Do any of you guys fall prey to what I call "mission creep"? It goes something like this. Say you've decided that new valve stem umbrella seals are needed. You get in there, and wanting to do a good job, start measuring stuff. And other stuff too. Naturally it's all out of spec. And .... before you know it, a $20 set of umbrella seals turns out to be new valves, retainers, guides, springs, shims, machine work to install hardened stellite seats yadda yadda. And, those Aluminum Mummert heads are looking kind of tempting...Hm.
So I've seen this movie before. I've got to stay focused. I've convinced myself the need to replace the timing set in my otherwise stock 292. I can trust that a stock cam in a stock engine with a stock replacement timing chain and gears, should offer a noticeable improvement. "But as long as you're in there ..."
I can see where this is going. I don't have a degree wheel or a dial indicator with fixtures. But, "I gots to know!!" right? So I said to my self, "Self, you just know there's got to be a good ole' boy way to do this." In other words, a compromise or middle way between doing nothing and hoping for the best, and, spending a week waiting for more tools, immersing myself in a crash course on the finer points of valve overlap and lobe separation. Like here:
http://www.eatonbalancing.com/2015/09/24/degreeing-in-the-camshaft-part-i-finding-tdc/#more-907These are GREAT articles, I love reading stuff like this.
This is of course the way to do it. Though I'm not building a high performance engine, OCD means I'd like to ensure at least that any tolerance stackup is towards the "advanced" side of things. This begs the question, why isn't the cam already advanced? Or is it? Why don't they grind them that way in the first place, and compensate for inevitable chain stretch in the first place? As always those of us not spinning 6000 RPM kind of have to read between the lines on some of this stuff.
It DOES look like one way to achieve a rough measurement on valve overlap would be to measure this way taken from the Iskenderian website, without using any special tools or equipment. It might be interesting to see what it is right now, before timing set replacement with what I estimate is significant chain stretch or wear, and then afterwards.
CHECKING VALVE OVERLAP WITHOUT DEGREE WHEEL OR DIAL INDICATOR
When installing a camshaft, or when an occasion arises where it is necessary to make a check on valve timing and no appropriate instruments are available, the recommended Isky procedure is as follows:
Insert the camshaft and mesh the timing gears on the stock marks. Do not as yet install the timing gear cover.
Adjust the valve lash of the intake and exhaust valves of the No. 1 cylinder.
Using a long wrench or lever, turn the engine over in the normal running direction. Use enough leverage to get an even, steady movement instead of a jerky motion. Rotate until the intake and exhaust valves of No. 1 cylinder are in the overlap position (both valves opened slightly). Stop exactly on T.D.C., which is marked on the harmonic damper.
Now loosen and back off the rocker arm adjusting screws until the intake and exhaust valves are just barely closed. Lock the adjustment screws so that the intake and exhaust valves are at exactly zero clearance.
Now turn the engine over exactly one revolution of the crankshaft to T.D.C. on the harmonic damper. You are now at T.D.C. on the compression or firing stroke.
Take Notice! Now there is a large space between the rockers and valve stem tips. The space indicates the actual amount the valves were open at T.D.C. of the overlap period (less valve lash, of course).
We will measure this gap space by probing with common feeler gauges of various thicknesses combined until we determine the gap space. After computing the gap, record the figures for both intake and exhaust in your notebook. If the amount of gap on intake and exhaust is exactly the same, you have a perfect split overlap.
AN EXAMPLE USING AN RPM 300 CAM
Advanced Cam Position: If your intake happens to come out with .100 gap, and the exhaust with say .080 gap, your cam is in an advanced position. In this position, the came will produce more low-speed power or torque. However, there might be a slight loss of power at high RPM.
Retarded Cam Position: If, on the other hand, the intake came out with .080 gap, and the exhaust at .100, your cam is in a retarded position. In this position, there will be some loss in low-speed torque and power, and probably some subsequent gain in high-speed power.
Split Overlap: If the intake and exhaust gap read out exactly even, or within .005 of each other, you have a split overlap. Generally speaking, all racing cams run best in the split overlap position. While there are exceptions to this rule, it is usually best for overall performance.
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Ted, fellow Y-blockers, etc any thoughts on this method or other factors to consider? Would a few degrees of camshaft advance generally be adviseable for a stock 8-1 compression 64 292. I see that offset woodruff keys are available.