Shit happens - Rolling Road Piston Failure nearing start up (update 27 Nov 10)
Turbo Mini Forums

Over the winter, I'd made good progress with the Megasquirt mapping and boost signal re-plumbing which had stabilised the boost and ignition issues I saw at the TM rollers last October.

So I was hoping for reasonable results at the RR day at Iron Acton today organised by Bman (Ben) - thanks mate.

Cutting to the chase .... despite what we thought was a head gasket today, I've stripped the head off tonight and ...

I've blown No 4 piston

The pics attached show about 1/3rd of the circumference of the piston has melted away and deposited itself above the ring land on the non contact area of the cylinder wall in the squish area between No 3 & No 4 cylinders and there are signs of ali all around the chamber wall in way of the inlet valve in No 4 combustion chamber - this looks and feels like it's been 'metal sprayed' and the texture is like fine sand paper to the touch.

In one of the shots shots, I've inserted some feeler gauges between the piston and the cylinder wall - the gap is about 0.030in and by looking directly above, I can see the inside surface of the top piston ring ! It's fecked.

Worryingly, two of the other cylinders/pistons also show very large clearances but there is defo no sign of det on these which is strange.

This is with +0.020 Cast Omegas, modified to a 10cc dish, and a de-beaked and flowed 36x31 MPi head collectively giving me a static 8.4 CR.

The gasket on No 4 shows excessive crushing of the fire ring compared to the other three and a little burning directly above the piston damage so I'm wondering if this was the cause of the det initiation site.

If so, this is the second time I've had this. The last being on No 3 pot just before the IMM last August when the fire ring deformed and blew out to the coolant passageway.

Apologies for the quality of the pics but I DNGAS by then !

I'm assuming this time around it's classic det but I'd welcome some views please, particulary regarding the ignition advance which is shown in purple on the two logs I've attached for the 3rd run at 8 psi - 151 KPa (about 108 nanas - a little down on last October TM RR day) and the final run where despite a reasonable 147 nanas and 160 curley wurleys, I made what I think was a fundamental error in judgment and upped it to 17 psi - 221 KPa despite not having trialled this on the road before (I know, I'm a feckin IDJUT !!!!).

In summary: I think I ran too much boost for the size intercooler I have, I think I lifted off on the throttle during the high boost run and this leaned off the AFR and I think I was running too much advance (25-26 deg at 8 psi, 16-18 degrees at 17 psi).

Views anyone ?

Big thanks to Rob H for trailering me home.

Hope to be back some time late summer but realistically speaking, with all the DIY I've got on at home, it's looking like a winter job and missing all the summer shows.

Any recommendations on what pistons and rings to use next assuming the current bores clean up ?

Bummer.

Hey ho, shit happens.

Richard.

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Edited by turbominivanman on 27th Nov, 2010.

Minivanless, but reluctantly happy living with the decision. There'll be another one day.
http://www.youtube.com/profile?user=minimadmotorman#p/u

And a pic of the No 4 combustion chamber showing the grey 'metal spray' of the ali from the piston which has adhered to the chamber wall ........

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Minivanless, but reluctantly happy living with the decision. There'll be another one day.
http://www.youtube.com/profile?user=minimadmotorman#p/u

I really wish that we had met under better circumstances Richard -but I,m pleased to have met you at last.

The on the spot diagnosis was all wrong then and its probably the worst outcome you could have anticipated.

I hope you do find the time and inclination to sort it so that you not miss the summer meets.

Commiserations, mate.

is that 1.255 lambda and 221 mp on the 2nd graph richard?if so that could just be the cause of it all.in fact if you look about 3mm to the left ,it gets even leaner .

lots of sympathy chap , i was really hoping to be wrong when you asked me what wrong and i said ring lands , hopefully the other pistons are fine and another one for no4 .

im using the cast omegas ,and have had no probs.

did you burrette the head and piston for the cr ?

id have thought that 8.4:1 and 18 degrees and 17 psi should have worked ,but not if thats as lean as it looks .


hmm , looking at the lambda ,am i reading it wrongly , it seems to show 1.255 ...18.44:1 afr ,and seems a lot leaner a bit earlier ,id have thought that was too lean to run ,is that an accurate afr richard ?if so id suspect it was detonating a lot earlier in the run ,and just eating away at the pistons .


also looks like a max boost of 231= 19.26 psi.

i think your right on the backing off a little has leaned it off ,is the lean off pipe on there ? any pressure diff from the plenum to the manifold can kick this into play a tiny bit sometimes .

Edited by robert on 11th Apr, 2010.

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

o mate im gutted for you, all the hard work you put in to the van, was looking forward to see you at a few show this yr , good luck with the rebuild mate hope to see you back on the road very soon mate keep ya chin up mate ps put the diy on hold lol

Very bad luck Richard...

Looking at the plots, I agree with Robert, there are some very lean parts during the acceleration with additional leaning of as the throttle is partly closed.

I don't quite understand the first plot though, it seems to show it happening only at mid-RPM but it didn't happen when the throttle was part closed near peak RPM.

Having said that, The MegaLogViewer is very hard to read from a static photo so I may be reading it wrong....

Schrödinger's cat - so which one am I ???

absolutely gutted for you richard, all the work you have put i to your van, on the plus side ( i think) from the photos, the cylinder wall doesnt look badly damaged, would a light hone clear it up?
and number 4 cylinder runs the hottest of the 4 doesnt it, could be a contributing factor

Yes i moved to the darkside

Instagram @jdm_brett

Bad luck fella.

bad news mate..

Cheers for the comments guys.

I’m pretty easy about it really. It was going to happen sooner or later and I’m a twat for jumping to such a high boost without doing more fuelling work. Trouble is, I’ve been at the fuelling for more than 18 months now and have learnt a lot but this proves you can get it wrong quite easily.

More funny than anything is the way the wife took the news (bearing in mind I’ve been working on the Mini every year since 1998) and it’s probably the reason why I’m not gonna get too worked up over it. I was all for packin it in and taking the T3 off but she has convinced me to stick with it. I may however decide to go the GT17 route, not decided yet.

Just means a bit or work to sort it but no worries, it'll be done, I ain't gonna lose any sleep over it – as I said, shit happens but it was damn good fun - the adrenaline was pumpin (read 'brown adrenaline') !

I haven't got all the answers at the mo, but I'll try with the stuff I'm aware of at present :

Edited by turbominivanman on 11th Apr, 2010.

Minivanless, but reluctantly happy living with the decision. There'll be another one day.
http://www.youtube.com/profile?user=minimadmotorman#p/u

id stick with the omega cast ,they didnt shatter or fracture ,just eroded which is much better for bore surface .


''On the basis of approx 1 psi = 7 Kpa, 221 KPa = 17.3 psi. ''

lots of things to vary this ,but i tend to go 14.7psi=1bar , 221Kpa is 2.21 bar absolute.. 1.21 bar boost ,so 1.21 =17.78 psi.

Edited by robert on 11th Apr, 2010.

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

I guess it has to be pointed out that a single AFR reading doesn't represent what the inners and outer are actually doing.

The outers run lean and No4 is hottest (usually).

Richard, considering you have gone this far using MegaSquirt (rather than MegaJolt) for ignition and quite a few other things, have you thought about going for Fuel Injection ???

Paul S has put a lot of work into this and there are a few of us following on (albeit a long way behind in my case) but a lot of the issues you see in your graphs could be dealt with even with a simple SPI/wet manifold system.

Upgrade to MS2 (I think from previous posts you use MS1) and you could then join in with the siamese code with all its additional advantages.

Probably not the best time to suggest it considering what has happened to you but I felt I had to mention it.

Schrödinger's cat - so which one am I ???

i would adjust the fueling between 12.5:1 and 12:1

and aim for that which will give a margin for saftey due to that little extra fuel cooling the piston crowns

my next thought turns to a larger more efficient intercooler you need to install painted matt black to give its heat up 25% more efficient

You have all my sympathies dude :(

ouch

Yes i moved to the darkside

Instagram @jdm_brett

thats a point richard ...chin up ,could be worse!!

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

Sorry to hear it did a piston Richard, based on the coolant droplets I'd have put money on it being head gasket, so god knows what that was in the cylinder.

I hope you get it back together before too long.

James

Thats proper shit news mate!!

Hopefully it'll be back together soon enough.

Bad news buddy

Hopefully get it back together soon.

Minivanless, but reluctantly happy living with the decision. There'll be another one day.
http://www.youtube.com/profile?user=minimadmotorman#p/u

Minivanless, but reluctantly happy living with the decision. There'll be another one day.
http://www.youtube.com/profile?user=minimadmotorman#p/u

Sprox.

Great shot mate, makes mine look like a walk in the park to fix.

I guess it's a fair question but with the valve cutouts for the 16v bimmer conversion, the work on the piston crown leaves a shit load of sharp thin edges in the flame front.

In their own right, aren't these a source of detonation ?

Is there scope to smooth these out without affecting CR or ring land ?

Richard.

Minivanless, but reluctantly happy living with the decision. There'll be another one day.
http://www.youtube.com/profile?user=minimadmotorman#p/u

bore clearance is normally at the skirt at right angles to the pin ,rich ,around 2 to 4 thou , depending on piston material and usage .

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

Gutted for you this car is a great build maybe all that boost isn't needed.good lick with the rebuild

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

Minivanless, but reluctantly happy living with the decision. There'll be another one day.
http://www.youtube.com/profile?user=minimadmotorman#p/u