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Thread: Machining M50 head. Finishing /RA (Roughness Average) factory spec?

  1. #1
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    Machining M50 head. Finishing /RA (Roughness Average) factory spec?

    Hi everyone,

    This isn't discussed a lot, but finishing plays a significant role in how your brand new head gasket will perform. A lot of times new leaks develop due to incorrect finishing of the machined surfaces.

    So far, I learned that finishing requirements differ, depending on what Head Gasket will be installed.
    Multi-Layer MLS head gaskets require much smoother finishing than the OEM gaskets.

    I am trying to find factory specs for the finishing of the machined head for an OEM head gasket. I will be installing Victor Reinz from the gasket kit I bought from ECS Tuning.

    So far I've found conflicting information:
    Here VAC Performance offers an MLS gasket requiring finishing of RA = 50 or finer.
    Here the author is stating that factory spec on M50/M52(?) is RA = 20 or better (factory gaskets are not MLS).

    Do you guys have any helpful information about this spec? My head is in the shop now waiting to be machined. I'm trying to find some information and call the shop if BMW has a specific requirement. Better be safe.

    Cheers!
    Last edited by make it easy; 04-23-2019 at 02:44 PM.

  2. #2
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    Quote Originally Posted by make it easy View Post
    Hi everyone,

    This isn't discussed a lot, but finishing plays a significant role in how your brand new head gasket will perform. A lot of times new leaks develop due to incorrect finishing of the machined surfaces.

    So far, I learned that finishing requirements differ, depending on what Head Gasket will be installed.
    Multi-Layer MLS head gaskets require much smoother finishing than the OEM gaskets.

    I am trying to find factory specs for the finishing of the machined head for an OEM head gasket. I will be installing Victor Reinz from the gasket kit I bought from ECS Tuning.

    So far I've found conflicting information:
    Here VAC Performance offers an MLS gasket requiring finishing of RA = 50 or finer.
    Here the author is stating that factory spec on M50/M52(?) is RA = 20 or better (factory gaskets are not MLS).

    Do you guys have any helpful information about this spec? My head is in the shop now waiting to be machined. I'm trying to find some information and call the shop if BMW has a specific requirement. Better be safe.

    Cheers!
    No matter what gasket is used, a higher RA is always better. 20 is good, 10 is better, organic gasket or not.

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    A stock gasket will take 180ra no problem. But, that being said, its best to get atleast 120. I think the mls needs a wants atleast an 80 (which is factory spec).
    I found threads where people overcame ra values with spray on viton between gasket and the surfaces. But i couldnt find commercially available viton anywhere.
    Nobody would recertify these machines after somebody screwed with them without any visibility into what they did.

    HONK! HONK! Clown car coming through!

    -Oakdizzle

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    Not to hijack as it is on topic... But with modern machining capabilities being what they are... Why a head gasket at all? I seem to remember hearing that nelson engineering just uses a thin layer of symtech to weld the cylinder head to the block. Not sure if its bullshit or not, but I have often been curious as to why we still need these at all.

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    Machining M50 head. Finishing /RA (Roughness Average) factory spec?

    Quote Originally Posted by FiberFast View Post
    Not to hijack as it is on topic... But with modern machining capabilities being what they are... Why a head gasket at all? I seem to remember hearing that nelson engineering just uses a thin layer of symtech to weld the cylinder head to the block.
    While you may have a point ALL old school engines were designed with a gasket minimum thickness between the head and block. The same gasket thickness proper for piston/valve clearance.
    That and dissimilar metal expansion with iron block and aluminum head, a gasket allows for dissimilar metal expansion rates.



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    Last edited by bluptgm3; 05-04-2019 at 03:43 AM.

  6. #6
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    Quote Originally Posted by FiberFast View Post
    Not to hijack as it is on topic... But with modern machining capabilities being what they are... Why a head gasket at all? I seem to remember hearing that nelson engineering just uses a thin layer of symtech to weld the cylinder head to the block. Not sure if its bullshit or not, but I have often been curious as to why we still need these at all.
    I am no expert at all, but I assume it's due to different types of metal coming in contact.

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    Quote Originally Posted by bluptgm3 View Post
    While you may have a point ALL old school engines were designed with a gasket minimum thickness between the head and block for valve clearance.
    That and dissimilar metal expansion with iron block and aluminum head, a gasket allows for dissimilar metal expansion rates.



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    Fair point. That makes plenty of sens with dissimilar materials in us m50/m52 ect, but the aluminum block and head motors... why? Slightly different expansion rates due to geometry? As an engineer I wonder why we bother separating the head at all, you could drop the valves down the bore from the bottom, and use a bolt in main girdle for piston access/clearance. I was designing a motor like this a few years back, steel core with an aluminum shell. Im sure its kicking around on an old drive somewhere.

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    Its just because of the different expansion rates of the metal. It has alot to do with holding the head down to the block. People dont weld aluminum to cast iron. Specially when theres parts that may possibly have to come out. Valves, pistons, ect.. Thats like building a swimming pool jumping in and then haveing a friend weld a permanant cover on.
    Engine blocks are designed that the block takes the forces of the piston and convert it to torgue through the crankshaft. Haveing a removable piston through crankase design only makes the block larger to accomodate the now nessesary longer rod length instead of having a bolt on head that is smaller, lighter, disperses heat better, makes valve systems more accessible, and allows for an overall quicker repair time. . Its alot less trouble, weight, and backwards engineering to just have a simpler and easier towork on engine. (Like the way it is)
    Last edited by spyderg0d; 04-26-2019 at 11:55 AM.
    Nobody would recertify these machines after somebody screwed with them without any visibility into what they did.

    HONK! HONK! Clown car coming through!

    -Oakdizzle

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    Quote Originally Posted by spyderg0d View Post
    Its just because of the different expansion rates of the metal. It has alot to do with holding the head down to the block. People dont weld aluminum to cast iron. Specially when theres parts that may possibly have to come out. Valves, pistons, ect.. Thats like building a swimming pool jumping in and then haveing a friend weld a permanant cover on.
    Engine blocks are designed that the block takes the forces of the piston and convert it to torgue through the crankshaft. Haveing a removable piston through crankase design only makes the block larger to accomodate the now nessesary longer rod length instead of having a bolt on head that is smaller, lighter, disperses heat better, makes valve systems more accessible, and allows for an overall quicker repair time. . Its alot less trouble, weight, and backwards engineering to just have a simpler and easier towork on engine. (Like the way it is)
    That's just not the case. I can model it and show you, but the rods don't need to be longer. You can drop the girdle on a mating plane just below the cylinders. This actually makes the block allot stronger, because the "webbing" designed into the mains is all in the girdle. As for the torque/applied forces, that will always be between the cylinder head and main journals. Bolt in the head, or bolt in the girdle, its the same with the exception that you can stuff god inside you cylinders and not blow a headgasket that doesn't exist.

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    So you still have a cylinder head but the pistons sit in the head?

    - - - Updated - - -

    What would be easier to work on,. Your engine, or the sort that every manufacture uses?
    Nobody would recertify these machines after somebody screwed with them without any visibility into what they did.

    HONK! HONK! Clown car coming through!

    -Oakdizzle

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    Machining M50 head. Finishing /RA (Roughness Average) factory spec?

    Quote Originally Posted by spyderg0d View Post
    So you still have a cylinder head but the pistons sit in the head?

    - - - Updated - - -

    What would be easier to work on,. Your engine, or the sort that every manufacture uses?
    Keep in mind that aircraft air cooled piston powered engines have integral cylinder/cylinder head. Ridiculously expensive to overhaul, ask any piston powered pilot.


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    Last edited by bluptgm3; 05-05-2019 at 11:55 AM.

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    In my conceptual design there is no separation between the head and block. It is unnecessary, the head and block can be integral. Pistons and valves can be installed from the bottom of the bore if the crankshaft main caps are removable. So basically the head/cylinders are an internal steel structure with an aluminum shell that bolts over it. The main caps are made from a sandwich plate (Upper main) and a girdle (Lower mains) that would bolt directly onto/into the internal steel structure. The reasoning here is that you already need bolts for the main caps, so you are utilizing those bolts to function as the cylinder head as well, by allowing you to install the valves at the base of the bore. Now you have no head/gasket to blow, if it lets go you just malformed the steel structure (Not happening) or launch the crank out the bottom of the block. This is all hypothetical of course as we are moving to electric cars, no one is investing in internal combustion anymore.

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    Huh? Did you just say no one is investing in internal combustion anymore? Wtf
    Nobody would recertify these machines after somebody screwed with them without any visibility into what they did.

    HONK! HONK! Clown car coming through!

    -Oakdizzle

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    Quote Originally Posted by spyderg0d View Post
    Huh? Did you just say no one is investing in internal combustion anymore? Wtf
    That's what I said, I designed a four stroke engine that has 270 degree strokes (As opposed to 180 degree conventionally). I showed it to a bmw engineer and he said it might be useful as a hybrid range extender but that was like 10 years ago. No one is actually investing in internal combustion anymore, if you are you are going to lose your shirt. All of the OEM's are going electric, all of them. The internal combustion engine is not going anywhere, they are just going to get more and more expensive to get parts for and operate as time goes on. Try finding parts for an old anything, if it was manufactured before 1950 chances are you are screwed (Flat head style cause phillips screws didn't exist yet) and will need to manufacture it yourself.

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    Yeah...I don't buy that. Yes OEMs are moving heavily towards electric no doubt, but there's still some pretty impressive innovations going on with ICE. See variable compression engines in the last couple years, Mazda's gas compression ignition engine...

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    Im giggling pretty hard rn. ������. The masses demanding ethanol and diesel tech, along with multi displacement engines, the invention of direct injection,.. Im absolutely baffled and humored at the same time.
    All with the almost complete failures of electric cars in most any market. Sure some people want a tesla,,. But thats far away from being actually being in demand.
    I also have some inventions that are unconventional. But unfortunatly, manufacturers are alot more experienced with billions invested in every bit of attempt to improve anything and everything, they know more than we do. And if it isnt on a car right now, they already have a planned piont and perfect sales pitch and a date for it being released at some piont in the future.
    Nobody would recertify these machines after somebody screwed with them without any visibility into what they did.

    HONK! HONK! Clown car coming through!

    -Oakdizzle

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    Opinions area opinions and dollar are spent. Go look at where its being spent.
    Direct injection is new?! Its almost 100 year old tech. Only now we have high pressure electric fuel pumps instead of mechanical *Jazz hands*
    "The first Otto cycle engine direct injection system was designed by German engineer Otto Mader. It was used for a Junkers airplane engine in 1916."
    "They know more than we do" Apparently, which is why most oem's are healily investing in EV's.
    Pretty much everyone wants a Tesla, and that's exactly what demand is.
    Last edited by FiberFast; 05-07-2019 at 09:29 AM.

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    Quote Originally Posted by FiberFast View Post
    Opinions area opinions and dollar are spent. Go look at where its being spent.
    Direct injection is new?! Its almost 100 year old tech. Only now we have high pressure electric fuel pumps instead of mechanical *Jazz hands*
    "The first Otto cycle engine direct injection system was designed by German engineer Otto Mader. It was used for a Junkers airplane engine in 1916."
    "They know more than we do" Apparently, which is why most oem's are healily investing in EV's.
    Pretty much everyone wants a Tesla, and that's exactly what demand is.
    Apparently, which is why most oem's are healily investing in EV's. - Very true. I know a lot of people who were laid off from powertrain at GM. However, like my earlier comment, they're still investing in ICE. Funniest part is a company I worked with on an opposed piston diesel engine, although really efficient, wound up getting heavily invested in by a Saudi investment company...reading between the lines an efficient engine can delay people from jumping to electric by minimizing the operational cost saving benefit. To say no one is investing in ICE is a stretch.
    Pretty much everyone wants a Tesla, and that's exactly what demand is. - This is not true though. Maybe in California But exactly 100% of my friends (low 30's), think I was insane for buying an i3. They think an electric car is just a toy car. Maybe because it's the motor city, but I think there's still a very significant number of people who will despise being forced to go electric, whether by the OEMs only offering them, or by lawmakers.

    My choice to get the i3 was to have one car in the garage still covered by warranty, and have a nice reliable, (and fun tbh) form of transportation just for my daily commute. X5 is still the wife's daily and our long distance car. E36 might stick around now as the fun car since I won't need to worry as much about constantly maintaining it.

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    Yeah, its kinda like a new Ferrari. Sure everyone wishes they had one, but no one is putting leans on their homes to go get one. Tesla and much like other top tier cars are reserved for the people that can afford them and thats the only demand they get, is from that consumer base that serves the buy. Even the few that say they want a tesla, most likely would figire that they displace the want for another want thats associated, like having the money, or the capability, or the whole "new age innovation"bs of themselves in a retrospect. I find it mostly a giant wad of B.S. and a scam.
    Nobody would recertify these machines after somebody screwed with them without any visibility into what they did.

    HONK! HONK! Clown car coming through!

    -Oakdizzle

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    True, but in time those electric cars will become cheap and plentiful. As a result, internal combustion engines will become more of a rarity. Parts will get harder to find and become more expensive. I have helped a few people with projects involving parts that don't even exist anymore and it can get $150+hr expensive real quick lol. There will always be a niche auto market cause old cars are fucking cool! But as far as a mainstay... Ice is pretty much done, mostly because we are past peak oil production. I like ethanol!

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