Excessive Crankcase oil pressure in Piazza motor?

devilishdesigner
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Excessive Crankcase oil pressure in Piazza motor?

Post by devilishdesigner »

Just gotten a $1000 quote for the rebuild of my Garrett M24 A/T6.0 turbo for the Piazza, supposedly part of the reason for the failure is likely to be highly excessive crank-case oil pressure pumping WAY too much at the turbo. Just wondering what the common reasons could be for this?

The engine is only 2000km old, and was supposedly built to race, but never used, but that aside I have almost no information on it, as the previous owner knows very little about cars in general and could tell me nothing of the engine specs.
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Post by IZU069 »

Do you mean oil pressure from the pump, or blowby pressure (rings & guides etc)?

I assume oil pressure, though I don't see how that should wreck the turbo - not that I know much about that sort of thing, but AFAIK high pressure would be more likely to damage shell bearings (big ends & mains) rather than needle & rollers etc in the turbo.

Have you measured the engine's oil pressure? (57psi @ 1400RPM?)

I presume there has been major damage for a $1,000 repair bill.
Who gave you the quote and the diagnosis?
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Post by devilishdesigner »

Quote was from a local turbo specialist, who has been fairly good and honest about everything. the main damage was the ball bearings and seals from what he said. he suggested that it could have been caused by excessive pressure from the sump feeding into the turbo.
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Post by IZU069 »

I don't know how. Maybe you or he could explain?
So is it only the bearings, or the impellor/s & seals, or other bits as well?
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Post by devilishdesigner »

bearings and seals. damage is similar to if there was a blockage in the oil return, but oil return is fine. taking a look through the receipts this engine has been trouble since the previous owner purchased it.
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Post by IZU069 »

I can't see the block pressure having much impact - even if it was 10-20psi.

Isn't it more likely to dirty or poor oils?
Or someone's $multi u-beaut modification?

So you remove the oil filler cap. How bad is the pressurisation?
(I don't think the problem has been correctly analysed - either it is getting sufficient oil or not. Why the dump & not the supply etc?)
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Post by devilishdesigner »

I've been doing some more reading, sounds like ballbearing turbos like this one can be damaged if they are outside their operating range of 40 to 45psi, so it seems possible that a restricted should have been fitted and wasn't. I also discovered that the controller fitted was for a different model. What exactly does the wiring on the airbox control on a piazza? I am wondering if this could have caused an airflow restriction that caused the front-rear play which aided in killing the seals? It's seeming more and more like the mechanic who set this up didn't really know what he was doing.
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Post by IZU069 »

If it's only supposed to get ~45psi and there is no regulator, then you have your problem.
The airbox electrics is merely airflow for the fuel delivery.
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Post by devilishdesigner »

IZU069 wrote:If it's only supposed to get ~45psi and there is no regulator, then you have your problem.
The airbox electrics is merely airflow for the fuel delivery.
That's aboutwhat I figured. If the wiring has been played with could that be partially closed and restricting airflow?
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Post by IZU069 »

No. It's a measurement device - not a controller.
If that turbo only handles 45psi & is getting more, then its seals will pop etc. Bearings themselves will handle more pressure - the weakest are shells (like big ends & mains etc) which break down above about 85-90psi.
But seals will only handle whatever amount.

The typical Piazza EFI uses the AFM (flap etc) to measure actual air intake. The ECU knows the RPM so it knows what fuel quantity to deliver )from maps).
The O2 sensor provides the "real" feedback (rich/lean) for map compensation.
The delivery or map is also effected by temperatures and TPS (throttle position), but these are primarily "predictive" to provide variation ahead of O2 feedback.

The AFM etc won't wreck the turbo.
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Post by devilishdesigner »

Thanks. I'm on a steep learning curve, used to cars built well before computers were fitted to them. If the piazza is running at 57psi oil pressure at 1400rpm, what is it at max revvs?
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Post by IZU069 »

devilishdesigner wrote:I'm ... used to cars built well before computers were fitted to them.
Computers? WTF?

Don't worry - me too.
I consider the Piazza to be a "new" car. It post-dates my runaround buy over 20 years (1965 Wasp) - my newest car ever being 1969 Florian (until 1986 Piazza).

But I was into electronics as a hobby and built an electronic speedo back ~ 1977 'cos Halda's (rally odometers) were wrecking my Bellett speedos.
IN the late 1980s I designed an electronic distributor since the 20 year old Bellett dizzies were old & worn.

I knew nothing about this new crap until a I found a bastard at work that owned a Piazza and.....

Sorry, I just needed to take a tablet.
Glad it's not a full moon tonight.

But thanks for letting me know your situation etc - it makes things a bit easier.

As for max pressure - I'd go by what the relief is set to. IE - oil pumps have a relief valve that pop above a certain pressure. It's usually to guard against blocked oil filters. In fact now that I think about it - does it bypass the filter (hence pushing hi pressure to the rest of the engine) or does it dump to sump - maybe with a separate "filter bypass"?
Damn you "know nothing guys" - makes me question things that are so obvious "to have known".... Thank You!!!

Again, point is that if Piazza delivers 50-60psi and turbos handle max 40-50psi....

Do you have the "PiazzaManual" CD available from this site?
Essential - get it if dealing with Piazza. For $15, a small investment.

I/we should find out what reducers (oil pressure regulators) to the turbo were used.
If non - why not? Is your turbo different?
Not too that I see the issue as being a seal issue - seal break down if pressure is above a limit. I also reckon this limit is to atmospheric pressure or thereabouts as opposed to say input pressure (say 60psi) less restricted output pressure (say 25psi) - hence say 60 - 25 = 35psi which is within "turbo 45psi tolerance", but input 60psi exceeds 45pis hence seal blows to atmosphere, hence oil leaks, hence oil diverts from bearings and bearings run dry or hot etc.

Make sense? Blind leading the blind? Or blind stimulating blind (from exam experience - I knew 5% & my study-buddy knew 5% - between us we worked out 95%. (If exams weren't in 6 hrs time at 10AM we would have had 100%!!).

Alas, maybe too much wine, and I'm presently blind!

Till next,

Peter.

(PS - Wedgy - where are you??)
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Post by devilishdesigner »

Thanks. Yes, I've actually printed the manual, slowly working through it. I have a feeling that if the reducer is missing ( I don't know what to look for, but it appears the oil line runs direct from the block on quick inspection), I imagine this is simply due to the fact that the turbo was plumbed by a general mechanic with very little turbo experience. Btw, each car I've owned has been older then the one before, I started with a 76 and now drive a 67 volvo 122s daily, and I may get into trouble in here for admitting it, but the piazza will be donating it's whole driveline, suspension, steering, wiring, everything but the shell and interior, to a 64 Simca Aronde P60 Wagon. (so far this has gotten me the cold shoulder from the v8 boys and French car lovers, but the piazza is the perfect donor for what will become a fun and reliable driver)
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Post by IZU069 »

AFAIK, there is no reducer for the Piazza turbo.
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Post by devilishdesigner »

I imagine there isn't, being a roller bearing turbo they have far greater flexibility in their oil pressure range. Since I am not looking for big HP (MAX 10 lbs boost - need reliability more then power) I am looking at buying a standard t28 roller bearing turbo so that I can re-use all my plumbing (including i think 3" Remus exhaust :) ) and get away with no reducer/restricter/regulator/whatever and lower rebuild costs down the track.
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