Topic: Cam degreeing 101(cont')

[scondon]

  So i've got all the tools (slotted cam sprocket, degree wheel, pointer, piston stop, dial indicator w/base) and some pretty easy to follow instructions for finding "true" TDC and cam lobe center, thanks MReick. I'm heading out to the garage now to "do the deed".

  My question is: Am I looking to set the cam to the specs supplied on the Timing Card for my Megacycle cam or is the whole purpose of degreeing to "advance" the cam a few degrees for performance? I'm going with just nailing the specs on the Timing Card but, since this is all new to me, just want to make sure before I button up the engine.

  Also, does it make a difference if I take my readings form #4 cylinder rather than #1? My degree wheel is set on the ignition shaft so #4 would be easier to read 'cause it's closer.

[Steve F]

take some pic's of what you're doing, as I'm about to go through the same process too.

[scondon]

Will do. There's another "Cam degreeing" post a page or two back that has some pics of the initial intrument setup as well as some good advice. I'll try and post some new pics this weekend.

[MRieck]

Sean, you can use #4. Make sure you set TDC to #4 if you do so. It really doesn't make a real difference- I'm just picky.

[scondon]

The Megacycle cam Timing card gives these specs for the intake.

Measured at .040 lift
Zero valve lash

Open:  25 BTC
Close:  52 ABC
Lobe Center: 103.5 degrees

I found "true" TDC and adjusted the pointer 2.5 degrees to read zero at this point.
Then I set the cam so that intake read 25 BTC at .040 lift, but when I spun around to check the valve closing it reads 54 ABC which gives me this-

Open:  25  BTC
Close:  54  ABC
Lobe center: 104.5 degrees

    I stopped at this point 'cause it was getting late. I set the valve lash "finger tight" but I'll try giving it just a little positive lift in case this is throwing my readings off. If I end up with the same readings which spec should I aim for, "Open" or "Lobe center". Of course I will double check by going through the whole process on #1 cylinder( currently measuring #4 ).

     Geez, these tech data posts are a boring read

[MRieck]

Sean..... stick with the 104.5 lobe center- it will work great. Sounds like you have done a great job and don't worry about the 2 degrees closing. What are the exhaust #'s. Should be close anyway as it is a single cam.  Recheck #'s after tightening the bolts.

[scondon]

I set the dial indicator on the exhaust and got this reading:

Open:  50  BBC
Close:  24  ATC
Lobe center:  103 degrees

Timing card specs are:

Open:  50  BBC
Close:  23  ATC
Lobe center: 102.5 degrees

      Yee-frickin-haw! I'm pretty happy with that. Especially considering that until a few weeks ago I was planning on just bolting the cam on the stock sprocket and calling it done.

      This seemed like a pretty daunting task when I first started checking in to it. It looked like a few expensive tools I had never used before and the process, with all those degrees and equations, was hard to wrap my head around. Gotta say thanks, MReick, for pointing me to the inexpensive tools and for sending those books with the simple to understand instructions. Ya really made this easy for me. Now, having done it, it seems easier than slipping the cam chain over the sprocket. Knowledge is the greatest tool so thanks for that.

[Steve F]

  Now you gotta write-up a step-by-step on what you did, and post it.  Q: what is meant by "measured at .040 lift and zero valve lash"? That confuses the hell out of me.  Where/when do you start making the lobe lift measurements to set the cam at?  Is lobe center at the highest point of the lift?

[MRieck]

Nice work Sean. Cam timing is like riding a bike- once you learn how.....

[MRieck]

Now you gotta write-up a step-by-step on what you did, and post it.  Q: what is meant by "measured at .040 lift and zero valve lash"? That confuses the hell out of me.  Where/when do you start making the lobe lift measurements to set the cam at?  Is lobe center at the highest point of the lift?

"Zero Lash" is simply removing the clearance between the rocker arm adjusting screw and the valve stem tip. The .040 lift is the amount the valve has started to lift off the seat(opening) AND the amount right before the valve hits the seat(closing). I check cam timing under actual running lash. You simply subtract the amount of lash(clearance) from your checking number.  I.E. .006" of lash subtracted from .040" lift  = .034".  The number on the cam card should show up at .034" rather than .040". The dail indicator will tell you that and that's where you get your opening and closing #'s. Subtract the opening from the closing number, add to 180 and then divide that number by 2.....there's your lobecenter. The lobecenter is just a number to determine the position of the cam, and valves, relative to the position of the piston during running conditions.

[scondon]

Now you gotta write-up a step-by-step on what you did, and post it. Q: what is meant by "measured at .040 lift and zero valve lash"? That confuses the hell out of me. Where/when do you start making the lobe lift measurements to set the cam at? Is lobe center at the highest point of the lift?

I took a few pics of the process and will make a new post describing the process. It may take a couple days.

[Sam Green Racing]

How's it coming on Sean?

[scondon]

     I have a big fat grin on my face now The cam is locked in place and I'm putting the painted covers back on the engine. It's really lookin' sweet. It will still be some weeks before I can put it to a road test. but after 9 months of sporadic weekend work I can finally see the light at the end of the tunnel, and it is GLORIOUS. Choirs of angels singin' and #$%*. No, really, they're jammin on the harps and havin' a good ol' time. 

     I'll post a beginners guide to cam degreeing as soon as I can. Probably end of the week.

[Sam Green Racing]

I want to see this brutes dyno figures.

Good luck  Sam.