I put a brand new 350 GM Target engine in a few years ago - it now has 55,000 miles on it. Last weekend, the engine started taping. By the time I got it home, I thought I wiped a few lobes off the cam, like I did on the old engine. I pulled the intake and valve covers to check the cam lobes. They feel fine - no sharp edge on the trailing side of the lobe. So, I installed a new set of lifters, and set the valves up with the engine cold. (The rocker arms are all about the same distance down from the top of the stud.) I started the engine, and after a couple of minutes of taping, the lifters filled with oil and quieted down. The engine ran well all week, back and forth to work. This weekend, the taping started again with about 200 miles on the new lifters, but not as severely, and, after a few minutes it quiets down. Oil pressure is 55-60 psi at highway speed, 30-35 psi at idle. If I run the engine at about 1500 RPM for a while, and then let off the gas, it taps for a second, then quiets down. I don't want to crank down on the rocker arms any more, for fear of burning a valve. Does anyone have any idea what could be causing this? Oil pump? Oil pressure relief valve? Clogged oil gallery? Thanks for your help! Dave (1980 Silverado 4x4 short bed)
I'm gonna take a stab at it. I don't think it would be the pump, because you're keeping such pressure, and I assume that it has a high volume pump. My best guess is you've got a clogged gallery. One of the easiest ways I know of cleaning out an engine is to use some stuff called, ironically enough, "Motor Flush". It's made by Gunk. It's almost like diesel fuel. Just poor it in, make sure you don't over fill the crank case, run the motor for a few minutes, then drain the oil. Just for the extra assurance I would put a can of Engine Restorer in with the new oil, just in case there's any hot spot on the camshaft. It's probably gonna be the cheapest method, you can do. Good Luck!! Robert 74 Chevy C/10 350 c.i.d. (Currently undergoing brain surgery)
Thanks Robert. I know this is a difficult one to diagnose without seeing or hearing the engine. I think the oil gallery is clogged too, but I wanted to hear someone else say it. Rather than use motor flush, I'm going to tear the engine apart and blow compressed air through the gallerys. I bought a new cam, and I'm going to buy another set of lifters. This truck is a daily driver, and I want it to be dependable since I take it on 300 mile weekend trips occasionally. I re-adjusted the valves again last night, this time while the engine was running. I had to back out each rocker arm nut a little over a full turn before it started to tap, which tells me all the valves were adjusted properly, but it still taps during deceleration. When I get this thing fixed, I'm going to post the solution, so no one else has to figure this out. Thanks again for your help. Dave 1980 Chevy Silverado 4X4 Short Bed
soak lifters overnight in oil and use cam lube generously. put in a temporary mechanical gauge do not rely on the dash one. change oil shortly after break in. you were damaging the lifters when ticking at start up take an old distributor and modify so you can prime motor with a drill before starting. motor might be loose cause of alot of wear and leaking the pressure past bearings also 86 c10
