Bearing Knock Issue

[Shiven]

Ok, so I'm having some issues with a bearing knock on a freshly built engine. Here's the background:

My dad was driving the car quite hard, and somehow oil was pushed out of the oil dipstick and the car was low on oil, enter the bearing knock. So being budget and hoping for a miracle we opened the bottom of the engine and No.6 bearing was run, so we put a fresh set of big end bearings and hoped for the best. So I drove the car at low rpms to run in the new bearings and oil pressure was fine, unfortunately 50km down the line the bearing knock came back. What were we thinking, right? of course the crank journal and rod were damaged even though they looked fine.

So we decide to do it properly. We got a good deal on forged pistons and rods so we went that route instead of resizing the stock rods. We couldn't find another crank to use, so we had it reground 10thou. A new set of 10thou ACL race bearings were used. We opened the oil pump and inspected it, the back cover seemed to be developing a small crack (hadn't gone all the way through, but was a disaster waiting to happen). We managed to get another back cover which was in good condition and bought a set of Reimax oil pump gears. We took the pump to an engineer who specialises in Rb26 oil pumps, he machined the back cover flat to ensure no leaks and he check the clearances and pressure tested the pump with paraffin, all was good and the pump was ready to go.

The entire rotating assembly was balanced and we also added an ATI street damper to the build. The motor was assembled and the bearing clearances were in spec. Started the motor up and it showed 2kg/cm oil pressure on idle and the motor sounded 100% . I drove the car around for about 10km, all under 3500rpm to run in the new rings and bearings. I noticed a slight rattling sound at about 2500rpm, go home and when I hold it at about 2000rpm I can clearly hear the bearing knocking!

What can be causing this? I've replaced the rods and bearings, crankshaft was reground, everything was balanced and the oil pump was fine. The oil level was also fine, but the bearings didn't last 10km?

I've researched this and people have been saying that the oil plugs should be removed and the galleries in the block should be cleaned (which I didn't do, there was no metal filings in the oil, but I should have done it.)

Is there anything else that could be the problem and what else should I do? I was thinking about getting a new crank and taking out the oil plugs and cleaning the channels, and also putting some oil restrictors for the head.

Excuse the long post, I wanted to get everything included so you guys can assist with some ideas as to what the problem is.

[MattiasJacobs]

If I was you i'd buy a crate LS3 and drop that in there lol. I am on my third motor too and if anything ever happens to this one then fak it.

[Skym]

Check the clutch, if too strong (pressure plate) it can damage the thrust bearing and take out no 5, 6, etc bottomend bearings (crank walk).

Oil restrictors is the other area to look at, especially if running a N1 oilpump with Reimax gears and Tomei or Nismo baffle plate in sump to keep oil around pickup during launching, high G corners, etc. Also Accusump setup can help with oil starvation problems.

But if have forged internals, you should be running a higher pressure, volume Tomei oilpump (or similar oilpump, Nitto, Group-A oilpump, etc) and bigger capacity sump to suit with box section, one way trap doors around pickup (High Energy sump or similar).

Tomei recommend to run their oil pump with their forged internals, enlarged sump -

http://www.tomei-p.co.jp/_2003web-catalogue/000_complete-engine/en_engine_rb26dett.htm

Another option is running a ROSS single stage external oilpump setup, etc where you can adjust the pressure, etc and solves the powersteering belt failure problem (common with high hp rb engines) in one go -

http://blog.rossperformanceparts.com/category/engine-protection-kits/nissan-rb26/

I would say dry sump setup to be 100% sure all oil, etc related problems are sorted, but not many can afford it.

Popping the dipstick sounds like engine is overpressurising (pressure has to go somewhere) and would point towards catchcan restriction problem. I think it should be at least 2 litre (minimum) for the capacity of engine and properly vented.

Also if sump is pressurised, would make oil stay in head (block oil drains) instead of returning to sump via oil drains thus less oil in sump and pickup uncovers when cornering, launching, etc which causes oil starvation. Common problem with wet sump RB26 engines.

A person in Japan created this part (many have copied it) to equalise the pressure in sump, head, so oil returns to sump through the drains -

http://www.spoolimports.com/spool-oil-drains/spool-rb-twin-cam-cylinder-head-oil-drain-kit

There's a story behind why many thought it was a oil drain only (probably does act as a oil drain as well). But if you look at where it's placed on sump, it's above the oil level in sump, hence there to equalise the pressure in sump, head.

[Shiven]

Thanks Skym for all the information!
I actually looked up getting a Tomei pump, baffle and sump extension after all of this happened. But I thought about how the knock happened this time, there was no hard driving and all below 3500rpm, so can it be an oil starvation issue at such low rpm if the oil pressure is sufficient? Or is there something else I'm missing.

I actually haven't stripped the motor yet, but maybe I'll find some clues when I do

[Skym]

You're welcome. Pressure can build up in sump at lower rpm, but if it was, should blow turbo oil seal first (weakest point). Excessive blowby could pressurise the sump, so ring to bore clearances could be wrong (too wide).

Are you using mineral oil (run in oil) for run in??? Could be oil temps (thinking high oil temps and mineral oil could be breaking down hence bearing failure)??? Motul sell good oil.

Are you initially running engine in on a engine dyno, hub dyno, roller dyno or on road???? It's best not to rev engine to high rpm (above 3500rpm and some tune engine to 5000rpm with run in tune for 2000km and retune for above 5000rpm up until 5000km, where you switch to synthetic oil) while initially running engine in.

Could be clearances (don't use a plasti gauge to check bearing clearances, use proper measuring equipment that engine builders have that helps to avoid this problem). Was crank balanced with flywheel, crank damper, etc attached??? I think you said it cracked oil pump backing plate, bearing failure, reused crank (first time the bearings were only changed without checking crank balance) points towards crank balance problem (crank needs to be replaced).

Wear on bearing surfaces, thrust bearing failure should tell the story (if it's clutch related or oil starvation problem).

[Shiven]

The Ring end gap was checked during the build and was in the spec set by Wiseco. I used Shell HX7 synthetic oil and was running the car in on the road, and only did about 10km before the knock happened.

Should I be using a micrometer to check bearing clearances? The crank was balanced with the flywheel and I if I remember correctly the run out was 0.7mm (I could be wrong though, I don't remember clearly what the engineer said). ATI says not to balance with their damper, so it wasn't included when the crank was balanced.

will have the motor stripped by the weekend so we'll see what the damage tells us then

[caliber676]

Yes, all engine measurements should be done with a micrometer. Some people just trust machine shops word but its always good to double check/plastigauge

[Dragon Humper]

You got a banana in your tailpipe........

What I mean is, there is a blockage in the oil gallery that feeds that end of the block. Could be some foreign material or casting flash/garbage left over from original machining. You have more than enough volume and pressure of oil, it just isn't getting to where it should be.




Jon.

[christdeyoung]

I thought these crank journals needed to be nitrided after grinding or something to that effect.

[Skym]

Get a motorsport engine specialist (someone who builds racecar engines) to check parts, balance parts inside engine, check clearances. Each engine is different after machining parts and following recommmended specs is sometimes where it can go wrong. Best to get engine builder to assemble engine, as they know what needs to be done and some have engine dyno's to check if engine is ok and can run engine in for you.

Also did they line bore where crank goes on block, line bore camshaft journals (can cause low oil pressure problems)???

Also Dragon Humper is right, sometimes there can be metal, etc blocking oil, coolant passages in block, head.