Tell-tale signs of rod bearing failure?

[Slam]

Guys, can you tell me exactly what the warning signs are?

Here's what the oil gauge doing: Pegs fine at 5 bar on warmup and settles down as engine warms. So far so good. Once engine is warm, idles at 1.5 to 2 bar but bounces. Under acceleration, gauge will rise quickly to 4 bar, stick and lag, drop to 3 bar, then continue on up to hwere it should be.

I've R&R'ed the OPRV, using appropriate tools. It's not sticking. I've made sure the torque on the crank bolt is correct. I've made sure the connections to the gauge are happy. I'm running 10W30 dino oil right now - any thicker and the car just will not crank in the kind of winters we get here.

What I'm seeing the gauge do tells me it's time to call EBS.

Have you had rod bearings fail, and if so what were all the warning signs? I think I've got 'em.

[AznDrgn]

Sounds like normal operation for a 20+ year old oil pump. How many miles are on your motor? Do you dog it a lot? Never hurts to change them since they are prone to failure.

[nynor]

are you getting any noise from the bottom end?

[Usmellgass2?]

Cut your filter open, bits of copper tin or lead indicate that you are loosing a bearing. Bits of steel or iron (check with a magnet) usually indicate a cam or valve train failure.
Listen for a distinct knocking sound as the engine derevs. Have a helper blip the throttle to 2500-3500 then back to idle. A long screw driver or stethoscope from the side of the block to the ear will help.
Erratic oil press is usually a sticky pressure relief.
Oil press dropping of at higher rpm usually means the crank is spinning oil out faster than the pump can supply it due to excessive rod and bearing clearance. Or there is a suction side restriction.
Connecting rod and crank shaft parts bouncing off the bottom of the car may indicate a catastrophic failure, a brief visual inspection will confirm this. Btw you will suddenly be driving (spinning) on oil as will the cars coming up behind you. Been there, done that, sucks big time

If I can clarify or help please let me know
TC GW

[bigyagi]

hmmm. assuming your handbrake is in good condition, then pull it full on, bring the revs up to about 1800rpm,and then gently let the clutch out, in first gear until the revs start to drop. hold at this point. and listen. if you hear a regular, distinct knock, then your rod bearings are shot. if you hold the revs at 1800, and blip the throttle slightly, you would hear the knock, as the revs rise, and then fall. i'm leaning toward oil pump/ valve.
as a side note, my eng temp sensor, and air temp sensor both went tits up, and i swear to god, i could hear rod knock. however, it was detonation setting in, but sounds similiar. usually causes damage!

[Slam]

First off, I haven't had time to myself to troubleshoot but I'll do it this weekend - thanks for the tips, guys.

I have been keeping an eye on the pressure gauge, and here's what I've seen. Cruising in 4th or 5th gear, it reads about 1 bar for every 1,000 rpm on the tach. When I'm highway cruising, if I accelerate without downshifting (just put my foot down), the oil pressure drops slightly. If I let up on the gas and the RPMs spin up (decel), the pressure comes up. In short, when the engine is put under load while cruising, the pressure drops - betcha that's the oil being squeezed out of the bearings because of too much clearance. When the engine spins up as I decel, pressure comes up - no load, no squeezing.

Think I'm on the right track? I suppose this is mostly academic at this point. That motor must have 250,000 miles on it.

[bryanthompson]

I have the same mileage and almost identical symptoms, among a few others that aren't related to this. haven't had enough time to really dig in though.

[Usmellgass2?]

You might want to plum in a temporary mechanical pressure gage to eliminate any electrical gremlins. But at 250000 miles its probably time for a fresh bullet.
you might consider a thicker oil.

[Zero10]

250k miles, if your rod bearings aren't gone yet, they're going to be soon, lol. It wouldn't be a bad idea to do them as preventative maintenance.

Where in Alberta are you? I presently have my 951 in pieces in the garage, flipping over piston rings. I could show you how bad the job is. On an early N/A it isn't that bad. especially if you don't have power steering or A/C. Realistically, if you have a garage (need rafters ), or an engine hoist to hold the motor up, it only takes a few hours. Pull the steering rack, A/C compressor, drop the crossmember, and you're pretty much there. The belts stay on, belt covers, starter, etc, it's really not that bad. I had my 951 torn apart down to the rod bearings, and the head off within 1 day, and that was about 2x as much work as R&R'ing the rod bearings on a N/A.

Your oil pressure symptoms sound like worn-out rod bearings, but they haven't failed yet. When they go, you will know, there is no better way to describe it than saying it makes a knocking sound that will make you sick to your stomach.

[Zero10]

Oh, I should also have mentioned, use something like 0W40 synthetic for our chilly winters, it will help with your oil pressures, improve cold starting, etc.

[bryanthompson]

Zero, my garage is drywalled on the walls and ceiling, so is there any other way to hold the engine up? Is it safe (or possible) to use an engine hoist while i'm below it? While I'm in there (famous last words) is there anything that can be done with the oil pump to make sure it keeps on keepin' on?

Honestly, one of the reasons I'm considering the V8 swap is because I think this might be too big of a job... and if I'm going to pay someone else to do the work, it isn't that big of a jump to slap a v8 in there. If it's something I can do, though... I'll give it a try.

[bigyagi]

you could try using a couple pieces of 3x3 wood, supported on either side of the car. a small piece sits around the shock tower,on either side, and the 3x3's go across. hook up some chain or whatever, and it will hold no problems. i think there is something like this at clarks garage..

[Slam]

Hey, Zero, I'm in Wainwright, AB. Love Calgary, though. That's where the car came fom when I bought it all those years ago... I've got no A/C, no P/S. Got an engine lift but I may build an engine support tool for the front fenders like the pic at Clark's. Thanks for the tip, bigyagi. I don't know if I trust the lift to not sag while I'm under there. I'll switch to 0W40 next oil change (in about a month or so). Any good brands?

I've got no knocking (yet) and now the temp outside is colder the car idles at about 2 bar without bouncing. Oil pressure is still a little wonky with the car warmed up and on the highway (as described above). I'm gonna order the bearings with an eye to changing them when the idle oil pressure starts to alarm me. The motor should give me plenty of warning if I'm constantly listening for knocking, no?

I know about the horrid sound made by bad bearings. My wife's 931 threw a rod this summer - made me sick listening to the racket. That car's torn down right now - easier than the 944 bottom end 'cause the engine isn't supported by the crossmember.

Zero - I've read all about your piston ring fun. How's that going??

[Zero10]

I would run Mobil 1 or Amsoil, but I'm really anal.
For the most part, I believe for what Mobil 1 costs, it's good preventative maintenance.
So you know about how rod bearings sound. Argueably, that's one of the worst sounds in the world.
If you ask me, you should order the bearings, and set a time in the not-too-distance future to change them. If you hear any knocking before then, change them, but either way I think they should be done. Do you know if they have been done in the past?

I would use an engine hoist if you could, but I suspect a wooden strut-tower brace could work just as well.

As for the piston ring fun, it's getting less fun by the day. I ordered new rings a month ago, and was told they were shipped. I called last friday to ask about them, and he offered to send me a new set, but didn't ship them until (he says) tuesday. The tracking number still isn't in USPS's system. I was supposed to do the rings today, because the weather is only going downhill from here. I'm pretty damn mad about the whole thing really, since I'm paying insurance and registration while the car is just sitting there. Once it's fixed, it's going to be parked for the winter, so I can drop the coverage, so really, this is costing me a lot of money. I wish people could hold true to their word...

Anyhoo, I thought I would extend the offer, give you an inside peek at what you will find. But, since you've done them on a 931, you're probably just as well versed as the rest of us (perhaps better). I'm curious about how you could change them, do you have to split the crankcase?

[toolboy62]

My car has been exhibiting the same symptoms for a while now, but I never worried about it since the engine sounds fine. However, I'm reasonably handy, and if new bearings are easy to install I can roll some new shells in no problem. Are the rod bolts TTY or reusable? Can you drop the pan without jacking up the engine?

thanks,

nate

[Zero10]

Rod nuts should be replaced. If you support the engine from above, you can drop the whole crossmember no problem.

[Slam]

Hey, Zero, 931=924 Turbo, so no case splitting to be done. Thankfully. It's bad enough as it is. With my wife's 931 we got quite a shock when we dropped the pan. The number 1 rod had completely destroyed the #1 bearing - nothing left at all. So it's engine rebuild time. We just havent had the time to pull that motor yet.

Which is why I'll do the 944 before it gets too bad - lessons learned.

Hey toolboy, it's doable but you've gotta support the motor from above to drop the crossmember (it supports the motor). Good time to do motor mounts as well.

[Zero10]

Hahaha, brain fart. I always think 911 turbo when I hear 931.

Hey, there is a guy in the parts section selling some 50-over 924 pistons, no idea if they are N/A or turbo though, might be helpful if you're rebuilding.

Yeah, rod bearings are always best done as preventative maintenance, not as fixing something that broke....
That's bad, Mmmmmkay?
Sorry, couldn't resist.

Actually, speaking of rod bearings. My old 86 burned a while ago. Presently I'm working on parting it out, and am getting ready to drop the drive-train, in order to salvage some parts for my 951's track motor (crazy plan... 9.6:1CR turbo motor). I had no idea about rod bearing problems when I bought the 86, and thought 0.5 - 1.0 bar of oil pressure at warm idle was normal, so now I'm curious about how my rod bearings will look when I pull the crank for use in my new motor. I'll be posting pics when I get it down that far

[Mike Markota]

Hey Slam, ever figure out what the problem was?

I've had similar symptoms , but the clutch went out on the car before I could get any further. Now that I am replacing the clutch/torque tube/trans...and my motor needs oil cooler seals, has the same oil pressure problem...I figured just replace the motor For ~$500, do the clutch on the new one, replace the torque tube, do the belts...and rebuild the old one as money/time allows...

BUT if it isn't the rod/main bearings I wouldn't mind driving with this motor...I've already replaced EVERYTHING on my moneypit and would just like to cut my losses and put more then 300miles on my freakin car...

anyway, just wanting to see if the problem was figured out for sure and what it was..

[Slam]

Mike,

I still haven't had to open the motor up! I've been watching my oil pressure like a hawk and the symptoms aren't getting worse. In fact, they've stabilized and I'm not that concerned right now. There's no signs of rod knock and the oil pressure needle isn't dancing either. Still low at idle with a thoroughly warm engine.

When the weather turns warmer I'll do the rod bearings regardless of whether or not the symptoms have become worse. Right now the cold is helping to keep my oil pressure up!

Cheers,

S.