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

chrisp · 01-05-2004, 05:06 AM

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.

sammyg2 · 01-05-2004, 06:01 AM

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.

Zeke · 01-05-2004, 07:02 AM

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.

MY83SC · 01-05-2004, 07:35 AM

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?

chrisp · 01-05-2004, 07:47 AM

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

ubiquity0 · 01-05-2004, 08:01 AM

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

Superman · 01-05-2004, 08:13 AM

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.

chrisp · 01-05-2004, 08:20 AM

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

Superman · 01-05-2004, 08:40 AM

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.

William Miller · 01-05-2004, 10:38 AM

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!

chrisp · 01-05-2004, 10:58 AM

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!

Superman · 01-05-2004, 10:58 AM

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.

chrisp · 01-05-2004, 11:23 AM

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

Doug E · 01-05-2004, 06:34 PM

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:

TedSlick · TedSlick's Garage

Quote:

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

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

ohecht · 01-05-2004, 09:59 PM

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.

Am I screwed?

Olivier

chrisp · 01-06-2004, 06:03 AM

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

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

William Miller · 01-06-2004, 06:28 AM

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

William Miller · 01-06-2004, 06:33 AM

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?

Superman · 01-06-2004, 06:38 AM

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.