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Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
For the record this is the same 350 I've had for years in various iterations. The latest is with fresh cylinder heads, XR288HR (advanced 4°), .030" shortblock with high-ish mileage (re-ring/re-bearing about 30k miles ago).
Compression test results not great but OK.
Leakdown test was miserable.
In fact the results are so bad, with the engine generally running really well up to the point of misfire (5000 RPM) , that I'm thinking I may have screwed up the test procedure.
Anyway, I shot this video and with good audio, you can hear the knock I'm trying to hunt down. It's definitely isolated to the front of the engine, topside. I had removed all of the belts and the noise is the same. It's not in the valvetrain although the "sewing machine" clatter of the all roller setup is clearly audible.
Here are a couple of threads I started while going through the testing.
At the moment, it starts, idles and drives really well. No smoke.
Playback through my computer's speakers makes the sound more like a thud than a tap normally associated with lifter/valve/lash noise. Still I wouldn't discount anything although I've set the lash more than once and as far as I can tell, it's good. Valve job, intake valves and guides are new. Valvetrain geometry is spot on.
I'm thinking maybe there's something up with the timing chain set or the cam thrust button (it's a retro-roller).
I have to keep the vehicle more or less intact so it can be moved around so it's not going to coming apart anytime soon other than to test the valve springs as they might be related to the misfire at RPM.
And if the shortblock really is toast, the noise could be a piston bouncing around.
I running a chokeless carb and the cold starts really dump a lot fuel in the cylinders. There may be a lot of cylinder wear to add to the problem. Hopefully it's not a rod going away.
Kind of asking myself questions here: If the cam button has backed off and the cam is walking back and forth in the tunnel, wouldn't that upset the timing as well? Because the timing is rock steady. At least at idle it is.
Does the noise diminish somewhat as it warms up? If so, I'd say it's piston noise.
I have an old pickup with a 330k mile very worn out engine, makes a similar noise for ~20 seconds after a cold startup, then almost goes away. And that 20 seconds of noise turns into well over a minute on winter cold startups. I've been driving it for over a year like that, just using it like an old truck; no romping on it, WOT shift points turned down to 4k
My memory of the engine warmed up is pretty fuzzy seeing as it's been a few months since the car has been on the road.
I've also suspected piston noise and with the results of the leakdown test combined with a fresh valve job leaks me to believe the bores, pistons, rings might be whacked.
I've never determined where the fragment that was stuck to the drain plug came from (the engine has been kept a runner and will stay that way until replacements are ready to go) . I can't see how its possible for a chunk of a pistin ring could make its way to the pan without mangling either the piston, the cylinder bore or both. If it IS a ring fragment, then that would explain a lot.
And almost certainly the knock, fragment and misfire are all related.
That's not a bad idea actually and something we did back in the day when I first started hot rodding. That's how we diagnosed my friend's SBF bottom end problem.
I think the plan might be (when the warm finally arrives) is to get the engine up to temperature and run all the tests again. Including the plug wire deal. It's the leakdown results that were most alarming and I think that alone is worth revisiting.
03-31-2018, 11:31 AM
