Metal that can withstand lots of heat cycling (turbo vane actuator rod repair)

[Gazz292]

My car has a variable vane turbo, and the pivot for the vane lever seized due to me not using it for a while (i live near the seaside, rust gets everything) so when i next used the car the rod snapped where it goes into the pivot as the actuator extended :

Whilst i can buy a new actuator, it would mean the turbo needs to come off to be 'calibrated' for the new actuator's spring pressure etc, and that isnt happening anytime soon due to rust rounded bolts.

So i'm thinking of turning up a rod extension piece from some 10mm hex bar stock... something like this :

But with a longer male threaded end.

But as this rod connects to a lever that is on the hot side of the turbo, i can imagine it will get rather hot, then cool down, then get hot again over and over for it's life.

Any suggestions to which kind or material i should buy, ideally i'd buy a length of 10mm hex bar to make things easier, but i have a mill as well as a lathe, so can put nut flats on round bar if needed.

 

[Erie Fred]

Inconel might be the ticket...

 

[timgunn1962]

It's difficult: "rather hot" is a pretty nebulous term that could encompass everything from "probably best not to lick it" to "surface of the sun".

I'd be inclined to look at stainless steels initially. The way these tend to fail with cycling through high temperatures is that they form an Oxide layer on heating and then lose it on cooling when the differences in thermal expansion of the Oxide layer and underlying stainless steel exceed the Oxide layers ability to remain attached. Types 304 and 316 tend to keep their Oxide layer attached through cycles to around 800 degC and back to ambient. 310 Stainless has higher Chromium (25%) and Nickel (20%) than 304 or 316 and will usually retain its Oxide layer through cycles to 1100 degC. The higher Chromium makes for a stronger Oxide layer, while the higher Nickel moves the Thermal Expansion Coefficient of the Stainless closer to that of the Oxide coating, as I understand things. 310 tends to be pricy and hard to find.

If you are looking at temperatures substantially below 800 degC, I'd be looking at 316 or maybe even 304 stainless. If you are looking well below 800 degC, maybe even 303 stainless, particularly if you have a small lathe: it machines MUCH more easily than 304 or 316 and is available in Hex bar. In the past, I've bought it from model engineering suppliers.

Use a good high-temperature antiseize on the threads.

 

[dan.taylor.1]

Honestly it's at best stainless, but most probably mild with a zinc coating on it as standard.

 

[Rrobson]

B7 or similar if you want to get fancy, but in reality a bit of 316 would do you

Should be able to get a scrap ht faster if you need material

 

[Gazz292]

i would guess that the upper end could see maybe 800 degrees C, but the lower end has a rubber boot, and that's not showing any signs of getting hot (i guess it would be silicone or a high temp rubber)

mild steel probably would do the job, but i'm thinking of making my repair a little stronger than stock if possible, as i can see the pivot seizing up again over time (i will now remember to move the lever manually before i start the engine after i have not used it for a while, rather than when i notice reduced performance as i did before)

 

[hotponyshoes]

I'd go for stainless if the original problem was caused by corrosion.
I'd expect any grade of stainless would be fine for that level of heat cycling, inconel is ok for an exhaust manifold that's literally, glowing red hot, but probably overkill for that!
I've got plenty of 310, 321 etc grades of stainless if you want a bit of something fancy but they will all be round bar, mostly imperial sizes I think

 

[Gazz292]

i do wonder how hot the turbo exhaust side will get... on this engine about 5 inches after the turbo exit is the DPF, and when that's regenerating it sits at ~650 degrees C for 20 minutes or so, but that's the exhaust gas temp, so internal temps.
So the turbine housing normally wouldn't go much above 400 i'd guess, it's just a little diesel engine and not a hot rod after all.

 

[hotponyshoes]

i do wonder how hot the turbo exhaust side will get... on this engine about 5 inches after the turbo exit is the DPF, and when that's regenerating it sits at ~650 degrees C for 20 minutes or so, but that's the exhaust gas temp, so internal temps.
So the turbine housing normally wouldn't go much above 400 i'd guess, it's just a little diesel engine and not a hot rod after all.

Nowhere near as hot as you think I expect.
Dap some temp marking paint on it and take it for a blast if you want to check

 

[tom2207]

id just cut it back and use a long bolt to remake the end ,, a loose fit in the pivot would be more important and a taste of high temp ant seize ,, but if its a loose fit it will do. Its not F1 at the end of the day , same as turbo calibration etc ,,,, wouldnt be worrying.

 

[Ross365]

The existing rod shows no rust (and you live by the sea) and no temper oxidation film (blue or green), so it may not be seeing a temperature that needs anything other than stainless, or as you say, even mild. You mention 800'C (reasonably bright red heat) but I very much doubt that rod has seen 400'C.

 

[dobbslc]

It cant get that hot with a rubber seal so close to it. I'd say anything would do the job.

 

[Munkul]

Its going to need calibrated anyway... Have you managed to free off the vanes?

 

[Gazz292]

Thanks to everyone for the help, i've ordered a length of 316 stainless hex bar, will see how my little warco 250 lathe handles cutting that.

i kinda overthink things, and was imagining using mild steel would result in the rod melting

But now i think about it, the internal temps of the DPF canister only get to 650 degrees C during a regen (when extra diesel is being injected on the exhaust stroke, and lit off by the glow plugs)
At all other times the internal gas temps must be half that at least, so the external turbo temps likely don't get above 150 - 200... if that.

:
The vanes were always free, it was the pivot that connects to the vane lever that was seizing all along, so when the actuator pushed upwards to alter the vane / nozzle position, the lever moved in an arc, but as the pivot was seized, the rod was bending to try and follow the arc.

My fault, as i've had this issue for the last 5 years, and usually when i've not used the car for a while i will move the vane lever with a pair of pliers to free it off,
i forgot this time and guess the rod was sufficiently weakened to snap.