Calling the CSC brain trust (1 Viewer)

[1972FJ55]

Here's the situation: I had driven my 80 daily and it had been running fine, just turned 238k. I get in it to go to work and it started, but ran very erratically and a knocking sound from the engine. I shut it off, checked the oil level, which was fine, tried restarting with the same result. Seemed pretty weird since I had driven it the evening prior and it was fine. Another thread pointed me in the direction of the EGR valve or affiliated parts which I spent some time diagnosing today and they seem to be functioning correctly. I decided to compression test it and while I've only checked the front three cylinders, it seems to have <50psi on those three. What type of catastrophic failure would happen just sitting overnight? Any suggestions on what to test or do next? No sign of oil in the water or water in the oil. I just cranked it over and the oil pressure needle doesn't move-gauge was working prior, although I don't know if it cranks fast enough to generate enough pressure to move the needle. So for the sake of argument, if for some reason the oil pump let go, would running the engine less than 10 seconds spin some bearings? I'm not sure that would explain the loss of compression.

 

[murf]

check oil pressure yet? might want to. Ive seen many 80 HG failures without oil/water mixed. Strange that the front three cylinders are low. usually if a HG goes its one cylinder and usually #6.

 

[1972FJ55]

Haven't yet checked oil pressure, but if the oil pump let go, would the tensioner not functioning allow the timing chain to jump time and hence the low compression?

 

[murf]

it possible but also possible the pick up screen is partially plugged? I would eliminate it first imo

lets hope it something simple...

 

[1972FJ55]

timing looks to be ok. compression from 1-6 is 0-25-50-75-100-75

 

[packetstormin]

Something let go in the front of the engine for sure. Seems like a fair amount of the high mileage 80 series are starting to have engine issues. Could be sludge clogged the pickup like what happened to that guy in Utah. I would strain the oil through a coffee filter and see if there are any metal particles in it.

 

[ttubb]

Rex, sorry to hear about this. Please keep us posted on what you find out. Terry

 

[packetstormin]

If you think it spun a couple bearings you can always try and just replace the bearings before swapping the whole engine. I know this is done on a couple of the M series BMWs so I would think it could be done on a cruiser.

 

[BrotherRob]

When you say knock, does it sound like a rod knock or a ping?

Your symptoms sound a bit like mine when the HG went. It was the weirdest HG failure I've ever seen. Near as I can tell, the firing rings on one and six were separating from the block when cold, compromising compression. Upon starting, it was running on 4 cylinders for about 90 seconds, then it would seal up and run fine, until I let it cool down. Repeat............ I had no visible fluid contamination.

Murf's right, it's one and six that usually fail first. One, two and three doesn't make much sense.

 

[Rocky_LC]

Good Luck, Rex -

Let me know if I can help with anything. I saw this thread yesterday, but didn't realize it was you until just now.....

Chuck

 

[BrotherRob]

You might try cranking it over manually and lining up the timing marks. If the tensioner stuck or you broke a timing gear, the chain may have skipped a few teeth out of time and the valves would be opened at the wrong time. That might explain your compression numbers. Never heard of this happening on an 80, but it's a possibility.

 

[1972FJ55]

Thanks all of you for your suggestions and concern. I re-checked the compression after putting some new O-rings on the tester (zero on #1 just didn't seem right) and the numbers were better, but still not where they should be. 60-70-65-105-115-105 so now I'm suspicious of my tester. I put everything back together and it started, still sounds different when cranking, but you can hear the knocking. Oil pressure is good. Broken piston rings? My next step is to dig out the stethoscope and try to isolate where the noise is at. Will also check timing.

 

[medtro]

Sounded very much like rod bearings knock that I saw before. I would remove lower oil pan looking for debris, continue to remove upper pan if there are debris.

 

[packetstormin]

I agree with Jackson, it does sound very much like a rod knock. I am guessing you spun the first three bearings. If the crank is in good shape it could be an easy fix compared to pulling entire engine.

 

[1972FJ55]

If it's rod bearings, how did they spin while sitting overnight

 

[medtro]

I guess it didn't happen while sitting overnight. It happened right after you started the engine. Let us know what you find after listening with stethoscope.

 

[Funner]

I have had a mechanic tell me my motor sounded like it was blown ended up being an old belt coming apart. Worth a double check.

 

[medtro]

Not saying you have rod bearing problem. Good reading material, Bad Rod Bearing. Draining motor oil didn't reveal the problem.

 

[1972FJ55]

Naturally this had to happen while we're in the midst of a kitchen remodel, so I probably won't delve into this further until the weekend.
Thank you all for the ideas so far.

 

[inkpot]

Major mechanical failures like rod bearings usually create lots of metal bits in the oil. Just pull off the oil filter and cut the end off. Check the filter media for metals. Been trouble shooting an 80 with a significant knock, but no metals suspended in oil, and no change in noise after quite a few miles, so thinking it is something other than rod bearings which would probably continue to deteriorate rather quickly. John