My first experience of Lots Of Trouble Usually Serious

[StephenH]

After 4 years of Europa ownership I have run into my first actual problem of note with my S2.
At a track day today with the local Lotus club, all was going well until I lifted off to allow a faster modern to go by.
While off throttle there was a bit of a strange rattle then a cylinder went missing.

Looks like one of the pistons has gently tapped a plug gap closed, fortunately without catastrophic failure.
Those small shiny flecks are aluminium..... but no big bang, cloud of smoke or heavy breathing....
Engine has a light knock so I suspect a big end failure is a possibility.

Probably lucky it was when I had dropped revs down and was off throttle.

[BDA]

Yikes! I think you're probably right. Hopefully the damage to your crank and block is minimal. Keep us informed.

[jbcollier]

Off throttle at high revs meant that the rod could move that wee bit further.  You might want to use a slightly thicker head gasket.

[buzzer]

Back luck!!
 keeps us informed of the actual failure. I wonder how much more the piston has to move to do that!! I would suspect more than just big end bearing failure to get that movement. could take bets on what the failure is....also maybe a couple of bent valves. piston crown detached from rest of the piston?
But certainly catching it like that may be a blessing in disguise rather than a con-rod through the block!!

[EuropaTC]

When I had flecks of Al on a plug it signified a hole appearing in the piston....   (motorbike)  Now that was serious, I had to push the bike 10 miles home due to the mobile phone not having been invented and me being in the middle of nowhere !

It seems a lot of movement for a piston, how close are they to the crown on the Renault engines then ?

[StephenH]

When I had flecks of Al on a plug it signified a hole appearing in the piston....

You have called it correctly.
Looks like I have managed to induce some detonation where there hasn't been any previous sign

Initial investigation shows top blown top out of the piston.
Only change was to swap to a different plug (NGK B8ES from Bosch WR7CC) but that is a step colder rather than hotter, so I'm not sure about that being root cause.
I can't get a good look at the other piston crowns but there does seem to be some sign of detonation.
So either I just got it wrong on trying another plug (the Bosch plugs were fouling at low speed) and the heat range or there is another gremlin that has crept in or maybe dodgy fuel.
I generally run up to 6300-6500 max and was circulating about 0.5sec slower than last time this circuit as I was trying to smooth out technique.
But looks like it leaned out down the straight then completely when I lifted and melted through.

Anyhow..... I don't have this car to look at it so will sort out and use as an upgrade one way or another.

[EuropaTC]

Ouch.   

But there's always a silver lining to these things, now you have the perfect excuse to build a better toy !   

I can't imagine it's the plug change causing the problem.  Unless you've changed carburetion or it's been inadvertently changed by something going wrong I'd be wondering about fuel, especially if there are signs in the other bores.   But honestly, I've no idea, my escapades were caused by the stupidity of youth. (which was pretty normal for me back then )

It'll be interesting to see how you go with this one, especially if you can pinpoint the causation. 
Brian

[StephenH]

Managed to break my borescope before I could get a good look at the other cylinders, but the quick look I got seemed to be a shiny spot on another piston in the same place as the failed pot.
Short of some weird ignition/dizzy fault I tend to suspect fuel or some sort of fuel related leaning out (fuel pump/pressure?).

Will know more when the head comes off, have decided to have the local Alpine specialist look at resurrection as otherwise I won't get it running again for several months at least.
Once we get a good look I'll make a further decision as to how it goes back together.
If the block has to come out of the car then I have some ideas.

[Certified Lotus]

Where you running the car on the track with a low fuel amount in the tank? That usually causes a lean condition when cornering hard. It can happen quickly and the result is a blown engine.

I found out the hard way on my track Lotus Exige. After rebuilding a new engine I installed a baffled fuel tank and a fuel surge tank. Never had the problem again.

[StephenH]

No lower than I have run many times and more than at the same track last month. I was running longer sessions than last time but still only 20min.
Other plugs (about 90mins running) look OK for heat and mixture, not a lot of colour but certainly not cooked.
There is long 1g+ turns on this circuit, so could be a potential pickup issue. Possible I might need further attention to the fuel system.

[BDA]

By "not a lot of colour" do you mean the insulators were white or almost? I would consider that a sign of a lean mixture.

[jbcollier]

Modern fuels do not colour plugs the same as older fuel formulations did.  In compensation the motorsport gods have given us wideband O2 sensors.  Fit one (or four) and find out what is really going on.

What is your total timing advance at high rpm?

[LotusJoe]

Sounds like to much advance on the dizzy. Or to low an octane for a given advance. I suspect the closed gap on the plug is from something rattling around on top of the cylinder.

[StephenH]

By "not a lot of colour" do you mean the insulators were white or almost? I would consider that a sign of a lean mixture.

Just a touch of tan.

Modern fuels do not colour plugs the same as older fuel formulations did.  In compensation the motorsport gods have given us wideband O2 sensors.  Fit one (or four) and find out what is really going on.

What is your total timing advance at high rpm?

Good idea on the wideband, was something for the future previously, now will be part of the task.
Headers need a birthday anyway so will weld in a sensor bung for sure.

From memory about 32deg total (10deg static).

Sounds like to much advance on the dizzy. Or to low an octane for a given advance. I suspect the closed gap on the plug is from something rattling around on top of the cylinder.

Will have closer look with head off, plus check the distributor, fuel is from my 'normal source' but always a first time.
Rest of fuel system will also get a once over.

Pretty sure the aluminium that used to live in the crown of the piston was dancing around under the plug.

[jbcollier]

Normally I would say you were ok with 32° total advance.  What compression ratio are you running?