This is a good joke and I said earlier I would try not to be funny anymore. I have taken down two 32v one with very high miles 200k and one with 79k. The wear was virtually identical in the rotating mass as well as the valve train/cams etc. The shop my brother owns is nothing but GM builds. The engines he rebuilds at 100k are in NEED of a rebuild. Would they still run? Of course but the numbers suck and they are already smoking. The aircraft like tolerances on these engines always baffled him and our builder friends when they see them apart/open.
Timing belt failure is very rare in our cars it just seems like they are abundant as our group is very small here. The LT and the LS platforms are laden with other problems, just spend some time on those boards. There was millions of these engines sold . Would I use an LS engine? Yes sir, if I was building a 6(7,8,or9) Camaro, which I intend to do one of these days, but I wouldn't go putting a 928 engine in it though ,reliable as they may be.
Kevin

 

I am not going to be putting a LS1 in a 928 for me.

I guess we have had different luck with the LS1's, I can not think of one I have had come into my shop that has had regular oil changes that was any where close to being worn out at 100,000.

Like I said, the LS1 engines are very good.

 

I think the main thing that sucks on the 928 motors is the timing belt. Why would Uber German engineers ever put a belt in instead of a chain. My BMW even has a chain not a belt. For a one time super car why did they use a belt? I'm sure someone here knows the answer.

 

I am going to guess that a 7 foot long chain has some real force to it, spinning at 7 grand........

only a guess though.

Guess two is that a belt has a different, way of quiessing failure........

Again, a guess.

 

There's another question why not use two seperate belts or chains why have a 7 foot belt?

 

2 seperate belts and or chains would make the need for the front end to be alot bigger.

However if you really want a chain, make a setup and install it.

 

I think if German engineers didn't want to use it then who am I to try and make one work. I know there has to be a good reason why they used a belt I just don't know the reason. Does anyone know the factual reason.

 

They are smaller with chains. bu smaller I mean shorter in length.
MB uses a very long chain in some engines, as do others..

Given a choice I would rather the 928 had a chain instead of a belt.

Chains are a replacement item, but seldom do they fail with out warning.

 

This has been discussed before. There is no excuse for the 928 to not have a maintenance-free timing chain that would last at least 200k miles instead of a toothed rubber timing belt. Cars had them already in the 70's and a cayenne V8 has them now with a 4.8 liter DOHC engine and makes 84hp/liter NA with it. Also if they used a chain, the horrendous timing belt "tensioner" would never exist and the water pump would be mounted further forward and would be driven by an accessory belt. So to change the pump would be a 1 hour job and its failure would not be catastrophic. The only reason to use a timing belt was that it was CHEAP and EASY. This is similar reasoning as to why Porsche used a cork oil pan gasket.

Here's a pic of the Cayenne engine, and notice the double-row chain and that it drives all four cams so it's even longer than if it only drove two.

http://www.panix.com/~clay/cayenne/engine.html

Dan
'91 928GT S/C 475hp/460lb.ft

 

I'm not an engineer, but I think I read here somewhere, I suspect it has to do with the amount the engine expands at operating temp. I've never seen a tensioner used to take up slack on a chain. Honda and Toyota w/aluminum use a belt on 4 and 6 cylinders.

 

A Cayenne engine is an all-aluminum 90 degree 4.8 liter V8... sounds familiar? Timing chains do stretch and yes they have tensioners:

http://www.autohausaz.com/saab-auto-...placement.html

Dan
'91 928GT S/C 475hp/460lb.ft

 

Some of the Toyota's have chains.
We did a set of guides in one last month.

Edit, it may have been a Nissian.

 

I think the thing to keep in mind was the 928 was put on paper in the early 70's.

 

Timing belt drives have significant advantages when compared to chain drives. Some examples are excellent elongation behaviour and good damping characteristics under load, which allow a timing belt to achieve an accurate control of the camshaft timing over the entire engine lifetime. This guarantees the highest efficiency with respect to fuel consumption and emissions. Another important aspect is the ability for a belt drive system to incorporate additional components such as water pumps and injection pumps within a single layer drive. This leads to significant packaging advantage


There is no conspiracy on the part of automakers to use timing belts as a ploy to make money selling parts. The profit to the automaker from the sale of a timing belt is not significant enough to make a big difference in the bottom line. Dealer and independent service departments make a larger profit from timing belt replacements than automakers because the majority of the cost of timing belt replacement is usually labor, which is supplied by the shop. The automakers do not get a cut of service department labor.


Cam timing adjustments can be an important developmental tool on the dyno as well. Not only can you find the "sweet spot" in the power curve, you can move it around to best suit your total engine combination. By experimenting with cam timing and valve lash, a knowledgeable engine builder can determine if he has the best cam for a given application. If not, he may need to run several cams through the engine to find the right one. With a conventional timing-chain setup cam changes are time-consuming, labor-intensive tasks, and with the cost of dyno time these days, you can't afford not to take advantage of all available shortcuts.


A belt drive can make cam timing changes and camshaft swaps less painful. Cam timing changes can be made without removing the water pump and front timing cover. Camshaft swaps are almost as easy as the camshaft will come out through the front cover without removing the timing cover and oil pan, as is standard procedure with a timing chain With out a belt there would be no 32vR... To change a cam or change timing you would have to remove the entire sealed front chain cover. Remeber a chain needs oil and oil must be kept in somehow.

There are many advantages to a belt-drive system than ease of use. A belt drive can increase power over a timing chain through less frictional loss, more precise timing, smoother valvetrain motion and eliminating windage caused by the timing chain and gears running in oil. A belt drive also isolates the crankshaft's torsional vibrations from the camshaft better than a chain (and certainly better than gear drives, which can amplify crank harmonics).

 

Fuel consumption and emissions. SAAB was the first car to pass the CA emissions laws years before they came into effect. The efficiency and lack of emissions of the B234 engine was years ahead of its time. It has a timing chain. I have one in my garage that has almost 200k miles and not even so much as a peep from the chain, and it was never touched. Also, these days auto-makers are pushed harder and harder on the efficiency and emissions fronts. Wouldn't that then be the perfect reason for a timing belt in a Cayenne? Instead it gets a double timing chain.

To incorporate other components with the timing belt? Why on earth would anyone want that... oil pump maybe, but water pump is just a stupid idea because it will fail and when it does, it will take the timing with it. There will always be other accessories that cannot be driven by the timing belt, so you will need at least one separate plane for those anyway. May as well put all the other accessories in that plane, no? IMO, driving the water pump with the back of the timing belt was THE dumbest thing Porsche designed into the 928. Again, look at the Cayenne engine, one plane for timing chain and another for all other components driven by a serpentine belt, including the water pump. Or look at an BMW M3 V8 engine, same thing. Is the M3 not a "sports" car?

It is just as easy to set cam timing with a chain as it is with a belt. I've seen it done. Also, I doubt Porsche expected more than 1% of 928 customers and/or their mechanics to be messing with cam timing in any way.

Also, designing in a timing belt system in the hopes that the car is maintained better, hmm I don't know about that one. Seems like there are many easier ways to approach such a task. Like I said, it wasn't only cheaper, it was also much easier to design a timing belt system. Many others are doing it right, so we can too

We all love 928's, otherwise we wouldn't be here. But this model is definitely not without its faults. If you think that Porsche put this system into the 928 for a good reason, you are fooling yourself. Whoever at Porsche decided to go with this system made a big mistake IMO. They should have done what Mercedes did, like with many other things. Maybe it would make the 928 not viewed as so maintenance intensive and it may have sold more, enabling Porsche to make it even better and maybe sell it longer.

Dan
'91 928GT S/C 475hp/460lb.ft