Pulled a stupid (valve adjustment gone bad)... - BMW M5 Forum and M6 Forums

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Old 1st September 2009, 07:14   #1
AMP
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Pulled a stupid (valve adjustment gone bad)...

I took on the valve adjustment on my S38B36 today. Everything was going great aside from the fact that ALL 24 valves are out of spec. I need to look through the previous owner's service records, but I'm pretty confident that the valves have not been adjusted in this century.

In advance of my new shims showing up I decided to shuffle the few that could still be used in other positions. I had everything mapped out and knew where everything was going to go. Of course I got distracted when a customer came in and walked away from the car with a rag that had two shims wrapped up in it. This got left in my office and when I returned to the car I found no leftovers and completely forgot about the two shims sitting on my desk.

So I move on to the next set and rotate the engine.... adjust a couple more... rotate some more and then it just stops. I look around and realize that I left the shims (yep, the one's sitting on my desk) out of both E4 positions. The cam lobe has made a rotation through the bucket and is now getting caught up on the edge of the bucket. CRAP!

Through some very careful maneuvering I manage to free the cam from the bucket and get the shims in place. Unfortunately, the damage is done. On either outer edge of both lobes (right at the apex) I've managed to grind away a bit of mateial... maybe 1/2mm.

So now I'm sitting here wondering if I've completely hosed the cam or if I'm OK. Sure, the primary contact point is the center of the lobe (undamaged), but have I created a weak point? Have I created an irregular edge which will catch the shim when the engine is at speed and eject it? Should I just put it back together (with all of the proper shims) and see what happens?


Ughh...
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Old 1st September 2009, 08:50   #2
davidoli
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What a shame ......... Distraction can be the biggest source of destruction ...... we have regular tea breaks at our workshops and it is so easy to walk away part way through a job and have something like this happen .

I was recently part way through an oil change , left the oil draining , went for a tea and returned to the car , totally forgetting the fact that I hadn't replaced the sump plug , and promptly poured 5 litres of oil into the engine ....... thankfully , I'd left the drain tray underneath !

Meanwhile , back to your problem , it would be a brave man that would bolt the engine back up with compromised cam lobes .

It may be an opportunity to fit a set of Shricks , although I have a set of stock 3.6 cams if you would rather stay original ......shipping can be a bit painful though .

D
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Old 4th September 2009, 16:20   #3
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Well, I finished the valve adjustment and bolted the cover back on. Fired her up and crossed my fingers. Nothing went BOOM so that was a good sign.

The valve train is quieter, but not as much of a difference as I had expected. Engine performance on the other hand is much improved. Power delivery seems much more predictable and the motor revs up much more freely than it did before. I'm still convinced that my cats are clogging up, but don't want to tackle that until the following is taken care of.....

Now I just need to sort out all of the carbon that has built up on the pistons and I should be all set. I guess the previous owner didn't really "drive" the car. We ran a couple of cans of BG Injection System Cleaner through the fuel rail via canister and that made a dent (literally -- there is now a dent in the carbon layer) but after talking with my BG rep I don't want to try anything more drastic than that. I guess I'll be running many cans of 44K through the tank until it clears up. On the bright side the carbon appears to be limited to the piston tops and the upper part of the combustion chamber. All of the intake valves look clean and the exhaust valves that I could see with the borescope looked clean as well.
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Old 4th September 2009, 19:10   #4
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I think carbon build up on the pistons is pretty standard in any engine. I have yet to see a well used engine (inc S38's) with clean pistons, though it is important to give the car a few good high rpm pulls to clear excess carbon build up. Using a high quality fuel with plenty of cleaning agents, like Vpower, will help too. If I were you I would not be too concerned...
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