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I'm hoping someone can answer some questions/offer opinions regarding my turbos.
I just pulled the original stock twins out of my '95 to address leaking oil seals (heavier from the primary) and some expected wear. The set runs well, builds boost quickly, transitions to the secondary seamlessly, etc., This car has 70K miles, and is only street driven and never tracked.
Removal went very smoothly, with none of the common difficulties with removing heat seized bolts, shields, etc. With the set out of the car, everything looks as expected, except for this:
Secondary turbine inlet/precontrol flange.
This is the flange to the secondary turbine inlet and precontrol valve. The divider has cracked through completely. Note that the cracks do not reach the gasket mating surface (yet?). The obvious leakage past the precontrol valve was creating no noticeable symptoms.
After seeing this, I used a bore scope to check out the condition of the rest of the housings, in particular around the wastegate. The cracking around the wastegate is much less severe than around the precontrol valve:
Questions for the forum:
Is this level of cracking around the precontrol valve common? It seems strange that the housing in the wastegate area is in so much better condition.
How (or should) this be fixed? I'm assuming these cracks will keep growing until they compromise the gasket seal.
(If I was sure these cracks wouldn't grow, I would just proceed with the turbo refresh and reinstall the assembly.)
What options/experience have people had with repairing this kind of damage?
I know cast iron can be welded, but is difficult and prone to failure.
What are the parts options here? Is there a way to get new turbo housings (instead of a whole new twins assembly)?
If it matters, I have no intention of doing any upgrades to the car as I want to keep it as original as possible.
I would bet almost all twin turbos will show some degree of cracking.
I have only seen two used ones that have not had cracks.
(I have 23 used ones on my shelves.)
"The cracks not exceeding gasket cover area' seems to be received wisdom.
Concern would be if the cracks grow to affect the coolant and oil channels.
There used to be a least one firm that took in old twins and rebuilt them, but generally I have not heard they can be rebuilt succesfully lately.
I took my three best condition S7/S8 turbos to a well known local shop and, after researching, they said they could not be fixed.
I have heard of people sending to China to get the cracks repaired. but I heard that although they come back looking nice, there is some doubt that the repaired metal will stand up.
The concern you should have is if your turbo self destructs and sends metal bits forward into you motor
You can likely find used turbos in better condition than yours, for about $200..
If you are inclined to bet on the gasket coverage route.
By "The cracks not exceeding gasket cover area' seems to be received wisdom." I assume you mean that there is no problem until the gasket seal is breached. Correct?
I'd be interested to know how the severity of cracking in your used collection correlates with use. Do the cracks have steady growth, accelerating growth, or decelerating growth with miles?
Here's the Napkin math based planning:
The worst crack in my unit is ~75 % through to the gasket sealing surface at 70K miles. Assuming steady growth, that correlates to ~93K miles to failure, which is within the range I've planned for the engine's first rebuild.
As far as the condition of my turbos, if they weren't leaking oil, I probably wouldn't touch them. Out of the car, they both spin smoothly and have zero play, either axially or radially, Is replacing just the primary turbo housing (holding the precontrol valve and flange) an option?
I would like to add that these aren't 100% cast iron, the older turbos have some nickel in them and the newer ones have even more nickel. I don't know how much harder that would be to weld.
That's how I understand it. I think each manufacturer has a custom recipe for the "cast iron" in their housings.
Prior to this, I was not aware that the precontrol flange area was a weak point in the stock twins, or that there can be significant deterioration without any symptoms.
I have not kept a record of the mileage on the various turbos I have. In any event, I would suppose it would be difiicult to judge given not knowing other factors on the history of the units.
You'd have to do more research to see if anyone has mixed and matched spare parts of the turbo in a rebuild.
The turbo pro-shops I talked with refused to even try.
Oil leaks around the turbos can come from the number of small gaskets in the oil piping around the turbo and can even migrate from the other side of the keg or a main seal leak into the bell housing
Oil leaks from inside the turbos could come from the seals or cracks in the manifold.
You can swap primaries out. You have to worry if your luck holds on those fasteners holding the halves together not breaking in the process though.
A turbo, even brand new, without radial play sounds very unlikely though.
With the oil leak, I'd be checking oil injectors for function before assuming anything.
Just have to hope there are no more surprises at this point. Given how easily everything else came apart, I'm hoping those bolts are no exception.
The lack of play was a (pleasant) surprise. I'm talking about the finger test here, you can't feel ANY play at all in either turbo.
The oil leak is definitely coming from the seals on both turbos, and we didn't find any blockages in the drain lines.
Thanks for the link. I'll keep that as an option.
I can't read the Japanese in the add, but my turbos look to be in better shape than the ones pictured.
I'm getting the housing Tomsn16 posted.. Theoretically, it should accept the turbo cartridge from my turbo without issue. I'll report back when I know how this works out.
