Originally Posted by
HeliComparator
Hi-Chrome valves were installed on engines built after around 1998, that negate the need for that SB. Unfortunately for some reason, you can't fit Hi-Chrome valves to engines installed in rotary wing, so the SB still stands.
Are you sure? I did a quick search to try and find out why, and came across this directly relevant document for this post:
https://austhia.com/PDfs/AHIA-piston...ity-report.pdf
4.2.2. Component change review 4.2.2.1. Valve guides Prior to 1998, some Lycoming aircraft engines were fitted with exhaust valve guides that exhibited premature 'bell-mouthing' type wear; contributing to a greater risk of valve sticking and/or sealing surface degradation. Mandatory Service Bulletin SB388 (2004) was introduced to require assessment of valve guide and valve condition at minimum 300 hour intervals, with Service Instruction SI1485 following to introduce a new 'Hi-chrome' wear resistant valve guide material. SI1485A noted that all Lycoming cylinder assemblies produced after 1998 contained guides produced from the new material