rebirth of a Ferrari

tale of a thirty three year old 308GTB

Copyright © 2013 by Ron Smith. All rights reserved. Rebloging and personal use is however encouraged.

Timing Belts

The Ferrari 308 like many modern cars with over head cam engines, use Gilmer belts to drive the cam shafts.  This precision toothed belt turns the cams in exact relationship to the movement of the crank and pistons. The belts are a regular service item because they wear out with use or simply degrade over time.  Unlike other belts, like your fan belt, if these break it is a disaster of immense proportions.  It can at a minimum bend valves, or if the engine is really spinning fast, can punch holes in pistons. 

My car had sat for over a year at the painters without being started once, and the belts were due to be changed.  I decided before starting up the 308 again, I’d changes the belts as part of the prep to get it running again after the long sleep.


Getting to an engine mounted in the middle of a car can be tricky, but the Ferrari is amazingly easy.  The wheel well covers are fiberglass and can be quickly removed by taking out a handfull of bolts, giving exceptional access to both ends of the engine.


You can just see the AC compressor that is bolted to the front cam cover - it has to come out.  The large silver shape on the right with the black bands  is one of the two gas tanks. 




The belt covers are now accessible. 


These casting are beautiful. The protrusion in between the covers is the water pump with the pulley removed.  It had to come off to get the AC out.


Both covers off, and the belts exposed.  The pulleys at the top of the engine turn the intake and the exhaust cams, one set for each bank of cylinders.  The smaller pulley near the top is the tensioner, and the small pulley near the bottom drives all of this.  The alternator is in the lower right. 



To change the belts is quite simple, but the consequences of doing anything wrong is significant damage to the engine.  The basic process is to put the engine at a known point (TDC) and lock the cams in place, and replace the belt with out moving anything.  The wooden “tool” at the top I made to hold the cams in place.  It worked perfectly.




With the cams locked, the tensioner assembly is removed to rebuild it and change small pulley with an upgraded version that is now available.






To insure that everything is properly synchronized and not moved during belt installation, I mark the pulleys, then check them again after the belt is on. 



I removed the cam covers to clean them, check timing and generally inspect things.



Everything is back together.  I media blasted the covers, painted various parts, and replaced AC o-rings and accessory belts.



All back together.


  1. 308gtb posted this