Stu's NA6/SE

bruce · Postby **bruce** » Fri Jul 03, 2020 7:49 pm

FK.
Did Dann mod the engine internals or did he just do all bolt-ons?

StuwieP · Postby **StuwieP** » Fri Jul 03, 2020 8:09 pm

Bolt ons.

Data doesn't show any AFR anomaly, injector duty was healthy. No boost surges.

Very strange failure coincided with a massive oil pressure spike

bruce · Postby **bruce** » Fri Jul 03, 2020 8:12 pm

Perhaps just a dud engine.
Didn't you have troubles with sealant in the engine - maybe some of that resurfaced (or have I got the wrong thread)?

greenMachine · Postby **greenMachine** » Fri Jul 03, 2020 8:46 pm

That sux!

Symptoms?

StuwieP · Postby **StuwieP** » Fri Jul 03, 2020 8:54 pm

No compression cylinder 1, big oil pressure spike around the moment of failure. Crankcase overpressure blew the dipstick out and oil everywhere. As far as I can tell that all happened at once.

No knocking sounds, no (observed) warning signs or sounds of anything wrong, nothing evident in the data logging (except oil pressure spike).

Happened under load but (to my mind) not really any higher load than had already been applied on the road.

Tear down and observations will probably be the key thing

ManiacLachy · Postby **ManiacLachy** » Sat Jul 04, 2020 11:13 am

Aw man, that sucks. Didn't even get the chance to wring it's neck before it gave out :cry:

StuwieP · Postby **StuwieP** » Sat Jul 04, 2020 11:38 am

ManiacLachy wrote:Aw man, that sucks. Didn't even get the chance to wring it's neck before it gave out

Would almost be easier if it had gone bang while being thrashed - or some major boost spike, or I overheated it, but doesn't seem so... just went pop.

On the upside, everything else felt great on the track. Steering and grip felt really good even with cold tyres on a cold day, braking felt very positive, suspension was nice and controlled - didn't seem too bouncy or harsh. Obviously if I'd got up to speed, weaknesses might have been revealed, but... better take the positives where I can find them!

greenMachine · Postby **greenMachine** » Sat Jul 04, 2020 2:41 pm

Sounds like the boost vented into the crankcase through No1 - maybe dropped intake valve, hole in piston ... ? Holing a piston should make at least a brief noise though (don't ask me how I know this :oops:

), and as for the oil pressure spike - I dunno :frown:

StuwieP · Postby **StuwieP** » Sun Jul 05, 2020 7:08 pm

So some updates from the weekend... The engine is ready to come out (next weekend) - only fuel lines and clutch line need to be disconnected. I'm getting depressingly familiar with disassembly :roll:

didn't need a helping hand for anything, even getting Dann's now quite oily twistmount manifold+turbo+downpipe assembly out in one piece.

No scoring in the exhaust ports or exhaust manifold on cylinder 1 - I'm calling this a win! Happily, also, no chunks or pieces of metal in the oil (could still be in the sump of course).

I suspect the oil pressure spike coincided with the crankcase pressurisation - the oil went through the pump, pushing pressure up, and out the dipstick, the two possible escape routes? Glad I didn't keep my foot in it or I suspect all the oil would have exited the sump and onto the track/my engine bay.

So, if my luck holds (if an engine failure can ever be lucky) I may not have done too much damage to things, except whatever broke in cylinder 1...

greenMachine wrote:Sounds like the boost vented into the crankcase through No1 - maybe dropped intake valve, hole in piston ... ? Holing a piston should make at least a brief noise though (don't ask me how I know this ), and as for the oil pressure spike - I dunno

Both intake valves appear to be in the same place (and closed) looking through the intake ports - I don't know if a/the valves had failed it they would still look "right"?
As far as noise - Would I have heard it at 160kph with the roof off and a helmet on? I don't remember hearing anything but there was a lot going on at once... But yes it seems likely to be a piston or ring failure.

Lokiel · Postby **Lokiel** » Sun Jul 05, 2020 9:27 pm

Crankcase ventilation issues or blocked PCV?

Reminds me of this old thread: https://www.miataturbo.net/diy-turbo-discussion-14/dip-stick-blown-out-13783/

StuwieP · Postby **StuwieP** » Sun Jul 05, 2020 9:46 pm

I think the pressurisation coincided with the oil pressure spike. Which seems to have occurred about the same time as I lost cylinder 1 (GM's suggestion boost got past the piston and pressurised the crankcase seems to be consistent with failure of the rings or piston in cylinder 1)

I've never had an issue before oil blowing out the dipstick, and I don't have much blowby to speak of from the last ~400km since I installed the catch cans.

Will have to wait and see what went wrong in cylinder 1...

plohl · Postby **plohl** » Sun Jul 05, 2020 11:46 pm

Maybe a small amount of det doing damage to piston or rings? Boost by passing into crank case?

StuwieP · Postby **StuwieP** » Mon Jul 06, 2020 12:14 am

plohl wrote:Maybe a small amount of det doing damage to piston or rings? Boost by passing into crank case?

Seems the logical probability from all the info I have at the moment.

Just hoping there's no major scoring or anything to the cylinder that would make it more than a simple rebuild

greenMachine · Postby **greenMachine** » Fri Jul 10, 2020 7:35 pm

Did you do the 'tiny hole' mod to the VC? That needs to be done, and would allow a certain amount of over-pressure in the crankcase to vent to the catchcan and out the other side. That is not its intended purpose, but in these situations you take everything you can find.

What was the pressure spike in the oil pressure? If your normal oil pressure was say 60psi, I'd be interested in the spike peak.

If the compression in No1 is zero, there HAS to be a passage from the combustion chamber to the crankcase, or somewhere else. If the valves are OK, it has to be something else in that cylinder. If it blew the dipstick out, that means it is venting into the crankcase/valve cover volume, and that points to a serious detonation issue, probably holing the piston.

If it is detonation, look at your logs to see what spark and fuel are doing at that moment, and voltage in case there is a stray wiring problem (I killed an ECU that way).

:mrgreen:

StuwieP · Postby **StuwieP** » Fri Jul 10, 2020 9:21 pm

I have not done the tiny hole mod. I have seen it mentioned but thought I would watch the catch cans I had set up for blowby first. Given everything is coming apart, I might look into some better VC venting while it's all easily accessible (and since I have nothing and nowhere to drive locked down in Melbourne anyway!)

Agreed that piston or ring (or both) has likely failed pretty much completely (can a piston ever really partly fail?).

As for data, I've been through it all coupled with the video I had and can point to the following:
1. Oil pressure spike went up to 102psi at 6k rpm, from a baseline of about 67psi at 6krpm (consistent with the BE oil pump set to 66psi, on oil that was still warming - was short-shifting at 6k). Almost certainly this was after the failure.
2. There was definite boost creep - I hit boost cut and ECU cut fuel. I suspect the boost creep induced detonation which is what killed the motor.
3. Ignition timing was stable... no oscillations or spikes, just I think with the boost going up out of table perhaps meant it didn't retard ignition any further, not that it would necessarily have altered things.
4. Injectors had more to give - only at 80%DC when boost cut, so didn't run lean, just basically as boost rose, pumped more fuel in, which meant... more boost... which meant... well yeah that's boost creep right?
5. After the fuel cut, big AFR oscillation - not sure if there was possibly damage there as well if the injectors didn't shut off fast enough and leaned things out, but I don't think so, I think detonation due to boost creep seems most likely - mechanic and engine builder agree with that. Proof will be in the disassembly.

So yeah, too much boost, bad boost control. Not sure why that didn't show up on the dyno with Dann - don't think that was something he would have just missed, and the boost control wasn't maxed out, it just wasn't a closed-loop setup as far as I can tell (so, as I understand it, it had no self-reference to say "oh no, more wastegate please" - it just said "hold at x% open". I do remember having a discussion with him about it and that he had some trouble with the boost controller. So maybe he had set it up on the dyno in a way that seemed to work (and in fact did work) right up until it didn't.

Anyway, nothing I can do about it now, no hard feelings, just bad luck. Engine is coming out tomorrow, tear down tomorrow + Sunday to confirm, then off to the engine builder to rebuild.

Then a retune somewhere local, either based on Dann's tune and trying to get the boost control sorted better or brand new - essentially whatever that tuner feels comfortable with. Thinking Chequered (they did Beavis' car?) or my dad's tuner, though not sure of his Haltech experience. Any other recommendations in the Melbourne area?

Edit - I said earlier no boost surges. Until I went over the video + data I didn't pick the boost creep - was looking closer to the oil pressure issue and needed to go back 5-10 seconds basically where all the "excitement" happened