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ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

This question came up in a recent thread, but didn't garner any direct answers, so I'm going to repost here.

I have four complete K26 units. One of them (a series I) has been rebuilt and is sitting on the shelf, either as a last resort option for the UWB project, or hopefully as a replacement for the 941 when the time comes to rebuild its turbo.

Of the other three, two are Series I and one is a Series II. All three of them have cracked turbine housings, and two of them appeared to be in excellent condition before I disassembled them (i.e. very little shaft play, compressor and turbine fines in excellent shape, etc.). Here are some photos of one of the turbine housing after being cleaned up. All three of the turbine housings have cracks in the exact same location.

My question is whether these turbine housings can be safely reused without further repair. I realize it's probably not ideal, but given the relative scarcity and uniqueness of this style of turbine housing, if cracked units can't be reused, it really exacerbates the scarcity problem. Smoothie indicated in the aforementioned post that this seems to be a common problem to both Series I & II, and also that he wasn't sure if it would affect performance or operation, which is why I am asking about the feasibility of reusing these.

In the meantime, if anyone has an uncracked K26 turbine housing you're willing to part with, please contact me ASAP. I'm in the market, as I urgently need a solution for my UWB project.
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erstwhile owner of just about every 924 variant ever made

emoore924 · Joined: 13 Apr 2004 Posts: 2822

PM me. I might have an extra K26 housing that's crack free. In your message, tell me how I'd find a crack like that without disassembling the turbo.

462avi · Posted: Sat Mar 29, 2008 12:54 pm Post subject:

My opinion would be no. The turbo I removed from my car had similar cracks in the hot side housing. The crack when heated will expand into the turbine opening and damage the turbine.

Geoff
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2005 C230K
2002 grand cherokee with 4.7L

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

According to Majestic, those cracks are weldable.
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Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

KlaasyT · Joined: 20 Jul 2006 Posts: 25 Location: Ontario Canada

I had my cracked housing welded when I replaced the bushings. That was 10000 miles ago, so far no issues. The welder was very experienced, and knew what he was doing. I'm sure more have done the same.

Clarence
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81 931 Minerva Blue
72 911t Irish green
84 911 Carrera Targa sold
72 911t rs look project
71 911e rusty future project

462avi · Posted: Sun Mar 30, 2008 1:24 pm Post subject:

I know cast iron can be welded. The real question is, is it worth the money. I had my old/bad housing welded by a friend who wanted to try out a new type of rod. It still needs to be machined but it looks pretty good. I don't think it is a flawed design necessarily, but on other hot side housing there is a longer approach to the turbine. Ours seems to neck down very dramatically.

Geoff
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2005 C230K
2002 grand cherokee with 4.7L

462avi · Posted: Sun Mar 30, 2008 1:25 pm Post subject:

I know cast iron can be welded. The real question is, is it worth the money. I had my old/bad housing welded by a friend who wanted to try out a new type of rod. It still needs to be machined but it looks pretty good. I don't think it is a flawed design necessarily, but on other hot side housings there is a longer approach to the turbine. Ours seems to neck down very dramatically.

Geoff
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2005 C230K
2002 grand cherokee with 4.7L

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

This weekend I picked up a 6411 K26 from Vaughan that came off of an Audi. A couple of cool things about this unit is that it has a water jacket in the bearing housing, and it is a direct fit replacement for the stock 931 bearing housing (except for the bracket that attaches to the block...but that's another story).

More importantly, the turbine housing is almost identical to the 6365 turbine housing from our K26 unit, except that it has a four-bolt flange, and a slightly larger throat. The exhaust connection on the turbine housing has exactly the same bolt pattern as the primary exhaust pipe, and except for the flange insert on the 931 pipe (nothing a little machining couldn't solve), it is a direct fit

This is really the first time I've had a comparably sized 4-bolt turbine housing in my hand. After looking at things a bit, my buddy Larry asked why we couldn't just weld on some additional material to the stock ex manifold to convert it over to 4-bolt. It appeared to me that the 6411 turbine housing would bolt right up and could be mated to all of the other K26 components. Having said that, if we could add add'l material to make a flange that looks something like this...

...why couldn't we just convert over to a modern Garrett???? Am I crazy, or does this look completely doable? I've asked my welder and he thought it would be no problem, maybe 2 hrs max worth of work.
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erstwhile owner of just about every 924 variant ever made

john h · Posted: Mon Mar 31, 2008 9:46 am Post subject:

personally I wouldn't worry about the crack in the hot side. The turbo I've been running on my race/ road car for many years (since 1992) had a crack similar to your photo's when we put it on and it's now run almost 16 years and over 100,000 miles with out the crack causing a problem.

My view and my Mechanics was it was downstream of the motor and if it created a problem it would just destroy the hot side and in the very worst case it might throw stuff though the inlet side - but as I've an intercooler between the turbo and engine which will sort of filter out a lot of the crap and not much will get through to takeout the motor. And it if does go through the bottom end of the motor - no problems as I've about 5 or 6 short blocks all setup ready to swap over.
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emoore924 · Joined: 13 Apr 2004 Posts: 2822

Ok, here's what I found out.

I have two spare turbos sitting on the shelf. One I'd consider to be parts only because of excessive shaft play -- rebuild possibilities only. The second I would consider to be a plug-n-play -- in good shape, no problems.

Both have cracks at exactly 3 o'clock when you hold the turbo so the KKK triangle is at high noon. You can see the crack in the housing in front of the impeller, and they extend down into the housing.

That being said...,

The sort of good news:

The turbo that's in worse shape looks like it has had the crack for a *really* long time. The edges are eroded and rounded down, sand blasted almost. It is dull and open. Clearly, it had been run a long time like this without problems. I think this turbo eventually failed because the shaft bearing developed excessive play and the impellor finally hit on the housing -- I doubt that had anything to do with the crack but I'd have to disassemble to know for sure what the race looks like.

The sort of bad news:

The other housing in good shape also has a crack at exactly 3:00 as well. It is newer and sharper and more pronounced, but it doesn't seem to affect the runout of the shaft at all. So, while it is cracked too...

The other good news:

I'm not sure how much it matters.

I have another turbo coming off a running car in the next few days. The car ran really well with no noises or problems. If it has a crack too (I'd expect that it would), I'd start to believe the "don't worry about it" perspective. If it has no crack, I'm not sure whether that would be conclusive either way.

If you want pickies, please LMK and I'll send what I can.

emoore924 · Joined: 13 Apr 2004 Posts: 2822

Update: The turbo that came off the car doesn't seem to have the 3 o'clock crack. Looks good. I haven't checked really close (bright light, magnifying glass...) but I don't see anything upon a cursory inspection.

Shaft play is minimal too.

Another spare turbo for the spare turbo shelf.

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

If you want to be sure, have it magnafluxed.
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Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

emoore924 · Joined: 13 Apr 2004 Posts: 2822

Rasta, most of the cracks I've seen probably don't require magnaflux to find them. They're so big you could stick a quarter in there sideways. But certainly a great idea if you're not sure something is there. I'm not suspicious enough about the turbo I just took off to spend the $ to flux it. It ran well enough on the car, so whatever the crack situation, it'd probably run well enough again.

And ALL the cracks I've seen are at 3 o'clock. So when they're there, they're easy to find.

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

I'd put it in the blast cabinet first. On one of mine, the cracks couldn't be seen until the carbon buildup had been removed. Also, if you look at the pix in my original post, they do form cracks in other areas besides the usual "3:00" location. I saw one that had a crack longitudinally in the groove right where the scroll begins (also at the 3:00 location).
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erstwhile owner of just about every 924 variant ever made