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-   -   timing question, need advice asap! thanks (http://www.bimmerfest.com/forums/showthread.php?t=665458)

lovetherideUSMC 12-22-2012 06:08 AM

timing question, need advice asap! thanks
 
So i got myself into a head gasket change... All is going well until i realize somthing. I have the flywheel oick pin installed andthe cam lock blocks on, but from every instruction ive seen the #1 cyl cam lobes for intake and exhaust are facing up andand toward eachother. Not the case with mine. They look the exact opposite and are facing down and away from each other. # 1 and # 6 piston are at the top of the stroke, but i think i somhow locked it in a diffrent cycle of operation. Didnt notice until i go to put it back together because everything went smooth taking it apart. Now i dont know wtf to do! Advise anyone?

lovetherideUSMC 12-25-2012 05:19 AM

Ok sooo... Made some calls and what not. The cam shaft will rotate twice per crank revolution. Every revolution the crankshaft positon sensor will sense the engine is at top dead center. Every two revolutions the camshaft position senson will sense the camshaft at top dead center. The camshaft position sensor tells the ecu the cams are in the position for ignition. So technically you can install the cam in two diffrent positions, either it be tdc for the power stroke or tdc fot the exhaust stroke . With that being said, whichever way your cam comes out, just put it back the same way the manual sais with #1 cam lobes facing in, while the flywheel is locked at tdc. If anyone has any doubt that this correct, input is much appreciated.:thumbup::thumbup:

bigwong 12-25-2012 08:29 AM

Actually, the crank will rotate twice while the camshafts rotate once. A 4 stroke engine has two revolutions per power stroke. What you are doing is correct, because the power stroke is determined by the camshaft, not by the crankshaft. In cars with distributors, you would have to make sure the correct cylinder was firing when you hooked everything back up. If you were 180 out of phase, you pulled the distributor and rotated it 180 degrees so the correct spark plug would fire. In an electronic ignition with a crankshaft position sensor, I'm not sure how this works.
Just reread your post, and if the camshaft sensor works as you say it does, your good to go. I don't know enough about these newer ignition systems to be definite.

lovetherideUSMC 12-25-2012 09:27 AM

Oops ya thats what i meant 2 crankshaft turns for one camshaft. Which means the camshaft will be in one of two positions at tdc. Ignition is determined by the camshft sensor. You always time it from the cycle where #1 lobes are facing inward toward eachother

Stephen Max 01-09-2013 06:22 AM

Hmmm. So the crank position sensor doesn't enter into the picture at all? I've never torn into my M3 engine to know, but on other cars I have worked on the cylinder firing was determined by the crank position sensor, so you had to make sure that the crank was positioned so that number one cylinder was at TDC on a firing stroke.

Pinecone 01-09-2013 12:44 PM

But the crank position sensor will be in the same place for #1 to be at top dead center, but twice per complete engine cycle.

So if you locked the cams at #1 TDC, then reassemble with the #1 at TDC.

Stephen Max 01-09-2013 04:18 PM

Quote:

Originally Posted by Pinecone (Post 7301424)
But the crank position sensor will be in the same place for #1 to be at top dead center, but twice per complete engine cycle.

So if you locked the cams at #1 TDC, then reassemble with the #1 at TDC.

You are absolutely correct. I should drink my morning coffee before posting.


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