Flywheel has 0.030" groove at mating face to clutch. Ok to reuse?

777funk · Jun 6, 2019

I don't want to resurface if I don't have to. I have the tractor split and would like to rejoin asap. The groove is right where the clutch would ride.

RickB · Jun 6, 2019

You don’t have to resurface the flywheel unless you want the clutch to work properly.
Installing a new disc against a flywheel with that much wear is an exceedingly bad decision.

777funk · Jun 7, 2019

Here's my thinking of what will physically happen if the new clutch is installed and pressed to the old flywheel.

The groove will roughly match the face of the new clutch, but be very slightly larger or smaller than the new 8.5" diameter clutch material pressing against it. The concentricity of the groove from the old clutch may or may not be right on center, but will be close. If the groove is smaller in diameter than the new clutch, it will wear the edges into the new clutch until this material is gone. Then the new clutch will ride face to face in the old groove. At this point, I can't see what would be different from if it were riding on a flat brand new flywheel face.

But I may be overlooking something that could happen or I'm just plain missing. I'm just trying to visualize what could go wrong and how bad. I know I have replaced brake pads and shoes without resurfacing disks/drums without problems.

boomer1025 · Jun 7, 2019

777funk said:
Here's my thinking of what will physically happen if the new clutch is installed and pressed to the old flywheel.

The groove will roughly match the face of the new clutch, but be very slightly larger or smaller than the new 8.5" diameter clutch material pressing against it. The concentricity of the groove from the old clutch may or may not be right on center, but will be close. If the groove is smaller in diameter than the new clutch, it will wear the edges into the new clutch until this material is gone. Then the new clutch will ride face to face in the old groove. At this point, I can't see what would be different from if it were riding on a flat brand new flywheel face.

But I may be overlooking something that could happen or I'm just plain missing. I'm just trying to visualize what could go wrong and how bad. I know I have replaced brake pads and shoes without resurfacing disks/drums without problems.

Save yourself from a future problem and get the flywheel resurfaced.
It looks flat but it is not and the new clutch will wear uneven.

ruffdog · Jun 7, 2019

When resurfacing flywheels/brake drums and disks, you may not worry about removing a groove concentric to movement. If 99.9% of the surface is flat, runs true, and is not cooked with hot spots, then it should be fine. Back when I ran a brake lathe, you didn't remove a bunch of material just to get that one groove out of the surface.

RickB · Jun 7, 2019

It’s not difficult to figure the worst case. You trash the new disc and do the job over except maybe you resurface the flywheel the second time.

777funk · Jun 7, 2019

RickB said:
It’s not difficult to figure the worst case. You trash the new disc and do the job over except maybe you resurface the flywheel the second time.

What I'm more speculating about is how. I'm asking how it will hurt the clutch if it fits into the groove? It's still a surface against a surface... just recessed.

RickB · Jun 7, 2019

The old disc wore, it did not come out flat. The new disc will not conform to the shape of the flywheel without wearing, and until it does conform it will not transmit full power because of the limited friction surface contact with the flywheel. After it does conform to the shape of the flywheel it will not transmit full power because the springs in the pressure plate will not exert the designed clamp load on the disc. 30 thousands is a lot of wear on a flywheel, easily 1/3 of the allowable amount to be machined from some applications.

777funk · Jun 7, 2019

RickB said:
The old disc wore, it did not come out flat. The new disc will not conform to the shape of the flywheel without wearing, and until it does conform it will not transmit full power because of the limited friction surface contact with the flywheel. After it does conform to the shape of the flywheel it will not transmit full power because the springs in the pressure plate will not exert the designed clamp load on the disc. 30 thousands is a lot of wear on a flywheel, easily 1/3 of the allowable amount to be machined from some applications.

Thanks. So in other words air gap when the clutch is supposed to be tight. I get it. I always like to think about what can go wrong and why before I spend money. I can see that owning a tractor isn't cheap. Worth it? Probably!

I've cut corners on auto repairs where I think it's possible and many times it works. Other times I get to do something again. I've learned to ask more questions when I find myself in places where I'm asking, 'I wonder if I can skip this extra expense and be 90% as good' as I get older. I have a 7.3 Powerstroke that I rebuilt the injectors on and saved $1000 or more. I would say I cut some corners vs the full no expense spared treatment and haven't regretted it. To some extent it will always be a risk without knowing all the details within a design.

777funk · Jun 7, 2019

A member here pm'd me saying that maybe the recess is by design. I took a look at the closeup in this video:
Yanmar Tractor Clutch Replacement - YouTube
and it looks like there's about the same groove depth in this flywheel. Hoye calls it good. So maybe I'm ok. See the picture (and/or video).