Conference vmszoo::rc

    I would like to make a warning about Loctite and other such
    adhesives in high-temp situations
    	
    _Some_ heat will lock them tighter.  Past that point, and they start
    to decompose to char and ash.  I don't know if the muffler bolts
    get hot enough to do this; I know that on a tractor engine they
    certainly do.  The only dependable thread-lubricant I know of for
    those bolts is Nevr-Sieze - whose major lubricant components aren't
    organic!  (it's graphite, molybdenium disulfide, and aluminum spheres
    in thick oil.  The oil goes away the first time heat hits it- but
    the moly/graphite/aluminum stays around.  There's another
    even-higher-temp thread lube that uses copper spheres instead of
    aluminum)
    
    But what does thread LUBE have to do with thread LOCK, you ask.
    Well, the same things that kill organic greases on hot threads will
    kill organic thread-lockers.  You may need to go to mechanical locking
    methods (like thin tin washers that are crimped over a nut and an
    adjacent casting boss and _absolutely, positively_ prevent the nut
    from turning.)  I guess it depends on just how abominably hot your
    exhaust gets... and it sounds like pretty hot to me, seeing as the
    bolts expanded enough to loosen the lock washers and unscrew!
    
    I seem to recall a temp limit of 350F for standard Loctite.  Is
    this right or am I passing gas again?  :-).  
    
    Does the exhaust manifold get this hot?  Hotter?  Lots hotter?

    I can't admit to knowing exactly what case temperatures on a model
    engine are.  I _do_ know that the exhaust temperature is sufficuent
    to melt conventional solder but not [true] silver-solder if someone
    can interpolate at least the range from that.
    
    I memory serves, in articles I've read on flash points of synthetics
    versus castor-oil lubricants in model fuel, case temps in the 400+
    range spell big trouble for our engines so I'd SWAG that "normal"
    operating temps are somewhat less than this.              
    
    In any event, Loctite has proven effective for us for locking case
    and muffler bolts on 2-cycle engines.  I understand that exhaust
    temps are considerably higher on 4-cycles so it might not work as
    well there...I have no experience in this area (though Anker and
    others tried [unsuccessfully] to sell me on 4-cycles in the video 
    tape of the DEC fun-fly). ;B^}

      |
      | |      00	 Adios,      Al
    |_|_|      ( >o
      |    Z__(O_\_	(The Desert Rat)

    Re: .730, Dan,
    
    If the threads in the crankcase/exhaust stack are in bad shape,
    tou might be able to get away with re-tapping them to the next size
    larger screw, e.g. if they were originally for a 4-40, retap for
    [say] an 5-40 or 6-32.  I've done this with much success in the past.
    The only thing to be careful of is whether the flange on the muffler
    will tolerate the larger hole size and enough clearance exists to
    accomodate the larger screw head.    

      |
      | |      00	 Adios,      Al
    |_|_|      ( >o
      |    Z__(O_\_	(The Desert Rat)

Yes, you can retap it, but beware.  I had a hole in a muffler
that was tapped for the Japanese thread size (metric).  I drilled
it out and tapped it for a 6-32, which is the largest hole I
could put through the flange.  The tap cut just fine, but when I
put the screw in, it stripped because there wasn't enough metal
to properly cut the thread.

The hole size looks very tempting as a quick fix to 6-32.  Don't
do it, it doesn't work.

This is on one of my ill-fated .15s. Unfortunately, there is not
enough metal there to run out to 8-32, so you might say I'm
screwed.  I'll probably fill it with metalized epoxy and re-tap
it to 6-32, even though I don't expect that to work either.

	I have a K B .65 Sportster.  The standard included muffler is
	not set up for pressure to the fuel tank.  I'd like to
	either tap it and put a thing on or get a different muffler.
	Anyone have experience with this (on this engine)?
	Recommendations?

	Thanks

	Chad

    Taps are available from Fox. I did it in years past on aftermarket
    mufflers. The big problem is that the taps are a weird thread size.
    3-48 I believe. Put some high temp sealant on it before you tread it in
    so you have a good seal. Shouldn't be a problem. It will make your
    needle valve setting a bit touchier (and you'll have to screw it in
    further)

DUBRO has one with a 6-32 thread.  As -1 says, screw it in tight and
put something on the thread. I recommend blue Locktite.