Flywheel condition. How do I tell if it's okay?
 

I had a successful engine drop this weekend, the clutch is off and the flywheel is exposed but not off. Having never assesed te condition of a flywheel before, I can only dscribe it as looking like a worn brake rotor before it gets resurfaced. There are no cracks and no dark spots. Should a flywheel surface stay pretty clean throughout it's useable life? Do the grooves mean that it needs to be replaced? The engine (an '83 SC) has a spring centered clutch so I know that's been replaced at least once but my guess is that the flywheel is the original one and has 125k miles on it. The friction disc is worn to the point where some of the rivets were beginning to get worn down.

I am in RI, my flywheel is in CT, and I have not begun to look for a place to take it to be resurfaced. So, in the short term I wanted to check in with you guys in the event I can identify up front whether I need a new one or not.

If you went into the rivets, it prolly needs to be resurfaced.
Usually flywheels that are in good condition do not have any grooves in them IMO.
If you have grooves in it and install a new clutch disk there will be limited contact area that will either cause the clutch to slip or create hot spots and warp or damage the components.
You want as close to 100% contact as possible with the new parts.
Any pictures? That would help us make a better assessment.

What he said. If you got into the rivets, your flywheel likely needs to be resurfaced. If you resurface the flywheel and get a new or rebuilt pressure plate along with the new disc, you clutch will work so well that you will be rewarded for your efforts.

Just my 2 cents. I would think after all of the work to drop the engine, etc. I would have the fly wheel resurfaced. I wouldn't think that it would add much to the cost...and well worth having it done the right way, the first time. How much would it cost to have a fly wheel resurfaced anyhow?

Thanks for the input guys. Don't know whether I should just go ahead and replace it or get it resurfaced. Keeping it as is isn't an option. I don't know yet what a resurfacing will cost. I agree that with all of the effort involved in just getting to the clutch it's best to fix it right. My initial thought it to just replace it and spend the $200+. However I have done that many times over already and I am at $2500 of "while the engine is out" projects :)

When I had mine resurfaced it was around $80 I think

Some say our flywheels are too thin to resurface. I don't believe that, but some do.

If you're going to resurface it, be sure to do what JW suggests, which is to make sure that the shop doing the resurfacing uses a "diamond" grinding stone. This is the only stone capable of retaining the inside edge at the outer edges of the friction surface. If this edge is rounded, as most non-diamond stones will do, then your pressure plate will not properly fit onto the flywheel.

Is there a Porsche spec for '83 SC flywheel thickness and a minimum before re-surfacing?

I don't think there is. Again, I suspect the factory does not admit they can be resurfaced. In reality, a small amount of material can be ground off, just to make a new surface, without much danger.

I think it's in the little spec. book. Or that may just be the friction pad thickness. I had mine looked at by a machine shop because I thought it was fine. he agreed. I think he said he couldn't do it anyway because the friction surface is below the outter ring. This may be why some say they can't be done. (Probably because some shops don't have the right piece of equiptment.)

Again this is from my memory. Let us know what you see!

I just spoke with a gentleman in MA who was recommended by a local P-car race shop. He charges $60-$80 depending on the amount of work needed. He cuts first and then grinds to get the finish surface. He indexes the inner groove. Apparently indexing is more of a balancing technique when machining the inner groove as opposed to just machining in a groove with little respect for how on center it is. He was also aware that there are some grooves in the flywheel that are supposed to be there and he restores that. I am going to UPS it to him. 24-48 hour turnaround. He also makes RSR type flywheels. I won't get it to him for a couple of weeks but when I get it back I'll update everyone. Here's hoping that it's machinable!

Yes, because the friction surface is below the outer ring, the friction surface must be resurfaced all the way out to the outer ring. This is what necessitates the sharper diamond grinding stone. I do not believe any resurfacing specs are given in my '82-'83 Spec Book, at least from my memory. I recall looking for a spec, and discovering that only a few people believe they can be resurfaced at all. But again, one of the folks that believes it is a legitimate option is JW. And all you're doing is 'profiling' the surface, rather than actually grinding it down to a new thickness. These flywheels are not exactly the thickest I've seen.

He commented that it's a very light flywheel as it is (when I asked if I should go with something aftermarket and lightweight).

Here's a pic of my recently re-surfaced flywheel. Local machine shop did it for $57 and if my memory is correct he said he took off 10 thousandths of an inch:

http://forums.pelicanparts.com/uploa...1073360074.jpg

FWIW, although my Bentley manual only goes back to '84, it gives the following Flywheel Service Specs for '84 thru '86:
Wear Limit..... 8.5mm (.335 in.)
Max runout.... 0.1mm (.004 in.)

It states, upon inspection, if damaged or scored, machine to the above specs.

If '87 thru '89, replace it.

Maybe someone with the SC Bentley manual can let you know about '83.

G/L

Now I'm worried...
 

I have mine back on the car and I am about to reinstall the engine after 6 weeks of "while I'm in there stuff".

I took the flywheel to a shop recommended by a local trusted mechanic, and I passed along the requirement for the diamond stone JW pointed out. As often happens when I try to insist on or ask about a partiular technique or procedure, they did not know what I was talking about. I thought the diamond was referring more to the method to remove surface material more than the preservation of an inside edge, so I let the guy talk me into it by insisting it was a common job they did.

I just checked, and there does seem to be a very slight bevel on the inside of the raised "lip" around the flywheel. I have nothing to compare it to, though, as I did not look closely there before. It also does not look as "freshly cut" as the rest of the machined surface. Here is a picture with part of the bevel highlighted with yellow lines, but it is still hard to see even in person.

http://forums.pelicanparts.com/uploa...1073372285.jpg

Am I screwed?

Olivier

I got the Bentley specs for '78-'83:

Wear limit: 8.5mm
Machining limit: minimum needed for smooth surface
Max runout: 0.1mm

Doug, for future reference which machine shop do you use?
Thanks!

In comparing the pictures again you can see a groove in doug's just inside the bolt holes. Doug, it looks like the surface on the outside of the groove where the bolt holes are located is also machined.

I don't see the groove in Olivers.
Maybe the original groove is the wear limit?

Hard to say, Olivier. Perhaps JW can give you his opinion based on the photos, or better photos if you can take them. I believe the PP nestles down inside the outer lip of the flywheel. Is this right? If so, then this is where John's advice is. If that corner is not flat, at the level of the rest of the friction surface, if it's even a tenth of a millimeter higher there, then when you bolt the PP to the flywheel, the PP friction surface does not get close enough to the flywheel's friction surface, and therefore does not squeeze the clutch disk hard enough onto the flywheel. This is something you will want to know before you install it. Maybe better photos for John. Maybe take it to your local "John Walker" who might be familiar with this situation.

I wish I had the face-to-face expert support you have out there. People here usually respond with "that looks fine, why are you so picky?"

I am very picky after carefully brushing away every inch of grime I can reach, replacing all seals and o-rings, etc.

If the bevel is just at the very top of that inside edge, then it seems the PP would still rest inside the ridge, just without contact at the very top of the perimeter. I will have to test-fit the PP and check. The bevel does look like it has been there longer than the newly surfaced area, too.

What about that large groove in the surface of the other flywheel? I hope that is not a wear limit, because mine did not have it when it came out.

No problems with a slipping clutch, though, just a release bearing circlip that popped out. (I am up to about $1500 in while-you're-in-there parts, and technically nothing broke at all on the clutch!)

Olivier

I'm not sure you're understanding my concern, Olivier. I believe the PP fits inside the outer lip of the flywheel. And that the pressure plate is supposed to then be bolted directly onto the friction surface. At least the bolt holes are on that surface, and I believe the system was designed so that the PP sinks down into that flywheel all the way down to the friction surface. Well, if the friction surface of the flywheel is lowered, and if it is lowered all the way out to the edge of the friction surface, where the raised lip is located, then the INSIDE edge of that lip should have a perfectly square cross section.

But if the machining did not include the extreme outermost area of the friction surface, and did not create a brand new ultra-square inside corner where the friction surface meets the outer ring/lip, then that portion of the plane will be higher than the rest of the friction surface. Unfortunately, this will cause the PP to be mounted on a plane that is above the plane of the new (machined) friction surface. This means that the PP friction surface and the flywheel friction surface will be a teeny tiny bit further apart than spec. Well, the problem is that this system is designed with teeny tiny tolerances. The friction disk is only about 5mm thick, and if the PP is raised up from the flywheel friction surface, and if the PP and flywheel friction surfaces are too far apart as a consequence, then they may not apply enough pressure against the friction disk. They may not squeeze the friction disk hard enough. You cold bolt this together and find that your new clutch slips like an old clutch.

I'm not sure about any of this, Olivier, but I think this problem (not enough pressure against the friction disk) is the problem that JW warns us about when he urges us to use a machine shop with a diamond grinding stone. I think.

I'll confirm. The pressure plate does go inside the lip and should bolt flat against the newly machined surface. If that outside corner is not machined to allow this to happen there would be a problem. I don't think there would be a problem with slipping it would be that outer ring of the pressure plate where it is bolted would possibly be twisted as the bolts are torked. (Maybe not because that part of the pressure plate is pretty beefy and the bolts are not torked that much. I recall 18 or 20 some lbs.) In any case it wouldn't be right.

I don't know what JW wrote, but maybe the diamond cutter is the only one that will cut the corner out. I think I recall on mine that corner was relieved simular to the grove that you see in Doug's picture. In fact if you look at Doug's picture closely it looks like that relief is still present.

I would measure your thickness and compaire it to the wear limits posted. If it's less than the wear limits it may create other tollerance issues. Like maybe with the throw out bearing's position on the guide tube or it's relationship to the fork.

Doug, if you can measure the thickness at the groove it will confirm how that compairs to the wear limit.

I think I said the same thing that Superman said?

That does make more sense, I was thinking of the corner at the top of the raised lip. I will go check the inside corner and also try to measure my pressure plate's thickness.

Thanks,

Olivier

Ehh...i dunno about SC's but 930's have a lip too. My understanding is than outer lip is there just to center PP on the flywheel. You could machine flywheel pefectly flat and it would work, as PP is bolted on the same plane as friction surface. IMHO, only good thing about outer lip is that it centers PP perfectly so risc of lateral runout is decreased compared to running perfectly flat flywheels where PP is centered by holes only.

I think Hayden Burvil of WEVO is the man to ask about these things, they make custom flywheels so he probably knows thing or two about "the lip".

Bill - machine shop I used was Allied in Falls Church and I've posted about them on our local board. I can't find my caliper measuring tool (misplaed somewhere right now) but I'll figure out a way to measure it an report back.

This is basically what was described to me by the machine shop. The more centric this groove is to the shaft the more centric the pp is to the flywheel and the better the overall balance. With a good cut in this part of the flywheel not only does it get the pp the proper distance from the flywheel but it centers the pp properly. Otherwise you rely on the bolts to center the pp and that's not as accurate. It's sort of like a hub centric rim versus a bolt centirc rim. It's always better to have the two parts orient themselves together and use the bolts for securting it together. The other thing that was interesting with my diassembly was that the PP had to be pried off the flywheel. Not a ton of force was required but I had to get a screwdriver in there to carefully separate them. Perhaps this is an indication of a non-centric shoulder.

Mine did not come apart easy, but when I cleaned it up it fit like a glove.

Doug, I have some micrometers you can barrow but I'm not sure they would work. The small ones may not reach the groove and I'm not sure the 6" has an anval to mesure that small.
How far in from the edge is the groove? It looks like it's a little more than an inch.

Since I said I would update everyone.....

I sent my flywheel in and he turned it around in the same day. He included an invoice in the box (it's arriving tomorrow). No prepayment req'd. Cost is $60 and I will have my flywheel to check out before I pay. What a refreshing way to do business.

For those of you nearby who want to use him:

Circle Racing
John Andruk
971 Main Street
Brockton, MA 02301

Phone: 508 580 5844

Good news!

Doug, don't tell me you're taking the clutch assembly all apart again after all that fun this past weekend.

I'm a cheapskate with most things (beer, women, daily driver), but I would not cut corners here. Everyone who posted sounds unsure enough about this issue to make it worth the extra $100-$150 to just buy a new flywheel. If you wanna go all out, get a lightweight one.

Good info. on the specific details of the 915 flywheel!

Here's a snip from Wayne's book showing the flywheel specs.

http://forums.pelicanparts.com/uploa...1063628829.jpg

Above picture taken from this topic:

http://forums.pelicanparts.com/porsche-911-technical-forum/127351-clutch-help.html

Since TedSlick mentioned the non-serviceability of the 87-89 flywheel and it's also noted in Wayne's diagram, i'll add my two cents to issue. Just in case anybody with a G50 were to do a search for flywheel. This topic has some good machining info. that can benefit anybody.

The reason the 87-89 wheel is said to be not serviceable is because of the big rubber damper on the friction disc (also called drive plate). It's my understanding that if you were to cut the flywheel surface down too much, the release bearing could contact the top of the friction disc rubber damper because of the added travel needed by the pressure plate to clamp the disc to the flywheel. Makes sense to me.

BUT!!!! Many people replace that big honkin' rubber damped disc with a spring centered disc. So you wouldn't have to worry about the release bearing contacting the damper anymore since it's not there. The rubber is replaced by the springs.

I'm not saying you could now machine the G50 wheel to your heart's desire. I don't know the wear limits. But I imagine you could at least have it lightly machined to smooth the surface a bit and not worry about the damper-release bearing interference.

Sorry to get off topic here. Just thought this might save somebody some $ instead of automatically thinking a new flywheel is required. That's what I did. But at least I kept my old one! :D

Oh BTW, a light flywheel is certainly something to consider. Also consider the pressure plate. A lightened pressure plate is going to lose you MUCH more rotational mass than a lightweight flywheel.

What are the downsides to a light flywhel, and how much weight is taken off, from stock to lightened?

I also put on the aluminum PP that is part of the Sachs power clutch kit. How much of a weight savings is in that?

Should I expect a drastic difference in engine feel?

Thanks,

Olivier

I've sent my brothers 87 flywheel to Ollie's for light resurfacing and now I'm sending mine from my 89. Really just to remove the hardened glazing and to give the new clutch a better surface to mate with. Both of us have upgraded to spring centered "turbo" clutch plates.

Olivier,

The flywheel depends on what material it's made of, and how it's lightened.

Here are some fancy alloy ones from Lindsey Racing:

http://www.lindseyracing.com/flywheel.htm

Maybe weigh your flywheel to see the difference in weight?

Here's an example of a lightened stock flywheel:

http://forums.pelicanparts.com/uploads/lr20a.jpg

You can see it on the bottom of the crank. Looks like the machinist basically cut away the area around the perimeter, while still leaving enough "meat" for a strong area to attach the pressure plate.

The feel you'll get is:

- The engine will rev quicker (up and down).
- You'll need more throttle input to get the car going from a stop
- Shifting gears will be different because the revs will come up and drop more quickly than before.
- Other things i'm forgetting

The above mentioned stuff happens because the reduced rotating mass gives the engine less momentum. A body in motion tends to stay in motion- less mass means it'll slow down sooner. So this weight loss allows the motor to spin up and down quicker.

I got the flywheel today. $60 for grind, $20 for blast and wash (I didn't get to clean it and could never have done as good of a job)As you can by the pics it's looks brand new. I am not sure how he got it so clean. He must have sandblasted it. I wish I had a before pic because it was pretty ratty.

I am not sure if from these images you guys can evaluate the quality of workmanship.

Some interesting things:

1.) The surface finish is somewhat rough (not mirror finish) and the machining/grinding lines are concentric with the center of the flywheel. Not swirling like a machine cut on a bridgeport would create (like a pic earlier in this thread shows)

2.) I still don't know what critical edge everyone is reffering to so I cannot comment on how that part looks. Maybe you can see it in the photo.

3.) The groove that is near the outer edge (just inside of the PP bolt holes) is refreshed but with a cross hatched pattern. Almost like a knurling but clearly done as a rough cut. Not like it was done with a knurling tool. Maybe a small end mill with only a few passes.

4.) The outer most surfaces (radially beyond the PP bolt holes) were not touched at all.

5.) The [what I thought to be] extensive heat checking turned out to be a non-issue.

Any thoughts that you guys have from seeing the pics would be appreciated. http://forums.pelicanparts.com/uploa...1074794978.jpg http://forums.pelicanparts.com/uploa...1074794987.jpg http://forums.pelicanparts.com/uploa...1074794997.jpg

Are you sure that didn't have a porsche part's sticker on it?
I believe are in question is the outer most corner beyond the bolt holes where the edge turns up. It looks like there is a grove there so the pressure plate would have no restriction meeting flush with the area where the bolt holes are located. I'm still wondering if the wide grove that's just inside the bolt holes was originally the wear limit. It may just be a place for the dust to collect.

Great job!
Problem is: Now your going to have to make the rest of the engine and car look that good!
Let us know how it works!

Does anyone have an updated phone number for Circle Racing? I've been trying to get a hold of them.

-Scott

bump for a question.
I had the flywheel from my 83 SC motor resurfaced today. The groove pictured in the photos above by chrisp was originally there, but after being resurfaced, it disappeared.

is this groove a wear indicator? any problem with it being absent?

I don't think there is specific issue with the groove not being present, maybe someone else will confirm. I believe it's a thickness indicator. The larger issue with it being gone is how much material was removed. I would mic it if you can, the wear limit is listed above in the thread.

Mine was resurfaced and the groove was less pronounced, but still present. Pay attention that the inside lip has a 90 degree corner. A diamond bit can produce it.