Lightened Flywheels

[John Mason]

I am not thinking of changing my flywheel weight as I don't do any competition driving. However this string about modifying flywheels got my brain thinking about how light you could have a flywheel that still kept the engine ticking over. Also would an engine run without one. My limited understanding of engines tells me that it would'nt at least at low revs.
I awaite replies from member with greater automobile engineering knowledge than myself.

John Mason

[Austin in the Shed]

There is no problem at 10 1/2 lbs,when we used to trial I used to have the tickover set at about a thousand.
I don't think you can burst a 7 flywheel as they are made from something like En 16 or greater,an alloy steel as opposed to most flywheels being made of cast iron.
As Steve has found it is possible for the centre to break out if they have been thinned near the boss.
Modern motor cycles don't have a flywheel as such and drive ok.

[Terrytuned]

A counter balanced crank does not need a flywheel just some thing to mount a clutch on. Terry.

[AustinWood]

I imagine that the centre can break away because it will be stressed by the crankshaft whipping.

[Chris KC]

I imagine that the centre can break away because it will be stressed by the crankshaft whipping.

One of the beauties of a (properly functioning) 3 bearing engine is that they don't to any great extent.

---

There's certainly metal that can be removed from the engine side of the flywheel but a word of caution. I did this once but, eventually, the flywheel centre boss cracked away around its complete circumference due, I imagine, because too much was taken off. A good radius was formed at the junction of the boss and the flywheel but it still broke away. The only indication that this had happened was a slight 'rumbling' from the engine at tick over and when taking up load.

Steve

Steve, do you recall how thin it was where it failed? That would be fairly easy to compare. I've not measured mine yet but it does feel a bit skimpy betwixt my fingers.

[Steve Jones]

I'd love to Chris but you've touched on something of a mystery. For the life of me, I don't know what I did with that flywheel. I imagine I could have thrown it away but I don't tend to do that as anyone who's looked in my workshop will confirm!! However, as far as I can see, it's not about but if I ever do find it, I'd be happy to take some measurements.

Steve

[Zetomagneto]

A counter balanced crank does not need a flywheel just some thing to mount a clutch on.   Terry.

Back in the 70s when Austin Sevens were to play/ tinker with I built up an engine out of bits an pieces 
we had lying around, It was almost complete but unable to find a flywheel nut on a sat afternoon.
I was so keen to start it up did so on the handle , no flywheel fitted, it didn't want to idle but revved 
up and down very quickly

[Tony Press]

I imagine that the centre can break away because it will be stressed by the crankshaft whipping.

One of my early Austin 7 memories is of watching the flywheel on a light shaft engine with the starter removed - the rim 'widened' by what seemed to be 1/8" as the shaft whipped !

[jansens]

Since my flywheel was chopped up to be lightened I don't seem to have any markings on it. I would like to mark on the TDC and starting timing marks. If I am reading the books right you should start setting the timing with the flywheel 1 1/4 inches before TDC on number 1 cylinders compression stroke.

I made a little extension to my dial gauge and used that to find TDC on number 1 compression stroke. 1 1/4 inches seems to be 4 teeth so do I make the marks where the pieces of tape are in this picture? The one on the left being the BTDC mark and the one opposite the block nut is the TDC one.

I have also read (somewhere I can't find now) that with a automatic distributor the maximum advance is about 28 degrees which would be 6 teeth. Should I make the second mark there?

I know fine tuning needs to be done adjusting the distributor with the engine running but I want the marks there to get me in in the right starting spot.



Simon

[Bob Culver]

1 1/4 inch is a very conservative start place for full advance at medium rpm. The advance range varies greatly depending on the distributor, wear, mods etc. if modified so full advance only at high rpm it is esp conservative.
Distributor rotor shaft can be twisted to full advance and locked there using a long screw and washer.