V-8 Timing belt progress, 2nd evening . . . (1 Viewer)

[donco]

I don't have alot of time or energy to devote to this project in the evenings but accomplished what I set out to do on day 2.

Everything is off (except for the waterpump) and the belt is fully exposed, ready to come off:

http://www.nmia.com/~dgnrg/ttb8.jpg

The job is rather simple, just time consuming. I'm being careful to put bolts in individual baggies with notes for where they go.

The crank pulley bolt comes off easily with the end of a breaker bar up against the underside of the passenger chassis rail. One tap of the starter & it's loose. The pulley has 4 holes at 90 degrees apart, 2 threaded, to smooth. An 8mm bolt turned into one of the threaded holes drives it off with barely more than finger tight pressure with the tip of the bolt pushing against the face of the plastic shroud with the timing marks, behind the pulley.

The hardest part was getting the 2 little phillips screws off of the metal bracket on the a/c compressor that holds the connector. It either needs to come off or be bent to get the fan shaft mounting bracket off. There are 2 bolts on the side of the compressor that bolt thru into that bracket and they have to come out but the compressor can stay. One bolt is reached from above along the chassis rail, the other from underneath thru the opening for the axle with a couple extensions and a swivel, piece of cake.

All that's left is to remove the belt, swap the water pump, put the new belt in, and put everything back.

Observations:

At 100k miles, there was no way this job was necessary at this time, the old belt looks as good as the new one but will have a better assessment when I get it off and can bend it fully backwards and look closely for any cracks at the base of the teeth. There are no leaks anywhere of any kind. I'm going to go with my instincts and use the old idlers and tensioner, and do them next time at 200k+ miles. I'm going to go out on a limb and say the original belt could easily have gone 150k and coulda postponed this chore but it will be good peace of mind to have it out of the way.

The deal with rotaing the crank 50 degrees past TDC is it postions the pistons so they aren't near the top of the stroke, and the cam shafts are in a position where they have little imbalanced valvespring pressure on them to cause them to rotate when the belt is removed.

More later,

Cheers!

 

[fyton2v]

Was was the condition of your timing belt vs. the condition of your S belt? My serpentine belt is cracking after 6 years so I'm going through pre-timing belt maintenance jitters.

Tnx.

 

[donco]

timing belt vs. serp. belt.

I put a new serpentine belt on it a while back, maybe around 85k & don't know if the old one was the original (bought the LC used off of lease at 31k). The old belt was cracked for sure. I keep it in the jack cubby for a spare. I think the serp belt sees more severe exposure to the elements. I don't think you need to use it as a gauge as to whether the timing belt is in that condition. The timing belt is rightfully protected behind all of the covers and I'm sure it's spec'd for more severe duty. The timing belt is much beefier, perhaps twice as wide as the serp belt, and it travels at a much slower speed and is more constrained from whipping around so will outlast the serp belt by at least a factor of 2 or 3 in my opinion.

 

[Tinkerer]

The belt condition may not necessarily be judged visually.

Remember: The belt strength is not from the visible outer elastomer molding, but rather, from the inner "load carrying cords", aka reinforcements.

While visible degradation in the outer facing is definitely cause for concern with a timing belt, a belt that appears OK may also be near failure - with no outward clues.

This applies to any reinforced elastomer drive belt or timing belt, although the exposed serpentine (and other such drive belts) will show drive face cracking & other outward signs of wear & aging much sooner due to exposure, construction & application differences, etc. So the plain vanilla drive belt such as a serpentine belt will usually show cracking etc. before it fails. But not necessarily so for a timing belt.

Certainly, the OEM specifies a change interval that includes a large safety margin, for something with failure impact as severe as a timing belt - so, yes, it could probably last well beyond 90k. Key word: "Probably" - it's a matter of probabilities. Probability of failure is nearly zero up to 90k, but becomes increasingly significant the farther past 90k it runs. But most belts that are run up to, say, 150k, will make it. The question is: What is your risk tolerance? Do you want to be part of the population with, say, 5% to 10% failure rate, for your timing belt? (As may be the case at 150k)

Personally, I'll bite the bullet and replace the timing belt at the recommended interval, regardless of how it appears. I want to be part of the group with nearly zero failure rate.

(I keep seeing posts from folks who base their timing belt assessment on visual appearances and anecdotal stories alone...good luck! Let us know what happens if/when it runs too long and breaks!)