Well, I lost my motor last Wednesday on the dyno. Right now I'm in the midst of the autopsy and I am a little stumped, so I thought I would ask you guys.

The story is as follows:

81K L98, stock bottom end. Mild mods for 80K of it's life, 100-150 HP shot of nitrous for the last 20K of it's life. I recently added a converted LT1 intake, cam, and heads. I drove the car around for about 2 weeks, made some drag strip passes, and was having a pretty good time with everything. During this span I put about 1,000 miles on the car.

I finally got some free time to put the car on the dyno and dial in the tune last Wednesday. I don't know that this is relevant, but that morning I switched from conventional oil to synthetic. After the oil change, I drove the car 20 miles to the dyno and strapped it down.

Everything was going fine, tune was coming along, power was starting to come up, and then...

On the 12th pull on the dyno, at an indicated 6,000 RPM (which was probably more like 5700 or so because of the lazy factory tach) there was a metallic 'TINK' sound. The check gauges light came on immediately, and the oil pressure went to zero. I shut the engine off immediately.

I put the car on the trailer and towed it home. Once it was in my garage I cranked the key to see what would happen. The engine fired normally, idled smooth, and had good oil pressure. Unfortunately, there was a pretty loud knocking noise coming from the bottom end. I pulled the valve covers just to make sure I hadn't lost a rocker, cranked it up again, and was able to verify that the knocking noise was coming from the bottom of the engine. Again, idle was smooth, and the engine made 50-60 PSI of oil pressure.

Figuring that I had spun a rod bearing, broke a rod bolt, or something along those lines; I took the pan off tonight and pulled the caps off the rods. The bearings look abused, but none of them appear to have spun. The crank looks great on all the rod journals, and I'm a little stumped as to what was causing the knocking noise.

I don't have any experience diagnosing a failure based on what the rod bearings look like, so I was hoping some of you guys that had been around the block a few times could chime in. It looks to me like the bearings starved for oil at some point, but other than that I can't make much sense of it.

Here's some pictures of the bearings:

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Another

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Another

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Another

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Pictures when you click on them only appear same size. Anyway to enlarge them?

I think it should be working now.

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Another thing that concerns me is that the bearing tangs alternate sides until number 8, which is out of sequence. That makes me wonder if someone has been into the bottom end before. Maybe the factory bearing tang location is random and I just happened to get a set that alternated, or maybe number 8 is supposed to be that way, I don't really know.

the best way to determine if someone has been in there before is if the rod ends have been numbered.

I can't remember what bearing wear means. The center wear is significant to your problem.

This might help:

http://www.bobistheoilguy.com/bearingwear/bearingwearanalysis.htm

No numbering/stamping other than mine on the rods so I guess no one has done anything in there.

Hi Josh,

You're right, the bearings don't seem to be the real problem. They're not 'real bad', as in to suggest they have failed. The center wear would be attributed to inordinate cyl. pressure (your spray). So far as the rod bearings are concerned (assuming the other 4 look similar) I would look elsewhere for the sudden oil pressure loss (and the 'TING' sound).

The TING sound, coupled with the sudden oil pressure loss.....golly, that's a hard one. Perhaps the oil pump? Or the drive? Perhaps the oil pump/dist shaft failed? (doesn't make sense....should be way out of time/not running.) Unless it 're-centered' on the break and maintained correct timing? But that's a real long shot. What else would cause a sensor fault, coupled with an oil pressure failure?
(EDIT: Re-reading....No sensor fault.....your 'check engine guages' just responded to the zero oil pressure)

Soon as you said TING....I automatically thought of the front crank/timing set oil flange. And then I immediately thought of valve train......which of course would NOT cause immediate oid pressure loss.

Sorry man. Just brainstorming here.

Best of luck.

[QUOTE]The TING sound, coupled with the sudden oil pressure loss.....golly, that's a hard one. Perhaps the oil pump? Or the drive?[/QUOTE]
Ditto on that. The noise would steer me away from the bearings as the main culprit although some of the bearings look a little tired. (2nd top, 1st and 3rd bottom). Wether nitrous does that or not I dont know but it isnt healthy for sure. Surprised they took 20k miles of beatings with spray.

If it was a piece of piston skirt or ring land I dont see how that would affect oil pressure.Keep going back to the drive..

The tang you said was backwards, there should be a taper to one side of the rod (big end). Which way was it facing?

Can you see any copper in those bearings, feel your nail dragging across them?

The center of the bearing pounded out is consistant with detonation or excessive cylinder pressure. Especially with a stock bottom end, as the bearing clearance is usually quite tight from the factory.
If you need machine work, aim for .0025 on the rods.
They live longer on spray when they are looser.

All tangs should be faced towards the oil pan rails (outwards)
If one of the tangs pointed inward, the rod was pressed on the piston backwards.

Is it possible that something broke (ring or something) and a piece of it jammed in the oil pump? And possibly the knocking is the oil pump or oil pump drive? Or possibly the knocking is coming from a lobe wiped off the cam or a cam bearing? Let us all know when you do find out what the culprit is.

The ting has me curious, too.

And I agree, the bearings don't look bad enough to have taken oil pressure to zero. I know what those bearings look like... trust me on this, those aren't mine! Mine looked like they made love to 80 grit sandpaper. Seriously.

Something snapped or gave way. I wonder if the cam snapped? I know, a stretch... a valve spring wouldn't do this... I am with calm, check the oil pump drive. If that's stock, isn't it plastic or something? I know the high volume pumps use a metal driveshaft.

What has me really confused is that the oil pressure returned to normal upon restarting. There was zero other symptoms; smooth idle, everything seemed pretty normal, other than the loud low end knock.

I'm going to pull the distributor out tonight and check it out. That was my initial thought when the problem occurred for a couple reasons. I'm using a modified LT1 intake, which doesn't have a distributor hole. I bought the intake with the distributor hole done, and the required spacer installed and machined to what was supposed to be the correct dimensions. The spacer is not the correct shape, and it causes an oil leak because the distributor flange doesn't sit flat on it.

Since the shape of the spacer is wrong, the location could be wrong as well. That has me worried about the distributor gear lining up properly.

I'll know more tonight.

Were there any metal shavings in the oil?

As far as the spacer, I believe it is an angled spacer that makes the distributor sit level. Is that correct? It was a while ago that I was looking at those before I decided to go with big tube runners. I wonder if the distributor was off a little and that snapped or sheared the cam drive gear and the oil pump wasn't spinning. Just a thought. Have you torn any more into the motor?

Matthew

Possible hurt main?

I didn't get a chance to mess with it last night, hopefully tonight.

Hey Josh, sorry to hear about the mishap. Sometimes it takes a complete autopsy to get to the bottom of it. I would suggest using the "H" series bearing, when you put new ones in. Or it seems like they are also labeled as "N" narrow. The "N" bearings are for a chamfered crank. They are harder, and stand up to nitrous better, and it wouldn't hurt to open your ring gaps a little also. Usually a piston would be a good place to look for problems using nitrous, but it obviously wouldn't affect oil pressure.

I still think Dave from APEX V is on to something... It somehow seems logical. The lost and found oil pressure uummm. LS6 from Norbert would fix everything..