SC cam timing

80sc man · 10-04-2003, 09:01 AM

I have got a quick insurance question about the timing. I just started but I can't even get past the first step. I set the crank pulley to the Z1 marker, then I went to turn the left cam over so the dot is facing up, and it is very, very hard to do. basically impossible. What is wrong??? Right now the dot is facing torwards ten oclock and I just cant turn it so it gets to 12. I didn't even mess with the cam towers when they were out so nothing could be messed up in there... Any sugestions?????
Thanks

mb911 · mb911's Garage

I think you are 360 degrees off. Reread BA preformance hand book or I think waynes new book should have the info as well. I prefer my haynes manual over them all as it seems the easiset to understand when timing the cams. Any how what is happening is the valves are hitting the pistons and won't let rotate the crank any further. You could back the rotation of the crank up a little then move the cam into position and you will be good to go. Been there done that>

Ben
77 911 3.0
75 914-6 2.7

dtw · 10-05-2003, 12:41 AM

You must set the crank to Z1 and the cam to "dot-up" before you install the pin in the sprocket and assemble the cam nut (or bolt as the case may be). If you've got rockers in right now, be very careful, as you may be way off time and risking a valve/piston contact. And of course, if the pin is in and the cam nut is installed, it would be impossible to turn the cam independently of the crank.

On the other hand, if you haven't installed the pin, or rockers, or cam nut/bolt, and the cam still won't turn, it sounds like it is binding in the cam tower. Could be uneven head heights or a bad torquing. Loosen up the cam housing, see if the cam spins freely then. If so, remove the cam and retorque the housing. Reinstall the cam and try spinning again.

Can you provide a little additional information on what stage of assembly you are at? I guess that would help us to diagnose.

80sc man · 10-05-2003, 05:00 AM

ok well here is the deal. I didn't mess with anything in the cam tower, so nothing in there should be messed up, and the rockers are on. Also in the case that I did touch the valves to a piston is that an immediate bent valve, or is it just that I cant go any further and have to back track to do something else. I do have the sprckets and everything on but can take those off no problem in about 5 minutes. Also, how would I know if I am 360 degrees off or not??

Wayne 962 · Wayne 962's Garage

Hi there. You are very confused. You need a copy of the Engine Rebuild book (http://www.101projects.com) before you make any more mistakes and end up costing yourself big $$$. Spend the $35 - it's worth it...

In a nutshell, it makes no difference if you didn't touch the cam towers - the cams have to be correctly timed with respect to the crankshaft. As mentioned previously, you are probably off by 360 degrees.

-Wayne

Wayne 962 · Wayne 962's Garage

Quote:

Originally posted by mb911
I think you are 360 degrees off. Reread BA preformance hand book or I think waynes new book should have the info as well. I prefer my haynes manual over them all as it seems the easiset to understand when timing the cams.

How can you say you prefer the Haynes manual, when it appears you haven't even read my book? The Haynes manual is terribly unclear on this subject and most others as well.

-Wayne

80sc man · 10-05-2003, 01:50 PM

Ok, now I have another question. It is definately not the valves that are causing the engine to bind. It only the other weird thing is that I didn't mess with anything in the cam towers, so I doubt that it is something in there. Any ideas on what it could be that is causing the engine to bind. I was just about to tear the heads back off and start over, but I don't want to if someone out there might possibly know of what it could be.
Thanks,
Mike

David · David's Garage

Without knowing what exactly your doing, it's hard to tell what the problem could be. If you had the heads off, it could be that the chains slipped off the driven sprocket.

mb911 · mb911's Garage

Its got to be the valves hitting there really is not much else possible except maybe the timing chain slipped off the gear on the layshaft and is hitting the case causing it to bind. I don't think you bent any thing it just is the wrong timing for the valves versus the pistons. I would suggest pulling all the rockers off except number one that way the only valves that could be open are number one.

Ben

77 911 3.0
75 914-6 2.7