TURBO Rebuilding

[JohnEd]

These things are very expensive to have rebuilt.  I have handled them and I cannot see what is so complicated.  All I see is a shaft, a couple impellers some bearings and some seals.  Apparently, all those things get pressed together on a shaft with the proper spacing and order,,,,order is important also.

Recently I had the opportunity to look at a 8V92 Turbocharger.  I found that the turbo compressor shaft would move in and out 20 or 40 thousandths.....guessing there but it moved enuf to clunk.  I figured it was completely shot but the board corrected me and it turned out to be very serviceable.  I guess how much play and in which axis is different for each design and I am sure that must be written down.  When I first started reading about turbines it was in the Air Force and their tolerances for gap separation from fins to wall was measured in thousandths of an inch and the thrust was not in the "clunk" neighborhood.  I know I can have my parts balanced and then I can have them balanced to turbo spec and I thought that was much closer.  I got it done for free so I never questioned anything.

Anybody know?  Is it so difficult that I would only want to deal with certain "known" shops?

Thanks,

John

[kyle4501]

One needs to consider the cost of failure when looking to cut costs. If the compressor side were to fail & come apart, you'll probably loose the rest of the engine.

The biggest issue with turbos is the speed at which they turn - in the 100,000+ rpm range.
The clearances may be measured in thousandths, but the runout & balance are much more critical (meaning a much smaller number).
I'm sure the handling of the bearings is important too, lots easier to damage a small ball bearing than most think. Bearing life is measured by revolutions - at speeds of 100,000 rpm, the revolutions add up quickly!

I'm sure lots have had success doing it on the cheap.

As for me, I'll stick with a reputable rebuilder with experience & the proper fixtures for the turbo I need.

[Zeroclearance]

John,  I'm a little confused with your post???

Do you have a turbo that needs rebuilt?

You wrote>  I know I can have my parts balanced and then I can have them balanced to turbo spec and I thought that was much closer.  I got it done for free so I never questioned anything.

The turbine wheel and compressor wheel are balanced seperately.   Then once assembled they are balanced as a complete assy.   This is either done or it is not done..    You got the turbo balanced for free or you got the rebuild done for free??

If the turbo went clunk/clunk that usually means that the thrust is pounded out.   This will usually wipe out the backplate, which will eventually leed to wheel rub..

Part on these turbochargers add up very quickly  $$$    You typically cannot cut corners with these animals, or you will paying to have it repaired again the second time around

[luvrbus]

JohnEd,I will go any place on and engine even the injectors but the turbo is one place I don't go it is a lot more to rebuilding that one would think as Kevin said parts are hi dollar just price a center section for one
.Don and I use a shop in Lake Havasu Tom has been rebuilding turbo for years he started the turbo rebuilding program for DD in Utah and with all the years behind him I have had one of his fail.
A good turbo rebuilder is worth the price to me if Kevin wasn't so far from me I would give him a try and so would Don



good luck

[JohnEd]

Kyle,

All solid advice.  Truly!  Solid advice that i would expect from a knowledgeable Knut.  And, I thank you.

For clarification:  I am one of the worlds biggest believers in "Qualified Experts" and I place the greatest value and respect on "experience".  I also confirm that almost anybodies skills and profession are seen as simplistic by lots of folk but their own as really complicated, full of innuendo and hard fought skills and richly deserved/earned.  I can not remember ever not having this respect for my elders, superiors, craftsmen and professionals.  Someone long ago made an impression and taught me an important lesson at a young age. I am not offering this as a defense or anything as I don't think any has attacked me, but it is background.

The consequence of a failure is the determining factor in how much will be spent to assure success.  NASA spends like a drunken sailor if the item is a "single point of failure" for the space mission.  And that last few percentage points for confidence usually cost much much more than all the funds used to get to 97% probability of success.  I would not risk a $18K overhaul on saving $500 or so on "unqualified source" workmanship.  I surely might do so on "personal challenge", however.  Might was the operative word there.

In general, I agree with all you said about it being complicated.  With all the cautions I hear, however, I doubt that "lots have had success doing it on the cheap".  That I truly doubt.  And there is little chance I won't follow your lead and buy, instead of rebuild, any turbos I might need in the future.


I thank you for your comments,

John

[johns4104s]

John Ed,

Well said,

John

[kyle4501]

I doubt that "lots have had success doing it on the cheap".  That I truly doubt. 

I doubt it too, seems my sarcasm needs some work . . . 

[NewbeeMC9]

if you do try it,  add an aftercooler(intercooler) in case it needs to filter some parts for ya,  if it don't then you have cooler intake air

[JohnEd]

Kyle,

By definition, "sarcasm" is the wit of the master.  Nice work.

New Bee,

I have pondered that a lot myself.  The intercooler is sooooo prooooven.  Why aren't more people modifying their 2 stroke config to include one?  They prevent power drop off and add efficiency.  Beats me.  Your right about them catching the debris from a desintergrated turbo.  Either one of those, by themselves, would justify the cost of the intercooler.  Just to make sure we are both on the same page: aftercooler comes "after" the roots compressor/blower and "intercooler" comes after the turbo.  I'll bet that isn't written down in DD lit.

Thanks for your comments,

John

[bevans6]

I think the reason the intercooler isn't as common with DD two strokes, particularly the V series, is packaging and cost.  An intercooler isn't particularly cheap, it needs air flow to work, and you need to plumb from the turbo to the intercooler and back.  The length of that introduces turbo lag as well.  For marine installations that don't use radiators, it's just so easy to pop the turbo up on top of or right behind the engine, direct shot from the exhausts and into the blower intake, aftercool the air charge in a controlled fashion, and bob's your uncle, done.  Here is a cool twin turbo 8V-71, imagine trying to complicate that with intercoolers and how much more difficult it would be to package:  http://www.powerlinecomponents.com/literature/detroit_diesel/ddc_drawings/70837699ID.pdf

for bus applications, particularly where there are side rads or you are re-engineering the cooling system anyway, designing an intercooler is very easy and just part of the project.  Air to Air also removes the additive heat load that would be driven into the cooling system of the engine install, another bonus when you are already trying to remove additional heat from a power boost in your application.

BTW, to the original topic, my DD V series manual has detailed instructions on how to rebuild a turbo, and complete exploded diagrams.  a lot of "internet" rebuilders just seem to replace the seals and clean it good.  Not sure that's what I would consider a "rebuild".

Brian

[luvrbus]

Guys there are a lot of buses out there with 8v92 engines that have intercoolers it was always a option even on the trucks with 92 series.
DD was the first to use the intercooler
In fact I am stopping over in Albuquerque next week to install new injectors and a turbo for Jim who is installing one on his bus.
The intercooler has been in use for a 2 stroke for a very long time
You remove the aftercooler and install a air deflector in its place and the deflector is getting hard to find now days.
JohnEd it is in the book along with the water cooled intercooler for marine use 



good luck

[JohnEd]

Brian,

Thank you.  It all sounded good till Cliff's post.  Everything you said was so true. 

Cliff,

Thanks.  Doesn't seem that that was all that common pf knowledge.  You the MAN!

John

[Don Fairchild]

to further explain what Clifford said is that I rebuild most of the turbo we use, I use Tom when I don't have a core or I am buys and can't get to it. I have had some of Tom's turbos faill just like from time to time mine will go south on me. You can't do any kind of work for a linght of time and never have a bad day, ( just ask BK ) LOL  HA HA

Don

[JohnEd]

Cliff,

I am confused as to what the logic might be in removing the "aftercooler" in a turbo upgrade?  The after cooler does a good job, I assume, in reducing the temp of the air after the blower increases that temp but the aftercooler can only drop the airtemp to 180 degrees, engine coolant temp, because it is coolant to air.  I can intuit that the air temp after the compressor stage is above 180.  After the "intercooler" the temp must be something above ambient and I suspect it is a lot.  So now the compressor is ingesting hotter air than a N engine and it should profit from the aftercooler even more.  Why delete it?

Thanks,

John

[Zeroclearance]

The two area's that will haunt any turbo builder is the turbine wheel seal ring grooves and the bearing housing seal bore..    The 100% method is to replace the bearing housing and turbine wheel.   The 85% method is to cut the groove width .005" oversized, and cut the seal bore out of the bearing housing and CNC a new insert/seal and install and hone to std/std...

Tearing a worn turbocharger apart and installing new bearings and new turbine side seals will normally result in a 100% failure.  The reason is these units have already had the text book rebuild done 600,000 miles previous..   I see bearing housings with .040 over.     

For my personal engines and recommendations to friends and family, I strongly recommend buying a new bearing housing at a minimum.   Grinding a turbine wheel that does not have FOD damage to the blade tips is acceptable.   But with our 2 cycles wiped out turbine wheels is a common thing..

Most "new" TV series bearing housings will run you between $245 to 285.00  Genuine Garrett.  The days of slapping in std seal rings and bearing are far and few between due to the fact that Garrett is NOT manufacturing new turbochargers for these engines.