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Rough start and Idle

Discussion in '348/355' started by steved033, Oct 1, 2018.

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  1. steved033

    steved033 F1 World Champ
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    #1 steved033, Oct 1, 2018
    Saturday I get up and get ready to take the car out, fire it up, and it's definitely noisier than it's been. Then it stumbles once or twice then idles fine (and by fine, i mean okay). Is still doesn't sound right, too raspy. Pop the engine cover, and take a peek down inside. (Picture from when I was taking it apart, the answer isn't "there's a wrench on your exhaust coupling")

    It's cracked. ANOTHER one.

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    Now, a few months back, I may have posted here about one of my tail pipes just deciding to break free and hang down at an odd angle. Once I get it all taken apart, the same thing has happened with this pipe.

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    These look laser welded, but there's little to no penetration. So, fire up the old trusty MIG, and make some welds (ignore that mess at the bottom of the first pic below, I forgot to turn the gas on :confused::mad:, and it's back together.

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    The 02 sensor was getting some really really bad air, because when I fired it up, it sounded worse than ever. Oh...ECU reset. Disconnect battery, wait a few minutes, reconnect, start it up. Runs like new. Just wow. Now that i'm not losing 10 hp out that crack, it's a different car in sound and performance!

    sjd
     
  2. jjtjr

    jjtjr Formula Junior

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    #2 jjtjr, Oct 1, 2018
    Usually when cracks occur on pipes or flanges, it is often the result of stress on some or part of the exhaust system. As the engine moves back and forth in the mounts, it works on the exhaust bending it back and forth eventually causing a crack to form.
     
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  3. steved033

    steved033 F1 World Champ
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    #3 steved033, Oct 1, 2018
    Last edited: Oct 1, 2018
    Correct.

    Tightening order was important here. When I put it back, I made sure I could twist the test pipe into a position of little stress, with the muffler acting as an alignment guide. The muffler stayed lightly supported until i had the hangers in the correct position. Basically, i'm letting the muffler live where it wants to, tightened into place and noting the minimal amount of movement from the hanger springs. I tightened the flange bolts at the header second.

    Some of it is just sh*t welding.

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    This wasn't stress. (correction: it WAS stress, just not the kind you're talking about...)

    sjd
     
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  4. taz355

    taz355 F1 Veteran
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    #4 taz355, Oct 1, 2018
    It looks like your exhaust bolts being ontop could be very close to the drive shaft when the wheels move to their extremes.
    Not possitive from the picture though
     
  5. steved033

    steved033 F1 World Champ
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    #5 steved033, Oct 2, 2018
    There's no indication that anything is touching or has touched. It's in the same position it was always in. It's easy enough to crawl under there and clock it just a little. I had concerns of it hitting the trans case too.

    Thanks! I'll check it out tonight.

    sjd
     
  6. steved033

    steved033 F1 World Champ
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    #6 steved033, Oct 3, 2018
    I was thinking about it last night, and that picture taken is at full droop, so it's got plenty of clearance.

    sjd
     
  7. johnk...

    johnk... F1 World Champ
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    #7 johnk..., Oct 3, 2018
    The problem is the way the pipes are made. The flange should not be welded to the pipe. It should float, as does the flange on the headers. The two flanges squeeze the gasket between the flares but allow the joint to be flexible so the pipe can move relative to the header. That is why the bolts are spring loaded. See how the Fabspeed test pipes are made below. With the flanges welded to the pipe any movement of the engine generates stress on that welded joint. You can weld them again, but ultimately they will most likely crack again.

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  8. INTMD8

    INTMD8 F1 Veteran
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    #8 INTMD8, Oct 3, 2018
    It doesn't appear the flanges are welded to the pipe.

    Looks like a fusion weld without enough amps so agreed on poor welding.
     
  9. johnk...

    johnk... F1 World Champ
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    #9 johnk..., Oct 3, 2018
    Looking closer, yes, you are correct, James. They welded a flare to a straight pipe. But, looking at the 2nd picture the OP posted, the clearance between the flare neck and the flange looks like it is so tight it may not allow sufficient movement??? But, yes, poor weld for sure. (Still a problem with the way the pipes were made.;))

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  10. INTMD8

    INTMD8 F1 Veteran
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    #10 INTMD8, Oct 3, 2018
    Yes I could see that, looks pretty tight. (and not sure if it's beveled to match the flare on the pipe). May just be water jet out of flat stock.
     
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  11. johnk...

    johnk... F1 World Champ
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    #11 johnk..., Oct 3, 2018
    I think you nailed it again. Looking at the way the flange butts against the flare it's probably not beveled.

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  12. steved033

    steved033 F1 World Champ
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    #12 steved033, Oct 3, 2018
    The flange is not beveled, and the flange does float.

    sjd
     

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