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Old 03-09-2018, 07:45 AM   #1
meisterj
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Default Intermittent valve train noise

New to me '74 Scout II with a 345. I have had 3 episodes of valve train noise. The first was shortly after I rebuilt the carb and started driving it. Took it out on the xway and got valve train noise after a couple miles at 70 mph. I'm familiar with the 'oil starvation' problem and possible remedies. The noise subsided within 10-15 seconds of slowing down.

The second time (probably about 150 miles later) I was starting and stopping the engine in the driveway, checking the trans fluid level. Had an immediate loud tick upon one startup that persisted through several more start and stops. A couple days later removed the valve cover and one rocker (forward rocker of #6) was a bit loose, but when started and stopped a few more times, it became solid again and the tick went away. Oiling of the valve train seemed fine. Oil pressure on the dash gauge (for what its worth) was fine.

The third time (about another 100 miles later) was this morning. Drove about 7 miles on the expressway at 60 mph and the tick/noise showed up again. It didn't resolve with pulling over and idling a few minutes. I pulled off and started to limp home on back roads at 20 mph, and after several miles the noise resolved for the rest of the trip home. Oil pressure was again fine according to the dash gauge.

I think the first episode was just starvation, but not the second two. Seem more like a lifter problem, or intermittent oiling problem causing a lifter problem. Can a lifter fail intermittently like this? What might be the cause of a one-head (sided) intermittent oiling problem (the noises seem isolated to the passenger side)? What other possibilities am I missing?
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Old 03-09-2018, 11:04 AM   #2
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Default Re: Intermittent valve train noise

A sticking valve maybe? Seems the dreaded worn cam bearings would not be an intermittent problem. When you " limped" home was it misfiring, or were you just being cautious?
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Old 03-09-2018, 01:45 PM   #3
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Default Re: Intermittent valve train noise

Engine ran fine. Smooth, no missing, no loss of power, just the noise. Drove home slow just being cautious.

I agree a cam bearing issue shouldn't be intermittent, and from what I can tell from the oiling diagram, should affect both sides of the engine.

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Old 03-09-2018, 08:48 PM   #4
Robert Kenney
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Default Re: Intermittent valve train noise

This kind of intermittent lifter noise is typical of a bearing problem. When the babbitt layer breaks loose, it spins around the cam at random intervals blocking and unlocking the oil hole.
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Old 03-09-2018, 09:12 PM   #5
Scoutboy74
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Default Re: Intermittent valve train noise

Hook up a wet gauge so you have some meaningful OP numbers to digest. Either that or drop the pan and see what's lurking in the bottom.
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Old 03-09-2018, 09:13 PM   #6
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Default Re: Intermittent valve train noise

+1 on Roberts comment on cam bearings. Had that mode of failure happen to my T'ette. Sorry.
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Old 03-11-2018, 07:38 AM   #7
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Default Re: Intermittent valve train noise

OK, thanks for all the input. I'm still hoping for a sticky lifter - cheap, fast fix, but if that isn't it I guess I'm in for cam bearings.

So if the babbitt/bearing is spinning and closing off the oil hole, it seems like it would be mostly closed off (causing noise) and only rarely lined up to oil correctly. This is opposite the case where I only intermittently get noise. What's the explanation?
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Old 03-11-2018, 08:05 AM   #8
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Default Re: Intermittent valve train noise

If you have seen a failed cam bearing, the outer shell doesn't spin at first, the babbit layer comes off in pieces. Those pieces either come out the side or ride around until they do.

For lifter gallerys to become oil starved, the culprit bearing is the rear one. The bearing pieces also get carried with the oil in to the lifter gallery, contaminating the lifters. Click clack.



Pull the oil filter and cut it open. Look for bearing material in the filter element.
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