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68 250S, 91 300se, 98 SL500, 450SEL 6.9, 14 CLS550 Past MB's; 300SD, 300E, 300TE, 190E, ML420
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Discussion Starter #1
I'm going to chronicle the rebuilding of the engine for my 1967 250S. My dad bought the car new, I got it 42 years ago and at about 100K miles put a new short block in it and rebuilt the head. Saved the original block all that time and hauled it to Seattle and back to Colo with me over the years. You will see the large Styrofoam original packing crate from MB. For those that are not familiar with a M108 engine, it is part of the M180 family which included the more popular M130 along with M129 and few others. The M108-I was only used in the 250S W108. The current engine has about 100K on it and the compression is now only about 85.

These pictures show the crate and the block as I start working on it.
 

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68 250S, 91 300se, 98 SL500, 450SEL 6.9, 14 CLS550 Past MB's; 300SD, 300E, 300TE, 190E, ML420
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4,155 Posts
Discussion Starter #2
Mounted to engine stand and removed oil pan, oil pump and front damper. Also of view of the subject car.

Note I punched a dot on the end of crank and also the damper so I can line them back again later.
 

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68 250S, 91 300se, 98 SL500, 450SEL 6.9, 14 CLS550 Past MB's; 300SD, 300E, 300TE, 190E, ML420
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4,155 Posts
Discussion Starter #3
Took block, pistons/rods and crank today to get cleaned and measured. The bearing for the most part looked pretty good, but the center main bearing had 90% of the copper layer peeled off and chunks hanging on. The machine shop showed me that the bearing cap and inside bore of that main was oversized from the factory, so the bearing shell did not seat fully. Thus the crank beat the crap out of that bearing. They will line bore to correct later. once I get the measurements back in about a week I will place orders for the pistons and bearings. One piston was stuck in the bore, so I had to remove the crank while leaving all the pistons in. There was also too much of a lip at top of cylinders to easily push the pistons out.

Will probably be using 2nd oversize pistons and bearings. The M108-I has different part numbers for all of these parts compared to the m129 and m130.
 

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2007 CLS63 AMG
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18 Posts
Any update on your project? I'm about to do the same to my engine for the same year/model
 

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68 250S, 91 300se, 98 SL500, 450SEL 6.9, 14 CLS550 Past MB's; 300SD, 300E, 300TE, 190E, ML420
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4,155 Posts
Discussion Starter #5
Thanks for asking. I did complete the rebuild. I sourced pistons from a place in Germany. The head rebuild was a bit more challenging, it had the top and bottom milled, all new rocker posts and arms and smaller shims. I put @1mm thick shims under the cam bearing towers to raise the cam up after the milling. To get the timing correct I used a 6degree offset cam key pointed the opposite way and skipped one tooth on the cam chain gear. The exhaust Manifold I had the heat risers welded shut with a 1/8" think plate and sprayed eastwood ceramic paint on the inside and outside. Re plated all the hardware.
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2007 CLS63 AMG
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18 Posts
Thanks for the update. I'll refer back to you for questions as i go along with my build
 

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2007 CLS63 AMG
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How's it running since the build? Also, did you reuse torque converter? Mine split in half years ago and it was replaced with a conventional steel one. I'm getting a thudding noise when in operation so I may have to replace it.
 

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68 250S, 91 300se, 98 SL500, 450SEL 6.9, 14 CLS550 Past MB's; 300SD, 300E, 300TE, 190E, ML420
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4,155 Posts
Discussion Starter #8
Randomly found these today - cam tower shims. I made my own but would have been nice to just buy them. fits m129, m130, m108, m127.
 
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