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Discussion Starter #1
The subject speaks for itself, as nothing is mentioned in the maintenance schedule for Timing belt! as most of you know I drive off-road alot on high temperature and lose sand where the engine is always under pressure at high RPM

Regards,
Ahmed
 

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Discussion Starter #2
In fact, it is a chain, not a belt
 

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I have to disagree with Rob....maybe. I don't know what kind of timing set the 4.7 has in it. It may be metal gears, in that case Rob is correct. However, in the case of my old Jeep YJ with the 4.2 had a nylon gear set for the timing. After about 120K the nylon gears turned into pulleys and had to replace the whole thing. The replacement for the gear set was steel so they may have mended the error in their ways. But that is the only situation where regular oil changes would not result in a timing set lasting a lifetime.
 

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My friend has 140K on his 99 Jeep Grand Cherokee with the 4.7 and its running strong. He has never had to mess with the timing chain.
 

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The 4.7 uses steel sprockets and roller chains with tension maintained by hydraulic cam chain tensioners.
There have been occasional tensioner failures with resultant noise from chains slapping, but thats about it.
The old 4.0 I-6 used a hy-vol non roller chain with flat gears.
The cam gear was nylon cast over aluminum, the crank gear was steel. There is no chain tensioner.
A hy-vol chain wears its pins at each tooth and begins to loosen. As mileage accrues, the chain wears (called stretching) to the point it can be heard hitting the inside of the timing gear cover.
Continued operation with the noise present resulted in the loose, slapping chain breaking the nylon gear teeth off of the aluminum gear, and cam going out of time.
There are no longer any engines using plastic composite gears as any cam or ignition timing variation will cause an engine to increase emissions.

Rob

Just to add for historians: That I-6 was introduced by A.M.C. in 1964 in Rambler Americans as a 199 c.i. It was enlarged to a 232 c.i. in 1964 and was used in the Classic and Ambassador as the base engine and the optional engine in the American. It was enlarged again in 1971 to a 258 c.i. (4.2 L.) and was the optional I-6 in all lines.
A.M.C. began using the 232 c.i. (3.8 L.) in the newly aquired Jeep line in 1971
Various versions of the engine were used in Jeep and a 2.5L 4cyl version was created in the 80,s. Prior to the A.M.C. version, they used the G.M. Iron duke 2.5, 151c.i.
The final years of the A.M.C. I-6 saw a displacement of 4.0L
All versions, be they I-6 OR I-4 shared the same architechure and beyond the mentioned timing chain concern, were incredibly reliable and long lived. Known as a high torque, low R.P.M. design.

Now you know, LOL
 

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Discussion Starter #8
Thanks Guys, then I will keep it until it breaks :)
 
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