Help rebuilding a stock k27 turbo

[Dazza]

Disclaimer: This particular k27 is off a 1982 BMW 745i. BMW made very few of these cars, and they were never officially imported to N America, so the knowledge base in the BMW community is very low. But while searching the internet for some answers, I found a wealth of knowledge here in the Porsche section of Pelican. So I'm posting here, hoping maybe some of you with more familiarity with the k27 might be able to help.

When I bought the k27 and related parts from the previous owner he told me the seals were bad and included a rebuild kit.



After taking it apart I found it was definitely due for new seals. I doubt it had ever come apart in it's 30+ years on this earth, so getting the turbine shaft out took a bit of persuasion. When it finally did come out all of the bearings and washers came out too, so I wasn't able to see the exact order they were in. A couple days later when it came time to put it back together I tried to follow this exploded view diagram that I found for the Porsche-model k27s that came in 930 cars and other similar-era models:

http://garage.ideola.com/downloads/k26-explode-legend.jpg


The problem is that my parts aren't exactly the same as those depicted in the diagram, and I can't figure out how to make it go back together correctly. The bearings and bearing clips (#1 and #2) go in just fine:


So does the thrust washer:


And the thrust bearing and splash guard:



But after that, it's really tricky. The diagram says I should have some kind of spacer, and it kind of looks like this original (not part of the kit) piece with the broken seal ring:


Followed by this stepped washer that they call a Mating Ring (also original):



But if I install them in that order, it just doesn't look right at all. It also doesn't fit!


However given the shiny areas you can see on the two parts, it does look like they may have fit against each other before disassembly:


Plus the diagram indicates there are 2 more sealing rings (#8) that are supposed to go on the compressor side, but where? I see absolutely nowhere to install any sealing rings, and none came off the turbo when I pulled it apart.

I know that if I try and put it all together the way the diagram indicates, I cannot get the backing plate on at all. But if I swap the order of the spacer and the mating ring, so that the mating ring is on the bottom and sitting inside the splash guard, it actually looks very good. But if I put on the backing plate and tighten the compressor wheel nut, the whole shaft binds and won't spin. I think it's because the spacer with the sealing ring protrudes past the backing plate:



So clearly I'm doing something wrong, but what? Am I missing a part somehow? I've been wrestling with this for several days now and can't figure out what I'm doing wrong. Help!

[JFairman]

Ebay rebuild kits are made in China most of the time and they are junk. I think you're wasting your time with it.
If you want this turbo to work reliably again and you don't mind spending the money to do it right then send it to Durabilt turbo.
They rebuild old KKK and more recent 3K Borg Warner turbos best of anywhere in the USA and they high speed VSR balance it afterward. If it isn't high speed balanced it's not going to last.

If the turbo they rebuild is installed by a reputable Porsche repair shop and you have the work order reciept they will warranty it. If you install it yourself there's probably no warranty but it's not difficult. Just follow their directions and prelube it good.
Durabilt-Turbo.com - www.durabilt-turbo.com

[Dazza]

Yes I've heard of Durabilt turbo, but the turbo doesn't need to be "rebuilt" per say. It simply had leaky seals; all the tolerances on non-consumable parts checked out perfectly.

The pieces I'm struggling with aren't even part of the rebuild kit, they're all OEM components. Note in the exploded diagram that the rebuild kit includes parts #1, 2, 4, 8, 9, 10, 14 and 17. I'm not having any issues with those parts, it's the original OEM stuff that's throwing me for a loop. It's just a matter of getting everything back together in the correct order and orientation.

I've also had the wheels balanced (by a professional shop) individually so I know they're good as well. I'd hate to fork over hundreds of dollars just so that some shop can put the parts I give them back in the correct order.

[kenikh]

Ditto JFairman - rebuilding turbos is a very precise process and if you can't assure that the assembly is high speed balanced, you're likely looking at a paperweight in short order. The community here long ago came to the conclusion that using a vendor - the one listed above is a good one - to do a rebuild is the only cost effective way to go. That doesn't even factor in that all of the rebuild kits on the market today are functionally forgeries and thus junk.

[Dazza]

As I said above, everything has been balanced. It's just a matter of putting it back together in the correct order and orientation.

Call me stubborn, but I'm not willing to fork over hundreds of dollars for some shop to simply bolt the thing together with the pieces I already have.

I'm looking for help on how to assemble this, hopefully someone out there knows a thing or two.

[JFairman]

"As I said above, everything has been balanced. It's just a matter of putting it back together in the correct order and orientation."

You're so wrong on that.. simply marking the position of the compressor wheel on the shaft with a sharpie pen and trying to put it back on in the same position won't cut it but you think you know what you're doing so have at it.

[kenikh]

This explains why, the moment you untorque the wheel nut, that your turbo is no longer balanced.

Turbo Balancing Facts

[Dazza]

As I said very clearly, the parts (compressor wheel and exhaust wheel/shaft) were INDIVIDUALLY BALANCED, professionally, by a turbo rebuilding shop. It doesn't matter what position they're oriented in, they're balanced individually.

I'm looking for help on how to properly assemble (order & orientation) the various washers and seals that are OEM parts (not part of the rebuild kit) and wholly unrelated to any type of balancing (they don't spin!)

Hopefully someone on here understands...

[Norm K]

I think I get it - you're looking for instructions, not for advice. Best of luck with your new turbo ...

[kenikh]

Got it. They are individually balanced. You don't value dynamic balance and are willing to roll the dice, as a result.

As far as assembly goes, most don't have your damn the torpedoes confidence, so you may not have much luck.

[Dazza]

First off, "dynamic balance" isn't really a proper term. If you're talking about VSR balancing (as opposed to machine balancing), then please use that term as it's confusing to replace words.

I'd like to point out, from your own article that you linked:

"In conclusion, the key to maximum life out of a turbocharger is proper selection of components, precision balancing of those components, and careful assembly of the turbo. An additional balancing operation performed on the completed turbo is not absolutely necessary in most cases"

The components have been properly selected as they're OEM components. The components have been precision balanced, by a professional shop. All that's needed now is the last part, careful assembly. That's were I'm looking for help. I don't see what part of that is hard to grasp??

[kenikh]

Totally agree with what you pointed out - I'm just saying everyone I've ever talked to here, on the Evo forums, on the Subaru forums, et al, all go the extra mile to individually and VSR balance their turbos. And given VSR requires an assembled CHRA, turbos just tend to get sent out. I don't know anyone who has reassembled a turbo themselves and run it. It's not hard to grasp that I don't know anyone who has actually assembled a k27 themselves and run it.

I've taken apart LOTS of them.

[LJ851]

I think it's safe to say dazza would agree that having the turbo balancing after assembly as mentioned provides a superior end result. That knowledge does not affect get getting the the turbo assembled which will be required whether he chooses to get it balanced afterwards or not. I wish i could help with assembly order, i'm sure someone here has the knowledge.

Are the k27 used by bmw much different compared to the porsche unit? I have considered using the bmw unit on my 3.2 as i have easier access to one.

[kenikh]

Originally Posted by LJ851

I think it's safe to say dazza would agree that having the turbo balancing after assembly as mentioned provides a superior end result. That knowledge does not affect get getting the the turbo assembled which will be required whether he chooses to get it balanced afterwards or not. I wish i could help with assembly order, i'm sure someone here has the knowledge.

Are the k27 used by bmw much different compared to the porsche unit? I have considered using the bmw unit on my 3.2 as i have easier access to one.

Fair point. Lots of different K27 variants out there. Have never seem a comprehensive list, but know that these found their ways into everything from gas powered Porsche and Bimmers, to Diesel Mercedes cargo haulers.

[Jim2]

Been a long while since I've been into one but I think you missing a spacer sleeve the width of the thrust bearing.

The sleeve with the two grooves (accepts two seal rings) goes on last, into backing plate.


Like I say, it's been a while for me.

[boosted79]

I rebuilt my K26 myself. When I first bought my 79 I dropped the engine for a general cleanup and some leak repair. I rebuilt the K26 at the time with a genuine triple K rebuild kit that I got from Vertex. I don't know if the genuine kits are even available anymore. I had the rotating assembly balanced and the balancing shop scribed the impeller and shaft and it was reassembled with no problems and has operated fine since but that's only 12 k miles. I've done the same with Holsets since then for a Cummins diesel project and they have been fine. I don't think VSR balancing machines even existed prior to 1984 so any rebuild prior to that was done on a low speed machine? But the K26/27's and Holsets turn relatively low RPM's (150k max, usually lower) compared to the more modern and smaller turbo's that spin upwards of 200K and require VSR balancing to really last. This doesn't help the OP's stack up problem. I'll take a closer look at that later and see if I can help.

[boosted79]

"After taking it apart I found it was definitely due for new seals. I doubt it had ever come apart in it's 30+ years on this earth, so getting the turbine shaft out took a bit of persuasion. When it finally did come out all of the bearings and washers came out too"

What exactly is a "little persuasion"? Are you saying that the bearing retaining clips came out along with the bearings when you were were persuading the shaft? I hope not, because that takes a LOT of force. The question is where is the location of the shoulder on the turbine shaft relative to the thrust washer, the thrust bearing and the mating ring? If the inside thrust washer butts up against the shaft shoulder then there has to be a spacer between the two thrust washers to prevent clamping the thrust bearing when torquing the impeller nut. Did you mic the thickness of the original thrust bearing and the replacement thrust bearing? Did this turbo turn ok before you took it apart?

[boosted79]

The only way I see that this can go together correctly is for the stepped washer to go on the shaft first butting up against the shaft shoulder and with the larger OD face towards the journal bearing. Then the thrust bearing, the flat washer, oil shield and then the seal ring which fits inside the backing plate. With this stack up the step on the stepped washer acts as the spacer between itself and the flat thrust washer and prevents the thrust bearing from being clamped. The difference between the thickness of the step on the stepped washer and the thrust bearing determines the axial float. But judging from your pics it doesn't look like the step will fit inside the ID of the thrust bearing? Is the new thrust bearing identical to the original?

[boosted79]

Ok, you are missing the spacer that goes between the flat washer and the step washer. Your stack up is correct except for that spacer. There is no way to prevent the thrust bearing from being clamped without that spacer. There is an ebay listing by turbos_r_us for a genuine KKK K27 rebuild kit and it shows a stack up diagram that shows the spacer between the flat washer and the step washer.

[billjam]

Dazza,
Welcome to the forum! Sorry your initiation hasn't been more helpful.
The parts diagram below is a little different to the one posted above so it may be a closer match to your turbo, so it may help.

Some us are aware that there is nothing mystical about rebuilding turbos if you know what you are doing. They are probably the simplest mechanical part of the whole damn car!