11-06-2004, 07:29 PM
I don't know who rebuilt the turbo but they should be flogged.
View Full Version : I hate bad turbo rebuilds. The K28/K27 tossed it's nut.
11-06-2004, 07:29 PM
I don't know who rebuilt the turbo but they should be flogged.
11-06-2004, 08:43 PM
11-06-2004, 09:32 PM
11-07-2004, 04:53 AM
Javad arrived in Austin Friday night and we had a late dinner at a nice 24 hour cafe in Austin. Saturday morning we went to start the car adn javad noticed that we weren't getting a reliable RPM crank trigger signal. We have 5 good guys working on the car yesterday morning and it was a good cadre of old school Audi guys. We had the Fluhr brothers. Ken and Eric fluhr who live and breath Old school Audis. Ken was the main hired pro on my car to assist in all means and manners to get it put back together. Jimmy Pribble was there. Yes, THE Jimmy Pribble. (sorry Jimmy I couldn't resist the running joke). Javad Shadzi was there. Yes, THE Javad Shadzi. LOL. And myself.
Eric being an electrical engineer and known wiring guru was looking at the ECU plugs. Javad went into the ECU itself to clean the pins and was watching us tweak the crank sensor to the Nth 100th of an inch to get the signal right. We had just a slight wobble in the crank pulley, which might of effected the signal. But, eventually from one or perhaps all of the above efforts, we got a steady 59 teeth signal and things got better from that point quickly. We had to change spark plugs again from all the previous cranking, but after a good cleaning we were back to reliable starting, smooth idle, and no load throttle and acceleration. So, it was time to button it up and take it for a drive. By this time the dyno chance was long gone. It was 1pm and the Dyno place closes at 2pm on Saturday so that was just not going to happen. I could of flexed some cash around to make it happen, but I'm glad I didn't cause things went from great to bad real quick.
Javad was masterful getting the map and throttle tuned to a very good degree very quickly. Within about 10 minutes of just tooling around some Austin streets we had (in my opinion) a very good and very fast car with good throttle response. The car is making some serious power. I didn't mess with the boost controller, but the car was making about 1.5 bar of boost with the defacto setting or possibly the wastegate. Either way from a rolling start at 3000rpm and 0 boost, it was making 1.5 bar by 4000 rpm. Very good response from such a large turbo. From 4000 to 7000 the motor was incredible and the car was scary fast. Howling like an S1 motor and making wonderful sounds. Not having a BPV or BOV when shifting rapidly is very interesting. I like the immediate surge in power when getting back on throttle. Its like a rush of compressed air blasting immediately into the engine and the effect is much more initial Pop when engaging the next gear. Accelerating from lower revs, the car makes 1.5 bar by about 3500 rpm so it seems to be ramping up just to the right of the surge line in the knee. I predicted that the compressor wheel will behave alot like a T04E/50 since its dimensionally identical, and it did. The only difference is the Larger #7 turbine and the tubular exhaust manifold had absolutly no problems spooling the wheel. EGTs were nice and low. So we weren't nearly close to the limits of what this motor will do. Javad estimated we got up to 300 at the wheels or so during that short time.
About 30 minutes into the initial test drive to map the ECU, Javad and I hear a mechanical whizzing sound. We were rolling down the highway offboost when it happened. No oil smoke, just a faint whizzing. We make a straight line back to home base. Car is running fine for the entire test drive with no heating issues or leaks so I'm happy with the build overall. We found the nut sitting inside the airbox and it just bounced around on top of the compressor. The comprssor wheel is kaput. We didn't know the damage to the housings and the precious #7 K27 turbine.
I was going to pull the turbo Sunday night preferring to talk with Javad and Jimmy about Audis, but Ken wanted to see the damage right away so everyone went back out to the garage to assess the quagmire. It was probably a good idea since we found out that the turbine side just barely scratched the inside of the housing. No real damage to the turbine or the housing. The shaft seems okay and it still spins freely with no oil leakage. The compressor wheel is definately gone and the compressor housing has some very light surface damage from the wheel. I think the housing is still good, but It might mean going to a larger trim wheel. Perhaps a 3054 instead of a 3050. We'll see. Trip to Majestic on Monday.
So its Sunday morning. Javad is heading back to California. It was a great weekend and alot was accomplished. Stuff like this is going to happen when working on such an oddball motor. Overall I'm extremely pleased with the motor before the turbo problem. Shouldn't be any problems making big sustained power with this setup.
11-07-2004, 05:55 AM
like I've seen from the nut dissapearing. Fix her up and enjoy:)
11-07-2004, 06:48 AM
11-07-2004, 07:12 AM
I bought the turbo rebuilt. The person I bought it from didn't know where it had been rebuilt. Visual inspection looked okay. Obviously the prudent thing would be to take it to a good turbo shop and have it inspected and pretty much reassembled, but who does that?
Luckily it looks like I'll need only a 3050 wheel to get it working again.
11-07-2004, 08:34 AM
11-07-2004, 11:06 AM
11-07-2004, 11:38 AM
It's not a bad idea at first glance, but there are common misconceptions about safety wire (SW). The primary purpose of safety wire is to provide a visual indication that the fastener has been properly torqued/secured. After that, the best you can hope from safety wire is that it will prevent a nut or bolt from completely leaving its post (as it were). Especially in this case, SW would not have stopped the nut from backing out far enough to keep the compressor wheel from being forced forward and machining the housing, though it might have kept the nut in place enough to prevent the other compressor wheel damage. Finally, I would think that safety wire would introduce a potential balance issue and would introduce another potential FOD danger, if not done correctly.
Since we are in forensic analysis mode, the nut did have green thread locker present. It is inconceivable to me that someone would apply threadlocker and NOT torque the nut correctly. Wrong torque value used? Was it something else? What else would cause the nut to back off? Dare I suggest a pressure wave? Remember, no BPV/BOV on this system. I bet we hear from ScottyJ soon. ;-)
Jimmy "who otherwise loves safety wire" Pribble
11-07-2004, 12:51 PM
I see what your getting at. There is always forces acting on the compressor to loosen the nut. The forces would have to reverse the compressor wheel relative to the shaft and also move the nut. Since many cars in the early 80s did not have either a BPV or BOV and ran some high boost around 1 bar. I suspect the factory torque spec is good for at least that plus a saftey factor and is good for the height of the compressor map which might be PR of 3 for a K26 and that goes to 4.0 for a K27. Otherwise urquattros would be dropping nuts like flies. If what your suggesting is true then Turbos made in the 80s without BPVs would have to have a higher specified torque spec than those made in the 90s. And, if that were the case the shafts of modern turbos could be smaller.
Looking at some Audisport turbos which have been untouched since 1985 and had no BPV or BOV and built on a K27 center, I don't see anything special about the nut or the shaft. Its probably just torqued to the correct spec.
11-08-2004, 06:03 AM
I'm 100% certain the Pike's Peak turbos had a single nut with loctite RED. Loctite Green is for slipping the Wheel onto the shaft and this turbo also used loctite green on the nut which is probably the mode of failure. I pulled the failed wheel off the shaft and didn't see any loctite green on that, but it probably rubbed off if there was any on there.
Loctite red adds considerable strength to the clamping of the nut and vibration resistance and can still be removed with heat.
11-08-2004, 06:39 AM
I guess finding out who did the rebuild is a dead end?
11-08-2004, 09:11 AM
Loctite green is standard. The Red on the Pike's Peak is there for a reason.
Just talked to Frank S. He still doesn't use BPV or BOV on his Audis. He does use loctite red exclusively on the nut and proper torque and has gone 10 years on the K27/K29 turbo in his S2. I'm going to have it rebuilt with loctite red.