Kingtal0n

I took some close ups. what did this and why?

Kingtal0n

another

Kingtal0n

Heres how the thrust plate sits on the timing gear wheel. notice how messed up the thrust plate is too.

that have anything to do with the cam bearing?

ede

damn i've never sawa cam bearing look like that before, but i've not saw everything. my guess is the bearing wasn't getting oiled or the wrong bearing was installed in that location.

Damon

What in the name of heaven ate into that thrust bearing??? I mean, there's nothing to chew a groove in it like that on the cam side. It should at least be a concentric goove if it was wearing into something sticking out and catching against it as it turned.

My guess? I'm stumped. You need someone smarter than me.

Damon

Wailt, wait, wait, wait!!!!!

Is that cam bearing shell sticking out beyond the front face of the flat flange that the thrust bearing rides against??? It looks like it is from the photos. If it is- even a tiny little bit then- BINGO!- we got it. The thrust bearaing is wedging against the part of the cam bearing shell that's sticking out and causing the grooove in the thrust bearing. The cam bearing insert should be pushed WELL inside the face fo the block that the thrust bearing rides against (at least 1/32" if poperly installed). This could explain everything including the weird wear on the cam bearing itself.

Could the front cam bearing have wiggled out? Could it have been installed wrong to begin with?

RB83L69

Since the cam was forced up and to the driver's side, and that's where all the damage is, I'd bet it has something to do with the gear drive. Every other force (such as valve springs) tends to push the cam downwards, toward the crank. Yours however has destruction with extreme prejudice in the exact opposite direction from where it normally wears.

(Note to self: never even accidentally put a gear drive in your own motor, only those that belong to people you really don't like who have already paid in advance, and who ignored your advice to the contrary.)

Looks to me like the gear drive wasn't sitting in there where and how it belongs, but rather was in there crooked. Those things often "require minor machine work" to fit, namely removing part of the timing cover flange, or little casting artifacts of the oil passages. Looks like that should have been done to that block but wasn't. Plus, with a block with as much core shift as that one has, there's no telling how goofy some part of it might be sticking out, in places that ordinarily wouldn't matter if the correct parts were used.

Lose the gear drive. Put a chain in there like it belongs. Replace the front cam bearing. All will be well.

Vader

Before you go back to remove that bearing shell, take a good reference photo showing the bearing oil hole position in relation to the front of the block. Then go back to your machinist/installed (or yourself) and ask " WTF?".

RB83L69

The oil holes look OK to me... the front bearing of course has 2 that are 90° apart, and the others have one each; I like to locate them at about 4:00 viewed from the front of the block, with the front one's at about 3:00 and 6:00.

The thrust bearing, viewed in that last pic, looks like a it could be a case of mis-assembly.... the only way for it to be worn off-center that way, is for it itself to have been off-center, and held locked that way; the easiest way for that to happen is if it was caught between the cam and the gear. There's no other way I can see for the wear to not be concentric. That would have forced the cam gear to wobble, which may have forced it hard upwards and in the direction of crank rotation (the applied force) at different points in its rotation, which would account for the way the cam bearing is worn.

Kingtal0n

I have an idea for the wear position.

The block was ALIGN BORED. they removed .004-.005 from the main caps (cut them) then re-bored them. that would have moved the crank gear closer to the cam gear which would have pushed the idler gears against the cam gear putting a pressure UPWARDS on the cam gear.

make any sense? or could .005" not hurt anything....

and as for changing the cam bearing... how? how can i pull it out and replace it? I dont have a puller or a new cam bearing..

Im not goina have to remove any rods / pistons am i?

im getting a cloyes double roller timing chain tommarow.

Kingtal0n

RBL your suggesting the thrust plate was installed incorrectly which cause the cam bearing wear then?

Whats the "right" way to install the thrust plate then? all i did was sit it around that grove on the cam gear and bolt it to the cam.

RB83L69

Kind of looks like it fell down between the cam & gear and got clamped in there, in between the time when it was put on and when the cam was tightened.... That would have gone under one side of the gear only, so the gear would have sat slightly sideways, which depending on how little tolerance there is in the gear teeth mesh, may have put quite a bit of force on the cam trying to push it away from the gear drive... just a guess

"The simplest explanation that fits all the facts is usually the right one"
— Occam, ancient Greek philosopher, from so long ago they didn't even have roller timing chains yet

Kingtal0n

well thats a possible cause i suppose. it makes sense, at the least. ill check it out. Ill install the camgear to the cam with the thrustplate PURPOSEfully INcorrectly installed, like you said, and see if theres a resistance when it turns. Ill put the good side (un-gouged side) to face the block so it can provide me with a "new" thrust plate. sort of...

and what about my align bore theory? Crap or possibility?

RB83L69

Probably not... get out your .005" feeler gauge and compare it to the clearances among things, I think you'll see it's a pretty minimal amount of movement, insignificant compared to the sizes and clearances of the things in question.

I'd look for something else in the system that (a) has the same diameter as the damage to the thrust bearing; or (b) has a mark on it where something has been rubbing; or (c) shows signs of side load on it, like maybe the axle of the gears in the gear drive; or (d) has a mark from assembly, where you can see how the parts went together. Looking over the parts with a magnifying glass would be the best. I keep a 15x jeweler's loupe around for just such things, as well as a pair of the strongest reading glasses I can find (about 3.5x). Very handy for autopsies like this. You can spot little tiny things that are invisible to the naked eye.

Vader

To investigate the align bore theory, check the gear lash. All the old 230 and 250 Chevy sixes had gears (AND oil nozzles - where did you think I got them all?) that had to be checked for lash on installation. I've put a few cams in those post office engines (long story) and seem to recall the lash spec was checked with a round wire gauge, about 0.004-0.006". There was also a thrust plate clearance of 0.001-0.005", but that may not apply to a roller engine.

Guest

I dont think they removed any material from the block when they did the 'align bore'. What they usually do is cut a slight amount off the main caps, and then bore those out to the correct side, leaving the block side basically untouched. That keeps the crank from moving upwards in the block. The blocks are usually machined ok anyway, align boring is somewhat of a waste most of the time. Creates more headache if you do cut the block side too.

Looks to me like something was binding. Is this a factory roller cam setup? Did the cam nose show any wear marks, like maybe it was up against the thrust plate too?

Kingtal0n

Well its over now anyways. There is now an XE262 Cam in it (not run broke in yet) and a brand new double roller crane cams timing chain. Ill be breaking it in tommarow.

No more gear drives! put me on the list.

CamarosRUS

Did you ever figure out exactly what caused that funky wear?