ANY misfire--including those NOT caused by valve sealing problems, will affect the vacuum gauge. Needle flicking downward does not guarantee the valve seal is faulty. Any misfire will drop the vacuum. Eye-watering exhaust is typically caused by misfire. The misfire can be valve related, ignition related, or carburetion related. (or some combination) A simple cranking compression test or a cylinder leakdown test is WAY better at spotting a valve-seal problem than the reading of a vacuum gauge.
I don't think so. I removed the heads less than 1000 miles ago to change all the gaskets and also took the opportunity to change springs, seals, and exhaust guides. Just in case I'm going to get a leakdown tester as soon as possible but I think I should be looking elsewhere. This weekend didn't have time to remove the intake and check what's going on with the lifters, but, did a cold compression test and most all cylinders were between 105 - 115 PSI range, tweak a bit the pushrod adjustment on three cylinders and the compression went up to 125 - 130 PSI on those which I think supports my theory of lifter preload going crazy
Lifter preload doesn't change once you set it, it stays the same. You may not be recognizing 0 lash and setting it from there. It can be hard to feel. Less preload is better than too much.
Maybe, it's a possibility. The weird part is that the first 10 - 15 seconds the engine runs extremely good, vacuum gauge steady and showing 20 - 20.5" and then after that the vacuum starts dropping and the engine starts running rough. I'm g0ing to see what I found this week after I remove the intake
Make sure you don’t have some sort of an exhaust restriction. With the vacuum gauge attached, raise the RPM in Park to 1500. Hold it steady and watch the vacuum. If it drops off, look at the exhaust.
You changed exhaust guides, but I haven't seen you post about cutting the valve seats. New guides will not be concentric with the existing seats. The exhaust seats MUST be re-cut to match the replacement guides. I'd suggest one sold for Aviation use, and suitable for Continental/Teledyne engines having a bore size less than 5 inches. You may need to specify that you want a spark-plug adapter of 14mm rather than aviation-standard 18mm. I got mine from Amazon, the last I saw them they were about a hundred dollars. I looked for them again a week or two ago, and there's no listing for them any more on Amazon, but they're available direct from Aircraft Tool Supply (ATS). https://www.aircraft-tool.com/shop/detail.aspx?id=2EM&AspxAutoDetectCookieSupport=1 This gets you the proper sized orifice* for automotive engines, AND a "Master Orifice" that represents the maximum allowable leakage (for Continental Aircraft engines) no matter what other variables you run into--altitude, air pressure, etc. Truth to be told, Contnental allows more leakage than I'd be comfortable with--but their spec is a starting point, and a feature not available in most "automotive" leakdown equipment. *This orifice size and flow capacity has AS MUCH effect on the indicated leakage as the actual leakage. There is no industry standard or legal requirement for orifice size in AUTOMOTIVE use. There's an FAA regulation for AIRCRAFT engine use, though, and that regulated size for smaller-than-5" bores works very well for automotive testing. The FAA regs specify a larger orifice for bores larger than 5", and that's too damn big for car engines. That's terrible. Not so terrible that the engine wouldn't run...but terrible enough that I'd be looking for problems rather than saying "Ok, that's what this engine does..." 130 psi is still nothing to write home about, but I'm willing to accept that if the engine cranks slow, or the test is performed at higher altitude, 130 is not completely out-of-line. I really like seeing 160--180, but I usually see 150 when I test '60s--'80s engines. Lifter preload does not "go crazy" but it's easy enough to adjust it WRONG. "Wrong" typically involves not recognizing "zero lash" accurately, and going way too tight on the adjustment. Carb choke coil misadjusted? Choke may be too rich or too lean, but the choke pulloff is spot-on. The engine runs a few seconds, the choke coil begins to warm up...and then the choke coil adjustment controls the choke blade position not the pulloff.
Or the lifters have gone down enough that it takes the first few seconds of running to get oil up there and get them pressurized. Then once they get full again they are holding the valve open. Another harder way to adjust lifters is with the intake off measure down the inside of the lifter to the cup, the measure it again after adjument too actually see how much preload your doing. But some lifters are hard to get to, the intake has to be off, and it's easy to not be on the same spot on the lifter cup. I think running a full set of adjustable pushrods is more work than needed. I just use a checking pushrod, measure both intake and exhaust and order what's needed. I do cheat here and use a solid lifter........since it doesnt give makes finding 0 lash very easy, once I know length, add my wanted preload to measurement, order and install with hydraulic lifters, all good to go
The valve guide replacement was done by a machine shop and they cut the new valve angle if I remember right. They vacuum tested all the valves to guarantee a proper valve seal , but anyway I'm going to get the leak down tester. What makes the aviation type tester special? I forgot to tell that I live at 5500 feet above sea level if maybe that makes sense for a 130 PSI result
Takes a lot of oil pressure to push a lifter plunger against valve spring pressure--unless a valve spring is broken. That could work well--IF (big IF) the pushrod seat on the hydraulic lifter is at the same height as the pushrod seat of the solid lifter, or if you take the difference in the pushrod seat height into account. Altitude definitely makes a difference. At 5500 feet, 130 may be entirely normal. The aviation leakdown tester has a standard size-and-shape orifice, and also the master orifice for calibrating the test results.
This weekend finally had some time to finish the valve adjustment process. I did it with the intake removed and spinning the engine 90 degrees per cylinder. You guys were absolutely right about maybe I was having issues finding the zero lash and over adjusting valves. I readjusted all the valves, reinstalled the intake and the engine now runs a lot smoother, I've 19" vacuum while idling at 700 RPM, sometimes I can hear a valve ticking but the noise goes away on its own. Also the exhaust smell is now less but I think it is still too much because it still burn my eyes, but at least isn't as much as it was before Anyway I'm still concerned because I tested the engine compression with the intake removed and 8 cylinders are between 110 - 120 PSI, I was expecting it to be a bit better even living at 5600 Feet above sea level, but I think the engine has never been rebuilt so maybe the rings are just too old and tired . By chance of life I had the opportunity to met the original owner who imported the car to my country back in 1970, he told me that he never rebuilt the engine just swapped the heads! because the originals were starting to fail due to unleaded fuel so maybe I have a pair of low compression heads . Does the compression difference between the 1970 455 and later 455 is because of pistons or heads or both?
The compression is mostly due to the pistons. If the heads are 75-76, they are open chamber and would lower the compression the most. Doing the compression test with the engine cold really isn't worth much as the pistons and rings have not expanded and aren't sealing the way they should.
With engine warm, block the throttle wide open. Removing all the spark plugs will let the engine spin easier.
I did the test this morning and the results were pretty much like the same as with engine cold, just a 5-10 PSI improvement on a couple cylinders but the overall result is still between 115-125 PSI
