Thread: a question from my auto exam

Originally Posted by CraigE

As per another post a Rotary is not a 2 stroke in the true sense ................

Exactly right, but 2 stroke in effect in that each rotor fires once for each revolution of the crankshaft.

Deano

Originally Posted by DeanoH

Exactly right, but 2 stroke in effect in that each rotor fires once for each revolution of the crankshaft.

Deano

A rotary doesn't even stroke. So perhaps its really something along the lines of a 1 revolution.

Originally Posted by Slunnie

A rotary doesn't even stroke. So perhaps its really something along the lines of a 1 revolution.

Don't they have two plugs per combustion chamber?

Originally Posted by V8Ian

Don't they have two plugs per combustion chamber?

so do a few conventional in line 4-strokes eg. Nissan Z series motors as used in the later Bluebird (and others)

Paul

Originally Posted by V8Ian

Don't they have two plugs per combustion chamber?

Yes. Anyway SWMBO's early RX3 did when we were young and silly. Also had oil injection same as 2 stroke motor bikes. 10A engine turned into a water pump when the seals failed. . Went like s**t of a shovel but the brakes, scary. The rears were reminiscent of a morris minor and the front discs very small. Definitely a fun car to drive.

Deano

Originally Posted by vnx205

I can't accept that unfair criticism of 4 strokes.

When I used to run my SL125 Honda (bored and stroked to 175cc) on petrol during the week and alcohol when racing on Sundays, it used to take me less than an hour to do the swap.

That included:

• removing the fuel tank
• removing the head and barrel
• removing the piston
• fitting the higher (or lower) compression piston.
• replacing the barrel, head and fuel tank
• remove the bottom of the carby
• replace the main jet with on that was 40% bigger (or smaller)
• lift the carby slide out and move the circlip down (or up) three notches
• drain the petrol (or alcohol) and replace with alcohol (or petrol)

I used to think that was reasonably slick but a friend of mine who was a mechanic and had access to a better range of tools than I did could do that same swap at the start of his lunch break and still have time to ride home across town for a bite to eat and get back in time for the afternoon.

I reckon with the right tools, I could have given you a run for your money with your 45 minute 2 stroke changeover.

I suppose it depends on the bike and set up. I have generally worked on Honda XL / XR, Yamaha XT, YZF 4 strokes in the past and they would take me a bit, but then I was learning and not in a hurry either.

I seem to recall an 8 stroke diesel. Cant remember too much about it some nice person donated it to the cause after Cyclone Tracy in Darwin 1974. It ran 4 stroke when under load and off load reverted to a second camshaft which allowed it to fire every 4th revolution. Had huge flywheels and ran a 32 volt generator if I remember correctly, was about 12" bore and 24" stroke. It is probably still sitting in a shed at Batchelor.

that particular engine was actually a very clever 4 stroke with valve and injection hitnmiss governing.

if power wasnt needed from a particular pot it was allowed to miss a turn and its subsequent strokes just kept on rolling but the valves opend for each turn of the crank the inlet for the downwards stroke and the exhaust for the upward.

it was setup so that each pot would only miss 2 turns before being made to fire again. Stupidly expensive, seriously complicated but very very effective.

Generally it didnt really count as an 8 stroke engine as if you loaded it up it would revert to normal 4 stroke operations.

there was however some serious looksee-ery into 6 stroke petrol engine and for the day (remeber this was before CAD flow dynamics) the engine produced the same amount of power as the same size 4 stroke there was that much extra power to be found by giving the engine an extra intake and exhaust stroke to purge all the burnt gasses out of the combustion chamber.

then someone came up with forced induction. (actually from memory it was the cost of manufacture and unreliable cold running that did it in)