Checking and setting 308 Cam timing

Here's a shot illustrating the dial indicator setup, with the engine in the car. There's only 1/2" or so of clearance above the plunger, and as you can see, the hose has to be positioned to avoid interference. But, for those of us without that cool spark plug port post, this setup works pretty well, and uses only stock parts from the JEGS kit. Now back to work, to finish up the job...
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That is over the intake, looks impossible over the exhaust cam

 

For what it's worth, here's a shot of the setup for the exhaust cam.
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How close did the factory timing markings come out to be?

 

Mitchell, have a closer look. In my post (#23) I have photos of the dial indicator over both the intake and exhaust cam on the front bank. ZOOOOMZ more recent post also clearly shows the set up over the front bank exhaust cam.

 

You are right, I got to get me one of those fixtures.

 

It's funny, I've yet to find the factory marks to be off. Now I'll preface this with that how the factory wants you to check the timing is not very explicit nor explained well at all in the WSM. It wasn't until I ran the cams to not only get a profile but also to note where the factory marks are and then using that data to create a 3d model for the engine design builds did it make sense.

The WSM notes the operating clearances and also the timing clearance. Here's what is not mentioned, the timing clearance of 0.5mm is not with operating clearance included. In other words the 0.5mm is from base circle, so to check timing the lash needs to be zero.

I've got about half a dozen cam profiles done and they all were within 0.2~0.6 cam degrees of the published specs.

Lets take the QV for example, assuming a lash clearance on the intake of 0.20mm and then if one checked the timing by measuring the lift of 0.5mm with the running lash the timing would be off by ~2 cam degrees.

Just thought I'd share that.

 

+1

Likely engine temperature would affect the timing even more.

 

I found the same thing. I had .20mm clearance so I thought I'd just go until I had .30mm of lift. That's the same, right? Well, when I measured the lobe center and the closing of the valve it never worked, it was always off, on intake and exhaust. The amount varied a little, but 2 degrees seems about right.

 

which means inner lobe....correct

 

If I understand you properly, you're saying that if I compare the two cases:
1) Set the clearance to .50 mm and then rotate the cam until the lobe just barely contacts the shim to mark the opening/closing event at .50 clearance
2) Set the clearance to .30 mm and then rotate the cam until the valve is depressed by .20 mm

Either way the top surface of the shim is .50mm below the base circle, but a different point on the cam lobe is making contact with the shim, meaning that the cam is at a different angle. So to get the cam timing right, I really do have to do the .50mm thing, #1 above.

 

I'll get a schematic dwg up sometime today that will help explain, as a picture is worth a thousand words

 

either one would work, but #2 requires you know exactly how much lash there is. The point here is that the WSM numbers are based on zero lash or from the base circle. Most all other cam mfg's base the timing on having the running lash already set. I've seen some try and check the timing by measuring 0.5mm lift against the running clearance.

 

I am setting valve timing on my 308/GT4. I attached a degree wheel to the crankshaft below the water pump. I determined TDC for the number 1 cylinder and set all the cams to that. The mark on the flywheel is approximately 1 degree to left of the 6 degree mark, estimate 7 degrees advanced. What is going on? In its original form that engine had 2 sets of points in each distributor. One set retarded for starting the engine. I am using single optical triggers instead of points and MSD units controlling the advance curves.