Yet Another Cam Timing Question

[930LDR]

So I've read Wayne's chapter a number of times now and have also done a bunch of research here on Pelican and I've got myself thoroughly nervous.

I followed the CIS timing methodology in Wayne's book for my 930. I'm using Dougherty Racing DC-15 cams (based on SC grind) with my stock crank and 3.3L setup.

My steps were as follows:

1. Installed the #1 Intake Rocker and checked clearance using a .004" feeler.
2. Set the crank to Z1 and ensured that both cames were oriented with the 930 marking facing up.
3. Installed a mechanical chain tensioner on the left side of the motor.
4. Installed the dowel pins in BOTH sprockets.
5. Installed the z-block and a dial indicator with a .001" - 1" range.

Based on the documentation from Dougherty I was targeting an overlap measurement of 1.8MM - 2.0MM. Converting that to inches I aimed for .075" (factor of 25.4) as the midpoint of that range. Understanding that the dial will move backwards as the valve opens I was looking to see a value of .025".

When I rotated the crank clockwise, the dial indicator remained steady until I was about 35 degrees from Z1. The problem I found was that I didn't reach my target overlap measurement until actually going past the Z1 which has me fairly freaked out. I know Wayne's book makes specific reference that you shouldn't go a full 360 before reaching your target.

At this point I'm wrenches down until I figure out where to go from here. How do I proceed to reset everything and start over without risking having the piston and valve come into contact?

[930LDR]

Trying to post some pictures but the site isn't cooperating... pics to come.

[JJ 911SC]

Originally Posted by 930LDR

Trying to post some pictures but the site isn't cooperating... pics to come.

Does you pic link disappear when you it Upload Now!

[930LDR]

Originally Posted by JJ 911SC

Does you pic link disappear when you it Upload Now!

Yeah that's what I was getting. Left the window sitting there a while with no luck too. I'll try again now.... still no joy.

Gave up on uploading pics for the time being. I've added them though to my rebuild blog... see below:

http://www.bloodsweatandbrokengears.com/

[Eagledriver]

No need to freak out. As long as you don't force the crank when you hit any resistance, you shouldn't bend a valve. The crank going past Z1 before getting the target lift means the cam is retarded and needs to be adjusted to a more advanced setting (this is the essence of what you are doing when you time the cams). There are many ways to advance the cam. You could stop at Z1 and loosen the cam bolt (hold the cam from turning with the cam holding tool) remove the pin, rotate the cam slightly forward to open the valve to the target value and find the new pin hole. Be careful because the valve spring will be trying to turn the cam. Another way to advance the cam is to rotate the engine back away from Z1 so the rocker is off the cam ramp and then pull the pin and rotate the cam slightly forward, re install the pin and bolt and check the results. Keep doing this until you find the right spot for the pin.

-Andy

[930LDR]

Thank you Andy. Nornally I know you don't want to turn the crank counter clockwise but is that okay to do in this situation with the cams pinned and the tension taken up on the chain?

If I am understanding the process correctly, I want to end the day with the crank at Z1 and the left cam opened to the target overlap measurement. The first of your suggested methods above would likely get you there on close to the first try but is going to be more difficult given the resistence on the cam from the valve spring. The second is a bit more of a hunting and pecking process but rids you of having to hold the cam still during all adjustments. Right?

Also, should I tightening up the tenion on the right hand side chain along with the left hand side when timing the left cam? In otherwords, I have two mechanical chain tensioners. Should I be using them both during this process or just the one specific to the side that I am timing.

Thanks.

[930LDR]

Well I enjoyed some success this afternoon. I think I got a technique down that worked for me and after several attempts (and a few hours) the left side is timed to the exact midpoint of my target overlap range. I think I read somewhere on Pelican today that timing the cams may be one of the most over hyped procedures in the rebuild and I think I'd have to agree looking back on my work this afternoon. Once I understood where I was trying to end up and how each of the moving parts worked with oneanother it really became an excercise in patience and attention to detail.

The big take away for me was that with the later style cams that take the large washer and bolt that screws into the end, it was easier to over advance the cam slightly, pull off the bolt and washer, screw the bolt back all the way into the end of the cam and then use an offset box end 19mm wrench to hold the cam in place before removing the pin and resetting the crank to Z1. First time I popped the pin out without holding the cam the tension on the valve spring pushed the cam out of spec. Once the pin is pulled and the crank is set at Z1 it was fairly easy to gently ease the cam back to the desired overlap measurement and then re-pin it. From there it was a matter of developing a sense of feel for loosening the bolt before replacing it with the washer and torquing it down to final spec without moving the cam off its mark. Next up... the right side...

[Eagledriver]

Glad it's working out for you. You are correct that you should have both sides tensioned for this operation. Some say you shouldn't turn the engine backward, I'm not one of them. As long as the chains are tight, the engine won't care which way you turn it.

-Andy

[Walt Fricke]

I'm with Andy - when I am futzing around with the pin out, if the crank gets a bit off Z1 I don't worry which way I turn the crank to get it back to Z1. But when I have snugged things down, I always turn the crank clockwise to see if the reading after two turns is the overlap I want.

Turning the crank counterclockwise means you are depending on the tightness of the idler sprocket to keep the chain acting as if it were a gear. Turning clockwise has the chain doing a straight pull on the cam, so looseness in the idler sprocket isn't going to affect things, at least when a cam lobe is opening a valve, which is what you are doing when dealing with the overlap value.

[MBruns]

Hi Walt, did the FW bolts work out for you ?

Mike Bruns JBRacing.com

[lindy 911]

With the newer cams that have bolts instead of big nuts I've come up with a slightly modified way of cam timing /adjustment that goes like this;

1. Rotate crank to TDC (Z-1)
2. Install both cams with dots or markings straight up.
3. Pin the sprockets and install washer, tighten the bolt lightly.
4. Install #1 intake rocker and adjust lash.
5. Rotate the crank 360 degrees to TDC again and install a flywheel lock so the crank can't move.
6. Remove cam bolt and washer then reinstall bolt and tighten lightly.
7. Remove pin.
8. Install dial indicator.
9. Rotate cam with bolt until the proper valve opening is achieved and pin sprocket.
10. Remove bolt, install washer and reinstall bolt and torque.
11. Check measurement after rotating 720 degrees.
12. If the measurement checks out, start at #4 above for the 4-5-6 side.

[Walt Fricke]

Mike

No - I'll send you a private message.

Walt