Wiped center main bearing
Turbo Mini Forums

Ok so i have had problems with excess noise and vibration under load on the engine.

Today I pulled the engine and split it from the box. There is a lot of copper/ bronze swarf in the sump. My initilal thoughs were it was the diff planet gear thrusts, but after pulling the diff apart and finding nothing wrong, I turned my attention to the engine. I pulled the center main first to find the bearing had wiped. The copper back has spread on both top and bottom. I pulled the big ends and number three main bearing and they are in very good condition. I have still to check number one main bearing. The crank is still very servicable without the need for a re grind, which makes me think that there is still lubrication there. Crank thrust bearings are perfect!!

Perhaps the engine is suffering bearing starvation at high RPM? The crank is a cross drilled jobbie and the bearings are the grooved top plain bottom VP2 veriety.

Whether this is relevant I dont know, but when I first started up the engine after fitting the BMW oil jets, the oil pressure gauge fluttered severely, but I had oil pressure where I previously did not. I thought it was down to taking the oil pressure feed off the feed to the head and using a 1/8" bore braded hose. I disconnected untill I got round to fitting the small bore capilary. Any one any idea why the oil pressure fluctuated so much? Im guessing it might have something to do with this failure.

The only other thing was that the engine was fine untill it went on the Dyno at RE Performance in Bury. The initial test run showed 85 at the wheels, then the power run shortly after showed 65, down 20bhp, now he did the first test run in fourth yet did the power run in third, can't understand why. Anyway, we let it cool and did a final run which showed 73 at the wheels, still 12bhp down. Initrial thoughst were that the nearside wheel bearing was getting tight, it was on its way out, but Even I was not convinced that one wheel bearing sapped 12bhp. Leaving RE performance it was instantly noticable that there was excessive noise and vibration, so I nursed trhe car home.

I suspect this failure happened while on the dyno, fine going on and fucked coming off

This crank was used previously in the 1400 100bhp 100lbft for nearly 2000 miles without issue, and used in this engine prior to fitting the BMW oil jets, for 1200 miles, two dyno tuning sessions and one dyno shoot out, with no issue. only 300 miles after the rebuild and the center main fails, yet not much has changed on the engine

This is obviously an partial diagnosis, as I have yet to pull the the crank completely from the engine.

Any ideas?

Edited by Sprocket on 15th Jun, 2009.

Bummer :(

its not something like not enough bearing crushfrom the centre main?

has the bearing actually spun or just smeared?

Oil too hot?


also didnt you have oil press issues on this lump a little while ago due to the zetec jets? i asume you changed the bearings when you changed to bimmer jets.

i cant comment much as dont know enough detail to help diagnose, but i cant see how a poor dyno tune can affect one main bearing in an engine and not the others, and the slant your post has hints towards an alternative view.

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

Get the crank magnafluxed before even thinking about re-working it. I wonder if this would also show a potential problem.

Oil pressure fluctuation is something I always got with the MS pump; prior to the powerflow unit. Not sure what you're running however.

In this case however; we'd need more info on the 'main' hose - did you tap off the gauge hose at the head, or at the block end? Are we taqlking -3 or -4 hose?

Did you check the internal diameter of the mains after the block was line bored?

Piccys ???

I'm surprised if the top half is as bad as the bottom.

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

I had a centre main wipe after only 10 1/4 mile runs last year, I cant explain that either

Paul

I seriously doubt it!

measure the circularity of the centre main once the crank is out ?

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

a bearing can fail over thousands of miles, never mind 40, could comfortably be a coincidence.. being rough on the rollers and unsympathetic to your gearbox doesnt affect your main bearings.(unless it was buzzed or ran low on oil/overheated)all im saying.

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

which revs did you pull on the dyno?
I think about crank flex,
what's your clearance on center main?

Right then

Crank DOES need a regrind, in my opinion There is some blue'ing of the center journal only on one part with some ridges.

What I dont understand is that if the center bearing has been starved of oil, why are nuber 2 and 3 big end journals perfectly ok?

I will check the bearing housing ovality, but I am confident that it is perfectly OK.

OK so I will also provide another piece of information that might have a big bearing (excuse the pun) on the whol episode. After I had put the engine back in the car after rebuilding it to fit the BMW oil jets, I found what looked like the oil pickup pipe gearbox/ engine O ring lying on the floor. I was sure it was one I had used, what with the episode I had with the baffle plate. Oil pressure was good, all be it fluctuating on the gauge. It was left as was.

Engine RPMs experienced were no greater than 8000rpm.

I'm not sure if its possable to regrind a hardened crank, but im taking it to my man tomorrow to get his opinion. The other option is to get another crank.

I am considering using the grooved bearings all round

Fast Carl, you have a PM

Edited by Sprocket on 27th May, 2009.

I,M puzzled as anyone, but you did say earlier that you re-used the bearings after a stripdown,which is something I would not do,personally.could this have any relevance do you think ?. Not trying to score points, just offering suggestions as the answer is still not found.

colin , in case this helps .

iv just taken a 1098 engine apart , and it had a v worn centre main,also it had worn the rest of the mains but not as badly ..the crank is cross drilled and the big ends were fine .

theory is that the big stroke on the 1098 centifuges oil out of the crank , and starves the mains , so the cross drilling is to stop this happening by putting the oil outlets on the big ends at 90 degrees to the flow path ..

so maybe your engine had fluctuating oil pressure ,the mains wore and the oil centrifuged out to the big ends ,so saving them damage ,and the centre main wore the most ,so was the first to get to the point where the friction/ovality was sufficient to create a further drop in localised oil pressure, and got so hot it eradicated all remaining soft bearing material .

Edited by robert on 27th May, 2009.

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

Wow...

If all the bits around the first two piccys are the remains of the shell linings, you are very lucky not to have had a catasrophic failure...

Being piccy, it's lead bronze, not copper, that is behind the lead indium, but to destroy top and bottom shell and still be running is....... unusual !!!

If all the other shells (main and bigend) are OK, I would not suspect oil starvation - if the feed to the centre was starved then 2/3 bigend should have failed as well...... do their journals look worse than 1/4 ???

If all the other journals and bearings are OK, I would think that pair of shells were not fitted right (sorry, something like the tab holding one out of place, or the cap not clamped down right) or the crank is bent....

Just my thoughts.

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

i'm thinking along the same lines as Rod,

perhaps the bearings havs lost their "spring" during their first use,

how do the bearing cap dowels fit? any signs of bearing shuffle?

Could the main cap have distorted clamping the journal too tight, causing heat and friction causing failure?

Paul

I seriously doubt it!

could it have been left some small pieces of metal from the machining for the BMW jets in the oil gallery? This could have found its way to the bearing, and on their way caused oil pressure issues?

could it not have been a drop in pressure on the centre main caused by the new jets on either side 'robbing' it of oil

133.5 bhp 123 lb torque 116mph @6640rpm 9.5psi
Shakespear RWYB 14.995 91.83mph

It could be the bearing cap, I dont think it has moved after all there are now four bolts holding it in place. It was a loose fit on the dowels when I removed it, it wasn't when it went on.

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