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How does this flywheel look to you?

Discussion in 'Technical Q&A' started by 8valve, Dec 28, 2003.

  1. 8valve

    8valve Formula 3

    Sep 3, 2003
    1,010
    Netherlands
    Full Name:
    Mick A.
    Hi guys!
    I am in yhe process of having the clutch of my 308 replaced. I went to the shop that's doing it for me yesterday, to take some pics of the work. I noticed the flywheel had some very tiny hairline cracks on the surface, each about a quarter of an inch long, and perpendicular to the axis. You can see it in the picture. The flywheel will be resurfaced (for the first time, by the looks of it), and the mechanic said he had seen similar marks on flywheels before. Can anyone elaborate on this issue? Thanks, and kind regards, Mick
     
  2. andrewg

    andrewg F1 Rookie
    BANNED

    Sep 10, 2002
    4,667
    Chester, England
    Full Name:
    AndrewG
    looks like a little surface crazing (havent a clue what the correct term is) I've had this on my 911's brakes, apparently just caused by the heat, if your worried about the cracks getting worse have the flywheel crack tested after its been skimmed.
    Don't forget to only have the surface skimmed once, otherwise you'll loose some of the timming marks!
     
  3. pete04222

    pete04222 Formula Junior

    Nov 1, 2003
    613
    Maine, USA
    Full Name:
    Peter Cyr
    The cracks look like they are just surface cracks. Pretty common. As long as they can be machined out you'll be fine. If the cracks don't come out with machining the new clutch will wear out prematurely.
     
  4. Steve King

    Steve King F1 Rookie

    Feb 15, 2001
    4,353
    NY
    Does look like surface cracks. I normally would just take some emery cloth here with a block of wood and go over the FW surface. It looks to early to shave it down. I'd wait until the next time if you keep the car that long. Don't have much history on 308 clutches but I would expect to get 80-90k on a clutch if you don't slip it a lot. I used to get pretty long life on my Jags and Vettes clutches even with some minor abuse.
     
  5. Verell

    Verell F1 Veteran
    Owner Consultant

    May 5, 2001
    6,951
    Groton, MA
    Full Name:
    Verell Boaen
    Based on what I can see in the photo it doesn't look very worn at all.
    However, it's hard to tell for sure with the low-res of a posted photo.

    Assuming that the worn area is essentially quite smooth,
    It may only need the surface glaze broken so the new clutch disc will seat.

    Before having it resurfaced, try block sanding it with 600 grit. It's likely to pretty well clean the surface up. After block sanding you'll be able to tell a lot more about how much wear there actually is. Also will be able to tell if it cleaned the cracks off.

    Another alternative is to a coarse scotchbrite pad or 600 grit on a DA (NOT ROTARY) sander, followed by a block sanding check to make sure you didn't create any ripples. CAVEAT: This is a bit risky if you aren't very experienced with a DA sander & or don't have a light touch with it.

    Talk to whoever's going to be doing the resurfaceing & ask them to take as little off as possible. Then double -check the cracks. I've seen them on clutches before resurfaceing, & the new clutch was still going strong tens of thousands of miles later.
     
  6. atlantaman

    atlantaman Formula 3
    Rossa Subscribed

    Mar 31, 2002
    1,726
    Roswell, Georgia
    Full Name:
    Charles
    It looks fine--I was worried about mine too ( look thru posts about 5-6 weeks ago) I took it to NAPA and had it ground ( only about .010") and it is like new---$35.00

    I went to TRutlands and pulled out about 5 others lying around and they all looked a lot worse than mine
     
  7. 8valve

    8valve Formula 3

    Sep 3, 2003
    1,010
    Netherlands
    Full Name:
    Mick A.
    Thanks for all the valuable input everybody, I very much appreciate all that! I will talk to the guy doing the work, and I will keep you guys posted as we progress. I agree that if possible, it is best to avoid the lathe. I would like the flywheel to last a couple of clutch replacements before it needs replacing. I think a new one goes for 555 British pounds, excluding VAT(roughly $1000 incl.taxes and shipping....)I'll let you know!
    Happy New Year everybody, Mick
     
  8. atlantaman

    atlantaman Formula 3
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    Mar 31, 2002
    1,726
    Roswell, Georgia
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    Charles
    I see you mentioned LATHE---yo do not want to go there--yes you will need to remove some material--about 10-15 thousanths inch but it should be rotary ground--using a lathe to remove will damage it worse and will put in a directional pattern that will propogate more cracking
     
  9. 8valve

    8valve Formula 3

    Sep 3, 2003
    1,010
    Netherlands
    Full Name:
    Mick A.
    Thanks Charles, I am not the one doing the work. The guy that does it knows what and how to do it, and I assume he won't use a lathe if that is not common procedure. Me using the word lathe is just my lack of knowledge on the subject of engineering. Thanks anyway. Is there a thread with pics of your car with the v12 installed? That must have been an interesting project!!!!
     
  10. atlantaman

    atlantaman Formula 3
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    Mar 31, 2002
    1,726
    Roswell, Georgia
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    Charles
    if you go back to the old archives(link at bottom of page) and look up 308 v12 in the showcase files there are lots of pics
     
  11. henryk

    henryk Formula Junior

    Dec 9, 2003
    479
    Door County, WI
    I recently replaced my Boxer clutch, and the flywheel looked like yours, cracks, and burn marks, etc. I had it grounded down, using a rotary surface mill. The mill took off about 0.012 inchs down to a perfect surface.

    The manual calls for a maximum grind of 1mm, or about 0.040 inch.....that allows about 3 grinds (or clutch jobs), before a new flywheel is needed.

    I would NEVER put in a new clutch without grinding down the flywheel. I would NOT attempt to "hand sand" the surface, either. While watching the grinding process, I could see high and low spots, due to the heat......those are high and low spots you are looking at when you see the areas of blue, on the flywheel. The surface MUST be uniform, or else you will only wear out the new clutch sooner.........a process which hand grinding cannot possibly achieve.
     
  12. Verell

    Verell F1 Veteran
    Owner Consultant

    May 5, 2001
    6,951
    Groton, MA
    Full Name:
    Verell Boaen
    It's quite common for flywheels to NOT have significant overheating marks, just uniformly smooth wear. This is particularly true if the clutch is being replaced before it's started slipping.

    I must quibble. Hand sanding with a large (6" to 8" long x2" or so wide) flat rigid sanding block (ie: wood, metal, or hard plastic, not rubber) will rapidly tell you whether or not you've got a rippeled surface that may need a full grinding. If you quickly get a uniformly sanded surface then you have a perfectly adequate surface.

    Even with some slight remaining ripple, if you're not tracking the car or otherwise pushing the clutch, I seriously doubt that clutch lifetime will be affected.
     
  13. atlantaman

    atlantaman Formula 3
    Rossa Subscribed

    Mar 31, 2002
    1,726
    Roswell, Georgia
    Full Name:
    Charles
    dont be cheap---if you are spending the 300 to get a new clutch--pay the extra 30 to get the flywheel done--juts tell the machinist to take only the minimum off--maybe .010.

    when you grind on a piece of iron the vibration tends to relieve some of the internal stresses in the metal too. This will help in slow down some of the cracking---but then again--the heating will re-stress it in 6 months too.

    Dont take a chance and damage a new clutch disk----do it right.
     

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