Machining a flywheel (2 Viewers)

[Eurasiaoverland]

I have a flywheel for my (diesel) engine which needs machining. From factory it has a 0.60 mm step between the outer part of the flywheel which the pressure plate bolts to, and the inner area which makes contact with the clutch disc.

Should I just have the inner contact surface of the flywheel machined to remove surface imperfections? Or should the outer section have a similar amount removed to maintain the step height?

Thanks

 

[samc2447]

Maintain the OEM step height. Any good machine shop will do this

 

[DrRock]

Maintain the OEM step height. Any good machine shop will do this

Exactly. The machine shop will grind the surface and should have the factory nominal dimensions and tolerances to achieve the correct step and runout.

 

[Eurasiaoverland]

I had the flywheel machined, but the heat patches and cracks were not machined out. It's a smooth surface but the machinist told me that the discoloured patches are where the flywheel material is very hard.

Everything I read online tells me this means the flywheel is basically junk and will lead to uneven clutch wear and juddering. That said, most of the Forum posts I found were for more performance-oriented vehicles than an old Land Cruiser.

What do we think?

 

[DrRock]

Looks like this was turned on a lathe versus done with a surface grinder. A couple questions:
1. Did the machinist say how much material was removed?
2. Do you have any close up pictures showing the cracks?
3. From your picture, those “spots” look like oil residue. Did you try cleaning the surface with acetone or similar?

For reference, here is a picture of my refinished flywheel as done by a surface grinder. I had this redone at 200k miles and it came out perfect. Photo makes it look like the surface is rough but it’s actually a very fine finish. I can get you the spec if needed. Lathe and surface grinder are both capable of getting the correct finish required.

EDIT: I zoomed in on your picture and now see the cracks. The question now becomes if they can machine more material off to get beyond the cracks and still maintain minimum limit of thickness per factory recommendation. I don’t have the factory spec and have searched Mud and seems like this number is pretty elusive.

 

[TheBussman]

the cracks are nothing to worry about actually, if machined on a lathe those hot spots get very hard and a carbide cutter will cut the softer iron and almost skip over-top of hot spots. The way to get around this is to take a deep cut like .020 or even more in one pass to get underneath the hot spots. there are no specs for how thin you can machine a flywheel unfortunately. make sure the clutch springs wont hit the flywheel bolts.

 

[Rodger1957]

Take your flywheel to someone with a flywheel grinder. That surface will clean right up, those little cracks aren’t an issue.

 

[Eurasiaoverland]

Thanks guys. Although the machine shop I went to is a very well respected place (which can make new gears, do metal spray repair and turn huge pieces), they are focused on oil and gas and plant equipment, so they just turned the flywheel in the lathe. I didn't ask how much material came off. There was a reasonably deep groove in the friction surface of the flywheel from what I assume was a rivet in the old clutch plate, so I would guess something like 0.2 to 0.5 mm. The flywheel came from a workshop which preps off road vehicles for Borneo Safari type events and I'm sure it was ragged to death in a mudhole (it came off a tuned 15B-FT engine) until the clutch smoke came out of the bell housing etc.

I'm not worried about the cracks but even with the cut there are still big patches of hardened material. To find a decent automotive machine shop that can do Blanchard grinding, if possible at all, would be at least a seven hour drive away (each way, on often less than pleasant roads) and I'm not keen to take too much material off the flywheel. The later 60s do not have an adjustable slave cylinder rod and I don't want to be in the situation where the clutch is not fully disengaging.

So I'm just going to order a new flywheel while they are still available for my engine.