The Triumph Dolomite Club - Discussion Forum

I forgot I put this in my track Sprint resto...

Std flywheel weighs 9.6 kgs whereas my lightened one weighs 7.8 kgs.

You can see on the front that just a large chamfer has been removed around the edge...



...and on the rear a large scallop has been removed from the middle...

There's quite a bit more you can take off.

Is there consensus about a minimum weight for the flywheel on my 1850?

soe8m wrote:Be patience. There's not such a thing as a too light flywheel on a dolomite.

Jeroen

As it happens, my flywheel is having some more taken off it as we speak, along with some balancing of the crank, rods etc.

Yes I read that reply, but I thought some exact figures would be known. I'll give you my numbers when my flywheel is done.

A friend made a program for a dolomite flywheel. Mine are machined from the back like Martin's one and at the front big recesses are machined out. These areas do not add anything to the strenght and have the maximum effect as it is at the outer side where the acceleration and deceleration of the rotating weight is the highest.

Jeroen

Excuse my ignorance, but why do manufacturers fit flywheels that are so much heavier than necessary, when they could make them lighter as standard without causing significant running issues?

We are interested in performance and will put up with the side effects.
Heavy FW will help engine run even when engine is running rough it will still tick over.
It smooths out clumsy gearchanging.
Might even run when 2 cyls are down.

Triumph were not very good at balancing rotating parts so conrods and cranks could be quite bad.
If you were to check a modern Honda you would struggle to find it out of balance, but a standard Sprint

All these things are worse with a lightened flywheel.

Oh and mine was lightened similar to Marts

Sprint engines were also designed in a time when the 2 valve heads and push rods and such meant typical max revs of around
4500 to 5000. The Sprints are red lined at 6500, which is probably among the highest of its contemporaries. The out of balance forces become much more significant at higher revs.

So to be fair to Triumph or Ricardo or whoever else was involved, they did what they could with the out of date under-invested
kit that they had. In these days of much finer tolerances, lasers and computers its possible to get much better balance on the
line... and some of the kit trickles down to some back street tuners and balancers too...

Its just a matter of finding one you can trust and afford...

Jonners

Back in the day there was a gimmick known as blueprinting which literally meant getting rid of manufacturing "tolerances" so that your engine conformed exactly to the original blueprints and it was a rare motor that would not benefit from such a process.
Its not done much these days, simply because manufacturing tolerances are much tighter therefore making potential rewards vanishingly small.

But its always worth chopping a kilo or two out of a flywheel since they're always made with a big jigger factor to smooth the engine out for joe public. As Colin Chapman famously said, "to go faster, ADD LIGHTNESS!"

Steve