Any engine experts that can help re some technical questions on an bmw s85 motor?

Base timing, compression & leak pretty much thumbs up or thumbs down a motor. Then it's all the junk. Bmw overengineers for no real value. Based on the posts once basics are established I'm looking at that kooky electro mechanical throttlebody system.

 

Do you mean re-cc'd? I don't know what "recoed" refers to, but if you mean they cc'd the heads, that means they measured and equalized the volume of the cylinder head chambers down to usually around 1 or less cc of each other.

Let me know if maybe that's what you are referring to here.

Ray

 

Just for clarification, are you saying it has 0 PSI compression through some sort of measurement or it just 'sounds like' it has no compression because it spins over and does not fire?

If the latter (e.g. it just spins) that can be a result of flooding. If the engine mis-fires, it can wash the spark plugs with fuel so the point where they are what is called gas fouled and then you have no further spark. If the motor is cold and the pistons rings aren't making a great seal and/or there is some mild sealing issue with the valves, for example, the engine will spin over with no spark and basically it just pumping additional fuel through the mix. This further exacerbates the gas fouled situation with the spark plugs.

Next time this happens, you might want to pull a spark plug out and see if it smells of gasoline.

Ray

 

I'm not sure I would polish your crank. I have polished (micro polished) cranks in the past and never had any issues. However, you are referring to ISF / REM finishing here, which generally take the RA surface roughness down below a level of 4 (if memory serves me correctly). That might be good in some respects, however it could introduce some other issue: specifically the ultra slick surface would be serving to mitigate the oil's ability to adhere to the crank surface.

With bearings and bearing clearances, they are very specifically made to produce an oil pressure wedge. If you create too smooth of a surface on the journal, you could actually be inadvertently introducing some other issue. The journal could be so slick that oil could be escaping too fast (out the sides, for example) or you could be altering surface adhesion properties so greatly that you are accidentally increasing oil cavitation, etc.

Here's a link to some information:

https://www.substech.com/dokuwiki/doku.php?id=hydrodynamic_journal_bearing

You can jump around the different links, but the link above gives you an idea of how delicate things can be in terms of producing the proper.

The companies that do ISF polishing will tell you how great it is. However, I've used it and had issues also. I did a differential a while back and ISF finished all the gears (R&P, spider gears, etc.) and found it had a bit of a subtle whine to it. I spoke with another company that does ISF finishing (and they also do cyro-hardening) and from what I can tell, they don't recommend putting that ultra slick polish on gears, because it defeats oil adhesion. So I'm wondering if perhaps that's a factor here with your crank and you are accidentally throwing off something.

When everything is working correctly, the crank journals should never touch the bearings. There is an oil film between them. So to be spinning bearings right and left, either someone didn't re-size something correctly, or the ISF / REM finishing is doing something bad (or you just have a flat out oil system failure of some kind or another).

Ray

 

It's not easy to find good engine builders. This is why I do all my own work on motors. Even the stuff I have to farm out (line boring, etc.) I always, always, always double and triple check the measurements using my own measuring tools.

It sounds like the people in charge or building your motor are just guessing here. They need to figure out what the cause of the failure is, not just randomly add oil coolers.

Ray

 

+1 to that. BMW can suck it as far as I'm concerned.

There's a reason I only buy old Toyotas now

Ray

 

Truth!!! Took me 4 chevy motor builds to get one race worthy. I rebuild so infrequently I hate to gear up for it but I'm going to have to do as you are doing next time

 

Yeah, it's no joke. I'm even having a hard time finding anyone in our town who can bore blocks any more. I spoke to the machine shop I have used over the years, but they were saying they aren't able to find anyone qualified enough to run their boring/honing machine. They have a Sunnen CK10 - which is a nice machine - but nobody that knows how to use it.

Once I move and build my own shop, I think I'm going to purchase a Van Norman boring bar, unless I can use a mill maybe somehow to shave down .005 at a time from cylinders.

Basically, I trust no one below .001" When you start working in .0001 or even .0005", you gotta assume someone is gonna mess up something at least now and again. I mean even tool temp or work temp can throw you off at that level.

Ray

 

Okay, got it. Yeah, that makes more sense.

Can you get photographs of the failed bearings front and rear? A spun breading (which I've had happen to me) is a pretty extreme failure. It's indicative of more than just a small problem looming. Also, to have this happen on two bearings (unless perhaps they are on a shared journal) seems extreme (unless there is some systemic oil failure).

I'd also be interested if they checked the crankshaft and rods for straightness / flatness as part of the rebuild. Sometimes when an engine undergoes a failure, it can mildly impart a twist to the connecting rods. If this isn't detected, the rods can cause a tilt in the bearing journal area and this can create all sorts of issues.

Ray

 

Sure, no problem.

Ray

 

Don't throw a lot of money on new parts; do a leak down test. Do you have any information on what work was done with the valves?
The VANOS system is known to cause problems if the solenoids are dirty. This condition will cause the engine to run poorly and even die at low RPMs, but it shouldn't result in no compression.

 

I think what Michael meant (although I don't want to speak for him and I could be wrong) is that the motor cranked "like it had no compression", not specifically that it 'did have zero compression' via any sort of measurement via a compression gauge. In other words, it just spins over freely.

Ray

 

I think it is hydraulic lifter pump up. I think the lifter is getting over pressured and holding the valves open until they bleed down. When it is warm, the oil may be too thin to pump up the lifter. The set up height may be too tight if the seats and valves were reworked without correcting the stem height. It may be the oil is too heavy when cold, it does take 10-60 from what I read. That is the only thing I can think of for compression that goes away and comes back.
Maybe try thinner oil as a diagnostic tool and see if it changes. Monitor the cold oil pressure vs warm pressure and see if it is very different. It is dry sump and should have the ability to move a lot of oil quickly.

Just my thoughts.

 

I think you could be right on the money. I was emailing privately with Micheal and had similar concerns that something wasn't allowing the Vanos system to relax. I haven't heard back from him (he's traveling I believe right now), but I had suggested maybe disabling the solenoid which allows oil flow to the Vanos gear thing, just to see if the motor suddenly runs okay.

I was also wondering if maybe some debris got into the oil system, which could be causing the Vanos gears to not move as freely as they should.

Ray

 

That perhaps oil viscosity / thickness isn't a factor in the operation of the Vanos system.

Ray

 

I learned years ago you can’t be a “blank filler” you need to know why things work the way they do and then fill in the blank so to speak. sounds like you have it figured out; which is cool.