My unusual Piston failure. Diagnosis would be helpful to stop reoccurrence.

A bit of history to the failure on the day, it may help ?

Golf went to Bedford yesterday.

Out lap, I accelerated hard down the main straight, up to 132mph. The Golf has NEVER gone that fast before !

Anyway, did that outlap, then going round the first `flying lap`, I noticed the oil light flicker in the left handers. :shock:

Asked Matt to watch the gauge in the next left hander, I kept the revs low just incase.. "It went to zero..." was the reply. Oh. Bugger. Slowly back into the pits, oil gauge never flickered again. Checked and the oil level was low, doh

Topped it up, went back out.

Did 4.5 laps and it was fine. Oil pressure rock solid, NO noises or anything untoward. Well, apart from my lines and braking points. I need to relearn those.

Unfortunately, halfway round lap 5, we slowed for the hairpin and both heard a bit of a tapping noise. Slowed and it was noticeable, so slowly back into the pits. Oil pressure never flickered at all. Matt was watching it on all the corners and it flickered to 4 bar, but no lower.

http://www.youtube.com/watch?v=h-Sj0mKVhH4
[video=youtube;h-Sj0mKVhH4]http://www.youtube.com/watch?v=h-Sj0mKVhH4[/video]

Back in the pits and it was obvious there was something not right. A very unpleasant knocking / tapping noise. Obviously, first thoughts were lack of oil had caused a problem with the bottom end, but the noise was really tappets and from the top.

Listened with long bars and I was certain it was coming from the top.

Every single person at Bedford who came for a look, without exception said "Sticking tappet". That was without knowing what anyone else had said before them.

I said "what about a big end bearing ?" Nah, it`s definitely top end was the unanimous response.

That spurred me on to have a closer look. For the first time in YEARS, I didn`t have my compression tester with me .

So, Cylinder No1 to TDC, check marks on cams. All line up :thumb:

Remove Cams. Everything was HOT. You couldn`t hold a nut in the palm of your hand, it burned !



Remove followers.


Split followers. What a Pain in the backside that job is !


Check operation of spring / ball bearing. All appeared to be fine.


Washed everything in Petrol anyway and reassembled. Refitted cams, timed it up, removed plugs and disconnected injectors.

Turned it over to build oil pressure, then replaced plugs and restarted it. Exactly the same :sad:

By unplugging the injectors, it seemed Cylinder #1 lost fewer revs when disconnected, suggesting it wasn`t doing as much as the other 3.

Took the plunge and rang local GSF. They had some in stock. Talked her into doing them trade price for me and Andy Jebson VERY kindly drove over to GSF to pick them up whilst Hayley & Colin were left as the sole Javelin staff at the venue.

Removed cams again, removed followers from Cylinder #1

Fitted brand new followers, rebuilt it all again and restarted it.

Absolutely NO difference

That was day over, it was now after 3pm and I`d done 6 laps.

"well, at least you haven`t used much fuel" was one helpful comment.. lol




Looking at the data, on my 3rd lap of the day, I went 4 seconds quicker than I`ve ever gone round Bedford in my Golf. That`s without starting to nail the braking points and corners. Also without the boost and the spark optimised. !

I suspect I`ll be going through brake pads quicker in the future...



Today, I`d finished some other jobs and had a few hours spare.

I`d finished them and it was passed by 11:30. That meant I had some time this afternoon... I wonder...

Yep. I can get it out in a few hours. Easy.


Checked Mains, all good. This is the worst, a tiny bit of pickup, but nothing really...



That meant I needed to take the head off. All looked good. Absolutely NO signs of det on the pistons


Head looked fine too. A lot of carbon, but it was idling a lot at Bedford. No det marks on the head either.


Turned over the cams with the main pulley and each valve opened and closed with it`s partner and the same amount. Hmmm..

The oil looked OK, but has a tiny bit of metal. Let`s check the oil pickup. This looks familiar.


It`s a circlip for holding the gudgeon pin into the piston.


All good, apart from Cylinder #4


Other side is intact.


This is how it should look, sat in the groove on the piston.


The outer ring has broken off, allowing the pin to drop out.




The end of the gudgeon pin had been damaged.


Against the bore wall


A lovely groove down the side of the bore.



So. That`s it folks. A broken piston securing ring that allowed the circlip to drop out and the pin could then hit the side of the bore.

My foot had a bit of oil on the sole, I`d wiped it off, but must have missed a bit. I slipped off the clutch whilst going up through the gears, in the video, you can see both Matt and me look down at the pedal afterwards. This caused the Engine overrevved to 8,140rpm The rev limiter is set to 7,400rpm. The fuel and spark is cut, but too late. I`m not quite sure why that happened ? Maybe the throttle and boost meant it revved so quick, the ECU couldn`t catch it in time :fish:


I`m not convinced the overrev caused this, but I`ve included it for completeness.


I AM confident the circlips were installed and seated properly when the pistons were cleaned / refitted to my fresh block with new rings.


What next.

• I need to get my OTHER block refurbed. A hone at a minimum, but this one doesn`t need a skim.
  
• I need either 1 x 82.475mm Piston or a set of 4 if they are 82.48 which is the other common size.
  
• Mains and crank are fine. Obviously, they`ll all be removed and everything cleaned to remove any debris that has ended up in the oilways
  
• Head is fine, again, I`ll strip it to check it`s all OK, but I`m confident it`s good.

I suppose, in the scheme of things, it`s not that bad. I was lucky with the low oil pressure at Bedford which I`ll be sorting with better baffles. my Map was obviously good, there was NO signs of damage due to mapping.


I have 2 months to source the Pistons (or a complete engine if they are too expensive), get the necessary machining done and rebuild it before Snetterton.

Oh, and I`ll also have the larger injectors and ECU Boost control working by then



Obviously, I don`t want this to happen again, so I`m asking if anyone has seen this failure before and if so, what caused it ?

 

Sorry to see this nige. Could you afford to go to New low compression pistons to match what you need for the turbo. Or is it just easier and reliable to go with stacked gaskets, if that's how you are doing it.

 

I'd have to say manufacturing fault in the piston. Side loading on a gudgeon pin circlip would be tiny unless there was a substantial issue with a warped crank etc.

 

Sorry to hear that Nige. I'm sure you'll get it sorted.

Cant see revs doing it tbh. Ben had a skip when we were in the R.R. He missed a gear and selected 2nd instead of 4th at the end of the and it screamed but was fine. although a turbo motor has more energy.

 

That has nothing to do with "low compression pistons though" or stacked gaskets.

 

If you're on about the failure then I didn't say it was. I was on about the rebuild

 

ther is a correct way of postionin the circlip

the c should be facining down wards or up wards not like this c

at high rpm it can contract inwards thus jumping out ,

plus its been removed once and springiness in clip will proberbly be a bit weaker.

just a suggestion nige hope it helps ,

 

Looking back at your post mortem and knowing the history a couple things spring to mind:

The gudgeon pins and clips were disturbed and reused to fit the H sectioned rods.
The engine would have to run a custom calibration to control the higher cylinder pressures without dieseling or knock.
We also know a calibration was completed just hours before running the car at Rockingham week before last, where the car did quite a few laps. Det cans were used to develop the ignition calibration
The area of piston degradation requires quite a bit of energy to disintegrate like that.
Shock energy from det, can cause this and is usually commonly demonstrated by breaking ring lands.

Unknown:

What was used to refit the gudgeon pin clips?
Did the engine experience destructive det ( big shock load) between its outing at Rockingham and Bedford.
This engine was pulling over oil at Rockingham. Was any of this oil re routed back into the engine via an intake passage?

 

Ah got you!

Two MLS gaskets say 35 and are robust to sealing cylinders pressures worth up to 350lbft I have seen ( in excess of the torque required on this project). Plus they lower the CR sufficiently to raise the knock threshold closer or beyond MBT for a given road fuel.
Pistons are forged as std and can tolerate reasonable levels of det or heat.

Alternatively, you can purchase a set of CP, JE or Wossners and use 1 MLS at significant cost for say a 250lbft engine, when it has been proven those components are not required at this level.

 

Very old, rounded end screwdriver to push the pin into the groove, then worked that round until it clicked into place. I then use the end of the screwdriver to `rotate` the clip, this checks it is seated correctly in the groove.

The engine wasn`t run between Rockinham and Bedford apart from off/on the trailer for a spanner check.

The oil vapour was not rerouted back into the intake until Bedford, however, investigation of the hose from the catch tank and the inlet shows zero signs of oil residue. I believe the large amount of baffling / mesh in the catch tank meant no oil made it to the inlet.


Point of note. The clip didn`t fall out of the groove, the outer part of the groove failed, which allowed the clip to fall out and it wasn`t retained.



It is entirely possible that there was some installation error on my part, but if so, I don`t know what it was. Every clip rotated freely and was seated correctly. If not, I would have noticed and removed / reseated it.

 

Well that's solved that mystery then. I know it's not good news but at least you know now nige and can rectify, lots of scratching heads on the day with a lot of theory's but you never know till you crack her open.

I'm sure you will have it sorted soon and be back on track showing up more expensive machinery mate

 

if the clip was installed side ways , or close to that , I think its possible for the clip to vibrate under high rpm , the more it vibrates and springs backs on it self the weaker the clip becomes ,continuouse vibration would damage the piston eventually and fail.
also may be the extra pressure from the forced induction combustion is putting more pressure every where,could have been some wear in the piston and gudgen pin its self .
so what the hell nige you done a great job on that engine,proberbal cause was that one moment of over rev pushing the strength of componants over the edge ,
race teams spend millions on engines and some times they don,t even last three laps ,
just pick up a block piston and new cer clips , bung it to gether , and beat the hell out of it again .
good luck hope you get it fixed soon. do you think the bore will hone out or is it deeply scored .

 

The reason I asked that was in case a notch was accidentally marked on the piston creating a stress riser.

Marks such as seen in the picture below ( other side of damaged piston)

My bad for not being clearer on running interval. The hours of engine operation include the Rockinham sessions and the 6 laps of Bedford. Plently of time for the problem to develop.

Looking at the picture on the short engine, is there a close up of the piston area circled?

Agreed, however the area that disintegrated must have had some sort of thermal shock to expose the clip.

Doubt the installation procedure was wrong, other than refitting used clips, which has been done before without issue. I am of the opinion the area of disintegration went through a shock event. Was that event present during the over rev saga or during a brief high load enleanment period between the hours of operation is the question.

I will show one of the P and E lads in work the piston pictures and see what they think.

 

Good spot

Sharp edges a burrs will definitely cause stress risers. A thing that was drummed into me as an apprentice.

Seen it happen on a cut down engine mount. Snapped clean in half at the corner of the cutout.

 

Did the rods small ends fit perfectly with the pin. I found that I needed one H beam machined as it was a too tight on the pin.

 

Yeah, a really nice fit. Not slack, but not tight either.

 

Has the pin flexed and popped the clip out under the force ??