Anonymous

Anyone have pics of a lightened flywheel?

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PeterTR7V8
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Postby PeterTR7V8 » 02 Apr 2010 10:15

The further out you take the weight from the better the result but why do you want to lighten the flywheel?

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Postby Beans » 02 Apr 2010 10:24

Engine will rev better/quicker, but idle will suffer and become lumpier the more weight you take of ...

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PeterTR7V8
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Postby PeterTR7V8 » 02 Apr 2010 10:48

I know why you do it. I had mine lightened but if I didn't use it in competition I wouldn't have bothered with the cost or the risk. I was wondering what Rob's reason was. You can get alloy flywheels which is safer than modifying a steel one but it will set you back a few hundred quid.

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Postby Shauniedawn » 02 Apr 2010 11:54

[quote]<i>Originally posted by Bobbieslandy</i>

That's fantastic information guys, seems like there's a few ways to lighten it. So to sum up, most of the weight is taken from the back, the outside edge is tapered from the ring gear inwards along with what looks to be a complete skim across the face. Anything less than 6kg makes the car a bit of a handful (to be honest, without milling it i don't reckon i could get near that) so as long as it's a few KGs less than 10KG and no less than 6 we're laughing. I'll be doing this on an old 1970s Colchester triumph 2000 lathe, it's in pretty good condition and is accurate enough. Is there any thoughts on having the flywheel balanced?

Thanks again chaps!

Rob.

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Hiya Rob.

It MUST be balanced. Ideally (as far as I know) the way they do it is...

Balance the crank, add front pulley and balance, add flywheel and balance, add clutch assembly and balance the whole lot. That's more or less how mine was done.

However, if mine turns out too light, I'll machine another a bit heavier and just get that balanced and the clutch on a slave crank to save pulling the motor completely apart.

I machined up a mandrel and bolted the flywheel to that as my lathe (Student) isn't big enough to 'get round the back'. You might well be able to on the Triumph as they're a chunk bigger.





Shaun

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Postby Shauniedawn » 02 Apr 2010 12:01

<blockquote id="quote"><font size="1" face="Century Gothic, Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by willywonka</i>

Shaun.

Do you have any dimensional drawings for the lighted flywheel you could share with us?




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Sorry. All calipers, micrometers and scraps of paper in my workshop - no drawings!

Shaun

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Postby Shauniedawn » 02 Apr 2010 12:04

<blockquote id="quote"><font size="1" face="Century Gothic, Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Bobbieslandy</i>

................... with what looks to be a complete skim across the face.

Thanks again chaps!

Rob.

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Yeah - I took a fair bit off the face as I recall - compare the lengths of the clutch cover dowels that are protruding on my skimmed one.

Shaun

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Postby Bobbieslandy » 02 Apr 2010 15:47

Just ordered myself a Triumph dolomite workshop manual for all the torque settings etc, built myself a bench, nipped to Asdas for a load of tupperware boxes and labels, had a bit of a tidy up and stuck the digital camera on charge because it's going to see a lot of use!

Peter, i don't have a couple of hundred quid spare for a new flywheel, but i do have access to a workshop and some incredibly knowledgable people on here. By seeing how it's done and seeking advice i am minimising the risk. It won't be used in competition, but as far as enhancing the whole driving experience goes it's a good move.

Shaun, i'm glad you mentioned the whole lot gets balanced as i was only thinking about the flywheel. I'll make a few calls after the weekend and get some prices through. Thanks again for the pics.

Mac,

If i remember rightly, taking a pound off of the flywheel is equal to removing 50 pounds off of the total weight of the car (something i was told years ago so may be wrong, will need conformation). this is most obvious in first and second, less so in the upper gears as more factors come into play. the risk is if you go mad and remove too much "meat" the flywheel can shatter, this is most likely at the upper RPMs and will smash through the bellhousing, bonnet, dash or windscreen, the drivers ankles / legs. You get the picture! thats why this is such an important job to get right, if it's wrong then you wont know until about 5000RPM.


Really appreciate the info guys, it's my first complete engine rebuild and i'm going to need all the help i can get.

Rob


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PeterTR7V8
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Postby PeterTR7V8 » 02 Apr 2010 21:07

Its worth knowing that the flywheel acts as a dampener to changes in engine speed (RPM) so just like the suspension dampners it does have its uses. The flywheel soaks up the changes in the accelerator so when you are adjusting the gas to maintain speed the revs go up & down smoothly. This is why the car accelerates better with a lighter flywheel because without the extra weight the motor can respond faster. It also means that the revs drop faster so gear changes can be rougher - at least till you get used to it. Without the flywheel it would feel like you were jumping up & down on the gas pedal like when you first learnt to drive. Another byproduct of the dampening action is that the lighter the flywheel the easier it is to stall the car from take off. An engine with a heavier flywheel can have a lower idle speed & requires less clutch slip & fewer revs to get moving. So when deciding how light you want your flywheel to be it all comes down to how you want your car to behave. Just like when you are tuning your suspension, stiffer shocks will give you a rougher ride & so will a lighter flywheel.

Having said that, I don't think that the amount of weight you can safely take off a steel flywheel is enough to make the car particularly uncomfortable to drive. I had a couple of Kilos taken of mine (a V8 mind you) & the only real difference I've noticed is that it is now harder to start off in 2nd gear.

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Postby Bobbieslandy » 02 Apr 2010 21:54

A lightened flywheel would be more noticable on engines with a steeper torque curve, on one with a flat (ish) one like yours Peter it wouldn't notice so much. For example, a motorcycle has a very steep torque curve and very little in the way of a flywheel. because they produce so little low down torque, a flywheel would kill its acceleration. If i were to lighten the flywheel on my landrover which has one of the flattest torque curves ever i would not notice it, there's very little point in lightening a flywheel on a V8 unless it was very cammy IMHO.

Because the sprint engine is mostly top end power (talking about most 16v engines, havent got any experience of the sprint lump yet) a lighter flywheel would help it low down. i Agree that a seriously light flywheel would make pulling away a nightmare as you'd be relying on the engine to supply enough torque to get the car moving, there'd be very little stored in the flywheel. but as i'm not going for a massive reduction, just enough to make it rev better i won't be having this problem. I don't have the torque to pull away cleanly in second anyway so no loss there.

Lightening a sprint flywheel is alllll gooooooooood[:D]

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PeterTR7V8
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Postby PeterTR7V8 » 02 Apr 2010 22:31

Dude, I can pull away from a standstill in 5th! [8D] The one time I did that though I got a call from the clutch to say "do not do that again". [:)]

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Postby Bobbieslandy » 02 Apr 2010 22:37

Sweet haha!, i might be able to pull away in 5th one day but as long as there's a 2 litre 4 pot up front it aint gonna be soon. that must be some engine you got there!

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