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Glyn Harper

Flywheel lightening

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So my flywheel will be off in the next couple of days so I can replace my rear crank seal.

As my gearbox will also be away for a couple of months I’m thinking about getting my flywheel re surfaced, as well as some mild lightening, then re balancing.

Firstly, is there much material that can be taken off a standard flywheel? Don’t want to make the car undrivable, so maybe a mild reduction as it’s getting resurfaced anyway.

Secondly, do the dowels come out easy enough in order to get it re surfaced and machined? I gather that the process on a raised type flywheel is to skim the raised contact face, then reduce the sourrounding lower area by the same amount to ensure the clutch bolts on the same distance as it did originally.

Just after some experiences from anyone else who may have had this done already, and possibly a good place to do it. I have found a place in the south of England, but I’m open to suggestions if there is a known expert we’re aware of. :)

Edited by Glyn Harper

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7 hours ago, Glyn Harper said:

secondly, do the dowels come out easy enough in order to get it re surfaced and machined? I gather that the process on a raised type flywheel is to skim the raised contact face, then reduce the sourrounding lower area by the same amount to ensure the clutch bolts on the same distance as it did originally.

Hi Glyn,   Some dowels are more awkward than others, but should not give issue.. the rest as you described for grinding is correct and very important to keep the correct clamp loading. 

As far as lightening the standard fly wheel,  I would not go there.. It was not designed to be different. There are load of stories around of standard fly's detonating due to lightening..  And they make one hell of a mess when they go...  

Also minor lightening or skimming will make little difference to drivability,  You need to work the peripheral weight to make major gains..  Drilling 17-20 mm holes is what is recognized as the usual way , along with milled letter box slots.  The later I again would avoid as I have seen these section out even on purpose built flywheels.   

If you want to improve your engine response then you need to get a recognized custom built fly wheel for the job made out of chrome molly steel.  You can specify your weight distribution to extract the required inertia for the type of response you desire. with design and manufacture expect to pay £500,   

The standard fly is 7.2 kg with high peripheral loading ,  you can get it down to 4 kg with a single plate set up , but needs a good design to dissipate the heat , down side is the clutch cover is wide and heavy , as a result caries a lot of peripheral  inertia mass, so a custom lightened cover would compliment any requirements..  ..  

So the choices are there, and as always with quality mod's it come down to £'s..  short cuts can cost even more.    hope this answers your questions.. 

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I had the flywheel ground by H.T. Howard in Slough. The clutch plate dowels knock out with a drive pin punch.

 

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Hi Dave. That’s an excellent reply, many thanks!

I think as you suggest, I’ll leave it normal ish weight. Obviously it’ll lose a touch due to being re surfaced (I’m guessing 1/2 a mm will need to come off) and tell them to then just do a balancing job on it afterwards without any extra lightening.

I’ve got some titanium bolts to hold the clutch on which will lighten things slightly as well. Not much, but enough to satisfy my desire to have made some improvements while I’m at it.

But yeah, good advice. I won’t get it lightened as a separate operation. 7.2kg doesn’t sound bad for a flywheel anyway. I was guessing it was more like 9 or something.

Still need to get it off the car! Tonight I’m hoping, now it’s slightly warmer. I’ll post some images of the surface when I have to describe its condition as the surface has some depressions in it. Not small pits, but depressions that are about 2 cm wide, and a few thou deep. Will be tricky to photograph the depth, but I’ll have a go.

2 minutes ago, Chillidoggy said:

I had the flywheel ground by H.T. Howard in Slough. The clutch plate dowels knock out with a drive pin punch.

 

That’s the place it’s going to, yeah. I couldn’t remember the name when I wrote my original post. :) I’ll let them knock the dowels out then. I’m sure they’re more used to doing it than I am, and I guess they’ll need them to balance it anyway so no point them rattling around separately in transit. :)

Edited by Glyn Harper

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All sound good. Have a look for fueltheburn posts. Kieran Lee had a special built when he upgraded his engine although I think he had problems with it. His engine was built to 2.5 spec but it was none turbo in an Excel. Big write up about it in the Excel group.

Try this link.

 

 

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2 hours ago, Glyn Harper said:

Hi Dave. That’s an excellent reply, many thanks!

I think as you suggest, I’ll leave it normal ish weight. Obviously it’ll lose a touch due to being re surfaced (I’m guessing 1/2 a mm will need to come off) and tell them to then just do a balancing job on it afterwards without any extra lightening.

I’ve got some titanium bolts to hold the clutch on which will lighten things slightly as well. Not much, but enough to satisfy my desire to have made some improvements while I’m at it.

But yeah, good advice. I won’t get it lightened as a separate operation. 7.2kg doesn’t sound bad for a flywheel anyway. I was guessing it was more like 9 or something.

Still need to get it off the car! Tonight I’m hoping, now it’s slightly warmer. I’ll post some images of the surface when I have to describe its condition as the surface has some depressions in it. Not small pits, but depressions that are about 2 cm wide, and a few thou deep. Will be tricky to photograph the depth, but I’ll have a go.

That’s the place it’s going to, yeah. I couldn’t remember the name when I wrote my original post. :) I’ll let them knock the dowels out then. I’m sure they’re more used to doing it than I am, and I guess they’ll need them to balance it anyway so no point them rattling around separately in transit. :)

 

I don't think HT Howard has any balancing facilities, but they can arrange to have it done. If you just have the flywheel reground to spec, then there's no real need to rebalance. If you have it lightened however, then it will need to be rebalanced, and I think I've already mentioned that it is better to balance the complete rotating assembly. Again, that's a personal view.

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When you say the complete assembly, do you mean the clutch as well, or with the crank? I'm not taking the crank out but could send the clutch.

Edited by Glyn Harper

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By complete assembly, I mean flywheel, clutch, crankshaft, con-rods, pistons and front pulley.

I'm sure there's plenty of info on the web about dynamic balancing, but call HT Howard and speak to them first.

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I spoke to HT the other day, but when I've posted the flywheel off I'll call them again to see what the recommend. I'm sure Lotus didn't balance the whole engine at the factory and I'm not racing mine, so as long as I can get the flywheel in balance hopefully it'll do for my meagre needs. :)

Good call using HT Howard though, as my own research had led me to them so it's good I've ended up with the right company.

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Just looking into this for the future... The far furute. What about billet aluminum wheels. Isnt there a shelf option abd what about clutch covers? Nothing already done?

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I think aluminium would be far too light for what I want. I think when my flywheel arrives they're just going to resurface it.

Funnily enough the post office weighed the whole box, complete with cardboard box and packaging and it was 6.78kg. That that heavy really compared to some flywheels.

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I know this is comparing bananas to grapes but I remember putting in a 9lb billet on a chevrolet street/strip car and it made one hell of a difference in response but it drove just fine. I know thats a gob of torque but I dunno I never had a problem.

 

The reason I was asking is for me. I really would like to do that snd I was looking into getting a twin cluth anyhow. Theres some nice stuff out there these days.

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1 hour ago, Glyn Harper said:

Funnily enough the post office weighed the whole box, complete with cardboard box and packaging and it was 6.78kg. That that heavy really compared to some flywheels.

Well that is strange Glyn ,  the weight of an S300 I use for my mock ups is 7.2 kg .. So you are well on the way already..   Going light is not really a problem , these donkeys are fairly torque'y anyway..  Its just messing with a std unit to much could give you problems.. It will be interesting to see what weight it comes back at. 

1 hour ago, Roberto Esprit said:

The reason I was asking is for me. I really would like to do that snd I was looking into getting a twin cluth anyhow. Theres some nice stuff out there these days.

We covered this before Roberto..  The set up height on all the twin plate push clutch's is to high for the bell housing clearance..    The only creditable option at the time was the V8 twin Lotus AP pull  unit , , this has now been adapted and tested with custom  3.9 kg flywheel to fit the 910 set up. ..  However this is all overkill unless you are powering the big numbers...  we tested and proved  a single plate paddle clutch with sport cover which easily handled 410 lbft torque without  a hard peddle..  This is comparable with the std V8 twin without the massive cost.. to get the 500+ lbft torque out of the V8 twin you also need a custom build unit from AP Racing... Pic's and details are half way down page 13 in the 412 thread.   You may find other types of pull clutches that will do the job , but you will still need to engineer in all the peripherals to make them work..    

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Yep, I've got the postal receipt in front of me! I can only assume it's been resurfaced before as it doesn't look like it's been lightened. The Post Office scales should be correct or it would be costing them lots of money.

It is a big box though, so who knows.. maybe the corner was resting on something and the lady didn't notice, I wasn't paying a massive amount of attention.

When it arrives at HT Howard I'll ask him to weigh if before we decide it there is any lightening to be had, but I did tell him I'd rather leave it standard and just re surface it, rather than compromise its structure more than is necessary.

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I know of one person who had their flywheel lightened INCORRECTLY.

There is a danger that if a shop doesn't understand how the crankshaft position sensor work, then they can cause problems with the operation of the sensor... The engine will not run if that happens.

There are 7 notches around the rim of the flywheel, you must not allow a machine shop to add any notches near the rim.

9qSpL_Pt-YFB4uKOZ9m2Ji-Z99-RAfWCTROxV3Wf

 

I've driven this car with the lightened (and balanced flywheel) and it revs very nicely.

BZ9BG0yCcyXTrPqfuoVpEVGKrQ3o2DgezfX6exv9

 

The step height between the friction ring and the pressure plate mounting ring, is CRITICAL, or else the clutch clamp load and life will be affected.

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Thanks for that Travis. You've actually reminded me to email them the step height specs from the manual, which appears to be 0.5 - 0.6mm unless I've read it wrong.

My car originally was a carb Turbo, so I don't have the notches in my flywheel.. My crank position sensor runs from a sensor at the other end of the crank. I don't have A/C so we machined the end of the pulley where the A/C belt would be and fitted a crank position disc and sensor arrangement there.

By the way.. does the flywheel only mount on the crank one particular way? I didn't mark it or anything before I took it off. When I finally got the bolts out, it pretty much just dropped off! I was so happy to see it come off I forgot to make a note of which way up it was. Are the mounting holes slightly off centre? (I'm hoping)

Edited by Glyn Harper

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Its the dowels that are slightly different pitch.. it will only go on one way because of this,  you will see when you offer it up.   

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Thanks as well. Speaking of which. Gomma jump in and hijack a bit again. Guys I gave reaf about quite a few crank triggers for the crank pulley and its looking like the safe bet... How mich should I be paying to have one made?

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2 hours ago, Roberto Esprit said:

Thanks as well. Speaking of which. Gomma jump in and hijack a bit again. Guys I gave reaf about quite a few crank triggers for the crank pulley and its looking like the safe bet... How mich should I be paying to have one made?

If you are going down the light fly wheel road , why not design a fly wheel for your application with a 36 -1 trigger as part of it.. This will conform with most after market ECU application. Otherwise front pulley trigger wheels are available off the shelf for the 900 series now..  They only require small amount of machining to the pulley and a sensor bracket..( circa £50 )   NB.. sensor bracket should be very rigid as harmonics can cause ghost signals in the 4000 to 4500 range effecting tuning..   Mark Kassim has managed to program his after market ECU to except the unusual Lotus trigger format , so you can use that is you wanted. Not sure it was that straight forward with complications but has been achieved.. 

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Lotusbis supplied a machined aluminium mount and crank pulley with the teeth cut into it for my old N/A esprit when I added mapped ignition so they might be able to supply fairly quickly.

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Thanks guys and sorry for thread jackin. Haltech told me no  specifically to the lotus pattern....

Ill look into your suppliers. Hey if anyone has a cad file. Id pay for it.

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