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1976 BMW 2002 Alpina Engine Rebuild


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Hi everyone,

 

So we are currently rebuilding my fathers 1976 BMW 2002 Alpina's engine. The car left the BMW factory on 04/1974 as a standart 2002 but 2 years later it was sent to Alpina to be modified. We have the original order sheets and correspondences between the original owner and Mr. Bovensiepen. According to these documents the car was order with a Alpina 2 liter special engine with 150PS with special request to use Weber's instead of Solex's  as well as the special exhaust. Order also specifies a oil cooler with thermostat as well as a electric fan to be added.

 

We ordered a modified 121 head from IE as well as 121 pistons. At the moment we are waiting for the parts from IE to arrive. I got in contact with them to ask several technical rebuilding questions but they suggested that I post it here. So while we are rebuilding the engine we need the following technical information in order to hone the cylinders to the correct surface roughness/finish: 

 

-Type of piston rings on Mahle (BMW) pistons

-Required/advised Ra, Rk, Rpk, Rvk values for the above rings

-Suggested ring end gaps

 

Would you advice us to use a torque plate while boring and honing or honing only with a torque plate?

 

Thank you very much!

 

Best,

Omer

 

 

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Just get a set of Perfect Circle Rings (now owned by mahle) with 3 part oliscraper.

Gap 0.010"
Roughness - I assume the guy honing the engine won't be able to match any of the ra values you provide - he should just make it nice.
A torque plate is a good thing to use, but M10 engines are not that depending on it like other engines where it makes 4/100 mm difference

Edited by uai
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44 minutes ago, uai said:

Just get a set of Perfect Circle Rings (now owned by mahle) with 3 part oliscraper.

Gap 0.010"
Roughness - I assume the guy honing the engine won't be able to match any of the ra values you provide - he should just make it nice.
A torque plate is a good thing to use, but M10 engines are not that depending on it like other engines where it makes 4/100 mm difference

Hi uai,

 

Thank you for the kind and prompt reply.

We are rebuilding the engine with a friend who owns his own retro racing garage, he was the one who wanted me to ask these values as they can get it down perfectly. He has the required machinery for it as well as the rebuilding expertise. If you have any ideas on these values I really would appreciate it. I’ll pass on any information you might have for us to use regarding the rebuild to him.

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Maybe I missed it, is there a reason you are not using the original Alpina cylinder head?  If Alpina build the engine, it will have 4 digit serial numbers stamped both into the head and the block.  Much more value in using the original parts, assuming you still have them.

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Posted (edited)
9 hours ago, markmac said:

Maybe I missed it, is there a reason you are not using the original Alpina cylinder head?  If Alpina build the engine, it will have 4 digit serial numbers stamped both into the head and the block.  Much more value in using the original parts, assuming you still have them.

The problem is that back in the day before we owned the car somehow the  original cylinder head got cracked and since it was either not available or expensive at the time they used a E21 M10 Cylinder head. So the original is unfortunately long gone. That’s why we ordered a new and modified one from IE with the original modifications Alpina made at the time. The block itself is original though, it has the Alpina numbers stamped on it.

Edited by Omera60
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Too bad.  Sounds like you had an 'A2' motor, 9.5:1 CR (probably had an E12 head), 300 cam, 45 Solex (substituted for your 45 Webers).  I am guessing they used a larger exhaust valve (39mm vs 38) and 46mm intakes.  I would suggest sending your intake manifolds (exhaust as well if your motivated) to have them port matched.  Alpina would have done both of those things.  Not sure what they did with valve guides on that motor - in the interest of longevity I would probably leave them.  Alpina used their larger downpipe as well attached to a tii cast iron manifold.  Good luck with your project. 

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23 hours ago, Omera60 said:

We ordered a modified 121 head from IE as well as 121 pistons.

A '74 wouldn't have come with a 121 head--it was superseded by the E12 head in mid-1972, and then by the E21 partway through squarelight production.  Did you mean you were ordering an E21 head?  

 

mike 

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1 hour ago, markmac said:

Too bad.  Sounds like you had an 'A2' motor, 9.5:1 CR (probably had an E12 head), 300 cam, 45 Solex (substituted for your 45 Webers).  I am guessing they used a larger exhaust valve (39mm vs 38) and 46mm intakes.  I would suggest sending your intake manifolds (exhaust as well if your motivated) to have them port matched.  Alpina would have done both of those things.  Not sure what they did with valve guides on that motor - in the interest of longevity I would probably leave them.  Alpina used their larger downpipe as well attached to a tii cast iron manifold.  Good luck with your project. 


It’s not exactly, according to the documents I have they stopped producing the A2 engine before our car went to Alpina. At this point in time the only offering they had at this HP range was the 2 liter special Alpina engine which is exactly 150PS. Not the full A2 treatment but rather only a special engine with extras as ordered. Our car had the special engine only exception being that the original owner specifically refused Solex’s and wanted Weber’s, oil cooler, front and back Bilstein’s (normally on a A2 it was a combination of Boge and Bilstein) with vented brakes as well as 13 inch Alpina rims. At this time point it gets very confusing with Alpina as there are a lot of options, packages, special combinations etc that were offered to the original owner.

 

7 minutes ago, Mike Self said:

A '74 wouldn't have come with a 121 head--it was superseded by the E12 head in mid-1972, and then by the E21 partway through squarelight production.  Did you mean you were ordering an E21 head?  

 

mike 

Yes you are right, however, according to the documents we have regarding this car they used a 121 head on the special 2 liter Alpina engine. So the original E12 head that came on the 2002 from the factory was taken off and it was changed to 121. I’m not sure why, maybe compression, rigidity or something like that was the reason behind this logic. E21 head is what came off our car as the original Alpina one had cracked back in the day before our ownership so the original owner at the time replaced it with E21 standard cylinder head with 1.8l pistons :(. Since we have the documentation for this car we know what it was built with and that’s what we are trying to restore it to. 

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Once upon a time I had an Alpina A3 motor, (block #1292/Head #2088), it had forged hemispherical pistons + the other (valves, cam lightened rods etc.,).  The head was kind of junky (been milled many times etc.,).  Alpina made me a new head, used an E21, took my 300 cam, put new Alpina valves and valve springs in it, port matched my manifold and sent it back with a new set of Mahle pistons....Converting an E21 head to a full hemispherical chamber is the easiest path

alpinahead(1).png

alpinahead1.png

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Yea, Alpina does pretty good work.  I saved this over the years, I was pretty stoked to have this come through my fax machine back in good old 1996.  I sent them the cam, intake manifold and upper timing cover, they did the rest.  Needless to say, I didn't hesitate to jump on the offer.😉

ALPINALetter2_Page_2.png

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