Carb'd 355, 5000 miles on rebuild. I had been driving it frequently without issue until a few days ago. I was just pulling into a gas station (lucky) and I noticed after a quick left and stop that my oil pressure had fallen off to zero. I shut the engine down in the middle of the parking lot. The engine oil was low (was going to get a qt).

When I restarted, I heard the characteristic clunkity clunk of a spun bearing. I assumed that the pump had lost its prime since I did not register oil pressure, and shut it back off for good after another 5 seconds. I had it towed to the house.

After much ado (yes you can get the pan off by lifting the engine and propping the motor mounts with wood block but it's hard), I removed the pan and found the pickup for the oil pump in the bottom of the pan. The engine is clean inside. I thought maybe I knocked it loose removing the pan, but I think I would have heard it, and I handled the pan very gingerly.

Due diligence says pull the rod caps and check the bearings. The cylinder walls and engine oil are clean, except for one piece of metal the size of a grain of rice I found in the bottom of the pan. The flywheel is dry, the valve train is undamaged. The timing chain is intact.

Thoughts?

disclaimer: I didn't do the rebuild myself. About two years ago, when I first got the car, the head gasket blew. The rebuilder used a standard bore head gasket on a 0.030-over block. The compression rings bulged into the cylinders and it failed as soon as I started hot rodding it. I used a proper-size MLS gasket.

This engine needs to be dynamometer tested, but I guesstimate about 400 bhp @ 7000 rpm.

 

Yeah, that's all you can do is pull the caps and check. Do the mains, too. Everything one at a time and remember it has to go back on in the same orientation (you can't flip it 180*).

Get the pump pickup brazed or welded onto the pump before you install it. You would think with all the force it takes to install the pickup into the pump body it would never fall back out. But they do with frightening regularity.

Frankly, I'd get a new pump even if everything checks out OK with the bearings. AND weld the pickup onto it!

 

The contamination of the oil system would also be of concern to me.Also if you find a spun bearing suspect of the bearing saddle(rod or main) should be checked.Recondition of the rod or line bore might be needed.With a spun bearing the crank needs to be checked too.Might need to be turned.Here is article given turning cranks the you can take as the gospel truth take to the bank from Engine Builder which is geared towards engine builder shops and is not anything like articles from comic books like Hot Rod or Popular Hot Rodding.

Written better than I could and notice the part about bearing failure and the crank needing to be mag checked.

Debunking the 10 X 10 Crankshaft Myth for Customers (#5)



As a retired crank shop owner, I really enjoyed the article on "Debunking the 10 X 10 Crankshaft Myth" (Engine Builder Shop Solutions, March 2008) and was glad to see someone tackle the subject to clear up the myth. You are 100 percent correct that grinding a crank undersize only reduces strength a small amount. Additionally, I think I can clear up some of the origin of this myth.





First of all, in normal use or even high performance use, a used crankshaft will not “clean up” to standard specifications and will usually have to be ground to .010˝ undersize. The crankshaft has then remained 98+ percent as strong as new. The problem arises when “spinning” or “hammering” (knocking) a bearing.
The crank will not clean up at .010˝ and must be ground down to .020˝ or more. A spun or hammered journal causes a crack in the majority of cases, even though it might not appear to be badly damaged.
In order to detect a crack, the crank must be crack checked or “magnafluxed.” Some crank re-builders do not crack check their product and depend upon the “law of averages.”

The backyard mechanic/racer was right when he found that crankshafts ground past .010˝ would have a tendency to break, assuming it was because of the reduction in strength and not aware that it was cracked already when it came from the crank repair shop.

Like any other machine in an engine shop, a wet system crank checking set-up is only as good as its operator and only works if it is turned on.

Many thanks,

Fred Geisel

 

Thanks for the replies, all. It'd be a fool's errand to push the pickup back on and reassemble. Having come this far, I will, at a minimum, pull the caps on the rods and mains.

I wonder if it is cost-effective to have the crank magnafluxed and turned vs. replacing it (DIY). Hopefully it doesn't come to that. Spun or not, I will probably replace the rod and main bearings simply because I know they ran dry a few revolutions and that will never sit well with me unless they really look undamaged (crazy hopeful).

There is also a sensor located near the lower right of the block just above the starter. I believe this controls the oil light. It certainly looks like the $5 sensor available at autozone for old chevys with only an idiot light. Is this right? If that's what it is, I can certainly wire it up to word the light & alarm. The oil light and alarm have never worked on this car--I must watch the gauge. That's hard to do all the time, especially on the roads around here (WV).

It's not consistent with a 1988 schematic, but the block is a 1970s-era 4-bolt main, all cast iron. The valve covers have 4 bolts each around the lip, not through the middle. I could ramble more about all that, but I digress...

 

In addition to teh cracking problem Gary mentions, there is also the fact that cranks are "surface" or "case" hardened by various treatments applied to the surface. When grinding them down, all the hardened metal is taken off, leaving un-hardened (soft) material exposed.

The sensor in the exact front-to-rear center of the block, between the #4 & #6 cyls, immediately above the end plate of the starter, is the knock sensor. Back in 1955, the GM engineers, being a bunch of real smart guys, and knowing the guys at Frod and Xler were looking over their shoulder, wanted to avoid tipping them off that EFI would be introduced in about 1980; so they included the knock sensor hole starting right from the very beginning of small-block V8 production, but cleverly disguised it as the coolant drain for the pass side bank. So that hole has been there since Day One, and no one ever suspected. Clever guys!!

On these cars with a gauge, there IS no idiot light or alarm. That's what the gauge is for.

A 70s block is completely consistent in every way with a 1988 schematic. Nothing ever changed.

It is not cost-effective to magnaflux a stock crank, in this day and time. Years ago, would have been the thing to do. Which of course, certain people on here will trot out those ancient magazine articles that they've been worshipping now for who knows how many years, and tell me all about "I've been fluxing cranks for xx years now and never had a failure", as if (a) doing that had something to do with preventing failures, and (b) just because they did it, it's automatically "A Good Idea", and (c) they're completely closed-minded and set in their ways and are unwilling to listen to reason. But YOU, as an intelligent, logical, open-minded creature of reason, smart enough to post on here and ask the question, can sse past the fallacy of equating correlation with causation. Nowadays, as CHEEEEEEEEEEEEEEP as replacement ones are, might as well just trash it and replace it. Magnaluxing stock cranks is a waste of time effort and money for reasons totally outside of .... the "success" or "failure" of the act of magnafluxing cranks, in and of itself. It's a waste of time effort and money because the cost is out of line with the benefits of alternative courses of action.

 

The point of the article is if you decided to 10/10 the crank to mag it so you don't end up putting back in a cracked crank.Beware of novice advise who thinks they know what they are doing and is just surfing my user for the sole purpose of harassment and to "try" to draw attention to themselves.
The second part of your alternative would follow to replace the crank and depending what you choose is going to be cheaper alternative or not.Maybe if you choose to take a negative and turn it into a positive spending some more money to purchase a stock forged crank.

Just for your ref-if said article was read,the date of it was 2012 written for professional engine builders who's customers might want to take the route of turning a crank down and is commenting on the safe practice of turning cranks down 10/10 in terms of hardness.That is of course if it would clean up at 10/10.The hardness factor come into play more so when it comes to turning it down to 20.

 

all of the rod bearing have evidence of lugging/detonation (1st photo) as the cap sides look decent while the rod sides have the soft underlayer exposed. I haven't got the mains yet. The #8 road bearing (see 2nd and 3rd photo) looks like it's been ground against the crank, and you can see some of the particles in the bearing surface in the 3rd photo. Photo #2 (01774) shows #7 next to #8 (order, L to R: #7 cap, cap bearing half, rod half, #8 cap, #8 cap half, #8 bearing half) The crank is already .020 under, though the crank surface at #8 still has a polished smooth surface, probably attributable to not running the engine for more than a few seconds and under no load after hearing it. The journals are going to get a good cleaning, though.

What's odd to me is that the #8 bearing part number, etc. on the back is still perfectly legible, and there is no damage (to the naked eye) to the bearing retainers on the #8 cap or rod. I had expected one or more bearings to have the retainers sheared away with shrapnel everywhere and a blued crankshaft with shrapnel in the journal and grooves in the crank surface. there is none of that.

I don't think turning the crank further is prudent, and may not even be an option (30/30?).

 

That looks more like poor lube to me... the soft coating material is gone, leaving the hard copper underneath exposed. Possibly too thick oil and too much load applied before the motor was fully warmed up.

Detonation tends to leave the bearing metal looking almost "flaked", lie it was hit with a hammer at the same time as enjoying too much friction.

If that completely destroyed main is the front one, that's further indication of inadequate oiling.

Look at the way the cam bearings were installed. There's a hole in them to lube the cam journal. Those holes should be more or less downward (toward the crank), and maybe a little "ahead of" th estraight down position (5:00 or so viewed from the front) so that as the cam tries to "walk" up the side of the bearing it's moving toward, it covers the hole. If the hole is placed at the top of the bore, it basically creates a giant leak to the pressurized system. Look particularly at the cam bearings whose bore feeds the wiped-out mains & rods.

And of course there's metal chips EVERYWHERE... looks like they were there from the instant the motor was first fired up, as though they were left-over from a previosu blow-up... I'd stongly suggest that if you rebuild that particular block, you take bore brushes to all the oil passages, and a wire brush sort of like a tothbrush to the grooves behind all the cam bearings. A trip to the quarter car wash with some engine degreaser, and with ALL of the plugs and the cam bearings removed, is in order.

Then after building it, run no thicker than 10W-30 oil in it.

 

That's lack of lubrication right there. If you knowingly ran it without oil pressure for a bit, that might be all there is to the problem. It's on it's way out, but not anywhere near "meltdown". If you actually spun a bearing, you'd know it. You just ran out of oil is all. The soft surface metal of the bearing did what it was supposed to do- sacrifice itself.

I see little evidence that there was systemic debris being washed into the bearings. You JUST started to "eat" the bearing material on #8 and put gouges around the bearing from material that flaked off the bearing itself. NOT from debris washed into the bearing from the oiling system.

Definitely no evidence of detonation-caused bearing damage. Sofa's got it exactly right what THAT would look like, but that's not the problem here.

If the crank journals look healthy I would put new bearings in it, fix the oil pump problem and fire it up. You just squeaked by this incident without doing more serious damage. Count yourself lucky. Another few seconds without oil and it would have been much worse.

 

No nothing beyond 20/20.

Thing is your relying on the bear journal that failed to be the right size in the first place if you just clean and re-bearing it.At this point if it where me I would trust only me and what I knew for sure.True to your point you can read the back of the bearing and maybe the heat of the failed bearing didn't get to the rod.Still a safer bet to have a machine shop double check that rod's size and if needed re-size.It a cheap insurance.Verify the rod's journals size to be sure the crank was ground correctly and a mistake wasn't made there where over the short time you drove it at the wrong clearance was wearing down the bearing until it failed.Then after that double check the bearing's clearance while reassembly.

Then if knowing all the bearings clearance's where correct,I would look at the oiling system for a cause.

The crate terminology used to mean something.When a customer gives us a short block or a crate for a build-up we still double check the bearings clearances.We have caught a number of issues and corrected them.

 

after much procrastination and a few concurrent repairs it's mostly back together. I'll hopefully get a vid and post it if nothing embarassing happens. The rear main bearing, though not spun, was actually in the worst condition of all.

Plastigauge revealed a rod clearance between 0.0012 to 0.0015 for all cylinders and main clearance of 0.0015 on all but the rear main, which was just under 0.0020. The plastigage didn't reveal any measurable variation in the crank surface. I pulled the lifters and the cam lobes look good. I also replaced the oil pan as every one of the bolt holes was bent upward, explaining the profuse leakage at the front and rear of the pan--you could watch oil fill the lip and drip down. I purchased a high volume oil pump with bolted and welded pickup.