Happy Thanksgiving everyone! On Thanksgiving day I'll be helping my brother-in-law with his '97 BMW. This is really unfamiliar territory for me but I think we can troubleshoot the issue. His inline 6 has been running pretty rough so I had him get the computer codes pulled. he had a misfire in cylinder 4 & 5. I had him get a compression check done. He had 0 in cylinder 4 and 25 in cylinder 5. I thought for sure he had a blown head gasket but he said he's been driving this way for a month. He doesn't have smoke out of the tail pipe. He doesn't have water in the oil. The engine isn't making noise other than rattling around from misfiring. The header tubes on 4 & 5 are not hot. Could he have a stuck valve? What else should I check for? Thanks, MARK
could be a valve train type problem. I'd say pull the valve cover and see if you have valve action or not. Also, make sure you are getting fire to the plug itself.
Someone esle said we wouldn't be able to "see" the valves moving with the valve cover off. I think we should, shouldn't we? I'm going to pick up a spark plug checker too.
I wonder if the timing belt is shot, causing the valves to open and close improperly, giving you those compression readings all over the place. Heck, he could have worn down a cam lobe also. How many miles are on this car?
I'm not sure how many miles are on the car. More than 100k, I'm sure. I would think a head gasket would produce other symptoms.
Mark, I blew a head gasket on my GSX one time between the cylinders and it produced the symptoms you describe. Didn't leak oil or water, just ran like crap with little to no compression in the two adjacent cylinders in question. While to do not pretend to know much, if anything, about BMW's, a head gasket would be my first best guess. Oh yea, I ran my car for several days like that too. None the worse for wear.
Ignition issues would not explain the compression readings. The fact that it's two adjacent cylinders with low compression and the history of gasket problems, pretty well locks in the gasket as the culprit. Cam timing or valve issues are not likely the cause, cam timing would affect all the cylinders. Valve issues would produce some form of noise that would be obvious.
I'm wondering if the head gasket can be changed without pulling the motor. There seems to be enough room to work.
Engine Installed Notes Removing intake filter housing with mass air flow sensor, refer to Powertrain Management Removing cylinder head cover, refer to Valve Cover Removing all spark plugs. Removing intake air manifold, refer to Intake Manifold Removing VANOS adjustment unit, refer to Camshaft, Lifters and Pushrods, Camshaft, Engine. Unfastening sensor for cylinder recognition, refer to Powertrain Management, Cylinder Identification Sensor, Service and Repair. Drain off coolant and dispose of correctly. Installation: Tightening torque, refer to Engine Specifications Bleeding cooling system and checking for water leaks, refer to Cooling System Remove exhaust pipe from exhaust manifold. Release water hose from branch flange. Unfasten heating intake and heating return hoses. Removal of cylinder head is described separately from installation. Assembly sequence for removal and installation is different. Unfasten screws and remove washer from exhaust camshaft. Unfasten nuts from thrust washer (intake camshaft). Remove thrust washer. Remove sprockets and chain. Remove secondary chain tensioning device. Unscrew chain guide. Lift off sprocket with chain. Note: Secure chain with wire to prevent it from dropping. Unscrew timing-case cover to cylinder head bolts. Untighten cylinder head screws from outside to inside with special tool 11 2 250 in the sequence 14 ... 1. Lift off cylinder head. Installation Installation of cylinder head is described separately from removal. Assembly sequence for removal and installation is different. Caution: Rotate engine on central screw counter-clockwise to approx. 30before TDC. This prevents contact between valves and pistons. Clean sealing faces of cylinder head and crankcase; if necessary, remove traces of sealing compound with hardwood spatula. Make sure that no sealing compound falls into the oil or coolant channels. Check that dowel sleeves are undamaged and correctly located. Apply flexible sealing compound three Bond 1209 to timing case cover. Fit new cylinder head gasket. M52 For machined (milled) cylinder heads, the M52 is provided with a cylinder head gasket 0.3 mm thicker than usual. S62 Caution: On the S52, the milled surface of the cylinder head must not be machined. Note: Check that all washers are in place. Caution: Cylinder head bolts must only ever be used once. No oil must be located in the threaded bores of the crankcase and the timing case cover. Risk of cracking, incorrect tightening values. Fit cylinder head and tighten with new cylinder head screws (slightly oiled) in sequence 1 ... 14. Note: For torsion angle adjustment, connect special tool 11 2 250 to special tool 00 9 120. Tightening torque, refer to Engine, Specifications. Tighten screw connection for timing case cover on cylinder head. Unscrew and remove the rear back screw pins which secure the cylinder head cover. If necessary, align the camshafts on the hexagon. Caution: Do not damage the cylinder head. Machine open-end wrench accordingly if necessary. Rotate camshaft until cam tips on intake and exhaust camshafts of 1st cylinder point towards one another. Fit special tool 11 3 240 to camshafts on cylinder 6. Note: Camshaft setting is OK if special tool 11 3 240 can lie flush on the cylinder head. Rotate engine from 30before TDC position enginewise to TDC position. Hold crankshaft in TDC position with special tool 11 2 300. Caution: Remove special tool 11 2 300 before switching on the engine. Fit primary timing chain to sprocket. Fit sprocket to exhaust camshaft with threaded bores on left side aligned down the deep bores. Install special tool 114 220. Screw in the adjusting screw to touch the tensioning rail, but do not yet tighten it. Long bores in sprocket are now centered. Install chain guide. Install secondary chain tensioner. Caution: Fit sprocket to intake camshaft correctly. Flat side facing VANOS adjustment unit. Collar facing camshaft. Mount both sprockets together with chain. Slots centered. Fit thrust washer to the intake camshaft and tighten down with nuts. Tightening torque, refer to Engine, Specifications Fit washer and screws to the exhaust camshaft. Fit screws with zero backlash: sprocket remains able to move. Installing VANOS adjustment unit, refer to Camshaft, Lifters and Pushrods, Camshaft, Engine.
I have all the illustrations that go with the procedure, I can email if you need them. Might want to do a leakdown test before pulling the head though.
