Flywheel Lighten & Balance

[Rusty]

Hi all, 2 questions -

Can the 3B and 7A FWs be lightened to the same weight? I'd be looking at about a 7-7.5kg effort. From pictures, it seems that a 7A item has a bit more meat added on and that either can be reduced to a similar, more sporty weight.

Are the OE 3B or 7A FWs in zero balance or do they have some built-in eccentric counterweighting at all?

Reason for asking is that I'm likely to need a stronger clutch at some point and want to look into getting things sorted, so it all bolts on... jsut like the 3B item did 4 years or so ago (sort of)

I guess the other option is a billet steel FW. Not sure where to get one of those beauties though, or cost thereof.

[Pembo]

I use an alloy flywheel, steel ring gear and steel clutch face plate. I've posted all the weights here before when the engine was built up. Competition clutch pressure plate added a bit back though but the 5 paddle clutch was lighter than the OEM clutch plate. Each component balanced individually including each bolt and washer because a small difference becomes a big difference when rotating at 7000 rpm! This was the same for crank and all rotating components.
Remember it is the splines on the clutch plate that drives the gearbox. It is the pressure plate that clamps the clutch plate to the flywheel face and the flywheel is bolted to the crankshaft. (Sound like a song ....)

[Rusty]

Alloy is too light. Crank and pulley are OE ABY do need to understand what part the flywheel plays in the system, as my crank isn't zero balance.

[driftin jo]

The 7A is essentially a 3B with a ridge on the back remove this and it is a 3B, then of coarse you can remove more. I have done many of these.
The flywheels are not zero balanced as the bottom end crank flywheel and pulley are balanced as one assembly.
I spoke to basset down a long time ago on the subject and the said that if you swap flywheels you should have the assembly balanced.
Many people have changed from dual mass and used 3B and 7A flywheels and will say they had no issues with not having it balanced but they may not do 180k miles without bearings wearing out as with a stock engine.
You can 'get away with it' but as basset down said you might be unlucky and destroy you big ends in in 5k miles.
They are not counter weighted as such but there is a familiar pattern to the balancing done that
does leave the flywheels in a slightly counterweighted state as part of assembly balancing with the crank and pulley. The dual mass ones have weights welded on the opposite side that holes are drilled in the solid ones to balance them .
If you want to go mad you can give you crank to basset down and for ~£550 they will do a
GP conversion on it, this involves machining it down nice and light and zero balancing it so then any zero balanced flywheel and pulley can be used. A friend of mine had one done and it revved like a Ferrari, tick over had to be 1500rpm though.
If you want to know more give basset down a call they are very friendly and informative

[driftin jo]

I always advise people to get the bottom end done after a swap, just for ref, basset down will do your bottom end crank, flywheel, pulley, pistons, and rods for £160 plus vat. Very reasonable considering the standard of work is second to none.

[mcandmar]

2nd that. I sent my project engine internals over to Basset down as i am converting it to a 3B flywheel, hes a perfectionist and a really nice guy. In hindsight im glad i did as my S2 avant had the dual mass flywheel replaced in its previous life and the lack of balance is very noticeable at high revs, its just dosent rev as sweetly as our S4 or other S2's i have driven. So dont even think about replacing the flywheel without balancing it IMO, it bugs me every time i drive the car.

[Rusty]

OK, that's fine. I spoke to Aelred and BDB a while ago about a rebuild and full lighten & balance but couldn't remember the score with just FWs. The car currently has a 3B FW on an ABY bottom end but as it doesn't do too many miles, hopefully, I have a little while to get it all sorted. If it's a matter of getting the whole lot done, then I'll not bother doing anyhting fancy to a spare flywheel and will just put the money towards doing it all properly... eventually.

[mcandmar]

In that case dont worry about it, just drive it until you plan for a rebuild. Also worth noting he asked for my clutch pressure plate too and balanced it along with the entire assembly. From my understanding he balances the crank/pulley/flywheel as per norm, then adds the pressure plate and tweaks it so the balance remains true.