott of the Flying Squirrel?
Being tried & tested is so much more valuable than published numbers.

[AlanJ]

Hi again,
The problem I have with info from Thomas Scott is that I have not asked him if he minds the info being shown, as he wrote a full story in the MZ
riders magazine about how he built his twin and there are certain aspects of it that I do not agree with, you have mentioned, Puffs, that the crankshaft
joining item might not be strong enough or have a long life in the hot atmosphere of the crankcase. The other thing is, he is running it as a parallel twin
I think, and I personally don't think that is the way to go, although it is running ok. Actually, until I get as far as Thomas, who am I to say what is or is not
ok though. Incidently if it was that Scott of the Flying Squirrel it would be water cooled.
Alan.

[Puffs]

Right, so it's not this one:

Nevertheless, it would be quite interesting to hear about riding experiences & how many miles Thomas Scott did with his 0° construction.

On experience with the conventional method (a pressed 180° crankshaft with a central sealing separation that also holds 1 or 2 bearings, like the Jawa twins and several others): it has been tried and tested for many millions of miles; little vibrations and quite reliable.
But indeed trying to make that from 2 ETZ engines has been done before, is quite a bit of work, and would likely cost more that just buying a new Jawa 350 (which you can still buy & register in the UK).

Here's another interesting read: https://www.motorcyclespecs.co.za/model ... lk_700.htm .

[AlanJ]

Hi,
A great read about the Scott and Silk, I must admit I had more than a smile about the introduction of the kickstart, over the years on my TS's, and every now
and again, just when it knows I have had time to forget, the kickstart goes from top to bottom without engaging the ratchet, quite a surprise to the right foot.
A few harsh words to do with pistons and kickstarts is often heard in my garage area.
Stay safe Alan.

[Blurredman]

just when it knows I have had time to forget, the kickstart goes from top to bottom without engaging the ratchet, quite a surprise to the right foot.

The way around this is to make sure you engage the ratchet before giving it a nice dedicated kick. If you're in a rush, you forget this..and kick wildly... and a pain goes through your leg..

[AlanJ]

Hi M.
This right leg is 84 years young today, but if I was to get caught out with the kickstart, when this leg gets to the bottom, it suddenly becomes 84 years
old with a vengeance.
Stay safe Alan.

[Puffs]

Congratulations Alan!

A 0° parallel twin will also have double the compression resistance on the kickstarter. You might need a longer kickstarter?

[AlanJ]

Hi,
Thanks Puffs, I will do me best to keep kicking.
Stay safe Alan.

[AlanJ]

Hi Guys,
Just a small update, I have managed to find a pair of ETZ 251 engine cases and a crank, so, if we can give this blasted virus a shove up the #### then
I can start looking at the problems, keep you posted,
Stay safe Alan.

[Puffs]

Ta for keeping us posted Alan! I'd love to see some pics of how the 2 will be married.

While the pandemic is on the up elsewhere in Europe, vaccination-wise you're doing quite well over there, with some 41% of the population having had their 1st jab. I suspect that particularly in the UK the worst will be over soon.

[AlanJ]

Hi Puffs,
Yes, I would like to see some pics as well, trouble is right at this moment i'm isolating for an op next Tuesday so I can't pick the cases up till
sometime after then. The other thing that's a problem is not having anything to get me head round or me hands dirty is driving me up the wall
I have seen a 1965 ES 175/1 Trophy for sale and I would love to go for it, but, ( what do you want all those bikes for?) is holding me back at the moment.
As for the jabs, our scarecrow has done a good job there.
Stay safe Alan.

[Puffs]

1965 ES 175/1:

A true DDR icon, and an acquired taste @12hp. I understand they can become quite pricey - a cult within a cult?

For me, it's riding them. I have 6, and have to admit 1 of those I rarely ride...
The season is coming. Well, here it has arrived.

Yes, but at least your scarecrow is effective - more so than our Ms. von Trapp. Blablabla.