Twin wobbler engine

Hi all

Having built a single acting wobbler engine that worked a treat I have just finished a twine cylinder single acting version, but alas this is not working. It attempts to turn under air pressure but as the pistons are at the midway point they are both being pushed at once and so they jam. I drilled the ports using the same method as the single version, that is when the cylinder was at the peak of its arc travel in both directions. The crank shaft is 180 deg. apposed to each other, so I am not sure what I have done wrong. Obviously the timing is out somewhere but how or what is the best way to alter it.

Mike

I think your problem is the fact that you have a 180 degree crank....

Most twins I know have the throws 90 degrees apart.....

+1 on John's thoughts, if the ports are drilled right, a 90 degree crank timing rather than 180 deg will probably enable self starting. JD

I can't add anything but can I ask, if it was a flat twin presumably it would it have a 180 crank?

Hi

Not sure what you mean by flat twine, but it is a horizontal engine with the cylinders side by side. Before I attempt any alterations I will try and post some pictures of it so that you can see the arrangement. If I have to alter the crankshaft it should be possible as its built from separate pieces pushed together using Loctite.

Mike

Try running it with one cylinder only. If it works it will be crankshaft position.

Vic - you may be thinking flat twin as in BMW gasoline motorcycle engines. They do have 180 deg cranks. But a STEAM engine built with 180 deg crank, whether a flat twin or inline twin, will have a dead centre position where no port or both ports are open to pressure. If the crank is a 90 degree one, there is never a state where both ports are at the same open or exhaust state. If each cylinder's port is always at a different state to the other the engine will self start. V twin wobblers using a common crank pin are self starting because the ports on each cylinder can not be at the same state due to the V angle. JD

Nice looking engine Mike! great job. I think if you reposition the cranks at 90 dge it will be OK, as long as the ports line up correctly as I originally mentioned.

You may get smoother running (once it is running) if the steam supply is midway between cylinders rather than teed as you have it.

Many thanks folks, I will alter the crankshaft and get back to you in due course with the results.

Cheers Mike

Hope you get it going, it sure is a monster size wobbler

Just as a matter of interest what size bore and stroke is it ?

Peter.

Looks to me that you have the air feed crossed. Just move one side to its opposite port, (so that both sides are fed either in each top or each bottom port, but both sides must be the same).

The 90 deg crank is only for self starting (and you'll still need to alter the feed as above).

Nick.

Edited By Nick Hughes on 30/07/2015 16:55:14

As Nick says, check out the port arrangement on Elmer's 'H' twin;
**LINK**

Edited By john carruthers on 30/07/2015 17:07:48

Hi

Bore is 7/8 and stroke is 2 inches. If its just a case of moving the pipe that would be great, watch this space.

Mike

No! Don't alter the crank!

As you said in your first post, that's a single acting twin engine so 180 degrees is right.

A double acting engine needs 90-degree cranks, but that isn't one. A 90 degree crank won't solve the problem and when you do sort it, the engine won't run as well.

The cylinders are positioned facing each other, so if made identically they will be be trying to run in opposite directions. Imagine turning to clocks to face each other - they both run 'clockwise' but their hands don't go the same way.

The answer is as has been mentioned already is to swap over the steam and exhaust for ONE cylinder.

Neil

Agreed, I missed the way the piping was arranged....my mistake.... Oops!

Hi again

Well I swapped over the pipe on one side of the engine and that was the problem, it now works fine, very smooth even down to low speeds. With hindsight looking at the connections now it was a silly mistake to make, we live and learn. Many thanks to you all.

Mike