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Discussion Starter #1
Hi Guys,

There's been lots of discussion lately about the strength and suitability of the stock Niassan con rods to handle forced induction safely.

It's been on my mind for some time and after viewing many pictures of damaged con rods from FI engines this started to get the better of my curiosity as we at APS have not seen or experienced a con rod failure to date.

After carefully viewing pics of damaged rods I have come to the conlusion that many of these rod failures have been caused by bearing failure (big end bearing spun/spinning in the con rod big end).

You see if the big end bearing spins then this causes the con rod to seize momentarily and then the con rod either bends or breaks as you would expect.

The best quality after market con rods are not designed to cope with a big end bearing failure, at this point you will either destroy the crankshaft journal or break the con rod, so now we are at the point of my post, what causes the big end bearing failure ?????

I firmly now suspect either oil starvation or very high oil temperature is the real cause of the bearing failure and I intend investigating this issue at much greater length now.

APS designed a larger HI volume air cooled oil pan with much improved baffling around the oil pick up, I suspect that this had reduced if not eliminated the oil starvation problem and hence why we have not experienced con rod failure at sensible power and boost levels. :doh:

In any event as this was on my mind (I could not sleep last night thinking about this issue) I thought I would share my thoughts with you guys, I welcome any input or feedback from you guys and I hope that we are onto the real cause/diagnosis of con rod failure with FI engines. :wavey:

Thanks

Peter
 

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Thanks for the info and continued research.


Are these improved oil pans available to those of us who may not have an APS setup?
 

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Excellent analysis. Wouldnt it be ironic if simply changing the oil pan would have prevented all the blown Z engines?

Continue the research and let us know what you find out!
 

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Discussion Starter #6
[/quote]


Will do, I'm sure that we're onto something very important here, it deserves a thorough investigation.


Peter
 

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I think you are probably correct that it's a big end rod bearing failure that has progressive damage to the connecting rod once the bearing seizes. Figuring out if it's a bearing issue is actually pretty straight forward. If you can get cylinder pressure versus crank angle any decent bearing supplier can do a simple oil film analysis of the joint. (there are also some simple hand calculations too) If the cylinder pressure increases enough with a supercharger or turbocharger the increased loads drive a significant reduction in oil film thickness. This leads to high local oil temps and the next thing you know you've lost all of your oil film and you now have direct contact and a catastrophic bearing failure. Decreasing oil temps, or increasing oil flow won't help much if at all. Unless...unless part of the problem is the added BOOST increases the heat rejection to the oil such that oil temperatures are WAY out of control. So if normal oil temps are 250 deg F and while BOOSTED you hit 300 deg F...you probably have a problem.

Higher engine speeds help increase oil film thicknesses so if there is a lot of boost at low engine speeds that is probably the point that is causing the bearing failures. Do you know what the bearing material is on the upper rod bearing? Is it aluminum or is it copper/bronze? (steel backed) If it's aluminum a different material might help....good luck. :cheers:
 

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Ok...the real question is what do the bearings look like with the stock turbo/supercharger system after quite a bit of miles?

IF they look like they are far too worn for only a certain amount of power, then the solution may be to get:
Larger oil pan and better (pumps more at a faster rate and has a larger capacity) oil pump.
or
enlargen the oil holes (not feasible)
or
switch to a dry-sump system (not feasible for the price).

So what we have weighing against us is:
Weak rods
Unshielded crankshaft and camshaft angle sensor wire may produce scattered ignition timing
Potential oil starvation problem which can be solved for the cheapest amount is a larger oil pan and larger capacity, quicker flow rate at a larger pace.
Stock fuel system is inadequate over 400rwhp.
 

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The problem im seeing is that there is not one aftermarket company offering aftermarket bearings. I certainly would have purchased them since I am building my engine...unfortunately its already in the final stages and getting ready to be placed back nice and tight into its home. Needless to say I will be PISSED if i find out that it is in fact a bearing failure causing the rods to break. That will almost make building this new engine pointless.
 

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****, I didn`t realize there was such a problem at hand with F/I`d Z´s. I was thinking of buying the APS TT after I get back from Iraq and this information would be of great help. Don`t want to drop over 7 grand and have my engine go because of a $50 bearing fix.
 

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Guys it's not the bearings being weak. It's an oil starvation problem (*IF* the bearings turn out to be worn). Any internal without oil for certain amount of time is going to break, it's just how it is, they have to have oil or they will break/wear/melt.
 

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First post here to say great work guys. :goodtimes: And best wishes with getting to a rapid conclusion on the root cause analysis for the FI'd VQ35DE failures seen to date.

I am considering the aps tt kit and rebuild incl rods, bearings and ceramic coating on the stock pistons. This info is timely for me. Especially if it will help save time and money :clap:

I agree re. bearings failure being the cause for the con-rods failing. However I would like to back up a few levels before we get to oil starvation. IMHO oil starvation is not the most common cause for a failure of bearings. From research the most common reasons in order of frequency are:

- Contamination i.e. dirt in the oil due to either unfiltered oil reaching the bearings and a lack or proper maintenance, and/or abrasive residue left over from machining operations when the engine was last rebuilt. This can cause a a breakdown in the oil film and catastrophic failure of bearings...

- Insufficient lubrication incl "dry start-ups under heavy load/high rpms" and oil starvation

- mis-assembly of bearings,

- mis-alignment e.g. twisted con-rod,

- overloading

- corrosion (doubtful considering age of cars...).

Contamination is the most common cause for bearing failure. However assuming contamination is not the root cause cause...(btw i see all assumptions as a risk until verified), then as per Nis350ZTT's post the apprearance of the bearings i.e. badly discolored with a dark, burned appearance, will indicate either damage due to a dry start or oil starvation.

Dry starts should be fairly easy to identify/eliminate as a root cause.

Now the issue for me is what may be causing the oil starvation. I read an article by Benjamin Nickless University of Missouri, about a condition called "aeration-cavitation". Here's an abstract:

"In current combustion engines, crankshaft rotation creates an adverse effect on the oil flow in the passageways of said crankshaft called aeration-cavitation. This condition is so named because effects similar to those of cavitation are caused by the crankshaft rotation when the oil is aerated (has air dissolved in it). What is actually happening is gas dissolved in the oil comes out of solution when the pressure in the passageway drops below a certain level. The rotation of the crankshaft causes this pressure drop. If enough gas comes out of solution, it can
cause partial or complete blockage of the oil passageway. This blockage can cause bearings in need of lubrication to fail, which is undesirable."

Conclusion I took from this article is to increase oil pressure at intake to help avoid the risk of blockages/oil starvation at bearings due to aerated engine oil...Sounds like an uprated oil pump and aps oil pan are a must...

Full article here: http://www.engin.umd.umich.edu/research/un...ow-2004.doc.pdf

- misassembly of bearings..Could this be a possibility on stock built engines? Perhaps stock bearings are not strong enough to cope with the load?

- misalignment e.g. twisted con-rod, if rods are weak and become misaligned under load, could this not lead to a bearing failure?

- overloading...Not sure of spec.s for stock bearings. However considering the price of this component, I guess nissan didn't over-engineer it in readiness for FI...so it could well be a weak link for FI applications :rolleyes:

Hope the above helps stimulate some ideas. Best wishes again in your search to find the root cause :clap:
 

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Discussion Starter #13
[/quote]

I have no doubt that the big end bearing failure is the cause of many con rod failures that I've viewed to date in pics from the internet.

The real question is what has caused the big end bearing to seize?

I have a strong suspicion that oil starvation (oil running away from the oil pickup under fast acceleration or cornering) is the real cause of the big end bearing/con rod failure and that a well designed oil pan with good baffling around the oil pickup will solve/reduce the chance of this oil starvation problem.

I will investigate this issue more thoroughly over the coming days.

Peter
 

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Discussion Starter #14
[/quote]

I very much doubt this will prove to be a bearing quality problem imho. It's more likely to be an engine oil starvation problem caused by the engine oil running away from the oil pickup under fast accelaration or hard cornering or possibly even the bearing clearances being very tight on some engines.

Peter
 

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Discussion Starter #15
[/quote]

There's not a bearing quality problem imho, I believe it's an oil starvation problem (oil running away from the oil pickup under fast acceleration or cornering which causes the problem) and the best bearings known to man will fail given limited or no oil supply.

I'm 99% sure that the APS oil pan reduces/eliminates this oil starvatiion problem, APS engineers suspected this exact problem during the Twin Turbo development, hence the larger air cooled hi volume baffled oil pan is stock equipment in all APS turbo systems.

Peter
 

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Discussion Starter #16
[/quote]

That's exactly what APS engineers believe the problem to be, if APS is correct with this oil starvation diagnosis then hopefully lots of engine damage can be avoided in the future for all 350Z enthusiasts.

Peter
 

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Originally posted by teh215@Sep 21 2005, 06:04 PM
Is this pan the stock depth or does it require a longer pickup?
[snapback]157120[/snapback]​

The APS oil pan?

If so, the APS oil pan has an extension for the oil pickup, or has a completely new (longer) oil pickup tube.
 

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I would think another option would be to retrofit with a dry sump lubrication system and oil cooler. that should all but eliminate the problem with starvation and temperature. However I am not sure that any one even makes a system for the 350z or what costs are involved.
 
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