Thoughts on Worn Cam

[Joe D.]

Ok, this is about my little brother's Scout. '76 Scout II, 345, 727, "gold-box", 2v carb, all apparently stock. He bought it at an insurance auction, so we can only can only speculate on it's history.

The truck actually starts, idles, & runs great. Hot oil pressure on the freeway is 40 psi, hot idle 10 psi. It has loud tick on the passenger side. Once it's warm, the tick goes away at idle, but always loud at freeway speeds. Investigation showed a fair amount of wear on the rocker shaft, replacement is in order. Observation shows lots of oil flow to each of the rocker "boats" at idle. 7 of the lifters spin merrily in their bores, 1 just goes up & down. We replaced that 1 lifter, the bottom was cupped pretty badly. The new one still doesn't turn. I think we've established that we've got a bad cam lobe.

This Scout will be a trail rig. It will need to drive several hours to the trail head, but won't see the miles of a regular driver.

Ok, here's the questions:
1. We'd love to re-build the engine, but time & budget won't allow it yet. I have 2 stock cams and 4 "welded" rocker assemblies. I haven't measured the cam lobes yet, but they appear sound. I want to swap out the bad cam and worn rocker assembly, and just run it that way for a while. Is it reasonable to think the cam bearings have some life left in them? Do you guys think it is worth the trouble to swap out the bad parts?

2. Would we be better off not touching it and just running it until we can go through the whole thing and fix it right?

3. Should we leave the cam alone, and swap in one of my better rocker assemblies? I was hesitant at first because I didn't want to damage good parts, but since then I've been thinking that we verified oil flow and the pressure reading is good, so why not? I should have measured lift on the bad lobe, but I didn't think of it at the time. Still, the valve is actuating, probably not all they way, but it's not a dead cylinder.

4. I'm betting the rocker shaft was damaged by skipping oil-changes, since oil flow appears fine, and I've verified oil volume. Should I be worried?

I'd love to hear your thoughts.

 

[Carl Wiese]

If oil flow appears fine, then I say either run it the way it is or do the swap with the used parts you've got. Ideal would be a tear down, but it sounds like that is out of the question for now. It May run a year, it May run a decade, you just never know. One of the guys in our club has a 304 in his trail rig that when it was sold to him was "about ready to die." I think that was about 10 years ago and it's still going strong. It doesn't sound like any failure you would have is going to be catastrophic, so at the very least you'd be able to get home. If you were risking getting left out somewhere because of engine failure, it'd be a different story.

 

[Michael Mayben]

You have done your homework well Joe!

And you have verified that ya have adequate oil flow to the rocker assemblies and the oil pressure numbers do not indicate a cam bearing issue!

Those are the two "deal killers"!!!

And in these engines...it's the cam bearing/journal clearance that controls oil pressure to the greatest degree, not main and rod bearing clearance as is found with many other engine designs...major difference!

Why'd the cam go flat? Who knows...but at least ya have done the diagnosis and ya know the issue ya face!

So what you propose is certainly what I would do given the budget crunch! Hell...I'd do it even with big bucks available if I didn't wanna scruu with rippin' down the motor!

No need to pull the intake and valley cover either.

Ya got the parts and knowledge to make sure the rocker assemblies themselves are decent. And pullin' the lifters outta their holes is no biggy. While ya got the front of the motor tore down in the frame...then make sure ya check the crank hub/balancer for a "wear groove" (speedeesleeve if needed) and replace the front timing cover seal. Pop the cam out...then use a good light and look down the cam bearing saddles and you can certainly see any delamination of the babbit layer of the five bearings. These cam bearings do not "wear"...they self-destruct as we've discussed so often before!

If the bearings show signs of damage, then go to plan b.

If the bearings look good, then slather 'em with assembly lube...I use a shotgun cleaning bore swab onna cleaning stick and goop the bearings heavy. Then carefully feed the replacement cam in the holes (goop all the surfaces first of course) and seat it.

Then give the rocker assemblies sum luv by popping the plugs and swabbin' 'em too, knock in the replacement plugs once the shafts are sterile inside.

Here's the deal...it's broke now. If ya continue to run it even with a bandaid, it's only gonna git broker...and most likely you will have major internal damage that will result in much more rebuild expense.

Heck Joe...with your experience with this stuff this is a satidy mornin' gig! But I know you would rather be hangin' drywall or replacing a water heater on the new digs!

 

[Robert Kenney]

Hey Joe,
just a point of view from a technical perspective. The bad lobe is worn to a convex shape that mirrored the old lifter. That gave a large contact area even though less than optimum. With a new flat lifter you will have a contact area the size of 1 square milimeter. That increases the loading at the lobe/lifter interface 10x or more.

The likely hood of a galling event and rapid failure is very high.

I know money is always a consideration but in the long run a failure like this with the metal making lobe/lifter interface can cause more damage and cost that a new bump stick and lifters now.

If you do the new lifter trick band aid, I would advise removing the oil filter and cutting it open to check for metal flakes. Say 100 miles after the trick.

Good luck!!