Interesting video about S65 rod bearing

[Jun 208]

Pretty interesting video for high milage S65 and applicable for S85 engines as well

Looking at the video, to be honest the rod bearings looks pretty good for its milage. 152k miles is 244k kms, even our 24 year old Prado doesn't have that milage.

We replaced our S85 rod bearings about 61k kms, better condition but definitely beyond normal wear.  Mechanical insurance paid the claim. 

I think @TermiPeteNZ maybe have the highest milage before rod bearing replacement?  Anyone else had high milage before replacing their rod bearings?

Maybe rod bearing issue is over-hyped?

 

[aja540i 1896]

I think mine was about 160k when I had them done, would have been damaging the crank if I had left them any longer.

[Jun 208]

NZ S65/S85 rod bearing replacement (highest to lowest)

1. @aja540i 160k kms
2. @TermiPeteNZ 140k kms ???
3. @Jun 61k kms

 

[Michael. 2312]

I think if all the S65 and S85 engines had proper mechanical sympathy from day one the situation would be different.

That would mean:

> Low rpm driving until oil is at full operating temperature.

> correct oil change intervals, ideally shorter than oem recommendations

> correct oil grade / quality

The situation would certainly be different 10+ years on. 

Many people that owned these cars beat on them when the oil was cold and/or had been overdue for a change, accelerating wear. 

It's easy to blame the engine but these aren't regular motors they are high compression NA motors making strong power at high rpm so if anything need to be respected more than more conventional lower rpm engines. 

[aja540i 1896]

There are design compromises in these motors that contribute to the short lifespan of the bearings, it makes correct servicing and carefull running a bit more important than usual but that won't totally prevent the issues from occurring.

[Jun 208]

5 minutes ago, aja540i said:

There are design compromises in these motors that contribute to the short lifespan of the bearings, it makes correct servicing and carefull running a bit more important than usual but that won't totally prevent the issues from occurring.

@Michael. I have to agree with aja540i here.  I have done really a lot of research before we bought our M5, there is no data that concludes the rod bearing will not wear if care it taken.  It does help, but doesn't stop it.  I saw one M5 owner who had done proper oil changes and adding ceratec for years.  I can't recall from new, but definitely he had the car for a bit before he replaced the rod bearings.  The rod bearings was in better shape, but definitely worn.  It looked similar to ours, but a bit better.  There are also those that have done 2nd rod bearing replacements by (forgot his name, but from what I read he has done in the several dozen rod bearing replacements).  They are a tuning shop and have done lots of S85 and S65 tuning.  They tried to also look at what happened on the 2nd set.  He has recommended his customer to use a particular oil and lower viscosity.  Initially some people told him that should not be done, but I think that particular oil is close to the original 10w60 Castrol when it's hot.  In fact if that was easily available locally I would probably use that personally.  You get a better cold viscosity and almost the same viscosity of the original Castrol oil.  I think the 2nd rod bearings set showed better wear, but it didn't NOT stop it from being worn down.

TLDR; rod bearing wear is part of the ownership of S65 and S85, but I think it is not as bad to what most people think.  I wasn't planning to replace ours, my original plan was when it was close to 100k kms.  But things went differently, long story... in the end it worked out better than I expected.

[Michael. 2312]

6 hours ago, aja540i said:

There are design compromises in these motors that contribute to the short lifespan of the bearings, it makes correct servicing and carefull running a bit more important than usual but that won't totally prevent the issues from occurring.

What are they? 

[leichtbau 525]

6 minutes ago, Michael. said:

What are they? 

High cycle fatigue of the bearing substrate as a result of repetitive peak firing load.

The upper bearings (from the rods) show a wear distribution that is exactly in line with the crank/rod angle you'd expect at Pmax. Be it S65 or S85, you'll see the same wear on each banks bearings, but mirrored as they're 90 degree engines.

The underlying copper is the support material for the primary soft bearing top surface. It acts to provide a careful mix of strength and compliance / softness. Copper is chosen because it's "tough" and hence highly wear resistant, yet soft enough to be able to catch and embed any debris. However, Copper work hardens; every time you load it, it gets harder, and eventually it can crack. For bearing substrates, the peak firing load (peak cylinder pressure) occurs at 8-12 degrees after top dead centre (TDC) and that load is carried cyclically (every firing event) by the upper bearings (and passed onto the crank to make torque).

This fatigue event happens all the time, and is primarily load, and not speed, dependent. Once the substrate starts to crack and degrade, the upper soft metal bearing surface experiences high localised stress and begins to pit and break up. This eventually destroys the bearing and journal's ability to "surf" on a nice even film of oil thickness, and results in catastrophic pick-up between those sliding parts, high friction, heating and ceasing (that then snaps a rod or pulls the little end out of the piston) all of which are curtains for that engine.

Now, how to the bearing f**k-up occurred:

In the early 2000's Lead was banned due to health concerns, which is unfortunate as it is a brilliantly useful metal for when you need to carry sliding loads - it's tough, crack resistant, wear resistant, has a nice "softness" and comformability. Early bearings without this holy grail of materials simply didn't cut the mustard. OEM bearings are getting close to being as good as Lead was, and race bearings are simply still using it, as they're not subject to type manufacturer constraints.

 

 

 

 

[leichtbau 525]

In the interests of S65/85 longevity, you want to avoid periods of high load at medium to low engine speeds - No inertial forces to cancel the firing loads means there's more time for the engine oil film to be broken down.

EDIT: the BMEP (brake mean effective pressure) on the S65/85 is the intrinsic design fault cc: @Michael.

Edited August 27, 2021 by leichtbau

[Michael. 2312]

Ohh lead free bearings. That explains a lot 

[Allanw 1051]

15 hours ago, Michael. said:

Ohh lead free bearings. That explains a lot 

Just like lead-free solder!

[thorns 20]

Is this issue also something that now seems to be appearing more and more with the later model F10 M5 engines as well, now most are out of factory warranty?

Have noticed a few US forums starting to make noises about it, but often they are not stock M5s so interested to hear if it is something that should be considered/budgeted for before buying one.

 

[Jun 208]

1 hour ago, thorns said:

Is this issue also something that now seems to be appearing more and more with the later model F10 M5 engines as well, now most are out of factory warranty?

Have noticed a few US forums starting to make noises about it, but often they are not stock M5s so interested to hear if it is something that should be considered/budgeted for before buying one.

 

Not sure, but rod bearing issues also existed on older M cars (S engines).  However they aren't as prevalent as the S85 and S65, as their rod bearings have super thin tolerance, high revving engines, etc.  As with any performance car like the M cars, always budget for things.  This is easier said than done, I myself budgeted, etc.  However when you are on that spot, for me it wasn't as easy.  Good thing is that after doing the big jobs, it's slightly feels better.  Having a community around the cars is definitely the best part of owning this eclectic cars.