l20b eating bearings?

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akara
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l20b eating bearings?

Postby akara » 04 Jan 2017 13:04

A friend of mine has a 510 with an L20b that seems to keep eating bearings, it started with a rod knock, so the engine was disassembled, and the crankshaft was freshly ground by a machinist to .010 on the mains and rod bearings, new oversize clevite bearings were fitted, all main and rod bearings were plastigauged before final installation and bearing clearances were dead on. Oil passages were cleared in the block, nothing plugged up, no sludge, 280zx high flow oil pump was fitted, engine was assembled with copious amounts of engine assembly lube, the engine was never run low on oil and was still full of oil when it had to be disassembled again for a piston ring issue after 500 miles, it was found that all mains and all rod bearings have significant wear already. Does anyone know what could cause this? Is there an oil drainback check valve for the oil filter? I am having a hard time explaining the bearing wear when it was assembled so carefully.

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RMS
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Re: l20b eating bearings?

Postby RMS » 04 Jan 2017 13:23

I will assume the pump was primed....

in he oil filter boss there is a oil bypass valve, when the filter is clogged the oil bypasses the mains and is dumped back into the pan. there is a hardened insert that retains the bearing and spring. gently pry, pull, grind, chisel, and remove insert , bearing and spring then tap and plug, no more bypass
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Re: l20b eating bearings?

Postby Chickenman » 07 Jan 2017 13:03

Was the crank micro polished after machining? Fresh crank turning with inadequate final polishing can leave a fish scale effect which shreds bearings.

Where the crank holes cleaned out thoroughly with rifle drills and solvent after machining? Are any auxilary oil coolers and lines hooked up?

Just throwing out ideas...

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Re: l20b eating bearings?

Postby datzenmike » 07 Jan 2017 15:12

The oil filter by pass does not dump oil back into the pan. If the filter EVER clogged (something that basically is impossible for a gear head to allow) the oil by passes the filter and continues on to the rest of the engine. This oil is un-filtered but far from full of sand and dirt. The engine will continue to run just fine. If the oil was dumped back in the oil pan the engine would simply seize up. It would be preferable to just run on un-filtered oil.


Bearing wear....
Too much ignition advance.
Low speed lugging of the engine.

Got an oil pressure gauge? Pressure relief valve on the oil pump might be stuck open and oil pressure never builds. All you need is about 8 PSI to keep the red oil light off. Hell when I crank my L20B it's enough to shut it off temporarily. Piston ring problem might also bear this out.
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zKars
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Re: l20b eating bearings?

Postby zKars » 07 Jan 2017 15:23

if all bearings and rings are showing problems, insufficient oiling is the most likely cause for sure. Now why?
If the oil pressure is ok at the oil pressure sender there is likely a blockage or crack somewhere that is preventing oil from getting to the right place.

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Re: l20b eating bearings?

Postby datzenmike » 07 Jan 2017 20:11

Once past the oil filter, oil is in a longitudinal gallery running from front to back and there is a supply up to the head with the oil sender on it. I don't know if the oil pressure is good or not and why I asked if there was a gauge. If there was a gauge low reading would have answered this post. The mains receive oil down from this gallery so if all are short of oil then the blockage must be before this.

I suppose the oil filter pressure relief could have fallen out and you were running on unfiltered oil. It would run a long time like this.


Occam's razor says the simplest answer is usually the right one.

A 280zx oil pump was fitted (note that only the 280zx turbo automatic with oil cooler got this high volume pump) I assume this is not the previous pump so very unlikely that both were plugged. If it was the same pump, then this is the cause. (commonality)

If this is a different pump then oil pick up tube is bent upward, gasket to block for tube is leaking air, screen blocked, dip stick wrong oil reading. Chain oil jet fell out, though I don't think this would drop the pressure enough except at maybe idle.
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akara
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Re: l20b eating bearings?

Postby akara » 07 Jan 2017 20:30

Thanks for the ideas you guys, this time an oil pressure gauge will be fitted. Timing was pretty advanced, around 17 degrees on a matchbox dizzy, 91 octane. No oil coolers or anything here. The pickup is in good shape and was sealed to the block with a gasket, the screen was clean, its a clean engine. The crankshaft was polished and is off to be ground again to .020"
I do wonder about the dipstick though, its an L20B with L16 oil pan. How long should the dipstick be?

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Re: l20b eating bearings?

Postby datzenmike » 07 Jan 2017 20:52

Stock timing 12, if modified even less. 17 is off the charts.

Empty pan, add 4? liters, push in dipstick, take out and mark the level. This is now the new correct full level.
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zKars
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Re: l20b eating bearings?

Postby zKars » 08 Jan 2017 05:25

Just another crazy thought. On the 6 cylinder L blocks there is a tapered plug in both ends of the oil gallery that is drilled through the length of the block. I'm assuming the L4 is the same. If the front one was left out after a rebuild, or is leaking, this could return/short curcuit a huge amount of oil into the front cover and down into the oil pan, which would be un-noticed from the outside.

Along the same lines, if the front plug is replaced with a 3/8NPT threaded plug, but is inserted too deep, it can block a passage down to the main bearings.

I know this is a really really long shot, but you have to investigate all avenues.

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Re: l20b eating bearings?

Postby Byron510 » 08 Jan 2017 12:25

zKars wrote:Just another crazy thought. On the 6 cylinder L blocks there is a tapered plug in both ends of the oil gallery that is drilled through the length of the block. I'm assuming the L4 is the same. If the front one was left out after a rebuild, or is leaking, this could return/short curcuit a huge amount of oil into the front cover and down into the oil pan, which would be un-noticed from the outside.

Along the same lines, if the front plug is replaced with a 3/8NPT threaded plug, but is inserted too deep, it can block a passage down to the main bearings.

I know this is a really really long shot, but you have to investigate all avenues.


Concur, the L4 blocks are identical in design. If a 3/8" plug is used at the front and installed too deep, it should only effect the #1 main. The #2 & #4 mains feed the four con rod journals. If you have wear on everything, I would agree that there is an oil supply issue. Check the piston skirts for scuffing while the motor is appart. Jims comment about the oil gallery plugs as worth noting.

Oil gauge is certainly a good idea. And do yourself a favour, install a -4 and 1/4" feed line to the gauge. It makes the accuaracy and response time of the gauge noticibly quicker.

Hope it works out for you. The L motors are not noted for any oiling issues, so you do have a bit of a unique issue. Certainly update is on this, there are many good and experienced minds here to help you out.

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akara
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Re: l20b eating bearings?

Postby akara » 08 Jan 2017 21:15

Thanks for the suggestions guys, the Block is off being hot tanked right now, ill be sure to check the oil galley plugs and relief valves on the oil filter and in the pump. The engine was overcammed with a 270/280 degree cam or some such, so the low dynamic compression of the engine seemed to appreciate the extra ignition timing, there was no evidence of detonation around ringlands, no scuffing on pistons. I will keep this thread updated with information on the build as it progresses!
Good tip on the method to check the dipstick, ill put exactly 4 Liters on it.
Thanks
Andrew

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510wizard
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Re: l20b eating bearings?

Postby 510wizard » 09 Jan 2017 08:14

To add, I would pull the galley plugs and use rifle cleaning brushes through all the oil feed holes and the main galley, you might find some obstruction and will take one other thing off the list.

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Re: l20b eating bearings?

Postby akara » 09 Jan 2017 14:36

Well, the machinist called me to let me know there are two cracks on the center head bolts to the water jackets, so I'm not sure if it will be cost effective to repair.
Can an L series block be run for a while with a crack? Or will it cause serious issues?

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Re: l20b eating bearings?

Postby datzenmike » 09 Jan 2017 15:45

Seen lots of cracks on perfectly good running engines that are torn down. What I haven't seen is an L series that failed from a crack like those. 10-30% probably have cracks if you look hard enough. If you were building a high HP engine maybe not, but for a DD cracks are over rated. If you can't live with the thought, throw it away.
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Byron510
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Re: l20b eating bearings?

Postby Byron510 » 09 Jan 2017 17:28

As noted, many member have run the bier cars with cracks in this location.

viewtopic.php?f=30&t=29434&hilit=Cracked+block

My suggestion is to run ARP studs and seal them into the block, problem solved if the cracks are minor.

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