Wednesday, July 22, 2009

Back under pressure

turbocharger is replaced, and we are almost ready to roll. We have one more test to do in the morning, and then we will resume our westerly course to Phoenix, where we should arrive in plenty of time to watch our niece skate. We went into the casino for one last dinner, expecting to partake of the $7 buffet (we had opted for the restaurant last night), but apparently Tuesdays are "progressive madness" or some such here, and we couldn't get near the place, so we went to the restaurant yet again.

I know many readers are waiting for the results of the great turbo debacle. The executive summary is that it appears to be completely fixed, and it also appears that it was nothing more than what we originally suspected, a blown turbo.

For all you die-hards, the longer version is as follows. As I wrote here yesterday, we decided to order a remanufactured unit from local Detroit Diesel distributor Stewart & Stevenson, and it came down from their Denver location overnight by bus. I called the Albuquerque office around 11 this morning, figuring I should have already heard something from them, and they informed me that it had just arrived.

We loaded the old turbo on the back seat of my scooter and headed the ~20 miles back to town, avoiding the freeway by staying on old Route 66. Sure enough, S&S had the turbo, and it was the correct item. Unfortunately, the gaskets we also ordered never arrived. No matter, since checking the order revealed they had ordered the wrong gaskets anyway. It soon became apparent why -- it took three different parts clerks and a service manager, plus myself, combing through three different parts books, to find the numbers for the correct parts.

(The issue has to do with our turbo being top mounted, unlike the more common truck installation which is side-mounted. Most of the diagrams in the manuals are for the more common type. The gaskets we needed are listed on some parts manifests, but do not show on the diagrams, nor are their functions listed on the manifests.)

Nearly two hours later, we had tracked down part numbers for the oil drain seal and the blower adapter gasket; the exhaust flange gasket was the easy one, and they had produced one within the first few minutes. They turned out to also have the drain seal in stock. Unfortunately, the blower adapter gasket was not, nor did anyone else in town have one. At least this was the least critical of the three, and it can be replaced later if need be without having to remove the turbo.

We loaded the new turbo, the gaskets, and a gallon of 40-weight oil back onto the scooters and headed back to the casino, where I arranged to meet Jim the mobile truck repair guy. He was so efficient at getting the thing out, I decided to enlist his help putting it back in, too.

As it turned out, he had to wrestle with it for nearly two hours to get it back in. Everything is tight in our engine bay, and getting the exhaust flanges, the exhaust pipe, the intake elbow, and the blower adapter to all line up and cooperate was a challenge. I had to open up the access hatch through the radiator intake so we could tug on the exhaust plumbing, and Jim ended up loosening the turbine and compressor housing clamps on the new unit to tweak the clocking to get it all to fit. eventually we had it all back in place, and then started pouring oil into the bearing through the oil supply hole.

Hmm... the oil does not seem to be going in. Nope -- it's just sitting there in the fitting. Even spinning the compressor wheel is not getting any oil to drain. After probably ten minutes of this, we decided the tiny orifice at the oil supply was clogged, most likely with assembly grease. We threaded an air fitting into the supply hole, and a quick blast of compressed air cleared the obstruction. After pouring a few ounces of oil into the bearing from a squeeze bottle, we re-attached the oil supply line.

From the rear switches, which allow for cranking the engine with the fuel solenoid closed, I bumped the engine around a few times in short pulses -- so many folks have warned me about a blown injector tip, that I was worried a cylinder could be full of fuel and hydraulically locked. But there was no resistance at all. So I cranked it three or four times for close to ten seconds apiece, closely spaced, to get some oil flowing up to the bearings and purge any air from the supply line. Then I set the switch on run and cranked it again, and it immediately lit off.

I noticed two things right away. The first was that I did not get a big puff of white smoke when it started -- we've been seeing such a puff of smoke on start-up for several months now, and it is one of the symptoms I have reported every time we've had anything done on the engine. We've now fired up three or four times today, with no smoke evident on any start. The second was that things sounded smoother than they have in a while, and the exhaust looked and smelled cleaner. All good signs.

After checking for leaks, shutting down, and rechecking clamp tightness, we declared victory and I paid Jim for his time -- two hours, plus travel. We then buttoned the coach up, loaded the scooters, and set out around the parking lot on a low-speed test drive. Kevin, from the bus forums, who has been very generous with his time and expertise over the phone during this project, had strongly recommended getting everything up to operating temperature (and then back down to cold again) three times before putting any real load on the turbo, and so we kept speed and acceleration down, watching the boost gauge to try to keep it under 2 psi (we hit 3 psi occasionally). I stopped occasionally to check for smoke and read the temps with an IR gun, but all was normal at every stop, other than oil spitting out of the exhaust and the muffler drains. I expect to be puking oil for the next fifty miles, until whatever's left in the exhaust and the airbox finally burns off or spits out.

After half an hour or so of "road" time (we made it as far as the historic Rio Puerco bridge on old 66, just half a mile from here), during which I noticed subjectively more power and less black smoke than we've had in quite some time (even at these very low boost levels) we parked for the night in the casino's RV lot, blissfully out of range of the incessantly idling trucks. After dinner, when all had cooled down, I popped the hatch to check all the clamps and look for leaks.

What I found was that Jim had tightened the clamps on the outlet hose with the jackscrews too close to the steel supports for the top of the turbo compartment. We've had problems in this area before, and so I loosened the clamps and rotated them 90° for clearance. When I did this, I noticed two things; one was that there was a ripple in the hose, because the clocking of the compressor housing had the outlet just a tad out of line with the blower adapter inlet. The second was that the hose looked torn in exactly the same spot as shown in the photo I just linked.

With both hose clamps loose, I was able to loosen the compressor housing v-band and inlet duct, then gently tap the volute around a couple degrees with a plastic deadblow, taking care of the first issue. Without removing the adapter, however, I could not remove the hose to see if the tear went all the way through. Moreover, I was afraid that I could worsen the situation by trying to remove the hose.

What I ended up doing was to tighten up all the clamps, fire up the engine, set the high idle to get enough compressor speed to bring the pre-blower boost pressure up above atmospheric (at extremely low compressor levels, the blower can clear the air as fast as the compressor provides it, yielding 0.0 boost, or just atmospheric pressure). Then I sprayed the hole with soap solution, just as one would when looking for air line leaks. No bubbles, so we think the hose is intact, and the tear we can see is just in the outer jacket. We will order a new hose and replace it as a precaution the next time we pass a Detroit shop.

As long as the engine was now already running, I closed up the hatch and we let it come all the way back up to temperature before shutting down for the night. Tomorrow, we will do one more hot/cold cycle before we leave; during that warm-up I will connect my diagnostic reader and test the injectors, just to be certain we are firing on all cylinders, to borrow a phrase. If all seems well, we will clear out of here and resume our previous route west to Phoenix.

At this writing, it seems as though we did not have any deeper problem, such as blown injector tips, or catastrophic destruction of rings or valves becoming "Foreign Object Debris" (FOD) and hitting the turbine. I can't rule out FOD as a cause -- it's possible something such as a rust flake or a clot of coke got knocked off into the exhaust when S&S in Farmington repaired an exhaust clamp, for example. But I am inclined to believe that what really happened here is that the turbine wheel became slightly imbalanced many moons ago, possibly due to FOD but also possibly just due to manufacturing tolerance issues -- it was a rebuilt unit to begin with. Over time that imbalance caused irregular bearing wear, and the turbine has been wobbling in the bearing for several months. Eventually, the edge of the journal scored the shaft, creating a weak spot right where the turbine wheel attaches. It was then only a matter of time before some combination of heat, load, and speed caused the shaft to shear along the score line. The extensive damage to the turbine blades then occurred almost immediately as the now loose turbine wheel ricocheted around the housing.

We'll know for certain that all is well once we've brought the engine into the powerband and the boost levels up into the high teens on the road tomorrow. But based on testing so far, I believe we will be back to 100% normal operation.

1 comment:

  1. Awesome news! Thanks for the extended turbo info (from a detail-oriented tech junky; I know I'm not the only one here).

    I hope your skating journey proceeds without problem.


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