Oil Starvation / Bottom End Failure - Or Not?

[revilla]

Posting on behalf of a friend.

K Series 1.6, dry sump.

On recent track day he had an "off" and went backwards into a gravel trap. Was towed out and drove back in. Oil pressure was normal as he was towed out and for the next half lap or so.

Suddenly the oil pressure gauge dropped to zero, oil pressure warning came on and it started making the most horrendous rattle.

Video here, bit of camera vibration noise throughout but the event of interest starts very suddenly around 0:35. By 0:39 it sounds like a loud and clear rod knock bearing failure.

Inspection revealed that the capillary for the mechanical oil pressure gauge had torn out; it appeared to have snagged in the alternator belt and was pumping out oil under pressure.

So it seemed clear; oil starvation, catastrophic bottom end (probably big end) failure and rod knock noises. We suspect it was still OK when he was pulled out of the gravel as the oil pressure was reading normal at that point, but it seems to have been torn from the ties securing it and then caught in the belt later.

So today he stripped the engine, expecting to find torn bearings and shrapnel ...

Firstly he drained 5 litres of oil from it, so it hadn't lost much. The gauge would have dropped to zero and the warning light come on as soon as the pipe disconnected as there would have been no supply of oil pressure to the gauge and switch, but it seems not a large quantity of oil was lost and my guess is the pressure to the bearings would still have been OK.

Secondly he found the spigot bearing was breaking up, which explained why gear changes had been deteriorating but doesn't seem like could have been related to the load knocking noise heard.

Thirdly, this is what he found inside the engine:

Very little debris in the sump (the four letter word written in the oil wasn't there when he opened it up but may have summarised his feelings at this point!)

An apparently healthy crankshaft with nothing other than normal wear and tear.

Healthy looking con rods with no sign of blueing or overheating.

And this is the worst of the damage to the big ends, which looks like long term wear to me, possibly running a bit tight, but not the typical result of a sudden and catastrophic lubrication failure and not something I would expect to give a sudden onset loud knock.

There was no obvious play in big ends or little ends and gudgeon pins. In short it doesn't look to us at all like an engine that has suffered a major bottom end failure.

As for other possible sources of the noise, it seemed related to engine speed not road speed so probably not prop damage from the gravel, no obvious damage to engine mounts and all seemed correctly aligned. No gravel found anywhere (e.g. inside the bell housing). In fact nothing at all relevant found.

• Anyone got any ideas?
• Anything we are not seeing in these pictures?

 

 

 

[Blue C7]

Was the capillary tube copper and if so could that have been catching altenater pulls 

[Blue C7]

Sorry pulley

[CharlesElliott]

Yes, gravel or something else rattling against something. 

I know everyone goes on about mechanical oil gauges but I really don't like them - yet another oil outlet to leak, split or get cut. 

[ncm]

Can't get the video to work(need to sign in?) so I haven't heard the noise, but I was wondering if the engine still uses hydraulic tappets? If so, could the noise be from the cam clearances opening up if the oil is not filling the tappets??

Brian.

[Wrightpayne]

Brian,

I thought the same - pressure escaping via the open pipe causing lack of pressure to the tappets.

 

Ian

[Jonathan Kay]

Movie works OK for me: macOS, Safari, and a Dropbox account.

Jonathan

[F355GTS]

Sounded like the noise continued even after the engine was switched off, did rather sound like gravel rattling around the trnasmission tunnel perhaps?

[CharlesElliott]

I did half a lap of Donington in a race having lost my sump plug at the chicane. I went down the straight, round Redgate, down the Craner Curves and pulled off at Old Hairpin. No oil starvation damage.

[p.mole1]

I bet it is gravel in the flywheel housing it is easy for it to get in there.

[John Vine]

Hi Andrew,

Just listened to your video.  That noise sounds too high-pitched and "tinny" for big-end knock.  I'd suspect something adrift in the clutch/bellhousing area.  If the spigot bearing had indeed failed, the gearbox input shaft would be free to move around.  Could it be the driven plate was hitting something?  Are there any witness marks on the plate or clutch cover?  Could the remains of the spigot bearing have been rattling around?

JV

 

[revilla]

An update ...

As my friend had already purchased a replacement bottom end (before discovering that there didn't seem to be much wrong with the old one!) which actually seemed to be a little bit newer and fresher than his current one and had forged pistons, we rebuild his engine a couple of nights ago using the replacement bottom end and the original head. We pulled all the cylinders and resealed them and had a good look at everything. I had a good look at the old bottom end, the cams, the lifters etc. Absolutely no sign of anything significant at all. When it came to reinstalling it in the car he had a good look at the clutch and the inside of the bellhousing. No gravel was found inside and there are no witness marks suggesting either gravel in the bellhousing or contact between mechanical parts. So I'm afraid the source of the rattle is still a complete mystery. The spigot bearing had broken up with some rollers loose so it might just have been from there, although it seems an odd coincidence that the onset of the noise coincided exactly with the oil pressure warning. Hopefully he should be in a position to fire it all up again next week, so we will see then if all sounds normal I guess.

Thanks for all the input.

Andrew

[John Vine]

Thanks for the update.  A mystery indeed.

JV