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Old 03-09-2009, 03:51 PM
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curtis73 curtis73 is offline
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Running it like that is a little tough on the pushrod tips, but as long as its running well, keep driving.

Try switching to a little thicker oil. Don't go nuts with 20w50; maybe 15w40. The thicker oil will have a tougher time bleeding out of the lifter and it will also stick thicker on the lobes. It might help diagnose what's really wrong.

You might also want to install a real oil pressure gauge. A failing oil pump or worn bearings can make oil pressure drop. Low oil pressure means the lifters aren't up to full pressure and they can tick that way too.

I guess I would suggest the following things first, and vaguely in this order.

1- switch to a thicker oil. You don't have to always keep thicker oil, but it might help diagnose a collapsing lifter for one oil change.
2- install or borrow a mechanical oil pressure gauge and test oil pressure. It should be high when its cold, but hot pressures should be 15-20 at idle and up to 70 at higher RPMs. If its below 12 or so at idle and below 50 at redline, its on the verge of being too low and probably the cause for your ticking valves. If this is the case, using a thicker oil will "fix" the problem. I put "fix" in quotes because it will just be compensating for things that are worn out of spec, but it will prolong the life of things greatly. The oil pump squeezes oil into all the bearing spaces. The clearances in those spaces partially determine how much oil pressure there is. As the engine wears those spaces get bigger and therefore less oil pressure. Switching to a thicker oil artificially raises pressure because it doesn't squeeze out of those spaces as fast and its a poor-man's way of returning oil pressure to within spec.
3- if that doesn't work, pull the valve covers off. You'll probably want to have new gaskets since the old ones are probably 40 years old and won't reseal. Check for obvious things like a bent rocker, smashed pushrod tips, a rocker stud that is taller than the rest (partially pushed up out of its hole), bent pushrods, etc. If there is anything wrong up top, that's good news. That stuff can be removed/replaced/adjusted at will. If you have bent a pushrod, rocker, or a stud is coming unpressed from its hole, that is like the equivalent of a rocker nut coming loose. It has added play in the system and just needs to be compensated. Just readjust those valves or replace the pushrod or rocker and you're done.
4- shine a flashlight down the pushrod holes. Depending on the casting of the engine you should be able to see a couple cam lobes. Shiny and uneven is OK. Scored and rough is not. You can also sometimes see some lobes if you take the distributor out and look down the hole.
5- you can take the pushrods out (keep them in order so they go back in the same hole) and roll them around on a table to make sure they're straight.
6- if everything checks out OK, then you can pretty safely assume its collapsed lifters. Put it back together and run it until it dies.

Or... just leave it alone and run it until it dies

Cams and flat lifters wear together. Cams are made of cast iron and have a mildly rough surface when new. The outer .003" or so of the lobe surface is hardened. Think of it like a hard-boiled egg. The shell is very hard, but if it wears through, the softer stuff under it won't last long. Lifters are steel and left with a machined finish on the bottom.

This is why you can't put new lifters on an old lobe. Think of a lifter and cam lobe like two pieces of sandpaper. Put the abrasive sides together and scrub. Eventually the sand will wear down and the two will be pretty smooth and you could rub them together for a long time. But, if you replace one of those pieces of sand paper with a new one and scrub some more, the new paper will eat through the old stuff really fast. Lifters and lobes establish wear patterns on their hardened surfaces, but if you try to put a new lifter on an old lobe it will wear a new pattern; right through the hardened surface of the lobe. Some guys have done it with success, but today's oils lack the proper additives to properly lube that process, and since your cam is 40 years old, I doubt it would survive.

When you switch to thicker oil, that pressure gauge will be helpful. You don't want to go too far. At about 70 psi, the pressure will bypass the filter and send unfiltered oil to the engine. At about 80 psi you can make a filter burst. Shoot for 20 idle and 60-70 psi redline hot pressures.

Here is what a proper wear pattern should look like. Notice that the wear looks uneven, but its shiny and not scored:

A damaged lobe might look like this, but it could also be more of a dull finish.

Last edited by curtis73; 03-09-2009 at 04:05 PM.
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