Engine Gurus . . . !

[mphatc]

Attached are images of a recent engine failure . .

not a common happening to a BMW S52 . . no history of overheating . .
but a heavily track used engine.

I thought some of you might have an idea what may cause this. Maybe some American engines do this? :hyper:

There are no signs of an over rev or contact between the valves and the pistons on any of the other cylinders.

The customer is trying to blame this on me . . or my shop . . FWIW we did not build the engine, no one has ever had the cylinderhead off. It was as built by BMW AG 8 years ago.

Mario

[SideshowRob]

What did that piston look like?
I've seen those gouges before, but I'm more of an expert at destroying 2-strokes.

[Barry Eller]

What year and liter engine. How many miles? Track Run, Racing engine? Broken valve? Heads appear to have a lot of burned oil and carbon buildup. Timing chain or belt? What did you/your shop do for this customer? What does your customer think happened? What was he doing when this happend?

[McGary911]

Wow, that's a mess. Looks like the valve may have blown off, bounced around in the chamber a bit, broke up, then been blown out the exhaust? I haven't had a BMW since my old 320i. What do they put an S52 in?

[mrfixxall]

i had one do this on a 535 last year,,,i found that it broke on deacceleration...
too much slack in the timing chain...cyl#1 it put a hole in the top of the piston too...if you deside to fix it check the cylinder wall for cracks because the broken valve wil rock the piston to ond side and crack the cylinder....
by the way i junked the 535 too much $$$$$ to fix...

[MOP]

Mario the damage looks like the seat came loose first, it in turn broke the valve. I wish I had photos of some of the old AQ Volvo 4's I had two that looked about the same.

An old farts opinion!

MOP

[Carl C]

On some motors the pistons will hit the valves if the timing chain/belt fails. Why they use rubber belts on some of these motors is beyond me.

[BUIZILLA]

closely study the bottom area of the valve seat contact area in the register bore in the head.... look at the outside corner... see that step...

there's your clue...

the seat came loose in the head, no fault of yours

I think it was improperly machined from the get-go, it was just a matter of time

JH

[MOP]

As you can see older eyes have seen a bit more, one look and Jim and I hit it on the head. Very true the initial machining may have been at fault but that normally show up pretty early in the life of the head, heat according to the Volvo factory is the biggest culprit. It may not be common on BMW but it is a fairly common thing with aluminum heads, many years back the Volvo factory rep told me never put a head that had been over heated without both shaving it and replacing the valve seats. The expansion and contraction rates of the soft aluminum and the extremely hard valve seats are very different, the aluminum tries to expand but the seat will not allow something has to give obviously the aluminum which when things cool down leaves a loose seat.

"That should give fair warning to those running aluminum heads to have the seats done over in the event of an overheat or chance having you the damage above."

Phil

[BUIZILLA]

the seat has an entry O.D. chamfer, the angle of that chamfer may very well clear the machined step.... however, one pic shows the chamfer edge hitting the step, which means the seat never was at the bottom of the register cut.

I have also seen first hand carnage of a seat coming loose from high EGT's from being run lean, trust me, it wasn't pretty.....

[mphatc]

Buizilla, both your posts make the most sense to me. I too saw these markings and felt from that that the seat came out first then causing the valve to break.
The valve separated at the joint from the shaft.

Unfortunately for the owner and us, we had just completed a bolt in cam swap, this is an OHC 24V inline six , 3.2 liter, single vanos in an M3. My lead tech did the install and I double checked the accuracy and cam timing, a routine procedure in my shop. He had driven the car 350 miles and this happened on track. The engine had 63K miles, it was a used engine with no previous disassembly. We did not do the swap.

FWIW, a cam swap on one of these engines only requires removal of the cam cover, timing chain, and 7 bearing caps . .and a reflash of the ECU by an outside supplier to change ignition timing and fuel mixture. We never even have to remove the cam followers for this swap. Designed to be done this way by Schrick and Sunbelt. This was a Sunbelt cam set up.

I have chosen to stand my ground and not warranty anything here. It's a race engine . .and IMO Crap happens.

We ruled out the high EGT or lean mixture . . from the color of the valves on the other cylinders, and the piston tops. Our experience with BMWs has consistently given us burned pistons and destroyed ground electrodes when a lean mixture is pushed hard on track.


Mario

[MOP]

Have to agree with the seat not being set properly on #5 scoped the pic better, Thanks Jim! The few I ran into were from heat issues. Mario like Jim said not due to anything you could have done, the seat was destined to fail.

Phil