Bad bearings or bend rod? Quick quiz

[Quantum TD]

So, I'm at a loss on this one (well not really, I just don't want to open the can of worms and find out).

I've had my friend's 1984 Rabbit 1.6D in my garage for about 8 months now. It came to me with absolutely no compression. I pulled the motor apart in July, and left it apart in the garage while I worked on other paying projects.

Just this past month, I decided to put it all back together. Here's what we did:

Head:
New valves (exhaust only)
New guides (all
New valve seals
Valve job (seats recut)
resurface (decent sander-type resurface)
Correct gasket (1 notch, the old one was a 3 hole).
New bolts
seals, etc.

Bottom end:
New Rings (Std)
New rod bearings
seals, etc
Hone cylinders

Here's where I'm nearly certain the problem lays. When I pulled the pistons, the #2 ring on each piston had cracked in half. I can only assume that someone was shooting ether into the intake for quite some time in order to crack those rings. The other rings were fine, but there was a ton of carbon buildup in the grooves. I didn't mic the bores, as the car is really not worth it.  But, the bores looked pretty bad. There was no pitting or scoring, but there was a noticeable ridge at the top. I tried to hone it out, but it would have taken forever. So I just honed each cylinder and cleaned out the bores. Then I reinstalled the pistons with new rings and rod bearings.

I told my friend that we could put it together, and it would run, but there was no telling how long the motor would last or how fuel economy would go, since the compression was bound to be a bit lighter than if we had bored the block and put in new pistons.

So, last night, I got it back together enough to see if it would fire. After some coaxing, and bleeding air from the injectors. It fired up, and  sounded quite good for a car that had been sitting for about 10 years. The oil light went out, and I ran the motor for about 10 sec before turning it off: quite pleased with my work.

Since I had started the car with a squirt bottle full of diesel fuel (the tank needed to be cleaned), I spent today cleaning the tank and the lines. I replaced the old crispy lines and bled the system. I also installed a new filter-to-pump line (clear) to see if it was sucking air.

The second I started the car up, it sounded HORRIBLE, as if something was knocking. At first, I thought it was some dirt that got into the injection pump when I replaced the filter-to-pump hose. So, I let it run for a few seconds (again, oil light went out), and loosened each injector line to see if it was air in the line, or if the noise went away when I removed pressure from them. It sounded the same on all 4, and ear-testing the injectors showed that they were not making excessive noise.

So, then I thought about oil pressure. I double-checked the oil, and it was a bit low (about 1 1/2 qts), but not enough to cause any damage, especially since the oil pressure switches showed good. So I topped it off, and went to it again. Same noise and quite loud.

Then, I checked the head. I reasoned that the valves might be hitting or something, despite the fact that I had measured the projection of the pistons, and had properly set the valve clearance (mech head). The lifters all looked good. There was oil in the head and on the cam, and no damage anywhere up top that I could see.

So, i crawled under the car and hand cranked the motor over. The wonderfuld compression I had before starting it, had softened up to mediocre, and there was a palpable feeling in the wrench, from where the noise was clearly coming  in the bottom end. Here's the fun part: the noise is continuous, and not episodic. That is, I can feel the noise at all parts in the rotation of the crank. So, it can't be from bent/hit valves, since that would only be noticeable when the pistons came up to (presumably) hit the valves. Also, the car was still running, so it must have decent compression (i.e. not bent valves). So that's good news.

The only thing I can come up with is a bad bearing(s). But what could have caused it? I lubed all the bearings with prep grease. The parts were all clean and grit-free. The car had good oil pressure, and I primed the oil filter before starting, and I primed the intermediate shaft (oil pump). The car sounded great last night, and now it sounds like crap. BUT, if you rev the car up over 2000 RPM, the noise goes away. While it's tempting to think that this fact would rule out bad bearing (or bent rod), all the evidence I have so far really makes me think bad bearings.

I guess it's possible that a ring broke (by hitting the ridge?), but the car idles perfectly (albeilt noisily). This makes me think that the injectors, pump, head and pistons are all ok.

Anyone out there have an experience like this? If so, what kind of damage can I expect on the crank? My dad (who's done this quick and dirty repair method several dozen times), claims that the crank should be fine. Could a piece of dirt in the injection pump cause this type of racket? I'm fairly certain that it's not the pump, but that is the only part on the car that I touched since I started it last night, and the noise appeared instantaneously when I cranked it today after fiddling with the fuel system.

Thoughts anyone??

[jimfoo]

You always need to remove any ridge when installing new rings.

[Quantum TD]

You always need to remove any ridge when installing new rings.

According to the book. Although I have never done it this way before, I have friend's who've done it dozens of times (simple hone and re-ring), and my father's done it to at least 2 dozen diesels back in the day. They never had problems. In fact, my VW mechanic friend who does side work, re-ringed a 1985 Golf about 7 years ago that had about 175k on it, and he still sees it on the road.

Also, I may have overemphasized the ridge. I would have liked to rebore, because I too like to go by the book, but it wasn't a 'fingernail -catching' type of ridge, just a wave near the top that seemed more pronounced after I honed with a straight hone. With the dingle-berry hone, it looked fine and you wouldn't even know it was there.

Anyway, I guess I'll find out tomorrow when I drop the pan, and/or drop a few sticks of TNT in the car.

[bigblockchev]

If you disconnect the rods and push the pistons up out of the way do you still get the resistance. If it is rod or ring related it should go away. If not I'm thinking thrust bearing worn or damaged to push the crank forward or back in the block, or even insufficient thrust clearance. Sounds like you will have to pull the motor and crank to determine the cause. I have found that taking everything apart is usually faster than trying to troubleshoot with everything still together. Not really enough information to do more than wild guess. Keep us posted, Dan

[Quantum TD]

Just inspected the rod bearings. They all look good. No wear on those.

Then I pulled the lower mains (#s 2,3,&4): all had wear (not excessive) on the lower bearings. Basically, the aluminum caoting had worn down on the centers. ON the # 3, it's close to the copper.  I haven't checked 1 & 5 yet, or the top beaings. But, there are some copper flakes in the pan (new, as I had cleaned the pan before reassembly).

Could this cause my problem?

What I'm thinking is this:
1) Before the rebuild, the car had no compression
2) The car sat for 5-10 years before rebuild. While I lubed all the parts that I installed (wrist pins, rings, rod bearings), I didn't lube/inspect parts that I did not replace (i.e. main bearings, intermediate shaft bearings)
3) Since I lubed all those parts, they're probably not the problem. Also, if the intermediate shaft bearings were bad, I'm sure that I'd get the oil buzzer on the dash, as I'd be losing oil pressure. No?
4) Since the car had no compression, perhaps had no lube on the mains after sitting for 5-10 years, then perhaps the new compression on dry mains may have caused the wear.

I'll post an update once I check the rest of the mains. In the meantime, if anyone has some idea.... My dad actually thought wrist pins.

[jimfoo]

Yeah, dry bearings isn't a good thing. Probably better check the intermediate shaft as well as if the mains got hosed, they probably did too.

[Doug]

Did you happen to do a ring end gap check in the bores before installing them on the pistons?

[Quantum TD]

Did you happen to do a ring end gap check in the bores before installing them on the pistons?

Nah. This was to be done on the cheap.


Here are some current thoughts on the matter:
1) Ring #2 on all pistons was cracked.
2) There was HEAVY carbon buildup behind the rings. It took me about 4 hours to scrape all the crap out.

Could the knocking be piston slap? It usually goes away when the motor gets warm. But I haven't gotten it warm yet, since the noise is so horrendous, I'm afraid to run it long. The cylinders were worn, and then I honed them, so there may be too much clearance now.

The only other option is bad main bearings. But would they make noise at low RPMs and disappear at higher RPMs? Seems like bad main bearings would make noise at higher RPMs and under load.

[Quantum TD]

Yeah, dry bearings isn't a good thing. Probably better check the intermediate shaft as well as if the mains got hosed, they probably did too.

I just checked the IS bearings. They look fine, and there's no play in the shaft.

[jtanguay]

maybe the rings need to seat? if all looks good maybe thats how the car will run...  any injector work done? maybe they're just stuck from sitting so long.  try running that diesel purge?

[Doug]

"Could the knocking be piston slap? It usually goes away when the motor gets warm."

More than likely this is your culprit. It will probably run for a good long time. Just be cautious to keep the rpm up and not lug the motor. Could also be in addition to the slap, a leaky or poor pattern injector(s) that is aggravating the slap condition.

[Quantum TD]

maybe the rings need to seat? if all looks good maybe thats how the car will run...  any injector work done? maybe they're just stuck from sitting so long.  try running that diesel purge?

Good points. I think I've narrowed it to the following possibilities or any conbination therof:
1) Bad wrist pins (unlikely)
2) Rings seating (likely)
3) Piston rock or slap (possibly)
4) Injection pump (maybe: I might have dropped a bit of dirt in there when playing with the fuel lines). Could air in the lines sound that bad (like hammering). I loosened all the union nuts on each injector, and the sound remained.

The noise definitely is not coming from the crankshaft, despite the slight wear on those bearings.

I can feel the pistons move in the cylinder as the rings scraping against the cylinder walls. Do seating rings make that much noise? It occurred to me that this is possible, since there is really nothing lubricating the pistons as they move. The rods are not rifle-drilled, so the only lubrication for the pistons has to be oil that is slung around inside the crankcase.

Another thing that occurred to me is that it may be a broken clutch disc or pressure plate or something? The noise really sounds like what you might hear on a Jeep or a Chevy with a cracked flywheel, but I've never seen it happen on a VW before.

As for the piston slap, from the few things I've googled that has sound bites, piston slap should make the car just sound MORE like a diesel, rather than sound like something hammering.

[jtanguay]

what is the timing set to? more advanced?  mines at 1.06 approx and with the cold start pulled all the way out it has a really pronounced 'slap'  :lol: maybe the injectors are worn though...

[Quantum TD]

what is the timing set to? more advanced?  mines at 1.06 approx and with the cold start pulled all the way out it has a really pronounced 'slap'  :lol: maybe the injectors are worn though...

Timing is set at .98. I did pull the cold start lever out. That's something to look at.

[Quantum TD]

After much research and deliberation, I think that it can only be one of two (maybe 3) things).

1) Piston slap. This would explain why the noise is present when cold. One test would be to see if the noise goes away when the motor warms up.

2) Broken clutch, pressure plate, or flywheel. While I've never seen this happen on a VW, the symptoms mimic that of a broken flexplate (although this car doesn't have one). When you rev the car up, the noise goes away.

3) Injection pump. Not sure why the car would make a knocking sound via the IP, but I guess anything's possible. Air or dirt in the pump? Don't know.

So, I guess I'm going to put it all back together and run it in the yard for a while to see if the noise goes away. If the noise goes away (or lessens) once the car heats up, I'll know that it's piston slap. If it doesn't go away except when the car revs up, then I'll look to the clutch, pressure plate, flywheel area. If the noise gets worse at all RPMs and temps, then I'll just start over and mic the pistons and the bores.