muffler gasket blowout

Discussion in 'Motorized Bicycle General Discussion' started by Crysisfreak7, Jun 6, 2014.

  1. Crysisfreak7

    Crysisfreak7 New Member

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    the rubber gasket that was between the muffler and engine fried on the bottom. my bike sounds like a dirtbike now, should i leave it this way (i doubt it), and could this be caused by the fact that my pedals brush the muffler when i pedal. it causes the muffler to tilt up a bit, but it then moves back.
     
  2. TakeiT

    TakeiT New Member

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    I had the same thing, the bolts backed off for me. I just used high temp gasket sealer.
     
  3. 2door

    2door Moderator
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    The welded flange on the exhaust/muffler is almost without exception warped from the welding process when the factore joins the pipe to the flange. You need to 'lap' that gasket surface to get a good gasket seal.

    Go to an auto parts store and ask for gasket material that will take exhaust heat then cut your own gasket. Torque the nuts to about 60 inch pounds then check them again after the engine has reached operating temperature a couple of times.

    I've found that gaskets made from 1/8" thick material will perform very well. Gasket sealer isn't necessary if the gasket mating surfaces are flush.

    One trick to get muffler/pedal crank clearance is to enlargen the holes in the flange so the muffler can be rotated slightly to clear the crank.

    Don't ride the bike with the muffler detached or leaking badly at the cylinder. That can cause a lean condition and damage the cylinder and piston along with making enemies of your neighbors.

    Tom
     
  4. Wild Bill

    Wild Bill New Member

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    I never use gaskets on exhaust, they will just blow out at some point. I use Permatex High Temp Copper Silicone. Put a thin coat on both surfaces and assemble, then let it set over night before using. I never blow out copper silicone. I even use it on street rods and in the past various race cars. Also without a gasket there is far less chance of the bolts coming loose which is caused by the gasket getting thinner with time by the gasket being compressed.
     
    #4 Wild Bill, Jun 8, 2014
    Last edited: Jun 8, 2014
  5. Davezilla

    Davezilla New Member

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    I've had the same problem blowing the exhaust gaskets on mine but I have a CNC machine and I'll be making some solid copper gaskets to remedy the problem of the gaskets blowing out and the nuts working their way loose.
    To remedy the nuts constantly working their way loose, I got some brass nuts from Fred's ebay store and drilled safety wire holes in them so I can safety wire them after they're torqued, the gasket still wears out and the nuts will be loose after a few more hours of riding, but I can re torque and re safety wire without worrying about the nuts coming off and losing my pipe on the road.
    I'm hoping the copper gaskets will remedy both problems.
     
  6. 2door

    2door Moderator
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    Dave, I'll repeat what I said above about the flatness of the exhaust flange. If it isn't flat and doesn't fit flush across the full face you'll blow gaskets. Also the metallic gasket, copper or aluminum, will leak if the flange isn't flat.

    Try this: Remove and clean the flange of any gasket material or exhaust residue. Use a magic marker, machinist dye or a Sharpie and 'paint tha gasket surface. Now rub the flange against a flat surface such as glass with a sheet of medium grit, about 280 sandpaper on the glass. It only takes a swipe or two then look at the flange where you painted it with the ink. You'll quickly see where the high and low spots are and what needs to be done to make the flange gasket surface flat.

    As for the fasteners coming loose, try replacing the nuts and studs with Allen head capscrews. Torque them to about 60 inch pounds then check the torque after a few heat/cool cycles. I think you'll cure your problems.

    Tom
     
  7. mapbike

    mapbike Active Member

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    I honestly dont have any issue blowing gaskets on mine because I double nut mine and like Tom said make sure that the mating surface is flat so good pressure is applied all across the flange and then like I said I get the first nut good and tight which will have a dab of Blue loctite on it and then I put another nut on behind that one and then tighten them against one another to a very tight level, nuts never back off and gaskets stay nice and sealed, been doing mine this way since the first time I had a nut back off on my first build back in 2009, never had any issues since.

    I'm looking forward to getting some of those nice gaskets Dave, copper and/or Dead soft Aluminum should do a fine job when installed right.

    map
     
  8. Davezilla

    Davezilla New Member

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    I fully agree about teh flanges not being true and I had to resurface mine on a sanding table before it was flat and true, then I painted the surface with blue machinist's dye and ran it over a sanding block made out of wood to check that it was perfectly flat.

    I really don't like using bolts or allen screws where I'm torquing into the aluminum just as a rule of caution against stripping the threads from repeated torquing unless inserts or helicoils are being used. The aluminum can usually withstand a few re torquings but the softer metal tends to wear faster which is why I still prefer studs and nuts or some kind of insert like helicoils or kingserts.
    The use of brass nuts on the studs also helps because the softer brass won't wear out the threads on the studs, it's easily drilled for safety wire holes and can withstand several re safety wiring. These also tend to stay put better when star washers are used if someone prefers not to safety wire them. I got a few sets of the brass ones that Fred sells in his ebay store and they're really nice because they are like 8mm wide so there's lots of thread surface to prevent stripping.
    I've also did the double nut thing on mine before and that works really well to keep them from backing out. I do prefer to safety wire them when I can tho because if they ever do come loose they won't work their way all the way off and will hold everything together long enough to get home.

    Another thing that causes the exhaust bolts or nuts to constantly work their way loose is when the pipe is installed without proper support from extra mounting brackets, the brackets that come in the engine kits are just thin metal and they can flex enough to let the pipe flex with the engine's vibration, this in turn wears out teh gaskets quickly and the nuts become loose enough to back off and fall out so I also strongly recommend making your own brackets out of thicker stronger metal that won't let the end of the pipe flex from engine vibes or a bumpy road etc...
     
  9. crassius

    crassius Well-Known Member

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    I have no problems with these, and don't even bother to replace the studs with stronger ones. When an engine is new, I fire it for a few minutes on the bench, cool it down, fire it again, and so on 4 0r 5 times. During these runs, I do not use the muffler hanger, so that the muffler will shake a bit to compress the gasket nicely.

    When this is done, I tighten it and then add the hanger.

    Then, like with the motor mounts, I check tightness before each ride for first 40 miles or so, then deliver to customer.
     
  10. mapbike

    mapbike Active Member

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    Sounds like you have a good system there and if it aint broke dont fix it....!
    dance1
    Map
     
  11. xseler

    xseler Well-Known Member

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    I spent an hour or so with a fine flat file, flattening the mating surface of the 'exhaust manifold'. I had to remove quite a bit of material to get the entire surface the way it needed to be. I used an aluminum gasket and haven't had to re-tighten the exhaust at all.

    Time well spent, in my opinion. Kinda gave me the delusion that I was an old world craftsman wielding a tool...........while listening to Aerosmith (I do believe at that time).
     
  12. Davezilla

    Davezilla New Member

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    That's the best way to do it when selling assembled bikes, the repeated heat cycles and re torquing will ensure the end user don't run into problems with hardware coming loose.
     

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