Wiped center main bearing
Turbo Mini Forums

Colin IMHO this looks like classic Oil starvation. I'm not 100% but looking at the pic again are they small scores i see in big end 2 and 3 ?

another thing I would like to note is in that Video is that circa 8000rpm near the end. IMO these cranks are not up to 8000rpm for this kind of time they will last a short blast to 8K but crank flex at these speeds is immense and he seemed to hold it a very high rpm for much longer than I would like !

Edited by robert on 28th May, 2009.

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

So, before you have anythign else done to that crank, i hope you're going to get it checked for straightness and crack-detected. No point throwing good money down the drain.

Dave's right.

i'm really not knowledgable on cranks but i rev mine to 7000 quite regularly, not been cross drilled and not been rebuilt in about 5 years or more.

also dont miglias rev to about 8000? and is the 998 crank that much different since the sevens i know rev to 10,000

Oh come on Sprocket, even I remembered to put my o-ring in

New crank, new bearings, new oil pump, Block off to the machine shop tomorrow to get the center main honed.

Pistons 2 and 3 have kissed the head. no damage to either, just no carbon where they touched. That goes to show how much wear was in the center bearing and how much the crank flexed, its a whole BK450 gaskets worth !!!

This is my first major failure, and while its a bummer, its also quite pleasing fixing it, though I dont want to have to do it again!

On 31st May, 2009 Sprocket said:
New crank, new bearings, new oil pump, Block off to the machine shop tomorrow to get the center main honed.

Pistons 2 and 3 have kissed the head. no damage to either, just no carbon where they touched. That goes to show how much wear was in the center bearing and how much the crank flexed, its a whole BK450 gaskets worth !!!

This is my first major failure, and while its a bummer, its also quite pleasing fixing it, though I dont want to have to do it again!

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as a beginner / not have much knowledge on engine building and reading lots of comments on here is shocks me how much money is takes to build a good A series and the amount that go wrong. I know most of you guys are taking them to very high spec but it seems a load of cash for the return.

I hope you get it sorted.

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

Colin this is very intresting, I was talking with a very well respected A series engine builder he is also a well renowned producer of steel cranks. He was of the opinion that t
hese 4 bolt main caps are not the be all and end all. He mententioned That the only Two Major crank failures where under these main caps!!

Was slowly losing oil pressure so took the car round to a mates for a second opinion after taking it for a drive he said there was a ver slight bottom end rumble. Turned out all the mains were on the verge of total failure. On removing the caps and extracting the bearings you could see where large sections of bearing material had just come away.

On showing thes to two diferent engine builders they both said the same thing Fuel contamination of the oil and or moisture in the sump.

Hope this info is of use.

Own the day

That's also intresting didn't you have an injector problam with this one colin ?

That's also intresting didn't you have an injector problam with this one colin ?

Ive done 1500 miles since the initia fuel problem, and its been stripped down completely since then and it was fine.

For the last time, this has only happened in the past 300 miles AFTER the rebuild to fix the oil jets

Colin its all well an good saying you striped this down 300 miles ago but you did not change the bearing shells so from a contamination point of view you efectivly done an oil change .

not sure wherew you are coming from

I built the engine up in october, had fueling problems in novemeber getting it running, using cheap shitty oil, replaced the oil with running in oil, replaced the oil with Millers CTV, all before the dyno shoot out at the begining of feb. engine stripped and rebuilt with cheap shitty oil run up to temp and then again the oil was changed to Millers CTV.

Im not sure how re using perfectly servicable bearings will cause oil starvation after only 300 miles when the exact same bearings were in use for 1200 miles without issue



Center main bearing housing out of round by -2 thou and number 3 bearing out of round by +1 thou at the mating faces. Block is now waiting to be line bored, and honed, Again,

I agree, fuel contamination can be a problem,but not in this case, given the number of oil changes.BTW I dont agree with using "cheap shitty oil" on a new engine. I understand the theory that it helps everything run in,(ruin in ?) but by the same token the first few hours running are probably as critical as any,so deserve decent oil, at least API SF grade.

Sprocket seems to have identified the problem as being main bearings out of line and it makes me wonder how many other centre mains could be, either from inaccurate machining or distortion from high revs,overheating oil etc etc etc

The cheap oil was only used as an initial flush in both instances. Once the engine was running the oil and was changed for the running in oil The engine saw no load with the cheap oil

Im not convinced the problem was the alignment of the bearings, as Carl suggests. Its probable that the lack of block to box O ring.

I asume the block was honed with the mains torqued up?