Lotus Elan

Flywheel quesion

PostPost by: seewin » Thu Jan 30, 2020 7:44 pm

I am in the process of restoring a 1969 Elan, and had a question on the flywheel. The flywheel had been surfaced prior to my teardown of engine, and I noticed while doing a preliminary check of the face runout while still attached to crank, that I was getting .048" total runout across the face surface. I checked crank flange and it has zero runout, so good there. Apparently someone had done a very poor job of surfacing flywheel at some point in its life. I have subsequently resurfaced the face of flywheel, and have it running with .002" TIR. This leads me to my question, is there any published or accepted standard for minimum thickness of the factory flywheel? This one had no dowel pins in face when disassembled, and upon examination, I can see why. The reamed portion of hole in flywheel face that retains the pin is only about .050" deep. I can take care of this problem on the milling machine, but am concerned that I might have a safety problem with the flywheel now being too thin.
Can anyone give me a measured thickness of flywheel taken between the 2 machined surfaces near the starter drive ring on a new or uncut factory flywheel?
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PostPost by: 2cams70 » Thu Jan 30, 2020 10:25 pm

Can you post a picture? 0.048" run out sounds enormous!!
Perhaps it's an aftermarket steel flywheel that's bent.
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PostPost by: seewin » Fri Jan 31, 2020 1:51 am

_DSC3273.JPG and
First cut of .006"
Not sure what you are looking for in the way of a picture. Attached is a picture of the flywheel in late after indicating in the the back mounting flange and 1 cut of .006". Next picture is showing the gap between cutting tool tip and opposite side of where cut area.
It is the factory cast iron flywheel, not steel. If you have ever cut cast iron, it creates a very distinctive chip, almost like sand.
As mentioned earlier, flywheel is now running true on crank flange, and I hat to remove a total of .052" to clean up all the way across face.
I know how much material I removed, but no idea how many times it has been surfaced in its previous 50+ years, or how much was removed prior to my machining it. Thus the reason for my request of an accurate measurement of thickness on a virgin flywheel.
Attachments
_DSC3268.JPG and
Opposite side of 1st cut
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PostPost by: 2cams70 » Fri Jan 31, 2020 3:11 am

That flywheel seems a bit weird. Looks too shiny for cast iron. What does the back surface look like and did you check the runout there?
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PostPost by: seewin » Fri Jan 31, 2020 3:36 am

No runout on backside of flywheel. It's cast iron.
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PostPost by: 2cams70 » Fri Jan 31, 2020 1:22 pm

seewin wrote:Can anyone give me a measured thickness of flywheel taken between the 2 machined surfaces near the starter drive ring on a new or uncut factory flywheel?


Mine measures 26.3mm thickness front face to back face. Been machined at some point but not excessively so I believe.
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PostPost by: types26/36 » Fri Jan 31, 2020 2:00 pm

I have three f/wheels.
1. 24.6mm (skimmed)
2. 26.0mm (skimmed)
3. 26.5mm ….I believe this one to be unskimmed but cannot guarantee it.
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PostPost by: seewin » Fri Jan 31, 2020 2:15 pm

Thanks so much, very interesting. Mine measures .781" (19.85) thick at the outer faces near starter ring. Also, it weighs 9.6 pounds (4.4 kg). This one has "A26E-717-BM stamped on back side. Wonder if it has just been machined excessively or is it something other than the stock flywheel?
Attachments
_DSC3284.JPG and
Stamping on back side
_DSC3279.JPG and
Backside
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PostPost by: types26/36 » Fri Jan 31, 2020 2:41 pm

Here is the stamp on my (un-skimed f/w) I believe it came from a Europa Special hence the 074 prefix, your A 26 prefix refers to an Elan.
I think the only difference between the Europa and Elan flywheel are that the timing marks are marked on the outer circumference of the Europa f/wheel as the timing is checked through an opening in the bellhousing.
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fw europa.JPG and
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PostPost by: gjz30075 » Fri Jan 31, 2020 4:42 pm

I have 26.8mm on a probably uncut flywheel.
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PostPost by: seewin » Fri Jan 31, 2020 4:53 pm

Thanks to everyone for taking the time to offer their opinions and take some measurements. These confirm my initial thoughts that this flywheel has been excessively cut down. I will most likely begin the search for a new one either in cast iron, steel or aluminum. I just do not want to chance it coming apart.
Any good sources in the states for a new one?
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PostPost by: 2cams70 » Fri Jan 31, 2020 11:20 pm

seewin wrote: I will most likely begin the search for a new one either in cast iron, steel or aluminum. I just do not want to chance it coming apart.


Mine is also A26E-717-BM from Twin Cam Escort so same as Lotus Elan.

I used a steel flywheel from Burtons in my build. I changed the crankshaft to steel and so changed the flywheel to steel as well. Both Burtons and QED ship internationally for reasonable cost.

Personally I'd be wary of changing to an Aluminum flywheel on a road car. I know of no OEM who has ever used an aluminum flywheel on a road car. Maybe there is a very good reason why.
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PostPost by: prezoom » Sat Feb 01, 2020 12:13 am

I am currently running a Fidanza aluminum flywheel on the Zetec in my Plus2, with a close ratio 4-speed gearbox and a 3.55 differential, and loving it.
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PostPost by: seewin » Sat Feb 01, 2020 2:09 am

Thanks again for all the comments. I'm running a 3.78 rear gear, so don't think I will have a problem with the aluminum flywheel. It is not a whole lot lighter than the "slimmed down" cast iron factory piece that was in it.
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PostPost by: 2cams70 » Sat Feb 01, 2020 4:46 am

My guess as to why aluminum flywheels are never used for OE even on exotic cars is because aluminum always has a fatigue life and steel / cast iron does not if it's always operated within it's elastic limits. Aluminum will therefore always fail at some point. It just becomes a matter then of correctly sizing things and doing the sums so that it fails well outside the expected lifetime of the product the part is in (one of the very few things I still remember from my early engineering training at university!).

In order to meet OEM test cycle durability standards an aluminum flywheel would probably need to be sized prohibitively large and therefore with little or no benefit versus steel.

Remember the pressure and clutch plate are 50% or more of the rotating mass so the overall benefit of an aluminum flywheel may not be as great as you first thought.

Personally, at least for a road car, my preference is steel.
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