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  #1  
Old 08-15-2003, 02:05 AM
sms sms is offline
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Help! Valve/piston Interference after guide rail job.

Tonight I finished replacing the upper timing chain guide rails as well as the tensioner. When I removed the cam sprockets I was very careful to bind the chain to the sprocket. When I was about to put the passenger sprocket back, I noticed that the mark that aligns the cam was off about 10 deg. Since it was aligned before I rotated the cam back to where the notch lines up with the mark. I then put the sprocket back on the cam. I then wanted to hand rotate the crank a bit to see if everything was ok. I then discovered that the valve was hitting the piston. How did I go wrong and what can I do about it?


Thanks,

Steve
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  #2  
Old 08-15-2003, 08:16 AM
LarryBible
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Most likely you are one notch advanced, but don't take any chances with this. CAREFULLY put the crankshaft at ZERO degrees, put the cam at the mark and put on the chain. With the chain in place, turn the engine two full turns until the crankshaft is exactly at zero and check the cam. The cam marks should align. If not you may have a "stretched" chain.

DO NOT CRANK THIS ENGINE WITH THE STARTER UNTIL YOU ARE SURE THAT EVERYTHING IS RIGHT AND THERE IS NO PISTON/VALVE CONTACT!!!!!!!!

Best of luck,
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  #3  
Old 08-15-2003, 08:37 AM
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Before you try moving the motor you will be well served by removing the rocker arms. Then you can roll it all you want and the valves stay closed. Get your marks lined up again and then reinstall the rocker (keep them in order).
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  #4  
Old 08-15-2003, 11:26 AM
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You didn't say what engine you are working on.

But be sure that when you line up the marks, that you have the slack in the chain on the tensioner side and that it is tight between the sprockets.
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Chuck Taylor
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'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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  #5  
Old 08-15-2003, 12:16 PM
sms sms is offline
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The engine is for a 560sl. The # is 117.967.
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  #6  
Old 08-15-2003, 12:32 PM
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So make sure the chain is tight over the cam sprockets and under the idler sprocket when you line it up. Then put the tensioner in, turn it over by hand a couple of turns and check the marks. Then pull the coil wire and turn it over on the starter, and make one final check.

Can I ask why you are not replacing at least the chain and possibly the tensioner as well? It's inexpensive insurance and fairly easy to do at this point.
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'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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  #7  
Old 08-15-2003, 01:19 PM
sms sms is offline
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Chuck,

I am replacing the rails and tensioner. I'm not doing the chain since I suspect it was changed prior to my owning the car in 2002, but the rails looked worn and tensioner is weak.

What I don't understand is how I can rotated the crank now that the valves are hitting the piston so that I can get back to the zero point on the crank?

Steve
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  #8  
Old 08-15-2003, 03:34 PM
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Steve gave you the how-to on that one. At this point you have to remove the rockers, which will keep all valves closed as the crank and cams turn. Once you roll the crank to zero, then you can remove the cam sprockets and turn the cams independently of each other till all marks line up. Replace the cam sprockets and rockers and you should be good to go.
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  #9  
Old 08-15-2003, 03:44 PM
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There are a couple of ways to go. One is as Steve B suggested - removing the rockers so that the valves don't move as you turn the crank/cams. The is a K-D spring compressor that you can get at a good auto parts store that works very well.

The other way to go is to determine which side you are hitting on, and move one link back on that side. You would remove the sprocket, move it back - CCW- in the chain and turn the cam back enough to line up the sprocket and put it back on.

I think that this will work because what is happening is that the valves are opening too soon relative to the crank and turning back a notch will close the one that is hitting enough for you to rotate the crank to TDC.
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'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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