Am I correct in saying that in the TwinAir engine, the two pistons go up and down together?

In an inline four cylinder engine, the outer two pots go up and down in unison and the inner two pots go up and down in unison but 180deg out from the outer two.

Is the TwinAir engine equivalent to the inner two pots of a four?

If it were the equivalent of the first half of a four, the two pistons would be 180deg out.

Which is correct?

Sorry for the silly question!
Mick

Mick F said:

Am I correct in saying that in the TwinAir engine, the two pistons go up and down together?

In an inline four cylinder engine, the outer two pots go up and down in unison and the inner two pots go up and down in unison but 180deg out from the outer two.

Is the TwinAir engine equivalent to the inner two pots of a four?

If it were the equivalent of the first half of a four, the two pistons would be 180deg out.

Which is correct?

Sorry for the silly question!
Mick

Click to expand...

They go together have a look at this https://www.google.co.uk/url?sa=t&s...kMsh3ICg8487cVGrg&sig2=0XdpVMQfkwWL1vuA550vwQ

Thanks!
I can sleep tonight ........

Mick F said:

Thanks!
I can sleep tonight ........

Click to expand...

This place is like the X-files......... The answers out there

If both pistons go together, the firing pulses are evenly spaced, but the engine is not balanced, hence the balancer shaft to compensate. The extra complexity and cost of the balancer is justified in the smoother power delivery. This is how most old British motorcycles were, but they didn't have the balancer shaft.

Most Japanese motorcycles with twin cylinder engines have the pistons at 180 degrees, giving better balance, but uneven firing pulses.

portland_bill said:

If both pistons go together, the firing pulses are evenly spaced, but the engine is not balanced, hence the balancer shaft to compensate. The extra complexity and cost of the balancer is justified in the smoother power delivery. This is how most old British motorcycles were, but they didn't have the balancer shaft.

Most Japanese motorcycles with twin cylinder engines have the pistons at 180 degrees, giving better balance, but uneven firing pulses.

Click to expand...

So, do they both fire on the same stroke or alternate strokes?

Piccolo Nero e Bella said:

So, do they both fire on the same stroke or alternate strokes?

Click to expand...

Alternate strokes...



~ 45 sec in - you can see the camshafts and they are doing different things for each cylinder.

A four-stroke engine fires every second time the piston arrives at the top.
Suck - Squeeze - Bang - Blow
Suck: Inlet valves open. Piston goes down, creates vacuum, air and fuel sucked in. (Pushed in with a turbo or supercharger)
Squeeze: Valves shut. Piston rises, compressing mixture.
Bang: Spark ignites fuel, which burns very rapidly, not explodes. Pressure pushes piston down.
Blow: Exhaust valves open, piston rises, exhaust expelled.

With both pistons travelling together, one is on the compression (squeeze) stroke whilst the other is on the exhaust (blow) stroke. This gives a nice even power delivery, at the cost of a lot of metal rising and falling together, hence the balancer shaft. Pop - Pop - Pop, etc.

If pistons are offset 180 degrees, they give an uneven firing interval, where one fires, followed immediately by the other, then a pause while they both go through their other cycles. Pop Pop - Pop Pop - Pop Pop, etc.

I have been rebuilding engines for 50 years. I started on industrial and tractor diesels and progressed to cars and motorcycles. I am now only interested in problem veteran and vintage engines, trying to get them run reliably can be very difficult, but is very rewarding in the end. The two-cylinder engine where both pistons go up together has to be balanced as if it is a single cylinder. The piston and connecting rod act as a reciprocating mass, but as you work down the connecting rod it changes from a reciprocating force to a rotational one. Because if this, when you go to balance it you have to take into account whether the engine is two stroke or four stroke, the length of stroke and the weights of the unbalanced parts, the formula can be between 50% to 70% of the reciprocating mass.

In motorcycles the engines are mounted rigidly and the frames can have harmonics, so the engine has to be tweaked to suit the particular frame it is being used in. The TA is not the ideal twin, it runs a balance shaft to help balance the engine. Experience has led people to alter the positioning of the rod attachment so they are 90[FONT=&quot]°[/FONT] apart on this particular configuration, this reduces the amount of balance weight required so the engines can be revved higher. They run similarly to a V-twin but I still prefer the 180° configuration as it runs in balance all the time, a horizontally opposed twin also runs in balance. There are problems regarding crankshaft loading with all these engines.

When I initially balanced my first single cylinder engine I took it back to a local motorcycle racing engine expert who told me the formula to use for that engine, and showed him that I had the quickest and smoothest 1906 6hp Rover engine in the world. Old ideas get resurrected and new ones emerge, but only some new ideas survive the test of time.

I used to have a 598cc 2 cylinder NSU Prinz. They used a motorbike engine: No distributor & aircooled as well. It was so simple and VERY reliable.