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Discussion Starter #21
pics of pistons #8 & #10 will be posted by next week along with crank picks including thrust bearing.

Mr. P
 

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PS: Do you know if the S85 bore is serviceable? It does not have liners from factory, but I seam to recall something about the BMW block material that could save me. Is it electro lined or bored raw?
If you can find a shop that manufactures plastic injection molds, they'll most likely have a laser welder and they'll also have great knowledge with respect to the material. I'm sure they could have it welded up in about 20 minutes if they have the right material. Then you'd just need to rebore to clean it up. That's what I would probably do.
 

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Discussion Starter #23
Hello M5board,

Attached are multiple pics of pistons #8 & #10. Ring lands not issue. #8 all rings locked, #10 still moving and "springy"

Crank looks good.

Thrust bearings also not issue with near ZERO wear or end-play.
 

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Discussion Starter #24
Hello NAK91,

Thank you for the comment. How would laser welding help my bore situation? I am interested to learn and am located in Metro Detroit with many engineers and shops. I am not familiar with the Alusil block, but am learning.

To my understanding the complete block is Alusil, then treated for pistons. Do not yet know process steps and sequencing, but my "base" understanding is the bore is cut 1st. Then "etched" to expose "hard" silicon to surface, then a final bore/hone?

Please advise and thank you again for the comment.

Mr. P
 

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Hello NAK91,

Thank you for the comment. How would laser welding help my bore situation? I am interested to learn and am located in Metro Detroit with many engineers and shops. I am not familiar with the Alusil block, but am learning.

To my understanding the complete block is Alusil, then treated for pistons. Do not yet know process steps and sequencing, but my "base" understanding is the bore is cut 1st. Then "etched" to expose "hard" silicon to surface, then a final bore/hone?

Please advise and thank you again for the comment.

Mr. P
A relatively common way to repair these blocks (at least in Europe) is to sleeve them with an alusil sleeve. I haven't really looked into shops here or Europe that specialize in this process.

However, if you can find a good tool and die manufacturing company (I wouldn't be surprised if there were quite a lot in the Michigan/Indiana/Northern Ohio area), they will very likely have a laser welder because they do repairs on injection molds of various hardened tool steels as well as mold quality hard alloys of aluminum. They use laser welding because positional control over the weld puddle is very precise and heat input is also very localized, which is important in maintaining the crystalline structure, and, therefore, the hardened properties of the steel or aluminum they're welding.

If you can source some of this welding rod or have the shop source it for you, they should be able to weld those areas up for you, thus avoiding sleeving. You could then rebore and hone to original size.


As far as any coating that is applied to the bore, I'm unaware of what is used, if there is any coating at all.
 

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Hello M5board,

Attached are multiple pics of pistons #8 & #10. Ring lands not issue. #8 all rings locked, #10 still moving and "springy"

Crank looks good.

Thrust bearings also not issue with near ZERO wear or end-play.
Wow. Piston 8 pic 2. I've never seen damage like that before, but it's not like I do this stuff day in and day out either. Hard to explain why the pistons were gouged like that especially above the first rings, it's like there was some sort of debris in there. It could have been that someone had rotated the crank long after the engine was pulled and any oil that was on the cylinder bores had long dried up and created the scoring, but I'd still not expect the piston crown being that heavily scratched. It's like I was scraped against bare concrete or a coarse file.
 

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Discussion Starter #28
Wow. Piston 8 pic 2. I've never seen damage like that before, but it's not like I do this stuff day in and day out either. Hard to explain why the pistons were gouged like that especially above the first rings, it's like there was some sort of debris in there. It could have been that someone had rotated the crank long after the engine was pulled and any oil that was on the cylinder bores had long dried up and created the scoring, but I'd still not expect the piston crown being that heavily scratched. It's like I was scraped against bare concrete or a coarse file.
Hello gmtegear,

Thank you again for the comments and response. I am also befuddled with the piston/bore situation. I am even more curious on #10 cylinder as crown shows the wear you mentioned on #8pic2, but just starting. Could this have been the start of what happened to #8? It is also "strange" that the wear pattern is not against the thrust angle of the piston, but instead more along the crank shaft axis (toward front of engine)......hmmmm. Do not have answer, thrust bearings & crank end play fine.

I will check for any piston pin play next week. Running out of theories for failure as it looks like engine had oil pressure and all bearings look "nice", including cam bearings!

Mr. P
 

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Maybe there was mud that slid down in the engine and got wedged around those areas and created the coarse abrasion.
 

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If piston has no lateral play on piston pin or on big end of rods this is what you get; lateral thrust loads on cylinders .example of piston guided rods below
06E9F633-B655-4D9B-ABB4-4FBB5BEAE18C.jpeg
 

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but not clear how that describes the coarse wear pattern on the piston in #8, that is not just due to lateral thrust....

also I'd think this would be a far more common problem...

I looked for side clearance issues that may have been due to inadequate clearance on the bearing caps side of the rod and I didn't see heat issues. There's no published spec from BMW on side clearance that I could find when I looked in to this before.
 

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Exact same pattern that happened to me on a sportbike engine while racing many years ago. Overheated. Oil pan temp reached 140C. Wish I'd been using TWS LMAO....
 

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Discussion Starter #34
Maybe there was mud that slid down in the engine and got wedged around those areas and created the coarse abrasion.
Good thought, but mud was on cylinder #2 and after cleaning bore is fine. Believe most problems with dirt in heads are related to 5 years of storage and bore was damaged 1st, as in before storage and rusty, crusty heads. Dirt, mud, water, would also never have gotten through the air intake system without affecting other bores on a running engine. All the internals of the engine as far as oil and water are CLEAN and NICE!

I would like to know if anyone has comments on cylinder #10. This could be the start of what happened in cylinder #8?

No heat signs of heat on any rod/cap for all 10 cylinders.

Mr. P
 

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Discussion Starter #35
Exact same pattern that happened to me on a sportbike engine while racing many years ago. Overheated. Oil pan temp reached 140C. Wish I'd been using TWS LMAO....
Hello flacoramos,

Possible that engine overheated on coolant and/or oil side causing expansion of piston in the bore. Makes more sense based on scaring being inline with crank and bores at the thrust angle start to "egg" with miles. Expanded piston would then be more subject to scaring in the crank shaft axis.

Interesting theory!

Mr. P
 

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Hello flacoramos,

Possible that engine overheated on coolant and/or oil side causing expansion of piston in the bore. Makes more sense based on scaring being inline with crank and bores at the thrust angle start to "egg" with miles. Expanded piston would then be more subject to scaring in the crank shaft axis.

Interesting theory!

Mr. P
this makes sense

To explain the coarseness of the cylinder wall damage could be classic case of “cold seizure”

If one goes full throttle on a cold engine, the pistons become very hot and expand ahead of cold cylinder block

the pistons become even hotter from friction in a very tight bore, thus momentarily welding itself to the cylinder wall and pulling away material evidenced by coarse surface finish
 

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Discussion Starter #38
Hello Siim Pallav,

Thank you for sending this link and I will investigate.

I comes at a good time as I just pulled the heads on my second engine and cylinder #8 is trashed!....grrr and my luck.

Mr. P
 

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Depending on cost to machine block for sleeves, Troy offers a 5.2 L, that comes with new pistons and a larger bore for a reasonable price
 

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Discussion Starter #40
Hello ticat928,

I was really planning on a "simple" build to OEM spec. Not working out that way at this time....grrr!

Worried about thermal properties, but based on what I have received, maybe I should not be that worried about sleeving or other options?

Do have 17 good pistons....so will most likely opt for a bare block and ....start again.... :-{... And :) happy for 100k/miles...?....! TBD.

Mr. P
 
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