I have an OS 55 fitted into a CMP Pro Cessna Skylane 182 (65 inch wingspan) . The engine is mounted horizontally so that the muffler lines up with the recess in the fuselage. To clear the fuse I have to use a 17mm spacer/adaptor from OS. Extra long screws are not supplied so I threaded up some 3 mm rod to act as studs. I have tried screwing the studs into the muffler and on engine side pulled it down with nyloks. Still works loose within a few minutes, lose back pressure and engine splutters.

Drilled out the muffler thread holes to 3.5 mm and made up some more threaded rod to pass through the muffler, this time with nylok nuts at both ends. Same thing happens - works loose everytime. I have even tried Loktite on threads.

Any suggestions other then welding the bugger to the engine block? I am at a loss at what else there is to do. I have a suspicion that the adaptor does not help but has to be fitted.

Try regular nuts with lock washers or no washers. The nylok may be too warm?

I have the adapter on my OS 46AX, but mine came with longer screws. I use thread lock, both in the holes in the muffler and on the screws. Did you try using thread lock with metal fasteners instead of the nylocks? Standard thread locker will not work with plastic.

Good luck.

Phil,
Your problem is the nylon locking nuts. They are getting hot and will not hold. Also, try to avoid using threadlock on muffler bolts as well. If you are using all thread use a double nut to lock the studs in place to keep them from coming loose.

Ken

Nuts with a nylon locking insert (nylock) are not to be used on exhaust systems, or for any application where high temperatures exist.

Use a steel lock-nut, with a flat washer underneath (for a bearing surface), and crank down tight.

I use gel super glue as a thread locker on metal to metal contact...works great....except on my OS 1.60....it eventually backs off...so I drilled a hole in each bolt head and safetied wired the bolts...If you don't know what safty wire is, it's genarally 20 or 32 thousands diameter stainless wire (can be 40 thousandths)...and you run the wire through the bolt head and twist it...route the wire so the bolt can not lossen..route the safety wire to the other bolt for the muffler and insert one leg of the wire into the hole you drilled in that bolt head so that that bolt can't lossen then twist the ends of the wire together cut off leaving a pig tail and fold over so you don't cut yourself ...now your bolts can not lossen...if I confused you I bet there is an explaination on the web on how to do it with pics...it's easy Good Luck

Ken why no thread lock on muffler bolts? Is it a temperature issue?

Yes. In my experience the heat turns the threadlock into a solid and makes it very hard to remove the muffler bolts. I used it a few times but after snapping a bolt off trying to remove it I quit using it. If you get the bolt tight it should stay in place without using threadlock.

Ken

Thanks, good to know!

Thanks for all your suggestions! A thought I did have was to use some loktabs - like motorcycles and machinery with vibration problems but there is no room in reality on this engine to have the fold-up type. I considered safety wire like they use on aero/jet engines where the wire passes through the nut/bolt head then pulled tight into the next nut/bolt - like one of you has already suggested.

I think the best option here is to make up new studs, weld some standard nuts to the top with flat washer underneath and drilled to accommodate safety wire.

It's getting a right pain in the proverbial having to keep removing the prop and cowl to tighten the muffler.

Thanks for your help - Especially to avoid nyloks!

I would make a trip to the local hardware store and pick up some metric socket head cap screws, or search Tower, they have several different sizes of muffler extension screws. Just cut them down with a Dremel if they are too long.

http://www3.towerhobbies.com/cgi-bin...P?&C=GMD&V=OSM

After you get the correct screw, re-torque when the engine is hot.

A point to consider. long, large diameter bolts don't work as well in a major thermal expansion zone, such as a muffler. A smaller bolt can be stretched more when tightening and when it heats and expands, it will remain tight.

A couple decades back, I was working with the design engineers on a large main frame computer. We had some serious copper bus bars, cabable of handeling 500 amps plus. We had problems where the bus bar bolted to a mother board. The joint keept loosening up after a few power cycles. We kept going to larger bolts but the problem kept getting worse. The copper was expanding more than the steel bolts. The bigger bolts wouldn't stretch, so the copper was deformed. The solution was to use quite small bolts that the copper could stretch when heated. There was enough elasticity to handle the expansion and contraction.

I would try some 2mm bolts if the problem persists after using the steel nuts and lock washers on you 3mm bolts.

Don

Regular threadlock won't work,even Permatex. Try the Permatex seal/bearing retainer. Works better than the others.