Flywheel debates - A series opinions welcome

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twin120ys
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Flywheel debates - A series opinions welcome

Postby twin120ys » Mon Aug 22, 2016 9:27 pm

Hi guys, I have started buying up for my a14 build now. Was going to be an a12 until the 14 came along.

So I have a camshaft from kelford which states 2500 to 6500rpm, I would like to think it would pull to 7. Specs on my build thread viewtopic.php?f=9&t=6131&start=100

85 pound valve springs from Franklin Camshafts Auckland (often ran in the ministocks up to about 7200rpm)
A15 head which will be skimmed down a bit, depending on valve clearances.


I am at the point where I need to decide on flywheel lightening? To or not to, I believe I can put a 9.5kg a12 one on (standard a14 is 10.7kg apparently), ill need to remove the engine plate to compensate for the thinner a12 flywheel.

How light is too light? I mainly drive by myself, 5 speed box
How/is it recommended to dowel the flywheel, I have heard a few stories. Unsure who would do this for me.

Cheers :beer:
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Re: Flywheel debates - A series opinions welcome

Postby Bartman » Tue Aug 23, 2016 3:57 pm

really light flywheels can be a whore on a road car. Your cam isn't a monster, so it wont be as terrible is if you had a minisprint grind. I've always run light flywheels, because I get them made light for free. On the open road you need to downshift a lot. Hit a rise in incline, and you'll see a bit of speed peel off. My last sunny had a lightened A12 f/wheel, behind a stock A12. It was a pig to get off the line with passengers.
That said they're great when you're ripping through the rev range, and giving it death.
My last "wild" A series had torque to burn. So it wasn't such a loss there.
It really is a "how long is a piece of string" question.

As for doweling the f/wheel to the crank, how ruthless of a driver are you? If missed shifts, and/or monster over revs are very likely then I'd say do it. Mine was done, but it was not easy. The flywheel had a PCD marked out on the same as the f/wheel to crank bolts. Then two holes were drilled through that part of the flywheel opposite one another. 5mm diameter. I bolted the flywheel to the engine using 12.9 tensile cap screws. Then using a hand/pistol drill, those holes were drilled into the end of the crank. It was hard. I think we used carbide tip masonary drill bits, with the tips sharpened. Fucked at least two bits doing it.
Then 5mm silversteel dowels were used to locate the flywheel. After the whole shooting match was balanced, the threads were chased out with a tap, loc-tite primed, loc tited the cap screws in, and the silver steel dowels were loc tited in too. Seemed to keep it in place. In that motors next life, the dowels were left out, and the flywheel came loose.
The issue is harmonics. And the fact that with the f/wheel bolts not fully tight, there is a bit of rotational slop in the holes. There was big thread about fixing it at 1200.com many years ago. I think the thread starter was oldmate?

On paper a good balance job should mean it wont come loose. BUt sometimes they still do. I've seen all the heads break off my cap screws. But I'm not known for mechanical sympathy. Quite the opposite....
They don't call me the man with the rubber arm for nothing you know.............


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