lightening flywheel - How much?

[yogidom]

Advice appreciated.
In the process of rebuilding a 2cv engine having ceased a big end on day two of becoming a proud owner of a 223.
I will be fitting 9:1 pistons and barrels to a second hand bottom end along with Boyer Bransden ignition from the club.
I have the thinner flywheel 9mm (6.2kg bathroom scales) and was wondering how much weight reduction would be sensible?

I would also like to say a big Thank You to Rocket Ron who has been a great source of knowledge and encouragement.

[SILLYCVS]

Thickness of the ring gear on the racers and its perfectly ok on the road, have done many like that everyone happy

[yogidom]

Thank you Sillycvs.
Hamlin of Bridgewater quoted approx. £60 - £80 to lighten my flywheel (a further £80 to balance on the crank). They seem to know what they are doing.
Visited Jon Davies of West Monkton nr Taunton. He has a field of Citroens being recycled. He produced a lightened 3.9kg flywheel at a very reasonable price.
On comparing both flywheels the timing hole is in a different place relative to the spigot on the crank. Any clever ideas appreciated.
Jon suggested marking the new flywheel by the top N/S gearbox mount (engine serial number plate) with the heads off to confirm TDC. I think I understand but its beyond my knowledge.

[Geoff Ryall-Harvey]

If they've offered to balance on the crank then they are probably not particularly 2CV friendly. The big end bearings are pressed on and are not part of the rotating mass when in situ - but they would be on the balancing machine...

I've never come across a timing hole being located in different locations in relation to the dowels. Are you sure you're not mixing up the holes? Maybe Ken Hannah can shed some light on this?

[yogidom]

Thanks Geoff
I will try and post a photo of both flywheels tomorrow.
The original has a single large hole, the 'new' one has numerous small holes (balancing?) but only one the same diameter as the first flywheel but not in the same position relative to the extra 'dowel' hole towards the centre of the flywheels.

I'm sure your correct re balancing being specific to these engines. The 'new' flywheel does look like somebody has done some balancing work. I'm sure I will find out if I can get the timing to work. I don't want to upset the balance.

[hutchii]

The "unusual" position of the timing hole suggests to me that someone committed the cardinal sin, i.e. not deepening the original hole before machining the unwanted material off that side of the flywheel!
I'm sure Alan at Silly Cvs will correct me if I'm wrong, but I'm pretty sure he's told me that he's never re-balanced any of the many flywheels that he's lightened over too many years.
Alan?
Just a thought, if you're prepared to sacrifice the original flywheel, you could locate the two wheels together, orientated by the crank dowel and drill right through the first (original) and into the "new".
Another option is to set the timing accurately with the original flywheel, lock the crank in that position, (the new flywheel bots don't need to be fully tightened) change the flywheel to the new, and the timing won't have changed 'cos the crank won't have moved. Then, using a 6mm diameter drill you could centre punch the correct hole position on the new flywheel through the timing hole in the crankcase. Remove the new flywheel and drill 6mm hole to suitable depth. It would probably be best to Loctite a pin into the rogue hole.
Let us know how you get on.

[SILLYCVS]

Just to clarify, i do pop machined flywheels on a simple balance rig, generally very little out of balance after machining, if anything at all, no one to date has reported vibration issues, but as usual will don tin hat and flak jacket just in case lol, timing hole should always be drilled through before machining, as hutchi suggests lay std over lightened drill through, easiest and accurate enough.

[yogidom]

Thank you chaps (assumed).
I shall sacrifice the original flywheel (seems a shame, but if it works guess I won't want a heavy one).
Will let you all know how I get on.

Any tips on tools/materials for de-coking head?

[Ken Hanna]

I've never come across a timing hole being located in different locations in relation to the dowels. Are you sure you're not mixing up the holes?
Maybe Ken Hanna ( ) can shed some light on this?

Hi Geoff,
is it possible that I'm the only oldtimer on here who remembers how to find TDC accurately using a spark plug with a longer reach than that used in the engine being worked on?
Although if the engine already used a long reach plug, it was necessary to modify a plug to make the required 'piston stop'.

A brief description of the procedure; position the crankshaft with the pistons just shy of TDC, then screw the long reach plug into the head which is on the compression stroke. Removing the rocker covers will identify which one that is.
Screw the long reach plug into that head, then gently bring the piston into contact with the stop by rotating the crankshaft both clockwise and anti-clockwise. For each direction, mark the flywheel edge with a scribe or a welder's pencil in reference to a fixed point on the crankcase.
For an A series engine, the offside 'horn' of the crankcase is best, even better if it has a pointer added as in the video below.
If the marks are too far apart or too close together, that can be altered by screwing the plug inwards or outwards a fraction.
I usually settle for marks about 6 teeth apart, then the TDC mark is estabished with a mark midway between the 2 already made.
Fwiw, the factory timing mark is invariably remarkably accurate.

https://www.flickr.com/photos/30132857@N06/5449076261/

Once TDC has been determined, it's easy to mark the 'static' timing mark as well as the (much more important) 'full advance' mark.
The latter should be around 34* TDC for a 8.5:1 pistons, 31* TDC for 9.0:1 pistons.

Ken

p.s. If the idea of using an old plug doesn't take your fancy, Ebay can provide a custom tool...
http://www.ebay.co.uk/itm/Motorcycle-Sc ... 8046&rt=nc

[yogidom]

Very interesting Ken, that is a good description of what Jon was telling me but I'm sure he had a pointer attached to nearside horn where the engine number is riveted.
But what your saying is copying the mark from the old flywheel should work too. (fwiw)

Thanks again.

Dom.