Although the basic engine design has remained constant for the XE engines there were a few minor changes made leading to the distinction between 'early type' engines (those up to engine number 14142838) and 'late type' engines (those from engine number 14142839 onwards).

Head Bolts- Early vs Late
The two types of head bolts are quite easy to tell apart at a glance, simply by looking at the bolt heads.

Both bolt designs are a six splined TRX fitting. The early type head bolts are a conventional bolt design which need a socket in order to fit them. These bolts are fitted with seperate head bolt washers.

The later type bolts are a 'cap head' design with an internal six spline TRX. These bolts need a TRX key in order to fit them. The later bolts are also supplied with a captive head bolt washer.