The best way to prevent the muffler from loosening is to ditch the high tensile bolts & replace them with mild steel or stainless steel bolts of maximum length (more surface cantact = more hold). The heat expansion coefficient between the high tensile bolts & head material is to great & they will loosen. There are suggestions to leave out the gasket & smear heat proof silicon on threads etc these suggestions are not addressing the cause but a band aid solution.
Solution for loosening RJX mufflers (or any muffler);
- Ditch the high tesile 15mm bolts & replace with 4 m4 20mm stainless steel bolts & 4 lock washers (no flat washers & supplied bolts are to short).
- Clean all surfaces & fix the RJX muffler backing plate to the head using an exhaust gasket between the head & plate. Make sure it is a proper exhaust gasket of metal composite formulated for high heat use otherwise use the high temp silicon & follow the procedure with silicon use. Do not use your left over roof & gutter silicon that you have lying about & do not use cheap 90 cents paper exhaust gaskets.
- Tighten the bolts, then DO not fit the muffler. Start engine untill hot then re-tighten the two bolts. Run a few heat & cooling cycles & tighten bolts while hot.
- Smear the surface of the muffler with heat proof silicon gasket material & lightly tighten the adaptor plate. Let the material harden for 1 hour then tighten.
- Now repeat heat & cooling cycle tightening.