How easy should turbo spin?

[rdurh]

I did some searching and really didn't find an answer, so please bear with me. I'm in the process of installing a pyrometer and boost gauge. I have the turbo off my 1994 Blazer to install the pyrometer. When I spin the turbo shaft if spins OK but there is some drag. You can't just push the turbo blades with your finger and then watch them spin. There very little to no side play on the shaft.

I'm also seeing some oil in the intake of the turbo. Some of that is from CDR, but I'm wondering if some is from a leak on the turbo shaft. I have no idea just how to check.

[rdurh]

Also should have added. On acceleration it's been blowing black smoke with no power. I'll be posting later after installing the gauges as to what I'm seem for EGTs and boost.

[More Power]

An oil film provides the "bearing" for the turbo shaft, so how freely it spins depends somewhat on the oil viscosity. If the bearings were bad, you'd be able to push the shaft and compressor blades into contact with the compressor housing.

Sounds like you may have a boost pressure problem. You'll know once the gauges are installed.

It is normal for an oil film to accumulate inside the compressor housing and intake manifold - it's just residue buildup from recycling the oily crankcase gases.

Jim

[markrinker]

If you have the turbo off, I'd be looking for a GM-8 model to replace it with.

Not a huge overall power difference, but you can make more peak boost with the GM-8 at lower RPMs, and it flows better overall than the GM-4 unit. Some say the GM-4 is quicker to spool up, but I've never seen any difference on initial acceleration between the two.

There is usually one or two for sale on the classifieds here. Used and reman units aren't expensive, either.

http://cgi.ebay.com/ebaymotors/GMC-CHEVY-TURBO-6-5L-6-5L-DIESEL-TURBOCHARGER_W0QQcmdZViewItemQQcategoryZ33742QQite mZ8032479275QQrdZ1QQsspagenameZWDVW

[ 01-24-2006, 03:50 PM: Message edited by: Mark Rinker ]

[rdurh]

I've thought the same thing about finding a GM-8 turbo. I've been looking but will have to see how muchr the checkbook can stand after I get the smoking solved.

After I get the gauges installed I'll be posting again with results. I've been getting codes 46 & 78 primarily. I did purchase a wastegate solenoid and turbo boost sensor that I may install.

[rjschoolcraft]

The rotor should spin very freely.

If you can move the shaft axially (back and forth) significantly, the thrust bearing/bushing is probably bad. This will allow the seals to uncover and leak oil. The drag may be from rub between the compressor impeller and the shroud or the turbine wheel and the housing or both. This will cause black smoke during transients due to slower than normal rotor acceleration. It will also cause lower boost pressures across the spectrum.

[rdurh]

Took the exhaust elbow off to check out the exhaust side vanes. All looks OK. I also blocked off the oil inlet and then flipped the turbo upside down in my vise. I then poured some kerosene into the turbo using the drain outlet. In less than a minute it was turning easy. After about 30 minutes I could give the turbo vanes a good spin with my finger and it would continue spinning for 10+ revolutions.

Thanks for all the input and suggestions.

[rdurh]

Don't know if I spoke too soon or not about everything seeming to be doing OK. Went out to drain the kerosene "cleaner" out of the turbo. Found some had leaked over into the intake side around the shaft. Maybe two or three tablespoons worth of kerosene. I'm not sure if this is something to worry about or not since kerosene is a lot lighter oil than Rotelle 10W-30.

[tom.mcinerney]

The intake side should have positive pressure to keep out the oil, other things equal, and the rotation within the bushing will probably act as something of a seal. If there's not much play (slack/tolerance/wear) it ought to be safe to run. The kero may have gone into the area you found it by way of the DRAIN , which can't work when you had it upside-down.
Suggest a couple drops lube in the top after mounting, before attaching the lube line.

[rdurh]

There is very little play side to side and none front to back. I'll run some oil through and reinstall. THANKS!

[gmctd]

Compressor end and turbine end seals are combo labyrinthine\centrifugal with one piston-type ring at each end.

Positive (boost) outlet pressure and exhaust back-pressure prevent oil entry to intake and exhaust in this seal configuration.

Shaft will spin more freely at normal engine operating temps because of lower oil density.

Oil is a thick foam under operating conditions, shaft spinning.

Shaft will spin somewhat more sluggish at ambient temp - due to cooler oil condenses back to liquid form on non-rotating shaft - but still should spin freely.

Wheels should never contact housing, particularly when hot and oil is less dense.

[ 01-29-2006, 08:15 PM: Message edited by: gmctd ]

[rjschoolcraft]

"Foam"... If the oil is foaming, it is heavily aerated. This is bad. Fluctuating oil pressure is one symptom. The oil operates in liquid, non-aerated form through the entire operating range, unless something is badly wrong causing the oil to become aerated.

The conditions you described are likely due to coking of the oil in the turbo charger center housing rotating assembly. The kerosene has done a good job of cleaning that out. Be sure to pre-lube the rotor before running the engine.

[gmctd]

The 100,000rpm spinning shaft foams the oil.

Don't believe it?

Unbolt the turbo oil drain and note the beige color of the efluent with engine running, indicating hi-aeration.

Don't worry - oil is not gonna squirt out at pump pressure or volume, causing loss of operating pressure to the engine bearings.

The purpose of the large diameter drain tube, with a direct-as-possible shot to the oil pan, is so the frothy oil can easily gravity-drain back to the pan.

It is not under pressure at that point.

That's my story, and I'm stickin' to it..........
:cool:

[rjschoolcraft]

Originally posted by gmctd:
Oil is a thick foam under operating conditions, shaft spinning. This statement is what I take issue with. The pressure oil supplied to the journal bearings in the housing is liquid form. End of story. While some air is introduced any time rotating components encounter oil droplets, the oil will not be a "thick foam" under designed conditions.

The clearances between the shaft and bushing surfaces is very small. The oil is actually under pressure in that small clearance volume and is not aerated at all. Some air will be introduced as the oil exists the close clearance volume, but not enough to cause "foaming".

The turbo rotor will spin more freely at operating temperature because of a change in viscocity as temperature increases (not density). This should not be perceptible, though, when spinning the rotor by hand.

When oil is aerated, it does not pump or circulate well and does not perform its intended function. Aerated oil has nothing to do with the problem being discussed.

[gmctd]

Is viscosity not, then, reflected in the spec'ed rating of the oil, as in 15W-40?

[gmctd]

Agreed - aerated oil does not pump or circulate well.

For your consideration: how do you reliably get 100,000rpm from a babbitted bushing-type bearing?

Turbo oiling

The turbine shaft rotates inside two cross-drilled (is that the term? up to 6 holes, sometimes grooved for oil distribution) bushing-type bearings, and the bearings also rotate inside the casting (cartridge) bore.

They are, indeed, full-floating bearings.

Oil @45psi enters the cartridge assembly thru the ~3/8"dia hi-pressure tubing, enters the rotating assembly at right angles to the bearings and shaft, exits between the bearing ends and the cartridge bore, and also between the shaft and bearing-ends, then exits the cartridge thru the 1"dia drain tube to the crankcase.

Ever notice the disparity in tubing size?

Ever wonder about it?

Pressurized oil enters the cartridge as dense liquid, where the shaft\bearing rotating assembly whips it into a frothy, foamy mix, which comes out expanded, not-nearly-so-dense, at almost no pressure.

The pressure loss is caused when the oil exits the small rotating-assembly clearances into the cartridge oil-drain gallery, a very large open area, comparitively speaking, which is at crankcase pressure, via the 1"dia drain-tube connection.

Of course, it does not simply ooze out of the bearings, as the rotating assembly is spinning at up to 125,000rpm - the whipped oil is slung out centrifugally, causing more frothing as it hits the gallery walls.

This frothy, low-density mix now exits the gallery, which is (hopefully) at crankcase negative pressure (the CDR, remember?), and is dependent on gravity, the continuing efluent flow from the rotating assembly, and low restriction afforded by the 1"dia drain tube, to ooze back into the crankcase.

Of course, when the engine is off and cooling, the oil froth condenses naturally, resumes it's normal color, then drips slowly out of any leaks in the drain-tube path.

Which is one reason why you get active drips when the engine is off, and few when it is running.

But, therein lies another tale.

[ 01-27-2006, 06:05 PM: Message edited by: gmctd ]

[rjschoolcraft]

Oil, liquid, is an incompressible fluid. It's density does not change appreciably with pressure.

If I continue to discuss this, I'll be called names again, so I'm gonna stop. You need to back up and re-think your dissertation here. I've given you clues as to the inaccuracies, but I'll never be able to convince you without causing hard feelings. Just be careful not to lead people off into the weeds.

I will re-iterate... Aerated oil has nothing to do with the subject of the original question. His difficulty in spinning the rotor was likely caused by coked oil in the bearings which the kerosene has successfully dissolved.

To prevent a recurrence of the coking, be sure to let the engine idle before shutdown until the exhaust temperature (pre turbo) is below 300F. If you do not have an egt gage, two minutes of idling should cover most circumstances.

[ 01-27-2006, 07:24 PM: Message edited by: ronniejoe ]

[gmctd]

Yeh - the po-lice do tend to get very upset when they find out there's weeds involved........ tongue.gif :rolleyes:
;)

(sorry - forgot the winky face)

[ 01-27-2006, 07:55 PM: Message edited by: gmctd ]

[Clark's diesel]

Code 46 is Malfunction Indicator Lamp (MIL) circuit fault, whatever that means. Code 78 however is the Turbo Wastegate Solenoid Circuit fault. I would definitely install the new wastegate solenoid. It probably wouldn't hurt to check your vaccum at the wastegate. You should have a minimum of 15 inches of vaccum per GM specs. Hope this helps.

[tom.mcinerney]

R. Dale--

You should understand what Ron writes here before operating :

>>The conditions you described are likely due to coking of the oil in the turbo charger center housing rotating assembly. The kerosene has done a good job of cleaning that out. Be sure to pre-lube the rotor before running the engine.
>>His difficulty in spinning the rotor was likely caused by coked oil in the bearings which the kerosene has successfully dissolved.
To prevent a recurrence of the coking, be sure to let the engine idle before shutdown until the exhaust temperature (pre turbo) is below 300F. If you do not have an egt gage, two minutes of idling should cover most circumstances.

J.D. and Ron :

This discussion answered several questions on the perimeter of my understanding of the lube scene. Thanks.

[gmctd]

Good, as is the intent.

To re-iterate the turbo test procedure, if the turbo 'spin' is sluggish when cool-cold, replace the intake duct, start the truck and run the engine to operating temperature, 180 - 200deg.

Stop the engine, again remove the intake duct and re-spin the shaft - it should spin easier, indicating good bearings\shaft.

Now - if still sluggish, this is a sign of 'coking'.

Remove the turbo to investigate the possibility of oil 'coking'.

If the shaft spins sluggishly when cold, and easily when hot, no need to remove the turbo.

This is normal operation, as the oil's effective density increases as it cools.

Remember, this is a M-U-L-T-I--V-I-S-C-O-S-I-T-Y oil, which thickens when hot, thins when cold.

Perplexing, right? Sluggish when cold, when the oil is thin, but easy to spin when hot, when the oil is thick?

For those having recently found themselves in apparent need of a good gardner wielding a bottle of weed-b-gone, which is denser -
a cup of oil - or - a cup of oily frothy foam?

Which would provide the least resistance to shaft rotation -
a solid film of oil - or - a film filled with jillions of tiny bubbles?

Therein lies the concept of a rotating shaft, with little-to-no radial loading, reliably and repeatably achieving 100,000 rpm in sleeve-type bearings.

Anyone care to post the allowable\max rpm for a non-radially loaded shaft in -

full-flow oil-lubricated sleeve-type bearings -
full-flow needle\roller bearings -
full-flow ball-bearings -

full-flow meaning circulated oil under pressure

radially-loaded meaning driving a spur gear, commutator brushes, etc

???

[rjschoolcraft]

Originally posted by gmctd:
Remember, this is a M-U-L-T-I--V-I-S-C-O-S-I-T-Y oil, which thickens when hot, thins when cold. I would rather not, but must correct some inaccuracies with this new post. Please take this in the spirit intended...a desire to share knowledge and increase the understanding of others.

Yes, this is multiviscosity oil. No, it does not "thicken" when it gets hot. Again, it's density does not change appreciably with changes in temperature.

The viscosity of any liquid will decrease as temperature increases. This means that its resistance to shear decreases.

Consider a straight SAE 40 weight oil. It has a specified viscosity curve vs. temperature. The actual oil viscosity can be measured at various temperatures to verify compliance with the spec. What we find is that the operating viscosity of a SAE 40 weight oil is what we want for the engine's operating temperature. However, its viscosity at cold start up (say -10F for talking purposes) is way too high and engine damage may occur. What we find here is that the viscosity of a straight SAE 15 weight oil would work. Once the engine warms up, the 15 weight oil is too thin. The viscosity of the 15 wight oil is significantly lower than that of the 40 weight oil at -10F (or anywhere along the curve if temperature is the same for both); however, the viscosity of the 15 weight oil is probably higher (I'd have to double check the properties) at -10F than that of the 40 weight oil at 200F.

What to do?

Enter muliviscosity oils. These oils have polymer chains added that change the viscosity vs. temperature curve. This change is essentially a flattening of the curve vs. temperature so that change is relatively small from one extreme to the other. In other words, a SAE 15W-40 oil will have cold temperature viscosity similar to a straight 15 weight oil and high temperature viscosity similar to a 40 weight oil. Viscosity still drops (the oil thins) with temperature increase, just not nearly as much as with a straight weight oil. Or looking at it the opposite way, a multiviscosity oil's viscosity will not increase with decreasing temperature nearly as much as a straight weight oil will.

Again, a multiviscosity oil does not increase viscosity with increasing temperature (or "thicken"). It's density definitely does not increase appreciably. It simply doesn't decrease viscosity nearly as much as a straight weight oil would.

[ 01-29-2006, 07:30 PM: Message edited by: ronniejoe ]

[rjschoolcraft]

Originally posted by gmctd:
Anyone care to post the allowable\max rpm for a non-radially loaded shaft in -

full-flow oil-lubricated sleeve-type bearings -
full-flow needle\roller bearings -
full-flow ball-bearings -

full-flow meaning circulated oil under pressure

radially-loaded meaning driving a spur gear, commutator brushes, etc

??? I have designed, personally, roller bearings that support a gearshaft (that I also designed) spinning at 51,000 rpm. There are those that spin faster.

Journal bearings can operate at very high speeds as well, even under heavy radial load, but their friction loss is much higher than rolling element bearings. Journal bearings work using two principles: elastohydrodynamic lubrication and hydrostatic lubrication.

Needle bearings are speed limited because of their high length to diameter ratio. They are very susceptible to skewing (misaligned rolling).

Roller bearings (with length to diameter ratio less than or equal to 1) or ball bearings can operate at over 2 million DN (DN is the bore diameter in mm X the shaft speed in rpm).

[gmctd]

Thanks, rj - I think I can assimilate that, tho' it's still what us LAY guys like to call - 'runs like 40wt when it's hot, runs like 15wt when its cold', which would, on the surface, appear to indicate thickening and thinning.

Any other input on shaft\bearing rpm?

Purpose? - all the new ball-bearing turbos appearing on the market, from IHI, MHI, and etc.

edited due to simultaneous, pre-emptive postings

[rjschoolcraft]

Originally posted by gmctd:
Thanks, rj - I think I can assimilate that, tho' it's still what us LAY guys like to call - 'runs like 40wt when it's hot, runs like 15wt when its cold'[...]This much is right on.



Originally posted by gmctd:
[...] which would, on the surface, appear to indicate thickening and thinning. They do change viscosity (or thicken and thin) with temperature. However, your earlier post said that 15W-40 gets thicker when it gets hot. This part is not true.

To help understand this, consider a SAE 10 oil and SAE 40 oil (my chart doesn't have SAE 15 on it and I didn't feel like interpolating). At -10F, the 10 oil has a viscosity of 93 mPa * s while the 40 oil has a viscosity of 604 mPa * s (don't really worry about the units, just compare the magnitudes). At 200F, the 10 is 4.9 mPa * s and the 40 is 11 mPa * s. A 10W-40 oil will have visosity close to the SAE 10 oil at low temperature and close to the SAE 40 oil at high temperature.

In reality, SAE 20, 30, 40 and 50 oils have their viscosity specified at 212F while SAE 5W, 10W and 20W oils have their viscosity specified at 0F. Multigrade oils (i.e. 10W-40) must conform at both temperatures. In other words, a 10W-40 oil must meet the viscosity specified for an SAE 10W oil at 0F and meet the viscosity specified for a SAE 40 oil at 212F.


Originally posted by gmctd:


Any other input on shaft\bearing rpm?

Purpose? - all the new ball-bearing turbos appearing on the market, from IHI, MHI, and etc.
This is most likely done to minimize friction in the bearing assembly. This will allow quicker spool up and improve transient response to reduce smoke off idle. There is probably a reliability improvement as well, although that is probably a lesser concern. Cost is increased substantially with the ball bearings, so there is a trade-off. Emsissions requirements are the likely culprit.

[rdurh]

Just a follow up.

I've posted some of this problem before and I'll try to summarize and I really want to thank all those that gave me advice and input. This is a 1994 Blazer with a 6.5L turbo diesel and a 4L80E transmission. The previous owner replaced the injection pump May 2005 and had the transmission rebuilt at the same time. I purchased this truck October 2005 in Ft. Worth, Texas. The cruise control wasn't working (and still isn't, but a subject for another thread if I can't get it figured out) but otherwise the truck ran fairly well when I purchased it only blowing black smoke at full acceleration with no loss in power. It was still running good when I got it back to Colorado Springs, Colorado. Also the truck has always run cold, even on warm days (65 to 78 degrees outside). Even on warm days it would barely get over 160 degrees on the dash gauge. When I added a 195 degree thermostat I found the thermostat had been removed.

The truck barely passed the emissions for opacity. Maximum opacity for emissions is 40% at all speeds and it was 30% at 40mph, 38% at 50mph and 35% at 60mph, tested on a dyno. We had a cold spell in early December and the best high temperature for a week was 17 degrees. The truck wouldn't start during this time even with a battery booster. The next week I replaced the glow plugs and after that it started with no problems. I found out I only had one glow plug that worked and it wasn't plugged into the relay. I also found I had an unused factory/dealer installed block heater which really helped on those cold days. Around two weeks later the truck started smoking really bad with tons of black smoke and no power whether cruising or accelerating. It would blow black or gray smoke slightly at idle. I then replaced the injectors with some rebuilt ones and then it only blew a lot of black smoke under acceleration and no power at all. We're talking no visability behind the truck and zero to sixty in ten minutes. At idle the vacuum from the pump was 20 inches and at the wastegate actuator it was 15 inches. The wastegate actuator moved freely and was nearly impossible to move with vacuum applied.

I decided to add in a pyrometer and boost gauge. The pyrometer was installed pre-turbo on the passenger's side exhaust manifold below the turbo. While doing that I went ahead and removed the turbocharger so I could vacuum out any loose metal from drilling/tapping. I took the exhaust elbow off the turbocharger and was able to see that the wastegate moved freely and sealed without a problem. The turbo was "coked" up some, but using kerosene freed it up. I also removed and checked the EGR valve and made sure it had no vacuum leaks. The EGR valve pintle shaft moved freely and sealed well. I then replaced the wastegate solenoid, since I was getting a code 78. I also replaced the turbo boost sensor just because I was frustrated. Since everything was torn down I also went ahead and added in a Flowmaster downpipe and cross over pipe and gutted the catalytic converter. Now at idle the EGTs are get up to 300/400 degrees and the boost is zero. At normal cruise the EGTs never get over 800 degrees with the boost usually zero or around 5 psi. On hard acceleration the EGTs will get to 1000 degrees and the boost up at 10psi. Going up a pretty good grade of 4 percent the EGTs would get up to 900 degrees but no further. The only smoke is right when you take off from a stop at full throttle. The truck is running way better than it did when I picked it up last October and again thanks for all the help.

[Hubert]

Glad its better now. Thanks for the update. It is nice to hear the whole story.

When you get new numbers for emissions testing I would really like to see before and after results.

[rdurh]

Unfortunate my emmissions on this truck won't come due until next October. If I remember I'll post or send you a PM.