I have been trying to measure camshaft lobes with my nifty new Starrett 436 micrometer and can not get consistent results. Specifically, I have been trying to distinguish intake from exhaust lobes on an ’02 LS6 cam. Intake/Exhaust is 0.551/0.547 at the valve, which divided by the 1.71 rocker ratio is 0.3222/0.3198 at the cam. Therefore the difference at the cam is slightly more than 2 thousandths. I am unable to make repeated measurements of the same lobe to that accuracy. Is it possible to make these measurements accurately with a micrometer or must I somehow use a dial indicator? Any suggestions will be appreciated.

-Gary

 

lol, u definatly need to use a dial indicator. you need one with a magnet base on it. the reason your not getting the same measurement everytime is because you aren't putting it in the same place exactly everytime.

 

Try using a venier caliper

 

To measure the cam with a mic, you are going to have to open the mic up to go from the peak of the lobe, to the base of the cam, you will alos have to sutract the base circle of the cam from this number. The best way to check something with a mic is to get around where you want to be. I would anchor the bottom of the mic on the bottom of the cam lobe, and then I would sweep across the top of the lobe with the other end of the mic. If it isn't open enoug, it won't go. Don't force it. Open the mic, and when it squeaks going across the surface that means you have your measurement. We do the same thing when checking a crank journal for size. When the mic squeaks going across the face of the journal that is where you maesue at. If you force it, you are only getting messed up numbers and may damage the surface or your mic.

Or, put it in a fixture or a block and measure it with a dial indicator. This is the best way, or a cam doctor.

 

Dial caliper imo is the way to go. You are going to need to setup the cam in something to spin it so the center does not change and then get your measurement from that. Hope it comes out ok.

Steven

 

I just measured a G5X2 tonight using a digital vernier caliper and it seemed to work pretty good. Its probably good enough to give me numbers within 10 thousanths of their real values.

Anyway, if you have one of those, you just basically hold the mouth of the vernier caliper shut with light force while spinning the cam lobe slowly in the mouth until the numbers read their absolute lowest value...then you write that down. That is the base circle.

Then, you do the same, except this time don't hold the caliper shut....just spin the cam by hand in the mouth and the number you get should be the peak of the lobe.

Here's the numbers I got...

 

1.454 base circle! You are going to need .050 longer push rods with that cam. My base circle on my stock cam measured 1.552.

 

Larry is right...

Quote: "1.454 base circle! You are going to need .050 longer push rods with that cam. My base circle on my stock cam measured 1.552".

The differance is .098" across the lobe (Base Circle)

Cut that number in half and you get .049"

Thats the differance between the lobe centerline to lobe heal. And thats the real number you need to be concerned with when determining pushrod length. He would need a .050" longer rod [if] the heads were not milled at the same time. This would be a 7.45" rod since 7.40" is stock.

Ron,

 

The stock pushrods are what, 7.38". We have hardened 7.400" pushrods here, thats 20 thousanths extra. Couple that with the excessive factory preload and we're gonna be just fine. We have 6 more springs to swap and then we'll find out for sure. I'm not worried.

 

Springs done, cam in, worked just fine. The car is on its way home and I have to say that the G5X2 sure sounds mean. It actually idled pretty well too with a 7/32" hole in the throttle body and stock tuning.

 

Car ran great all the way home. A little surging in the low rpm ranges (1000-1500). Deffinately a successful install though!

Its a mean ****!

 

Thanks, guys, for all the help. You’ve made be a better metrologist.

As recommended, I used dial calipers instead of a micrometer. I experimented with looking for a peak reading while I rotated the calipers over the lobe with slight pressure on the thumb wheel, but found that I got more repeatable results with a modified technique. I feel like I owe you pictures of my method but since I don’t have a digital camera, if you’re interested, you’ll have to suffer my verbosity.

I used two blocks of wood with holes that slipped over the journals as a camshaft cradle. Having the cam supported by these blocks is a big improvement over trying to make measurements while the cam is just lying on the dining room table. I originally intended to make the blocks fit snugly around the journals to ensure that the cam would not rotate while I was making measurements. I used a 2 ¼ inch hole saw and discovered that a snug fit is not necessary. The weight of the cam is sufficient to prevent rotation.

I rotated the cam so that the lobe to be measured rested at approximately the 2 o’clock position. With the calipers horizontal, I closed the jaws on the lobe with the throat of the calipers resting on the lobe's flank. Then, not touching the thumb wheel, I carefully rotated the calipers anti-clockwise while sliding the throat along the base circle. This ensures that both jaws are rotating. Otherwise I had a tendency to pivot around the front jaw’s contact point which leads to inaccurate measurements. I was very careful to keep the calipers perpendicular to the camshaft. I did this visually by keeping both jaws near one edge of the cam lobe rather than trying to keep them on an imaginary lobe centerline. As I passed the peak reading I simply continued rotating and lifted the calipers away from the cam. This gave me much improved readings.

I originally needed help because my micrometer measurements didn’t allow me to distinguish between intake and exhaust lobes. With calipers and care, my repeatability improved to approximately one one-thousandth of an inch. All exhaust lobe measurements were then near 1.818 and all intake lobe measurements were near 1.821.

With these measurements, I made an interesting discovery, something many of you are aware of, but was new to me. My original motivation was simply curiosity about my engine’s layout. I have not yet disassembled an LS1 but I am preparing to install heads and cam. I was puzzled when I found that the first and last lobes are both intake lobes and that the lobe sequence is IEEI... while the valve layout is IEIE... I solved my puzzle by remembering that the heads are interchangeable which means that bank 1 has an intake valve at the front and bank 2 has an exhaust valve at the front. Thus the frontmost and rearmost valves are both intakes. Cylinder head economy determines camshaft layout.

Thanks again to all who helped me learn a little more.

-Gary