Thread: Straight four Engine design.

hi mate.They do make 1234 firing order engines. I cant think of any advantage they may have.
the other more traditional engine firing order 1 3 4 2 were two opossing clylinder reach ydc at the same time.
is smother running less vibration..

a lot less need for counter balancing. the crank shaft
do you mean a inline 4 of a flat 4? 1 or 2 cylinder heads?
aaron

Are you thinking 2 or 4 stroke? The other reason for a particular firing order may be to make the power delivery more even/ regular.

Michael

The firing order on a 4 cylinder 4 stroke need to be 180deg apart.
Regards

Baron j
In a inline 4 cylinder engine it's all to do with balance, a engine with a firing order of 1234 would work but the balance would be a shocker.
Regards
Ted

Assuming you mean a 4 stroke engine, and assuming you want evenly spaced firing impulses 180° apart, you can make a crank such that you have a 1 2 3 4 firing order but you still need a flat plane crankshaft. (720° of revolution for a complete cycle divided by 4 impulses = 180°) If you have the crank throws at 90° to each other you will have uneven firing, ie power strokes 90° and 270° apart.

I don't know what effect this would have on engine balance and smoothness of running, which is always a problem with inline 4s, but I suspect it would not be helpful. Then again you could be onto The Next Big Thing in 4 cylinder engines.

I'm out of my depth but I know there's more to engine balance than even firing. V twin engines have uneven firing but work very well, eg Guzzi, Ducati. Flat twin engines have even firing but have all the charisma of a laundry appliance, eg BMW <flame suit on>.

Many years ago I saw a graphic representation of the firing effects of various engine types. I have not been able to find it since.

From memory 180 deg opposing is not too bad, single is awful, double twin a bit better. V4 is terrible, V6 a bit better and straight 4/6 improve in that order. V8 is very good and as the cylinders increase it just gets better. This representation was in the form of a degree circle which showed the force on the crankshaft as it rotated. The result could be seen by even/uneven segment around the circle. From this interpretation it seems to me that any order that works would be as good as any other as long as the firing order is evenly spaced.

I may be wrong tho. It has been known.


Dean

Why not try some more up to date thinking on the design, have a look at doing a cross-plane crank. Yamaha have been working on one for their supersports bikes, its said to have a smoother distribution of output torque (thus allowing lighter flywheels and less energy lost in accelerating a flywheel with everything else. Would make for a nice challenge to machine the crank, probably would need a fixture to mount it right.

Theres some documentation on the whole setup kicking around on the interwebs somewhere.

There are many reasons why 1234 engines are rare, primarily balance & vibration as others have said plus the need for a stronger (read heavier) crankshaft with that firing order.

The other problem with a 1234 engine which would be more of an issue with a home built engine, presumably running a single carburettor, would be obtaining efficient fuel distribution throughout the manifold.

Rgds - Gavin

I heard a story about 2 front up / 2 rear down crankshafts for morris engines with shared intakes to get more gas flowing through the intake port.
Personally, build 90 degree V8 instead to hear that sweet old sound of the rumble, yankee V8s are easy to scale down to hobby size.

Torque curve out of a book printed around WW1.

Originally Posted by BaronJ

Hi Guys,

I've been cogitating about having a go at building an engine !

One of the things that I can't make up my mind about is the crank shaft. In a four cylinder car petrol engine the power stroke sequence seems to be 1,2,4,3 or 1,4,2,3. Is there any reason not to use 1,2,3,4 that is to machine the crank with big ends consecutively 90 degrees apart.

Thanks:

First an apology I failed to add the word "Steam" in front of engine. Sorry

Thanks for all the replies and good info. Part of my asking the question was to help in deciding what was needed to actually machine a crank shaft from a solid billet of material.

How badly does it need to be one piece? You would only go to such significant lengths if the motor was expected to output a lot of torque. Id consider making it in a number of parts and ffitting them together. Also means that if you cock one bit up, youre not binning a large, expensive billet.