M3 3.0 Engine failure - advice please

[jac-in-a-box]

Kids M3 looks as though its suffered terminal engine failure.

Really heavy and distinct knocking sound that rises and falls with engine speed - appeared to be coming from towards back and top of engine. Isolated each cylinder in turn by disconnecting coil packs and noise virtually disappears when No4 cylinder is isolated.

Initial thoughts are that it's either a big or small end failure....came to that conclusion on the basis that the load is off that cylinder when not firing. Am I looking at the right direction?
Anything else that can be done to determine cause of knocking? - I'm aware that attempting diagnose "noise" by description is difficult!

Engine has done 130k without any untoward problems; oil changes on time, right grade and oil level/temp was fine when knocking started.

With used engines going for around £1.5k he can't afford that option - baby on the way and house purchase means any spare cash has to go there.

Was wondering if it's possible to use a rod/piston from another u/s engine...swap rings from his duff piston to the spare IF it is a small end failure. If big end failure I guess a crank regrind will be needed with all the associated costs of bearings, gaskets and machining - too costly again I'd suspect?

I fear that the car is going to end up being broken for spares - which will be a shame as he's spent close to a couple of grand on cats, suspension, steering rack and countless other odds 'n sods in the last year.

Thoughts appreciated especially on the wisdom of using a "salvaged" rod/piston if it should turn out to be a small end that's gone.
Suggestions for any other not too costly repair options would be welcomed too!

[stevieturbo]

If it was a big end, it would knock regardless of cylinder firing or not.

Small end...cant say Ive ever seen a small end failure.

And if a big end has gone, the debris will have gone everwhere, requiring a total stripdown and clean.

[Munter]

If a lot of work has been done on the car. I'd consider picking up another M3 thats got issues other than the engine and doing an engine swap, and then sell the other bits on through owners clubs etc.

Sometimes it's just cheaper to throw an engine away and replace it than spend the time repairing it.

[jac-in-a-box]

Thanks for the comments guys - appreciated.

I've asked the same question on E36.com: http://www.bmwowner.com/forum/viewtopic.php?f=1&am...

Seems that my diagnosis of a small end failure could be about right - noise virtually disappears when run with spark plug removed.
Small end/big end, whatever, it's sounding terminal.

Be pleased to hear any other views wrt to an "economical" repair.

Merry Christmas all

[Holst]

jac-in-a-box said:

Thanks for the comments guys - appreciated.

I've asked the same question on E36.com: http://www.bmwowner.com/forum/viewtopic.php?f=1&am...

Seems that my diagnosis of a small end failure could be about right - noise virtually disappears when run with spark plug removed.
Small end/big end, whatever, it's sounding terminal.

Be pleased to hear any other views wrt to an "economical" repair.

Merry Christmas all

Ideal time to get the engine out and have a look over the holidays.. if not ideal weather

[stevieturbo]

IF...big IF

If its only a small end, rod/piston replacement would sort it.

[jac-in-a-box]

stevieturbo said:

IF...big IF

If its only a small end, rod/piston replacement would sort it.

That's what I'm hoping Stevie; once I can establish it is a small end. It's been suggested that once the engine is out (it's coming out one way or another for repair or breaking) that the rod assembly could be replaced through the bottom of the lump once sump, crank, front end etc is removed - saves the costs associated with h/gasket, head bolt etc replacement.
Labour & time intensive, but do-able... unless anyone thinks any different?

Could be a little light at end of the tunnel!

Edited by jac-in-a-box on Wednesday 23 December 12:20

[Pumaracing]

jac-in-a-box said:

It's been suggested that once the engine is out (it's coming out one way or another for repair or breaking) that the rod assembly could be replaced through the bottom of the lump once sump, crank, front end etc is removed - saves the costs associated with h/gasket, head bolt etc replacement.
Labour & time intensive, but do-able... unless anyone thinks any different

Whoever suggested that has never stripped an engine in their life because a piston/rod can't ever come out through the bottom of the block. The main bearing saddles are in the way. That appears to suggest you've never rebuilt an engine either so are you sure rebuilding an M3 yourself is a wise idea? It ain't exactly an old A series Mini engine.

Before you do anything though I suggest a compression test to at least find out if the rest of the bottom end and valve seats etc are in decent shape. It may not be a big or small end knocking anyway. However any serious knock pretty much mandates a full rebuild, especially at that mileage, so it's unlikely to be within your budget whatever the problem unless you just want the cheapest possible fix and then get shot before the next thing breaks.

Small end failure is almost unheard of in modern engines with modern oils; I've not seen one in 30 years of building race engines and anyway the noise tends to be more like a tappet rattle than a knock. I've seen big ends worn down to the shell backing and they still didn't make any appreciable knock unless under heavy load but certainly a very badly worn one, or if the shell has already spun, would make a knocking noise and it would reduce with no load. I've certainly never seen one bad enough to make noise where the crank wasn't already shot and needing a regrind and that generally means that debris has already got into everything else - oil pump, lifters, bores etc.

It does remind me of yet another of my store of weird engine related tales though. Someone, I'm damned if I can remember who though, telling me about trying to rebuild an engine himself. The crank looked ok and miked up correctly on the journals he checked, which sadly wasn't all of them. Anyway with a set of new shells in and all the other necessary bits it went back together only to have no oil pressure. After much buggering about with no solution in sight eventually it all came back apart again. Turned out some cheapskate had just had one or two journals reground after a previous crank failure and had used the relevant shells from two sets of different sized bearings to put it back together again. Not spotting this and using just one set of standard shells had led to the reground ones having 0.25mm extra clearance which didn't help much. Moral of the story - measure everything - never assume.

Oh now that reminds me of another. I did a ported head for a guy's engine many years ago. He was a complete oik on a council estate somewhere who lived on the dole and did a bit of "debt collecting" i.e. beating people up for money they owed, on the side. If I'd known at the time I would have stayed well clear but someone else had already pointed him my way for race engine work. Anyway so I later find out he eventually rebuilt the engine himself but as above no oil pressure at all. Given the most accurate measuring equipment he owned was probably a wooden ruler this might not come as a surprise. So he had the crank checked again by someone else, rebuilt it all with another set of new shells of the correct size and still no oil pressure. Another rebuild with a different oil pump but still no joy. After a third rebuild with a high pressure "race" pump and more new shells with no change in the outcome he finally took it all to someone with a larger brain and better measuring equipment. The main bearing housings in the block had been line bored from new at the factory to the 0.4mm oversize that is commonly used for Ford blocks that don't clean up properly on the normal line boring op or have ended up out of spec when they get checked later.

The shells would also have been stamped as such if he'd thought to either keep the original ones or look at them properly or frankly even realise that the new shells he kept fitting just fell into the bearing saddles like a dick in a drainpipe instead of requiring a push and a click and then lining up exactly with the split line in the block and caps. Still, as my mate says, you can't educate pork.

[Marquis_Rex]

jac-in-a-box said:

stevieturbo said:

IF...big IF

If its only a small end, rod/piston replacement would sort it.

That's what I'm hoping Stevie; once I can establish it is a small end. It's been suggested that once the engine is out (it's coming out one way or another for repair or breaking) that the rod assembly could be replaced through the bottom of the lump once sump, crank, front end etc is removed - saves the costs associated with h/gasket, head bolt etc replacement.
Labour & time intensive, but do-able... unless anyone thinks any different?

Could be a little light at end of the tunnel!

Edited by jac-in-a-box on Wednesday 23 December 12:20

My Challenger has spun a shell. As soon as I suspected this- I stopped running the engine. There was a nasty big end knocking noise- and the oil pressure took an age to build up on starting. I found metalic parts which had been ground up under the valve cover. Did the oil pressure light take ages to go out when the car starts? When it's not firing- I can imagine the noise reducing because your cylinder pressures and therefore loading has gone down. Small end failure (unlikely) wouldn't show up with a lazy build up of oil pressure (due to excessive clearances). Don't run the engine anymore as you can throw a rod and really screw things up.

I also have an E36 3 litre M3 engine which I bought very cheaply (and use as a general ornament) because it spun a shell- I don't know if it's a common occurance on these. Everything I've heard about these older M3 engines has been that they're very durable.

[jac-in-a-box]

Pumaracing said:

Whoever suggested that has never stripped an engine in their life because a piston/rod can't ever come out through the bottom of the block. The main bearing saddles are in the way. That appears to suggest you've never rebuilt an engine either so are you sure rebuilding an M3 yourself is a wise idea? It ain't exactly an old A series Mini engine.

I'll defer to your much vaster experience Puma R!
You're right though engine building isn't somethng I do on a regular a daily, weekly or even 10 yearly basis Had a go at a few in my younger years but nothing approaching the (relative) complexity of an M3 motor.
The possibility that a piston couldn't be pulled or replaced through the bottom end hadn't occured me - even on the rare occasions that I've had a dabble with engines I've replaced pistons via the conventional route and never found the need to adopt an unorthodox approach.
Your words of wisdom are appreciated!

However, considering the engine is pretty much useless just now and if a piston rod/assembly can be picked up, it'll be a case of nothing ventured, nowt' gained...local BM specialist is available for advice, have access to special tools if needed and liberal doses of enthusiasm from younger one is on tap.
Has to be worth a go dependant on what's found when it's pulled apart...engine is coming out regardless for possible repair or breaking.

Edited by jac-in-a-box on Saturday 26th December 14:40

[jac-in-a-box]

Marquis_Rex said:

My Challenger has spun a shell. As soon as I suspected this- I stopped running the engine. There was a nasty big end knocking noise- and the oil pressure took an age to build up on starting. I found metalic parts which had been ground up under the valve cover. Did the oil pressure light take ages to go out when the car starts? When it's not firing- I can imagine the noise reducing because your cylinder pressures and therefore loading has gone down. Small end failure (unlikely) wouldn't show up with a lazy build up of oil pressure (due to excessive clearances). Don't run the engine anymore as you can throw a rod and really screw things up.

I also have an E36 3 litre M3 engine which I bought very cheaply (and use as a general ornament) because it spun a shell- I don't know if it's a common occurance on these. Everything I've heard about these older M3 engines has been that they're very durable.

Oil pressure appears to be fine, no guage just the warning lamp and it goes out as soon as the engine starts even in this freezing weather. I don't think there are any oil pressure problems.

Doesn't appear to be any debris in oil system either which I would have expected if a bearing had failed?

It seems from asking on other BMW fora that small end failure isn't an unheard of failure. Main bearings spinning on on the M3 3.2 lumps is a more common occurence which is why some owners fit ARP bolts to help avoid.
Main and big end failures are infrequent occurence's on both the 3.0 and 3.2 variants...guess the majority of those come down to an age group of ownership who don't understand the need for decent oil/correct oil grade and regular changes - or don't understand the expression "mechanical sympathy"

Sadly for junior, he's done all the right things and it's still bit him hard!

[stevieturbo]

How do you know there is no debris on the oil system unless you have the block totally stripped and checked the oil pump and all oilways ?

[jac-in-a-box]

stevieturbo said:

How do you know there is no debris on the oil system unless you have the block totally stripped and checked the oil pump and all oilways ?

I don't; hence the decision to repair is dependant on what's found once the engine is out and the bottom end removed.

The appearance of no debris in the filter led to my assumption that no bearing failure occured - well, it's a reasonably good sign isn't it?

[rash_decision]

Would it not be worth taking the rocker cover off and checking the top end is all ok before pulling engines out??

I've experienced weird knocking noised on previously owned cars and fortunately they were top end related. The latter "two" engines. had snapped rockers, coincidentaly BMW's, the older E30 325i Sport. For all the time it will take, I would say it's worth it.

[jac-in-a-box]

rash_decision said:

Would it not be worth taking the rocker cover off and checking the top end is all ok before pulling engines out??

I've experienced weird knocking noised on previously owned cars and fortunately they were top end related. The latter "two" engines. had snapped rockers, coincidentaly BMW's, the older E30 325i Sport. For all the time it will take, I would say it's worth it.

Thanks for your thoughts
Already had a look at top end - cams act directly on valves so no rockers...would've been good if it were something so readily easy to see!

[Justin S]

I don't see how fitting uprated big end bolts will 'prevent' bearing shells spinning. This is usually caused by overheating shells caused through lack of oil or worn journals causing low oil pressure, then white metal pick up and shell spin. The the inevitable knock. I believe, correct me if wrong..............
The best bet is to pull the motor out and take the sump off. I would have thought to pull the sump on an M3 in situ, would require subframe removal and steering rack etc and then see if you have rod to little end slop on that No 4 piston.

[Marquis_Rex]

Justin S said:

I don't see how fitting uprated big end bolts will 'prevent' bearing shells spinning. This is usually caused by overheating shells caused through lack of oil or worn journals causing low oil pressure, then white metal pick up and shell spin. The the inevitable knock. I believe, correct me if wrong..............

Can also be caused by metallic debris being sucked through the oiling system-which is what has happened in my Challenger I suspect.

[metcalp]

no4 big ends the common one to spin a shell. oil light can still show good pressure but piston makes contact with cylinder head and you would think its the top end. drop oil and see all the white metal. big bill mate sorry

[jac-in-a-box]

metcalp said:

no4 big ends the common one to spin a shell. oil light can still show good pressure but piston makes contact with cylinder head and you would think its the top end. drop oil and see all the white metal. big bill mate sorry

Thanks for your contribution...any thoughts on why No4 is usually the culprit? Would have thought the bearing would have to have virtually disappeared to allow piston crown to contact head!!

As mentioned earlier, the cylinders have been checked with a borescope and no damge to bores or pistons can be seen.

Looks as though problem is about disappear...junior has been offered £3k for the car as it stands, has to be the most pain free option from our POV!

[Welshbeef]

£3k on the table offer I wonder is it really worth going for another car when/if the one he has is a very good one avliet just needs new engine?