I have a G-38 Gas Engine. My muffler bolts have loosened. What is a good method to attach the muffler bolts so they will not loosen, but can be removed with hand tools if needed

Ed

Vibration proof lock washers. They worked for me.

Drill the bolt head and safety wire those bad boys. Absolute solution.

Bedford

Works for people flying in their planes, so I would have to agree there. My buddy is an aircraft parts chief inspector. He wires his stuff too. It'll never come off.

But....I have used blue lock tite on threads cleaned up thoroughly with brake clearner (use q tips to get in the engine threads). It has not come loose yet. I thin layer of permatex ultra copper for a gasket is good too.

If you wire them and use permatex ultra copper for a gasket, that would be the ultimate setup.

I do the same as Joe..I think a lot people dont clean the bolts enough when using Loc-tite..I use the Red on the muffler bolts and they have never come loose.

Green Loctite 609 or 638

here is a little removable locking bar I came up with
The 5mm bolts slide easily thru 5/16" holes -- and the set screws are 6/32x 3/8" cone (pointed end).
so - tighten and loctite the bolts into the engine -- then drop the bar in place a add a dab of loctite to each set screw.
their job is to prevent rotation of either bolt .
a dremel disc can make a tiny dished spot on the bolt head for a solid engagement of the setscrew

Loctite GREEN sleave and bearing retainer.

It's used for sleeving car engines and also on the rod and main cap bearing bolts.

It's permanent though. You won't be talking this off at the field with a crescent wrench or an allen wrench.

It's not going to come loose while your flying either. [sm=thumbs_up.gif]

How do you get it off? Heat it up with a propane torch SLOOOOWWWLY so that you don't cook your muffler. It takes about 500F to get it loose. Then you just unscrew the bolts. Piece-uh-cake.

I've used it several times. Never had a problem getting it loose when I wanted to take the muffler off. Never had another muffler come loose at the field or anyplace else--unless I WANTED it to come loose.

Remove the gasket and make sure the joint is planed. I have yet to see a metal-to-metal joint relax and come loose.
To prevent the last traces of oil sweat, lightly smear the contact faces with RTV silicone kit, let dry for 20 minutes and assemble.

None of you engine guys ever have to repair an engine with the flange beat to a fair thee well?
a perfect mating surface is ideal of course but not the rule rather -an exception
I don't like permanent locking setups as they can lead to breakage by the overly enthusiastic types
The major muffler problems I see , are from those who use large engines and the in cowl mufflers - not supported at the far end
the cantilevering simply stretches the attaching bolts if vibes are right
So
I like to support the far side of the can directly to the engine NOT the firewall- then use a mor standard thin gasket firmly seated .
here is a rather simple jury rig - where a mounting flange was not provided- may seem unnecessary to some--- but years back -- I fought my way thru those wretched four stroke engines in super light pattern planes -and the mufflers broke off -headers cracked apart -on an on-- due to the long cyclic period between power pulses - actually about the same seen on our gasser engines.
If you solve the loose muffler thru locked in bolts --I bet you end up seeing the muffler come apart -eventually -unless you resolve the real problem-- unsupported mass.
The stand off in the pic shown are boxed togetjer on top and one side-as stand offs in general are just asking for trouble from the possible twisting of the engine .
Smaller engines don't have as much of a problem but 60's on up will -especially if th Pits type is a larger can - these perform much better than the restrictive ones but I think - full support is a good idea
Like Jockey Shorts -----

I drill out my bolts and put a bent piece of wire in to keep them from turning out. Works for me.

I also ditch the gaskets and put a light smear of the permatex ultra copper gasket in place.

On some mufflers the bolts are recessed so you have to rely on some type of lock tight goop.

I use permatex ultra copper gasket on those, and the lock wired ones. No problem, as mentioned clean the bolts first, I use paint solvent.

Nothing like watching 150 bucks of muffler disappear into the weeds, anyone been there

Flip and Fly:
What you've done in that picture is safety wiring.

If you want to make it better, take that wire out of the back bolt and run the wire UP from the bottom. That way if either bolt tries to loosen, the wire stops it and pulls the other bolt tighter.

I never lost a muffler due to loose nut, but always lost them when the screw head broke off. just remember did you ever find the long screw still attached to the muffler? and if it did come out it would hit the prop before falling off.

roltech

That's the engineer's rule for you.
Hand tightened screws 1/4" and smaller tend to be over-torqued if one has the feeling that it is tightened well. The situation grows worse, the smaller the screws get.

You got that right, someone told me that the head due to fuel residue still left in the muffler cause rusting on the screw parts and weakens the shaft , they should be removed once and a while for inpectons, I only lost one , the other would get loose even after locktight applied. it seem like the wrong metal is used for those bolts and changes with heat.

roltech

here's a thought. Thermal expansion of two different metals, aluminum/steel.this is what works for me because of the difference.
Clean the threads on the cyl. head, same for the bolts. alcohol or similar, use green or red loc-tite, put the muffler on snug the screws, run the engine ttill its good and warm/hot then finish tightening the screws. also the can,if pitts style muffler must have a support bracket to the firewall.

Just an added suggestion -- make the support to the engine if possible somehow
sometimes the engine shakes on the firewall and the real support is lost.
(you want the muffler to move with the engine )

For my money, I like to use studs rather than bolts. I can then either double nut them or use squeeze nuts. Also saves wear and tear on the engine threads. Good luck, red

Amazing how many good ideas you get out of a single thread here...no wonder I hooked on this stuff.

Teflon tape.
Works great.

I have used a dab of permatex ultra copper on the end of each muffler bolt and they don't come loose and yet can be removed using hand tools.

-Ed

I agree with T-One on the thermal expansion idea.

Heavy industrial punch press manufacturers use huge (seen them as large as 5" dia.) studs that hold the top and bottom of the presses together, usually one or two on each corner. At assembly they carefully heat the studs in a controlled manner to get them to grow in length (which can be substantial since they are often over 10 feet long), then quickly assemble and torque everything down. As the studs cool over the next several hours (lots of mass there), they contract, resulting in an EXTREMELY tight joint, but not so tight that it fractures or otherwise compromises the molecular structure of the studs.

The great thing about T-One's suggestion is that using the heat from the engine guarantees that a fool with a torch (me) can't overheat the bolts and change the temper of the steel.

Here is my method of keeping a muffler (exhaust diverter) tight on a G-62. I use Permatex Ultra Copper with no gasket. The mating surfaces should be clean, flat, and lightly sanded. On the bolts I use a flat washer, a split lock washer, and another flat washer. The split lock washer keeps constant tension on the bolt. Finally, I use JB Weld on the bolt threads. Don't worry, if you need to remove the bolts, start the engine up and warm it up good. While hot the JB Weld will break loose.

I think General Motors used a metal flange type of deal on their exhaust manifolds back in the 70's that you bent over and against part of each manifold bolt to keep it from turning.