In a jam with a broken cam

[3400-95-Modified]

Both pieces turned freely before I took them out of the engine. The first machine shop got the bearings out and said the inner ones pushed out with little effort. They were thin. But that shop doesn't line bore cams. I found another shop that will. And some 0.080" oversize bearings are on the way. From my quick look today one of the end bearings looked worn -- it may have been the one at the bell housing end. Tomorrow night I plan to check with calipers and post a picture. (Don't have a ball fitting for the micrometer.)

What I mean was which side of the cam has the bad bearings? and where did it break? If there are bad bearings after the break in the cam then yes the bad bearing caused it to break... If only the half that was attached to the timing chain after the break has the bad bearings then that's simply due to not having any oil pressure after it broke and the engine kept running.

[Tbay99Venture]

Just a quick reply until I post pictures of the old bearings tonight. No doubt the inner bearings were spun. The outer ones have a swath worn to the base metal (copper/brass color) all the way across the bearing's width.

We're the original owners of the vehicle. I've seen pictures of coolant problems due to LIM failure. If there was ever any coolant intruding it was too small to see. Every time I've had the LIM off (3 times now) the gasket surfaces have shown no signs of failure.

I have a feeling it may have been related to wear and oil problems. 18 months or so back the head gasket failed leaking coolant into the #2 combustion chamber only. We took care of that very quickly, I don't think the temp ever got to the top of the normal arc. And probably 15 months ago the p/s pulley snapped so I drove it on short runs with no belt to get it home. It never got to redline temp but who knows, maybe the cam bearings were hotter (high mileage engine) and it set it up for eventual death.

What's left of the cam bearings indicate it was intact and there was oil pressure right up until they spun and caused it to snap.

[Tbay99Venture]

Yes, I am expecting some valves will have to be replaced.

[60dgrzbelow0]

You also should check your valves/piston tops. I wouldn't be surprised if a valve or two ended up smacking a piston.

I agree with 3400-95-Modified, LIM gasket leak.

But, I wonder if a clogged oil pump can "hydro lock" if the passages ahead of it were clogged. I've heard of metal pieces locking up oil pumps. I suppose pumping sludge might be enough to break a cam. Like trying to push syrup through a coffee straw.

I suspect that regardless of the "Which Came First? The Chicken or the Egg?" scenario...whatever GOO that mixture is eventually churned into...it probably has about as much LUBRICATING ability as a Bowl of Oatmeal. The other reality is that even if that junk COULD offer any real lubrication, you have five things attacking the Babbitt surfaces of the bearings simultaneously:

(1) High Engine Temperature (Heat speeds up ALL chemical and catalytic reactions).
(2) The Very Caustic aspects of Anti-Freeze upon the matrix of metals making up the inner surfaces of the bearings.
(3) An OIL Pump...constantly pressuring all that Bad Goo in and around the bearing surfaces.
(4) Friction that would expand the contacting metal surfaces closer, changing the acceptable "looseness" that allows oil to remain in circumferential contact with the cam/bearings surfaces, forcing out any lubrication and accelerating closer contact and increased wear... and the BINDING that cause the shaft to SNAP.
(5) The Oil Pump cannot PUMP either FROTH or a Semi-SOLID...only straight liquid oil without TOO much viscosity. Normally, oil that is pulled in by a vacuum suction happens easily because the mass of liquid oil present in the crankcase is sufficiently replenished to fill the void caused by the draw of the pump. But in time...the sheer VOLUME of the returning oil would be drastically reduced by the fact that once whipped into that green sticky paste...little if any of it is capable of free flowing back down inside the crankcase to fill up that void. The end result of which is OIL PUMP CAVITATION, The only thing that prevented this engine from complete destruction was the fortuitous stoppage of the motor by the camshaft breaking. Otherwise...much more damage might have occurred to the engine's moving parts (piston rings welded to the cylinders, bent rods, crankshaft bearing failure, etcetera).

These Unholy Five could conspire to guarantee the camshaft seizure in time.

If it turned out that you were going to replace your own cam bearings... and not have the block boiled out...it might be a good test job for "The FrankenUberLuber Machine" aka "Oober-Loober" to flush out all those oil galleries with an odd mixture of straight Kerosene and Wd-40?

http://60degreev6.com/forum/showthread.php/47790-Homemade-Pneumatic-Engine-Pre-Oiling-Machine?highlight=oober

[Tbay99Venture]

Well there was plenty of oil and the goo was accumulation at the bottom of the pan. Oil was changed on a regular basis but I didn't save records -- clearly not frequent enough.

To my surprise the filter screen was clean. Just the varnish along the pump and tubing, brake cleaner dissolved that quickly.

The role of the goo may have been to saturate the oil so it couldn't do any clensing. Chaning it would have much less effect of removing the unwanted byproducts.

[Tbay99Venture]

Here are the cam bearing pictures. The front 2 came out close to the same thickness, I give 1 measurement for them and then the two spun bearings.

0.069"
0.047"
0.033"

[TGP37]

60dgrzbelow0, that was quite informative.

My block was pretty well taken care of and seafoamed regularly prior to oil changes. But I might just get the block cleaned up professionally. Though, that DIY cleaning is interesting.

Tbay, good to see you can handle this kind of repair. A lot of people just toss their arms up and say, "It's dead"

[3400-95-Modified]

Another thing to remember, stock cam bearings are nothing special... This is on a decently low mile motor... The rod bearings did not have this type of wear, and this was all stock components.



Copper was also starting to show on the front bearings.

[TGP37]

I need to upgrade the cam and crank bearings. The rod bearings are upgraded and have ARP bolts. I could not imagine putting in a performance cam and not upgrade the bearings, pushrods, springs, retainers, etc.

[Tbay99Venture]

Tbay, good to see you can handle this kind of repair. A lot of people just toss their arms up and say, "It's dead"

Thanks for the recognition & the cutaways you posted a few pages back. Still waiting on the bearings, they should be in the machinist's hands Monday. Meantime he told me some of the valve seats in the head were loose. Heat seems to be the cause of these problems despite the fact that I thought I didn't abuse it.

Once this is all done I'll have to spend about 6 months reading BobIsTheOilGuy to atone for my lubrication sins.

[Tbay99Venture]

Stopped by the machine shop today. The didn't have the bearings but did show me an engine they were fixing with new babbit. Pretty cool stuff & I should have taken a picture.

[Tbay99Venture]

At last the block is home. The machinist was pleased with the cam lineup so I'll try to get some pictures looking in at it tomorrow.

[60dgrzbelow0]

Not to start the whole "Tri-Metal vs. Bi-Metal" bearing controversy all over again...and without knowing whether or not (or what you've either ordered or already installed)... the real truth is... bearings made along the lines of Clevite's patented CL-112 design do at LEAST one thing that the Aluminum-Silicate bearings can NOT do...and that is provide what one might call... "Forgivable Embedibility". To that extent... take a closer look at the internal shredding that happened on the stock bearing Babbitt linings from the ones removed from your engine. You can see that unfiltered debris tried its damnedest to penetrate into the bearing layers on ALL of those camshaft bearings. But sadly... Aluminum-Silicate bearings surfaces do NOT readily yield themselves to ingesting bits and pieces of hard metal deep into the Babbitt material and allowing the camshaft and crankshaft journal surfaces the chance to avoid the friction, the gouging, and the overheating (bluing) that can occur during the lead up to bearing failure caused by having TOO much junk in between that just has no place to go. Tri-Metal bearings wear longer and accept and will adjust well to minor, out-of-round errors in the crankshaft and camshaft castings-grindings. If possible, I hope you can get your hands on those Clevite CL-112 flavoured bearings and shine the bi-metal ones on down the road.

This is an interesting Bearing Failure Guide for a more in depth study of the problem diagnosis, done post-mortem in engine failures:

https://www.engineparts.com/publications/CL77-3-402.pdf

[3400-95-Modified]

I'm running the TM-77 bearings on my lower end and the AL-3 ones for the cam for a SBC 350 application. They do not offer TM-77 cam bearings for our application and only offer a tri-metal for some select custom applications (I would assume our block would be about last on that list), they only have AL-3 for the 3400's and you can get AL-3 or B-1 for the SBC, the AL's are listed as Heavy duty, and equivalent material to whats offered for our roller setup, so that's why I got them over the "stock" replacement type for the SBC.

I'm not sure what other companies offer though.

[60dgrzbelow0]

TBAY... Please forgive me for this momentary thread-jack...

3400....Very interesting... I guess the GM engineers felt that in some V6 engines running roller tappets, that the torsional stresses on the camshaft would be very much reduced from that experienced along the length of the convention hydraulic lifter camshaft applications. Wouldn't it be nice if these (see link below) were the commonplace, common sense replacements; readily available in proper sizing for the early model V6 engines? Geez.... I wonder what the theoretical RPM redline would be for your application using these roller needle type bearings on both the camshaft and crankshaft. You know....these look like they might work:

http://www.precisionenginetech.com/tech-explained/2009/05/22/camshaft-needle-bearings/