Spun a bearing, sweet, now I get to rebuild

[jwerty1]

So, I turbo'd my 74 620 L18.  Been driving it for a for a few weeks at about 8psi of boost.  93 octane, water injection, oil cooler, intercooled, radiator.  Runs cools, loud, so I really can't tell if there is any detonation going on, but I don't think there was.  Left work to run an errand today.  Hopped on the highway and started hearing this unnerving lower end noise.  Wasn't sure at first as I have relatively solid motor mounts and I get a lot of body noises, but it sounded familiar, like a spun rod bearing.  Pulled over and listened under the hood, yeah, that's what it was.  Finished my errand and decided to drive home to get my other vehicle and go back to work.  Didn't think much of it because I've driven one of my old Toyota trucks with a spun rod bearing for weeks before it got bad enough I thought it might make the block unuseable.  Just about got home and the noise got worse and worse(oil level was fine, and like 500 miles on it, checked it before I left work).  Put the clutch in at a stop sign and it shut off.  Started back up, but I called my wife to come get me.  Dragged it back home after work and started getting ready for removal.  Pulled the pan and sure enough #1 rod bearing almost gone. I'm not too upset as I was waiting for something like this to happen so I could rebuild it(definently did not try to blow it up though).  But I was expecting to kill a piston under boost or something, not a spun bearing.  Anything common to l18's for spinning a rod bearing?  I know I've read extended detonation can take out a rod bearing, but I won't know for sure until the weekend when I get it out and the head off.

 

Also, anyone with rebuild parts, l20b dished pistons, or just general tips for finding parts or for the rebuild let me know. I'm open to all suggestions.  I was planning on following Jason greys turbo l18 idea with l20b pistons in my l18, new bearings of course, get the crank/rods checked at a machine shop, bore the cylinders, etc. 

[banzai510(hainz)]

rockauto.com

ebay?

look up silvolte pistons

[620Turbo4X4]

Were you using the stock oil pump? If so, not enough volume for the engine and turbo...

 

Using the water injection as a way to retard your ignition timing was, and is, a bad idea too….

 

Myself…and from my own past experiences with my old turbo 620, I would never use cast pistons and a carb on a turbo engine again. Not saying it can't be done and still get good power from the engine, (my ol' truck was pretty darned quick.. well, for 20 years ago...), but forged is by far stronger and will bend, instead of cracking… JE offers a forged piston now that has very minimal thermal expansion (similar to stock). Unfortunately they don't make a stock type piston for the L series, so it has to be a custom jobber…. I live by the old saying "You can spend a little now… or a lot later" so thats what I'm running. No more turbochargers on cast pistons for me...

 

The carburetor is also bad idea as previously mentioned in your prior "turbo l question" thread… It is very important to have even cyl to cyl A/F ratios and precise ignition timing for power and reliability.. neither is really possible with your current setup… Considering that you said your old engine only had 68k? You'll most likely end up with the same result (engine death) by simply rebuilding another stock engine. So... consider the forged pistons, o-ringed block/head, stainless valves ,high volume or turbo oil pump, and or at least EFI on the next engine….

 

Go back and read my previous replies from your last thread… Lots of good advise for ya there….

[datzenmike]

To spin a bearing it first has to be pounded to shit so that the tabs can't hold onto what's left of it. The bearing slips out of place and blocks the oil feed hole, the heat welds the bearing to the crank eventually turning the rod blue, which doesn't matter much because it's toast now too. If going fast enough the rod and crank weld together, the rod is forced to turn by vehicle speed and engine power and snaps off, the end swings around and punches a hole in the block.

 

If knocking loud it may not have spun yet but either way the crank is almost certainly toast. If squealing it may have slipped and the rod is now likely bad too.

 

Oil pumps from KA24E motors in the 240sx (S13) and all KA24E and KA24DE D-21 Hardbody truck engines have a high volume output oil pumps. New are around $100 more if you ask for anything 'turbo' like from the 280zx. I pull mine from running wrecker motors and have them on all my Datsun L or Z series motors. I highly recommend them on any L series as good insurance.

[jwerty1]

have a brand new ka oil pump on it.  Still need to get the engine pulled out I haven't had the chance yet.  I did pull the pan and the #1 rod bearing was spun.  I'll have to do some research on the pistons and stuff once I get the motor taken out and torn down.  Need to see if the crank is still ok and that rod.  I'm going to have all the rods checked just to be sure.  I am really interested to see the inside of the cylinders to see how they look. As a side note I tore the engine down 2 years ago for a knocking noise and all the bearings were great, found loose flywheel bolts.  However, upon initial startup the carb wasn't working properly and the ignition took a poo.  So while I was messing with things my oil light was on, but I thought it was just an electrical issue because it had always flickered.  Got to thinking and put a gauge on it, 0psi!  Tore off the pump, verified it wasn't blocked, verified the pressure sender wasn't blocked, verified the pickup wasn't blocked, then put a new oil pump on.  So, I probably ran the motor for about a half hour total with no oil pressure before I figured out the oil pump.  So, I knew I've been on borrowed time, but it was fine till the other day.  I appreciate all the info guys.  I am going to install an oil pressure gauge this time, just to be sure I am where I need to be. 

[jwerty1]

I might be getting my hands on a l20b... I'm trying to figure out a decent way to lower the compression. If I swapped in l18 rods, obviously it would be destroking the motor, however, what kind of compression would I be at.  I'm trying to find a decent compression calculator, and I just want to make sure I'm coming out with the right numbers.

[datzenmike]

L18 rods would give you 4.14 compression... enough? Why lower the compression? It lowers the efficiency and will drive like a slug unless constantly boosting. Keith Laws 510 L20B runs 10.5 and cranks out 248 RWHP..

 

You have intercooler and oil cooler, so improve on them.

What is your oil pressure relief valve set at? Rule of thumb is 10 PSI per 1,000 RPMs expected to see.

Water injection? not water and methanol injection. The alcohol will absorb way more heat than water alone, course if you're 'in it' 24/7 it will cost.

Do you have a dedicated cold air inlet, or are you running warmed rad air?

Do you have some form of ignition retard based on boost PSI? 

Is your rad capable of absorbing heat spikes from turbo use or is it on the edge most of the time?

What thermostat are you running?

Are you running any gauges? EGT would tell you what's going on inside the engine and turbo. A/F would be VERY handy. 

[jwerty1]

I am picking up what you are laying down.  Yes it is about 1/3 meth injection (I get washer solvent free from work).  I have a stock KA pump, I have not read up much on differing pressure relief valves.  Air inlet is right behind the driver side headlight.  I was reading up some on Jason greys info on boost referencing the vac adv diaphragm, so I may go that route as that would be cheaper than buying an msd setup.  If I can get it to work.  Rad is working great.  Low rpm cruising or sitting and idling it will hit the middle of the temp gauge.  Higher rpm cruising the temp drops instantly.  Highway speeds it barely registers on the gauge.  Cooler is better right?  I'm not sure of the thermostat, its brand new however.  I have a wideband a/f gauge.  Tore the motor out last night and took it down to the crank. Here are the pics, showed a side pic of #1 piston had some vertical wear from bearing failure. 

 

 

 

 

 

 

 

 

All 4 pistons seemed to be worn the same.  As a side note my last teardown I took a grinder to the top of the pistons like an idiot, don't judge me!  I have never inspected for detonation evidence before so I don't know exactly what I'm looking for.  There may be some dirt in those photos from my garage, I tried to wipe it all off.  All in all, there were no cracks in the pistons or combustion chamber.  A lot of carbon buildup.  It did concern me, the exhaust valves except #2 all had a flaky build up on them.  I did chip away at them some just to see.  The top ring on #4 was broken.  I'm not surprised with the odd deposits and broken ring seeing how when I first got the truck, it didn't run for crap, when I put it back together the first time my oil pump took a poo, and also, my brand new weber was lean for 2 years, which I didn't realize until I put the a/f sensor on it with the turbo install.  So I drove it for 2 years lean backfiring a lot.  So all in all, it hasn't run great, until I put the turbo on and drilled the jets.  Let me tell you, off boost it ran better than it ever did with the drilled jets.  The spun bearing is a set back, but hopefully it will be back up and running better than ever.  My parts guy gave me a number for Bill Erdman, a guy local to me that has been racing z's for years.  I met with him at his shop yesterday and talked to him for hours.  Very cool guy, old school racer.  His cousin has 2 l20b's sitting around that Bill said he would probably sell me and also a z 5 speed.  He's calling me back today supposedly.

 

I apologize for the bad quality on the pics, thought my ipod would do better than that

[620Turbo4X4]

The l20b would be a better engine IMO. No replacement for displacement!!!

 

The compression ratio for turbos depends on what type of power your trying to achieve. For maximum top end power you'll want to lower the compression so you can get more air/fuel packed into the cylinder. That makes the engine a dog for normal driving. I would just run the stock 8.5;1 compression (not a stock engine!!!) with around 12-15 lbs boost for decent drive ability and power. Typically every 15lbs boost will double the air flow of an engine, therefore doubling horsepower, and everything else....

 

There's lots of good info on the Internet if you search.

 

Read this,

 

http://www.xcceleration.com/cr-boost%20101.htm

[datzenmike]

Top ring gap is critical. For a turbo it will get hotter than stock and expand more so needs more clearance. It the ends don't have room to expand they will break.

 

Stock hyper-eutectic pistons are very brittle and won't take near as much boost as a set of forged. Factory turbo engines typically keep it down near 6-8 PSI for good reason. With inter cooler, meth, ignition retard, oil cooler you can dare to go higher.

 

The pressure relief valve in the oil pump can easily be shimmed with washers to raise the oil pressure.

[jwerty1]

So, what do you guys think of the pictures of the pistons and valves? Does it look like detonation going on or just wear?

[620Turbo4X4]

Broken piston rings is not normal and is a dead give away that something is not right.

[datzenmike]

 

This is not a picture. I have no idea what this is.

 

This looks like an L cylinder head but what are we looking for?