Can You Remove This Flywheel?

[86esprits3]

I read something in the manual that said you cannot disturb the bolts on 912 flywheels with flexplates. My engine is a 910, and the manual says nothing about removing this flywheel. The bolts do not seem to be metric. They are sloppy with metric, and fit better with an 11/16. I dont see how you can remove the end cap without taking this off first.

I think it is okay, but I am proceeding with caution here until I get a definite answer.

Also the wear into the wheel from the clutch is approximately .007 inch. Should I let it go, or resurface? The other side of the clutch plate has virtually no wear.

thanks guys!

Edited April 4, 2007 by markd

[t70]

your flywheel.... doesn't look as good as your clutch.... I would like to see a better picture, but from what I see, it looks really heat scorched. I would resurface it even if it wasn't 7 thou deep. It appears that there has been a lot of high-rpm clutch slipping (ie... taking off at 2500-3500rpm and riding the clutch untill the car catches up, or holding hills at stop lights with the clutch instead of the brakes)

[WayneB]

Yes Mark, you can remove your flywheel from the crankshaft. If your 11/16 socket is a better fit than your metric, use it!

I would definately get the suface skimmed .

Dont forget to Loctite the bolts and torque them to 55ft.lbs (when you re-install the flywheel.)

The info you read in the manual was pertaining to a different lighter automatic flex plate style setup Lotus used only on the 912 engines. On these the flywheel is bolted to the thinner flexplate piece and Lotus advise against separating them as you could ruin the dynamic ballance of it.

[Esprit Aviation]

Wayne,

Any chance you would have a picture or diagram showing the flexplate type flywheel? Do you know of anyone that has one in CA or the US that they want to part with?

I've never seen one.

Lee

Edited April 9, 2007 by Esprit Aviation

[86esprits3]

Can you just simply machine this type flywheel straight across entire area? Or is there a step that has to be retained where the clutch is mounted on the circumference? I have seen differing views on this, and since I have no data, I dont want to remachine it and ruin it.

What do you think?

[WayneB]

Mark, I think you will find that the raised area follows the thickness of the casting, so If its machined flat, the flywheel will be weakened at the transition point of the raised area (might cause a catastrophic failure when in use)

So If you get it machined, be careful and follow the existing surface contours (and dont make it too thin)

[Artie]

Mark, I think you will find that the raised area follows the thickness of the casting, so If its machined flat, the flywheel will be weakened at the transition point of the raised area (might cause a catastrophic failure when in use)

So If you get it machined, be careful and follow the existing surface contours (and dont make it too thin)

Most automotive shops that skim flywheels will blanchard grind the surface, then skim the outer edge too. The dowels used to line up the pressure plate come out so that surface can be ground too. Be sure the shop blanchard grinds the surface and not turn it with a brake lathe as this heats the surface in an irregular fashion and can warp the surface to cause a vibration in the clutch/flywheel(unbalance and thus cause harmonics in the pedal and engine assy)

Artie

[WayneB]

Wayne,

Any chance you would have a picture or diagram showing the flexplate type flywheel? Do you know of anyone that has one in CA or the US that they want to part with?

I've never seen one.

Lee

Hi Lee, this is the only illustration I have of the flex plate type 912 flywheel.

I would advise against using it on the Turbo engine though as the torque might cause cracking and fatique around the mounting bolt holes ( leading to catastrophic failure)

[Vulcan Grey]

Mark, I think you will find that the raised area follows the thickness of the casting, so If its machined flat, the flywheel will be weakened at the transition point of the raised area (might cause a catastrophic failure when in use)

So If you get it machined, be careful and follow the existing surface contours (and dont make it too thin)

The raised step actually sets the distance for the pressure plate, reduce that step and the pressure plate will not have as much clamp force. The step must be maintained when they BLANCHARD GRIND the flywheel. (Blanchard Grind only! DONOT have it machined on a lathe).

It should look like this with the scale pattern (not like a record)

Edited April 20, 2007 by Vulcan Grey

[Esprit Aviation]

Wayne,

Thanks for the diagram and the input!

Lee

[t70]

cripes... i should have taken pictures of my flywheel... the guy who owned the car before me installed a new clutch and didn't break it in properly.... I found metal on the pressure plate! I had to clean it up as best i could with 320 grit sandpaper and a block of wood... hopefully that's enough... but in terms of heat scoring.. mine was just as bad as yours mark.

[Vulcan Grey]

cripes... i should have taken pictures of my flywheel... the guy who owned the car before me installed a new clutch and didn't break it in properly.... I found metal on the pressure plate! I had to clean it up as best i could with 320 grit sandpaper and a block of wood... hopefully that's enough... but in terms of heat scoring.. mine was just as bad as yours mark.

Doh! Aluminum oxide (the grit in sandpaper) is not good to use on a friction surface like a clutch or brake rotor. The particles can and will embed into the wear surface as inclusions. This will effect the lifetime and performance of the clutch and flywheel. The inclusions change how the heat and pressure is distributed in the surface. Those pockets will continue to get worse and worse.

Sandpaper with carborundum is better to use, but you won't be able to get the surface perfectly flat, so again the heat, wear, and pressure will be different over the surface and will cause those wear spots and distortion of the flywheel.

There are only two things that should be done to rotors or flywheels...

1) Replacement

2) Blanchard Grinding (limits allowing)

I was able to find a machine shop to blanchard grind my flywheel (in the picture above) for $30...

Grinding will leave a harder, longer lasting surface, with more consistent friction and even wear...

[t70]

Thanks man! I didn't know that... However, I am only expecting to run this clutch for the season and then replace it next winter when I re-do the paint as well. I did clean the surface with brake cleaner though so it should be clear of particles. The clutch will need replacement period, because the pressure plates are slightly out of alignment as well... If I notice any vibration at high rpm, I'll simply pull it off the road and re-do the clutch and flywheel.

[dazmans3]

Sorry to bring this one back. Excuse my lack of knowlage on this one, It may be a completly stupid Question:

But, can any one explain what 'Blanchard Grinding' is?

My Flywheel needs attention. I have been to a few places down here (Portsmouth area) & they don't either have the kit big enought to fit the flywheel or in some cases have not heard of Blanchard Grinding. & that was with showing a print out of this thread.

One company I visited today had not heard of, but could do the flywheel on a stone type flat gringer(I think he said) & come up with the pattern shown on previous reply.

Also, Lightening the Flywheel, Is it worth it, has any one done it, or is this worth a new thread for discussion?

Daz

Edited May 29, 2007 by dazmans3

[WayneB]

Daz, Blanchard grinding is a North American term for what we call skimming back in the UK (Rotary Surface Grinding with a stone).

Whilst its probably the ultimate surface finish for a flywheel, I have had them turned on a brake lathe in the past with no ill affects (the flywheel on my SD TA was done this way), and I have seen many new flywheels with lathe turned faces.

[dazmans3]

Thank you wayne. I thought it might be a phrase from accross the pond. esp with the looks I got from some of these engineers when I asked them if they could Blanchard Grind my Flywheel.

All is much clearer now

Daz

[86esprits3]

Well I took the specs to the machine shop, and they did a beautiful job on it.

Here is a letter I got directly from Lotus concerning the flywheel.

Dear Sir,

The recommended minimum thickness of the flywheel is 23.50 mm, which means

that only around 0.5 mm should be removed. The friction face of the

flywheel must be 0.5 to 0.6 mm proud of the surrounding cover mating face to

provide the correct clamp load. If your flywheel shows no evidence of such

a step, it is likely that the flywheel has been incorrectly machined

previously, which would exacerbate any clutch slip problem. You may choose

to use your own judgement, or that of a qualified engineer and machine the

flywheel to a lesser thickness than this, but on that I could not comment.

Yours sincerely,

Dave Massey - Technical Service

Senior Technical Author

Lotus Cars Ltd., Hethel, Norwich, Norfolk. NR14 8EZ