NIACAL4NIA

OK I get it. You're either a shop owner or a part seller. Bewar of EV cars. Don't be surprised to see old 928s with Tesla motors and mechanics closing shops unless they get into EV fixing.

Dmhager

This little conversation turned in a confused mix of different philosophies and irrelevant comparisons: drive your car until something breaks vs good preventive maintenance, EV vs. IC powered 928s, Toyotas vs. vintage Porsches.

There are not many 928s racking up 60k miles in 10 years any more, so its really all about time based decay. Belts dont fail on their own - the safety margins are ridiculously high (there were in the 80s and they are now), but water pumps, bearings and bushings fail with time. IMHO, 10 years is a good service limit with some margin (the last reported factory reco Ive seen), less if you want to be more conservative. Ive replaced many TBs/WPs on 928s that are over 10 years old, and while they were all working generally fine, bearings were dry and in some cases starting to make a little noise, tensioners were dry and the rubber hard. Thats just what grease and rubber does over time in the presence of heat. So, if you want to hop in your 928 and drive it 1000 miles on a rally or visit friends, with the comfort in knowing you wont be calling for a flatbed, good PM is a sensible approach. BTW, you wont get 10 years if the last tech didnt do it right, so I always do a TB service and pull the water pump when I buy a 928 regardless of the service records: I almost always end up replacing the old tension arm bushings, rebuild a neglected tensioner, and often more even when the records indicate it was just done.

As for EVs, Toyotas, and driving until my pistons pulverize my wee German valves, no comment (other than wtf would you do that?!)

Bill Ball

Fascinating but not terribly relevant. You do what you want, but I still change the belt every ~60K miles. I sure didn't notice any belt material change over the years. Even the pre-2000 belt seemed extremely durable, at least if it was Gates. Not so with Conti (my one experience is the Conti belt stretched out too much over time). Also, my primary concern is not so much the belt but the other wear components. The plastic tensioner arm pivot bushing is not going to make it far beyond 60k miles, and when that wears, the tensioner arm will cant forward and really mess up the belt tracking. The coated aluminum cam gears are notorious for not lasting very long. Same with the original aluminum oil pump gear, which Porsche did change to steel. I actually check the belt and these components every 15-20K miles when I check/adjust belt tension. The tensioner is notorious for leaking oil, so I check that too. I just don't see this as a 100K system. Yes, I saw even pre-2000 belts that were old and in seemingly perfect condition, but I was not tempted to re-use it. Since I am in there dealing with all the other not so durable components, a new belt is a trivial and very inexpensive part of the job.

I don't change the water pump any more with the belt, although that is popular here. Unfortunately I only got 110K miles on the last pump before it developed a seal leak. So, I had to replace it. We'll see how long the new one holds up. Maybe I'll get more than 200K like your mother's Toyota, but I've seen enough pump failures in my 928 buddies' cars and here that it seems unlikely. However, one of the 928 pump manufacturers did make a number of changes to the pump construction recently that should improve durability based on input by one of our 928 part vendors, so maybe there is hope for 200K+ now.

We don't have a serpentine belt and our old rotor and cap ignition system is not going to be very happy with 100K mile plug changes at least if you use the standard plug. The accessory belts on the 928 commonly start to develop significant cracking well before 100k miles.

worf928

I get it now too.

We’ve shared our belt change intervals and the thought processes behind them. You’ve just shot back ambiguous semi-coherent posts (like that one——^) without either answering questions posed or sharing your logic behind never changing the belt or rollers unless the water pump breaks. There’s a term for this kind of behavior. I made the mistake of not reviewing your original posts in this thread. Had I done that, I wouldn’t have bothered responding to your bait. My bad.

Jmcmahon66

I’m considering doing the TB and WP on my 79 OB with automatic since I’m the new owner and want to make sure it’s in good condition. I’ve read NorCal Dwaynes write up, and it has inspired me. Is the Porsche tensioning tool any different than normal? If so, do people rent them?

Wisconsin Joe

Keep in mind that Dwayne's write up is for a 32v car.

A 79 is a 16v.

There are some pretty good write ups specific to the 16v cars.


And the guy knocking on Dave (Worf) for 'being a shop owner', implying that he's profiteering on it, should get a clue.

Dave has a much longer interval than some 'experts' out there. I have heard of one that insists that all 928 motors are interference and the TB/WP must be done every 4 years, regardless of mileage.

Gary Knox

I can speak with a little bit of history regarding the first of six '87-'94 928's I've owned. That car had 55K miles on it when I bought it, and the timing belt had never been changed. Back in '97 when I bought the '87 car, there wasn't any significant information about 928's on an internet site, and I knew no one who had or then owned a 928 (other than the seller). I found no information on time or mileage for changing the belt in anything I read. But, I had a '91 Audi V8 with an interference engine and rubber timing belt. Their service information indicated the belt should be changed at 90K. I interpolated that information for the 928, and when I got to 90K miles with the engine (2001), I took it to the Porsche dealer near my office to have it changed. The mechanic was a semi-friend (but 911 owner/racer). He did the work, didn't change anything else, and said the belt he removed (OE Porsche) looked fine.

On future cars, I had become involved with the internet, etc., and bought into the 50K miles or 5 years schedule. Probably a good idea, but maybe overkill. I'm currently considering an S4 with 135K miles, and a new timing belt installed 8 years ago (pump etc as well, purchased from 928 Int'l) at 125K miles. Hmmm - what should I do about the belt etc. if I buy the car????? - ha.

FredR

Gary,

Good to see you interested. My own belief is that there was a lot of well intentioned opinions developed that are probably well into the overkill zone but quite understandable given the potential consequences. Some folks would have you believe that if the timing belt alarm went off one should stop the car and call a tow truck. The fact that the alarm wording says "Timing belt service" and not "32 bent valves" tells the owner something.

Knowing what I know about material properties the thing that would concern me most would be examples that have stood still for a long time going no where. Rubber likes to be exercised to keep the molecules pliable. 10k miles is not a lot of mileage but more to the point, if one does not know how those miles were distributed time wise then it would be prudent to simply change the belt out and be done with it. I might take a look at the pump to make sure it has a plastic impeller and that the various rollers, bushes etc are in good shape.

For my own system I reckon to change the belt after 100k km [60k miles] or 10 years knowing that my motor gets run regularly but not extensively. I have also concluded that cylinder heads get corroded not due to funky coolant [which could be the case of course] but most probably due to irregular use [as in leaving them stagnant for months at a time over the winter period]. The coolant stagnates in between the gasket and the head and consequently "acidifies" and corrosion is the consequence- the acid formed also eats away at the material of the head gasket in those specific locations. I believe regular use helps prevent this problem from happening.

Doubtless you are well aware of the TBF phenomena and know how to cover such.

linderpat

Hey Gary - Buy....the....CAR!