Common cambelt failures and service note

[gmendoza]

Most V8 timing belt failures I've heard about are from the bolt on the intermediate shaft (IMS) backing out causing the pulley to slip resulting in crunched valves. Very few failures from the belt actually snapping or even skipping teeth. Also, most failures I've heard about/seen are on 97-99 V8's. While reading the service notes, in the section on torqing the IMS bolt, it mentions to make sure you have the newer style bolt. It also makes no mention of applying locktite to the IMS bolt while it does mention applying locktite to the cam bolts.

Now this sparked a few questions. When did Lotus start using the new IMS bolt? If having the IMS bolt backing out is a common failure, why no locktite? Lastly, in the section that addresses adjustment and also the section on replacement, it makes no mention of re-torquing either the IMS nor the cam bolts. Is it good practice to do it anyway?

Thanks in advance

[mike_sekinger]

The camshaft pulley bolts have a Loctite thread sealant employed (Loctite 572) because of the camshaft drillings used for the timing procedure; This is not a high strength thread locker.

The intermediate shaft bolt was changed to a broader shoulder bolt (same as the cam pulley bolts) to increase the clamp load on the idlers.

If you have to re-establish your cam timing, you will need to re-torque the cam pulleys after alignment. For the simple tensioning procedure there is no need to re-torque the pulleys.

Remember: There is no need to remove the cam covers for timing confirmation and tensioning. If you need to re-torque the cam pulleys, you will need to remove the cam covers to arrest the camshaft during torquing and re-seal afterwards.

Cheers,

Mike S

Edited February 17, 2011 by mike_sekinger

[gmendoza]

Thanks Mike for the fast reply.

This is what troubles me, if Dave (see link below) would have done his timing belt service by the book, it wouldn't of prevented his failure.

http://www.thelotusforums.com/forums/index.php/topic/29566-engine-wont-fire/

Edited February 17, 2011 by gmendoza

[mike_sekinger]

It is sometimes difficult to trace the origin of these failures since you do not know who has done what?

If either the intermediate shaft idlers or the cam pulleys are not prepared and torqued properly, they can loose position. If the pulleys were indexed this would not happen, but then a different positioning and tensioning procedure would be required.

The manaul makes a clear definition between the tensioning procedure and the (re)establishment of correct timing/positioning. If the pulleys have been correctly torqued and have retained an acceptable timing position, there is not need to re-torque them.

Cheers,

Mike S

Edited February 17, 2011 by mike_sekinger

[gmendoza]

Great, thanks Mike!