M130 Engine Compression at 200PSI

[slfan1]

Hello,

I am in the process of purchasing a rare two-owner Pagoda with a 5-speed ZF transmission, Frigiking AC, original manuals, tool kit, Europa radio, etc... During the Pre-purchase inspection the engine compression figures showed 200 PSI across all 6 cylinders. It appears engine head work was performed some 8-10 years ago (2,000-3,000 miles ago) and the head may have been shaved too much. The car runs and idles perfectly, the temperature is fine and there is no water in the oil or any sign of head gasket failure.

As I would very much like to buy this rare Pagoda (previously owned a 4 speed manual), I ask your assistance and have several questions:

1. What are the dangers of running the M130 engine with compression figures in the 200 PSI range?

2. Can I do something to the head or engine to reduce the compression to the 165-180 PSI range? Or would I need to get a new cylinder head?   I would very much not like to have to source a new head.

Any advice would be GREATLY appreciated.

Best regards,
SLFAN1

[Benz Dr.]

Are you sure the gauge is working correctly?
 This such a rare car, why would you even ask if you should buy it? Of course, I'm assuming it's priced right and it's in good shape. The cylinder head wouldn't put me off.

[slfan1]

Benz Dr.,

First fo all, thank you for the feedback.

I see you own a 5-speed 230SL:  congrats!  Do you know how many of those exist in Canada?

On my side, where I live we have tough import laws & duties on parts (used & refurbished components are not permitted).  Therefore, I am scared with the logistics challenges of needing to import a new cylinderhead (assuming these are available).  Therefore, I ask (assuming the gauge is correct) if there is any type of work that can be done on the existing cylinderhead to lower the compression.

Best regards,
SLFAN1

[Cees Klumper]

I would imagine the combustion chambers could be slightly enlarged if necessary by someone who knows what they are doing.

[Benz Dr.]

You can't import used or rebuilt parts!!!? What kind of BS is that? Can you send things away to be rebuilt? In my mind it isn't the same as importing a used part - you're rerstoring what you already own.

 I imagine a new head would be available, for a price. However, arre you're customs people so familiar with 40 year old cars that they would know the difference between a new or rebuilt head? I suppose they would only accept a bill of sale from MB that proves it's new.......  

  5 speeds in Canada? Maybe a handful - a really small handfull. Less than 10 I would think.

[ja17]

A good performance shop can measure the volume of each combustion chamber and carve a little of the cylinder head to adjust the compression. Head thickness and valve train geometry could present additional problems. Check the timing chain also. Also under these sever conditions, you should check the "flatness" of the top deck of the cylinder head.

[Benz Dr.]

You can remove small amounts from the cumbustion chamber but you can also grind right into a water jacket if you're not careful.

 My engine produces about 175 - 180 PSI which I would tend to think is about optimal. I'm wondering where 200 PSI comes from. I just don't think you could get that much and still have a functional engine. There's only so much intake valve clearance at 5 degrees ATDC which must be no less than .9 mm. Milling the head down below 84.00 mm is risky and it still won't get you that much more compression.

 New pistons are often a bit shorter to comensate for clearances. I found that after I had my engine together ( short block ) that the pistons didn't even come even with the top of the block.
I had the top of the block decked to fix it.                                                         

[slfan1]

Benz Dr.,

Once I buy the car (hopefully early next week), I will start to understand things better.  Nevertheless, thank you for the input.  Will keep all informed of the next steps.

Best regards,
slfan1