CYLINDER HEAD REMOVAL/FRESHENING
OR: you never really know what you have until you take it apart!! (unless you built it yourself)

Well, as noted in the updates I had to remove the cylinder head to cure a slight compression leak into the water jackets. This caused the engine to run hot at higher RPM due to the air bubbles in the cooling system. The only cure is remove the head, machine it flat and re-install it with a new head gasket. While the head is off why not freshen the valve job and check things out. I found some interesting things while the head is off.

1. The pistons have a 9cc dome, I thought they would be flat tops. How do I know the dome is 9cc? I checked it myself, it's fairly easy-put the piston down a known amount, measure the actual bore dia, then fill the bore with a liquid-all the way to the top, keeping track of how much liquid it takes to fill the bore. I had the piston .331" down the bore, the actual bore dia. is 3.511", the math shows it should have taken 53cc to fill the bore but I could only get 44cc into it = 9cc dome displacement. How do you know you have the bore full? Use a piece of Plexiglas with a hole drilled in it-fill until there is no air bubbles left = full bore. Just like CCing a combustion chamber. BTW my combustion chambers are 62cc in this e21 casting head, it has been milled slightly twice. Using all this info I found I have 9.4-1 compression ratio (assuming a .035" compressed thickness of the head gasket), not bad for a streeter. In the past I had to run 91 octane due to detonation but the combustion chambers and piston tops were pretty loaded with carbon, all clean it should do well on mid grade.

2. The intake ports were previously ported fairly well. There are a few things that need re-worked to get to where I think they should be. In the top pic you can see a shaded line inside the valve opening, that's a sharp ridge that has been removed and reshaped into a nice round contour. In the lower pic you can see there are still some slight imperfections in the port walls, I did not want to enlarge the ports enough to completely eliminate them-they would then be too large for a street engine. This is "common sense" porting for the street. If you want full race porting-pay a race shop!

3. The exhaust ports were just port matched. They took some fairly extensive work to get to where I think they should be. Check these two pics and you can easily see which will have the least turbulence and most flow. Sharp edges and bumps in the air flow are BAD!!

4. I found a significantly corroded/eroded spot in the water jacket just under the #4 exhaust port with slight problems under the #1 and #2 exhaust ports as well as under the #1 intake port. The #4 exhaust port problem is significant so I will cover the area with MarineTex epoxy to prevent it going though to the actual port. This is a fairly common problem with m10 heads according to my machinist. Bottom line-Keep a good mix of coolant in your system! NEVER run just water, even for a short period of time.

5. The PO told me it was a Motorsports 272 cam but it's not, it's an Elgin 278 grind #695-12. Elgin Cams offers several nice cams for BMW's and there is a good tech piece on cam selection and his thoughts on cam design, interesting reading. I measured the total lift at the valve and came up with .358", that's not a lot of lift by performance cam specs but Elgin likes to keep lift moderate and have a broader nose on the cam for more duration under the curve without tearing up the valve train, it makes sense and this cam makes great midrange torque. Notice the light weight springs used for mockup, these are dedicated springs from Manley.

6. Rocker shafts are a real pain in the ASS! They are in the head tightly and must be driven out. My machinist got me some replacements and used his custom "M10 head rocker shaft hole reamer" to allow the shafts to be installed and removed without damage.

7. My rockers were slightly worn on the cam wear pads and quite worn on the adjusting eccentrics. I ordered new eccentrics and bolts/nuts. I sanded the wear pads as well as the bushings with 400 grit wet/dry paper and coated them with Techline Coatings WSX, interesting stuff. I also did the valve stems and ends with the WSX. I would have done the intake valve stems with their DFL but my jar is 3 years old and dried up! The cam shows very little wear, on the intake lobe heel the original parkerizing coating is still intact, I did the cam lobes and bearings with the WSX. I was going to coat the valve heads with their ceramic heat reflective coating but it too is dried up.... bummer.

Update 02 Aug 2005: I just returned from the machine shop, here's an update on my valve springs.

Stock single spring at installed height of 1.500" = 55# seat pressure/ full open lift of .358" = 155# pressure

Stock single + VW (waterboxer) inner spring at installed height of 1.500" = 75# seat pressure/ full open lift = 175# pressure

Stock single + VW inner + shims for installed height of 1.440" = 90# seat pressure/ full open lift = 190# pressure (still leaves over .100" lift before coil bind so you could run this with up to .400" lift cams)

The last set up is nice for a mild duration cam with moderate lift without the expense of new springs that would likely have too much pressure, causing excess wear and HP loss. The object is to run the least amount of spring pressure and still control the valve adequately-otherwise you just throw away HP!

Remember, this is on my head-every head that has had machine work is slightly different so you would need to verify your installed valve height (you should always do this anyway!) when your head is apart.

I started reassembly of the head today. I have 2 different design valve spring compressors. The first is a small clamp that works from the rocker side only, the second is a smaller "C" type-neither works on the M10 head!! I modified the "C" type and it worked to install the 4 corner valve springs but the 4 in the center require a large "C" type compressor. It's always something!!

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