Potential Piston Problem

[the_stoat]

Has anybody seen this on a piston before and what is the cause? It seems to be pitted and as if it has corroded. Think my rebuild budget is about to take another hit. For information they are Accralite forged pistons in a C20XE engined Westfield.

[the_stoat]

Max_Torque said:

One two three, all together now "DETONATION"......... ;-)

Thanks for the confirmation. Really annoyed at the amount of cash handed to an 'expert' for mapping. Had the car checked somewhere else and they did comment it was rather lean and required adjustment. Never mind this will just take me to 200% of expected budget!

[the_stoat]

stevieturbo said:

Looks like the piston has stood well though

That is what confused me as the engines I have seen with detonation before were in a much worse state.
Oh well I now have 4 interesting paper weights.

[the_stoat]

Pumaracing said:

Lol, nope. Never. Ok once or twice. Well several dozen times. I think it might be aluminium worm, otherwise known as detonation. If you get an infestation of those little buggers they eat the combustion chamber and piston crowns away. The easiest cure is a significant reduction of ignition advance or compression ratio.

The other cure is to get it set up and mapped by someone who actually knows what they are doing as opposed to claiming to know.

[the_stoat]

jontysafe said:

I had this aforementioned worm on my YB motor as well, it's an expensive bugger to sort. Took my VERY expensive cylinder hear with it as well as well as scoring the bore with melted piston parts and doing the big end in. I feel for you.

Was in a bloomin Westfield as well.

Thanks, I was using a new block anyway and the head is OK so I was much luckier than you. A quick phone call and whimpering at another payment for the engine and it will all be back to a state where I can build the engine. Plan is to assemble the engine next weekend, get it run in then mapped in mid-April.

How is yours going?

[the_stoat]

Max / Puma - Thank you very much for the information it has been great to understand the issue in more detail.

Puma the engine will never be run in the previous configuration as I was pulling it apart to ironically build for increased reliability. The previous spec had standard rods and was running hydraulic lifters, so the standard valve train. I always had the nagging doubt that the standard vale train was too close to the reliability ceiling for comfort, as on track it would regularly see up to 7500 RPM. The future spec is as follows and any advice on questions to ask to make sure I do not get to the same position again.

Engine is a Vauxhall C20XE, it is on ITBs and will be run in a Westfield. Cam spec is as follows:

Expressed Period: 294°
Inlet Fully Open: 106° ATDC
Inlet Lift @ TDC: 0.165”
Exhaust Fully Open: 104° BTDC
Exhaust Lift @ TDC: 0.125”
Lift: 0.458”

Probably obvious to you guys but will be on solid lifters, expected rev limit to be 8500 RPM.

Not sure on the compression ratio yet as will need to decide which pistons to buy, likely to be around 11.5/6:1 (as per cam manufacturers recomendation) but will work it out properly when I get the head back from the machine shop. For info the previous compression ratio for the damaged pistons was 11.1:1. It will be 2 compression ring pistons as opposed to slippers.

Again in my quest for reliability I have worked on keeping temps and pressures stable. It is dry sumped, running a water / oil heat exchanger and a decent radiator. On track oil temps are stable at 97 degrees and water at 93 degrees. On the road both figures are about 6-7 degrees less.

Annoyingly as the car is in bits I cannot power on the ECU to get the ignition data.

[the_stoat]

Sorry by stock valve train I meant everything bar the cam shafts. I would have to rummage in my records for the cam spec but it was aligned to the compression ratio and the specs were given to the all that mapped it.

[the_stoat]

Pumaracing said:

Ah! Hmmm.

Anyhoo. The Kent AST1627 you've chosen, if I'm correct, is a sensible general purpose grind. Not too intractable. The CR suggested should be fine with it. I can't see this spec posing the slightest problem for any competent mapper.

You might want to try and get the coolant temp down a tad. Low 80s would give you a bit more leeway on mapping settings and reduce the risk of det.

Thanks for the advice, it is actually a QED 450V and was chosen for tractibility. Have a lower temp thermostat that I can test for water temperature reduction.