Valve/motor diagnosis

[Dave535Phoenix]

I was kinda putting my foot into my '93 535im yesterday passing 5k in 2nd gear when the acceleration went from strong and smooth to hesitating and not smooth. I backed off and the motor dropped to idle normally, but revving of the motor without load still produced vibration and stuttering.

It didn't feel healthy so I pulled off, opened the hood and listened to it idle. It seemed that there was some undesirable mechanical noise from the middle cylinders. A straight-6 running on 5 cylinders could feel like my ailing car does now.

Vital stats; 1993 535im, M30 engine, 162k miles. Stock except for a (great!) De Sylva chip. Oil changed regularly. Was half-way through a 25-mile trip; car was nice and warm. The oil light never came on, the temp gauge never moved, no cockpit indications that anything was wrong. Oil level was right in the middle of the range.

Possibly important; it blew it's head gasket about 2 years ago and I replaced it myself. I drained 11 quarts of coffee-colored oil/coolant mix from the motor before fixing it. I had the head machined flat and was pretty thorough putting it back together - after 2 years of problem-free running I thought I got it right, but I have heard that coolant in the oil can cause accelerated wear in crank bearings. The pistons and valvetrain looked to be in very good shape.

I accelerate in the car like this in 2nd all the time (I don't do it in 3rd anymore since that 67-in-a-40 ticket) ; it was not an unusual experience for the car.

I'm pulling the valve cover this weekend to take a look. Any ideas of what to look for and how? My best guess is that a valve spring broke. I'll check compression as well, then maybe pull plug wires individually to see if a cylinder is indeed dead, and which one.

TIA

Dave

[George M]

Hi Dave,
Agree...first step is to pull the VC and see what you find. My guess is a broke rocker if you have harsh mechanical noise. Sometimes cracked rockers arms are hard to detect as the deflect under load. I would then pull all the plugs for inspection...see if you can identify a mis-firing cylinder and perform a compression test to determine level of valve sealing. Be sure to check your valve clearances as perhaps one of the eccentrics came loose and you dodged a bullet.
I would not drive the car of course until you pull the VC and have a look as you want to keep any damage to a minimum.
Good Luck,
George

[Dave535Phoenix]

Well George, you were only half right. *Two* rocker arms were busted.

Both rockers of the #1 cylinder broke in two. They pieces were just sitting there next to the valves. Everything else looks fine.

Soooo.....now what. I'm almost certain I have to pull the head to get these replaced (yeah, I'll be replacing all of them, probably the valve springs too). Someone tell me I don't have to! Please!

I already did that. It was fun, satisfying, but a buttload of work and kept my car out of service for a month. The busted rockers are *right there* in front of me.

Maybe I'll just pull the plug and injector and run my car as a 5-cylinder .

(I'd moved the pieces before this pic was taken)

[DueyT]

Dave, that stinks! At least this was a "fail-safe" mode, as opposed to a "fail-in-the-worst-and-most-expensive-way-possible" mode!

As those rockers aluminum? If they were ductile iron I'd recommend getting the set magnafluxed to check for cracks and if OK, just replace #1 cyl. If they're aluminum, I don't think magnafluxing works...I'd consider careful inspection and likely replacing them all.

Not positive, but I suspect the valve lash may have been off...

[Martin in Bellevue]

Hmm, cylinder #1 might be a bit oil starved. That is curious; I'd throw some rags over everything & crank, checking for oil from the spray bar.

I guess the half length rocker shafts can't get past the radiator core support & condenser; pulling the head can be fun, I guess.

[John B.]

Before you replace them it would be nice to figure out why both rockers on the same cylinder let go. It seems unlikely that both rockers were faulty.

[DueyT]

Hmm, cylinder #1 might be a bit oil starved. That is curious; I'd throw some rags over everything & crank, checking for oil from the spray bar.

I guess the half length rocker shafts can't get past the radiator core support & condenser; pulling the head can be fun, I guess.

Yeah, too bad it wasn't #6...either the head or the rad comes out. Ouch!

BTW, I don't think that's oil...I think the lash was off. Looking at the metal fracture on the spring side of the rocker, right at the base of the arm at the maximum extent of the cut slot for the roller tip. IMHO, that's the metallurgical stress/strain game...no issue with oil there.

Duey

[Bill R.]

may want to contact bmw about it. You might at least get some rocker arms out of the deal...
Rocker Arms

[George M]

agree with comments implied above...strong hunch oil starvation was at the root of your failure. Did you replace the rocker shaft end plugs when you rebuilt the head last time? The plugs maintain oil pressure to the rockers through the hollow rocker shafts.
There is a hole at each rocker through each rocker shaft for oil to penetrate rocker journals. My guess is either the banjo bolts, oil distribution bar was installed backwards or a rocker plug or three were left out of your last rebuild to precipitate your result...only a hunch.
If your cam is a bit scored, I would clean that up as well...possibly a regrind...Martin may provide some advice there for a touch hotter grind...as you can't remove the rocker shafts on the big six...in particular the rearward shafts without pulling the head.
Don't think I would replace the valve springs...stretch check the head bolts for reusage...replace all rockers and likely 4 shafts and fresh eccentrics.
Also consider purchasing Don Gale's banjo bolt safety wire kit since you need to rebuild your head.
HTH,
George

[e34bim]

only twice i have seen this and the cause was backfire and piece broken from piston jamming in the valves, other fault could be broken spark plug but the fault does sound like its inside the cylinder