I would put a dial indicator on the end of the rocker to see if you are getting full lift. A compression test could show if the valves are not closing all the way.
No.. While the masters that make these cams do vary somewhat, TA does not specifically endorse or promote this "fast ramp, area under the curve" theory. Scotty G did a whole bunch of testing years ago, that debunked that whole theory, in Buick motors.. A Buick 455's headflow and port velocity/cylinder filling potential/valvetrain geometry/adjustment limitations is a whole lot different than that of a SBC, where this theory was developed and tested by the cam companies. JW
Bob, Yardley.. It's actually pretty simple, a couple guys touched on it.. All engines with shaft mounted rockers, have a fixed pivot point for the rocker. That pivot point is the shaft. In a stud mounted rocker setup, that pivot point is adjustable. That's the only advantage of a stud mount. What happens is that when the valve tip gets too high, it creates a momentary "over center" condition in the valvetrain, and that creates an excessive valvetrain force on the hydraulic lifter. This force squeezes the oil out of the lifter, and there is not enough time for it to fill again, once a certain rpm is reached. That rpm can be as low as 4000, but most often manifests itself above 5000 rpm. When this happens, lash is developed in the valvetrain, and the camshaft loses positive control of the valve. Because of the greater weight of the larger intake valve, it most often loses control of that valve first. When it does this on the dyno, we can actually see the airflow number go backward, as rpm increases, and this can't happen in a positive displacement air pump, which an engine is. Airflow always has to increase, or stay the same, but it will never go backward, in a properly functioning engine. My experience has taught me that about 2.125 is as high as the valve tips can be, and still have the engine function properly. But the farther away you get from that stock height of 2.060, the more sensitive the engine becomes to all the factors that affect the actual force the lifter sees. These factors are: Valvetrain geometry Rocker ratio Camshaft opening ramp speed Valvespring pressure Valvetrain friction. I had one engine here, with iron heads, that we "fixed" the valve tip height, via the use of a different set of valves, that had a shorter stem. That engine, came in with the tip heights on the intake valves up about 2.160-2.175.. and we got it down to right around 2.125 with the different valves. But still it was sensitive to the above factors. On the dyno, with 1.65 roller rockers on it, it still would not rev past 5400 rpm.. On a hunch, I simply took the valve covers off, and installed a set of stock stamped steel rocker arms on it (1.55 ratio), and on the very next pull, the engine would easily rev to 6000 rpm. It attained it's peak at 5700, so of course it made another 15 or so peak HP.. but interestingly, it actually made more power from 4800-5400, and airflow was up at those rpm points, which told us that even before the engine "noses over" it's losing positive control of the valvetrain, and hurting airflow, thus performance.. And the engine was noticeably quieter in the dyno cell. As was previously stated, I had you change the oil to a thicker weight, thus increasing both oil viscosity and pressure. The lifters have a metered orifice in them, so thicker oil, at a higher pressure, will bleed out slower, causing the engine to have to attain a higher rpm, before your lifter failure (lifter crash) occurs. To further go down the road of testing, measure your tip height, and then, if you have an old set of stamped steel rocker arms, and the right pushrods to set preload properly (.025-.040 with iron heads, cold) then go ahead and try that, it may very well alleviate the problem enough, so that you don't have to pull the heads, and can get back to racing for the rest of the year.. then fix it this winter.. And when you do, you probably will be replacing the cam and lifters also, as this condition rapidly accelerates the wear on the cam lobes, and creates much higher forces on the cam bearings, rockers, and pushrods. I have always believed that a lot of the cam bearing troubles we had years ago, was a direct result of engines with the valves sunk in the the heads (which raises the tip height) as well as the more aggressive ramps of a performance cams, and the higher valvespring pressures required for those cams. Cam bearing failure of stock engines was basically unheard of. I know I have taken dozens of sets of cam bearings out of high mileage stock engines, that showed little to no wear. JW
I was going to mention that the rocker shaft should be checked for wear. But, I guess a worn shaft would actually help fix the geometry...
Wouldn't you be able to put some machinists blue on the valve tips and run it for a little bit to see where the tips are actually touching? Should be centered if it is right.
I like to see the rocker tip centered on the valve stem at 1/2 total valve lift; I do understand however that there are other philosophies regarding what constitutes "correct" valve train geometry. Devon
after repeated thrashings from "try this ... try that" Yardley's Rivi phoned me this afternoon and told me it hucked up the block and spit it out the gaping hood muttering "Figure this out without me"
Thats what I trying to type. I could visualize it in my mind but not explain it with out using my fingers as a diagram. Probably the same thing would happen if the springs were too tight as well. :3gears:
The engine is out and I expect to have the cam and lifters installed in about a week. I plan on doing a dyno thrash with it to see my numbers, confirm it isn't laying over and to nail down my shift points. All valve tips were at 2.080" - right on spec. I had oil weeping from the driver's head, so I'm replacing the head gaskets. And I literally can't wait to pressure wash the underside of the car on the lift. The leaky rear main has made a literal mess of my transmission and entire undercarriage. A new rear main, cam and lifters. I'm throwing a water pump on it while it's apart. It'll get scrubbed and painted. So will the frame. Oh, and we're planning on replacing the cracked frame sections while it is out. I doubt it will make Cecil, but we'll see. Oh, and the heater hoses were considering going geyser on me, so it is a good thing I pulled the engine otherwise I'd probably never have checked them, and we all know when they'd let go... probably about 2 hours from home.
LMAO- Now we know how JW lost his last job at the suicide hot line. He would wait until the pills were down the hatch followed by the bottle of vodka, before totally making sense of the problem. You're a sick man Jim, watching Yards walk the ledge for 3 days. . .:laugh: Seriously: What's the solution-different cam?o No: Less lift/more durationo No:
Yards,when you have that head gasket off,it may not be the gaskets fault for the oil leak.Did you plug the hole in the block near the front of the motor? gary
It's a 1971 455 block and 1970 455 Stage1 heads. Should there be a hole in the front of the block? And if Buick didn't block it off, why should I? Thanks Gary. Any help is appreciated.
Dyno Day is scheduled for Tuesday. We will run it with the current cam and lifters. Then, regardless of whether it lays over or not (we'll do 6 or more pulls to confirm) we will replace the head gaskets and cam and lifters then run it again. It is a shame I can't run my shorty headers on the dyno, but he has no provision for them. We'll be using an old set of Mickey Thompson headers.
