355 clutch fix

As I posted prior, I'm very familiar with Blanchard grinding for I'm a ME, machine designer and own a shop. What are these "carbide hot spots"?

 

I think what he is referring to is the formation of cementite (iron carbide) spots due to over hearting of the fly wheel.

 

Yes. One of the reasons for Blanchard.

 

Yes, but if you can only grind 0.8mm then there is a good chance the hot spots will be deeper and the flywheel should really be replaced. No?

 

The 0.8 is a surface roughness spec. 0.8 micro-meters. Equates to a 32 RMS surface finish. Not anything special, a standard machine finish.

 

No, I was talking about the statement in the WSM that says you can remove only 0.8mm, not the surface roughness. The table posted says 1.0 mm. The point is that if the hot spots go deeper than the allowable material removal you can not eliminate the hardened areas and the fly will not wear evenly.

 

That spec could be a maximum roughness measurement. If you measure 0.8mm, the flywheel should not be machined. Anything under your ok to cut. Same idea as a brake rotor machine spec..

 

That's not shown as mm, it's u (greek version not on my phone)

 

The WSM is pretty clear in its interpretation. If the fly wheel isn't flat it should be ground flat provided that no more that 0.8mm of material is removed to achieve flatness. Obviously it follows that any surface scoring or curvature can therefore not be greater than 0.8 mm deep. Let's not follow the usual FChat path of making something very simple obtuse.

 

If you look at the second image I posted, the specs for max reduction in thickness is 1.0mm, right below that is the surface finish requirement, .8u, not .8millimeters.

To imply a flatness of .8mm is really a bad assumption which is why I posted above. The WSM is only clear in the sense that a flatness specification is not given.

 

You mean, a reason for resurfacing, correct? Although a Blanchard can be used, it may not be the only tool to do the job.

 

A micron is a millionth of a meter, a millimeter is a thousandth, so 8 microns (.008 mm) is fairly smooth. Any good machinist can use that measurement to get the finish you want, assuming you have enough flywheel remaining to machine flat.

 

But they don't specify 8 microns, they specify .8, right?

 

No, I mean Blanchard. Blanchard is the standard in the industry for flywheel resurfacing. You can read up on it there are a bunch of reasons for it for this application. One is the nearly universal problem of flywheel heat checking causing those hard carbide spots. You don't get good surface treatment over those hard sections of the disc with lathe cutting for example hard soft skipping. Can you use other stuff? Sure. I've seen guys use a sandpaper wheel and the car seemed to work fine. It all depends on the application and how textbook you want to be. Honestly, if there is no resultant chatter and function is ok, you can't tell if new parts are used or if a plate is rebuilt and old pressure plate and flywheel are used with no surface treatment at all if all you are doing is driving to the grocery store.

I've done some pretty dodgy clutch work I posted about here on Fchat years ago. I took a 348 flywheel pack, cut the spider off gutted the voight dual mass, lightened it, welded it, balanced it, spent $15bucks on a clutch plate resurface deleted the marcel spring, used the old pressure plate and flywheel without surface prep. I raced that 348 for years never wore it out. It worked perfect and helped a low horsepower car launch out of the turns.
That's the real value in doing all this stuff departing from OEM part replacing to find a little more fun with a sportier modification.

 

A 32 micro inch finish is pretty damn good, not a standard finish at all. Not difficult, but not a "standard" the standard for parts we design (title block tolerance) is a 64.

 

You missed my point. A Blanchard is not needed to do what you are suggesting. In fact, most often Blanchard grinders are used for plain A36 steel. Hardened tool steels are usually ground via surface grinders. The normal finish on a Blanchard is not a 32, it's usually more rough, between a 64 and 125 (micro inches).

Have you ever seen a Blanchard operate?

 

Automotive Equipment Service Co., Inc. - Equipment Online - Flywheel Grinders

 

Yes John, I've seen them before. They are not true Blanchard grinders, but the concept is the same.

I was make the point that other methods would work also, such as rotary surface grinders and regular surface grinders, especially from the stand point of the "hard spots" mentioned.

While the best tool is a purpose built machine, if you don't have one or access to one, but you own a shop or have friends that do, other options are out there.

 

My point going back some was not how to grind, but whether it should be ground. If the reduction in thickness if limited to 0.8 mm, or 1.00 mm (take your pick) then it is likely that the hardened hot spots go deeper and just because you grind the surface doesn't mean you have uniform surface hardness and roughness. The hot spots will, over time, wear less and become high spots with increased friction and heating. It's no different than brake disks. No decent mechanic will resurface disks with similar hot spots.

 

We machine graphite parts for semiconductor applications. Most of the product we supply is machined to a 32RMS finish as specified on customer drawings. The larger product(+24"D) is machined to a 64RMS finish.
A 32RMS finish is easily attained on a lathe or mill. Grinders historically yield a finer finish.
Again, the bulk of my experience is machining synthetic graphite products.

Surface Roughness Table - Engineer's Handbook

 

John, I understand your point and agree. Even 1mm is not really much material. I suspect it's very important with these cars, escpecially the dampened flywheel (cost stand point) to be certain that one attends to a worn clutch right away, hopefully prior to flywheel damage.

 

I'm not saying it's hard to do, just not "standard". Machining graphite is a totally different story than metals, especially ferrous metals...

In nearly every case where I ask one of my blanchard suppliers to provide a 32 finish they say "no". They say, "we can surface grind if you like but 64 is the best we will promise from the blanchard..."

And that may simply be that they don't have the proper stones since most are not looking for that finish on industrial applications...

 

The OP like 99% of owners who would do this job will farm it out to someone like Fort Wayne clutch or Friction Materials. Rebuilders will use tools specific to their jobs. For flywheels they will be blanchard or blanchard like surface grinders. They will read the spec which is 0.8mu and has been the standard on Ferraris since at least the 1970's 308gt4 (oldest books I have on file 360 about double that). This is a great discussion to help understand the hows and whys. Then owners go in fully armed with good knowledge and know what to expect in the final product to get OEM reliability and function. Most rebuilders of this type are capable and experienced but the number one error I see is a failure to make sure the clutch plate thickness is correct and then the assumption by the owner that all thicknesses are correct and a failure of the owner to measure the set-up height. If something is wrong, the owners gets to take the clutch out again and scratch his head trying to figure out what went wrong. All that can be avoided by understanding how the system works as being discussed here or just buying a new clutch pack set up and swapping parts. There is nothing wrong with automechanics 101 part swapping. If one gets into rebuilding a "system" they either need to get lucky, and or know what they are doing, or have rebuilders who do their job correctly.

 

Think its nearly time to talk about re-balancing that flywheel next!

 

I'd love to learn about that, teach me- talk away