Some technical M120 questions.
 

Hello, I have some fairly technical questions about the M120 while I attempt to source one for a build. I have a line on a 97 S600 at the moment. I'll likely be developing a lot of parts during this build as the current aftermarket is either non-existent, or far too expensive.

1. Does anyone know the deck height of the block or the deck clearance of the pistons when installed? This would help tremendously with compression ratio calculations.

2. It appears the intake cams are reverse rotation being on the opposite side of the timing chain. Will an exhaust cam technically bolt in place of an intake cam? I don't need to be able to hook the chain up if so, I just need to know if it can physically go in place, with or without the cam gear, without any problems with oiling.

3. What is the length of the block, from front to back? I could also use measurements of the intake manifold of the intake runners closest to the flange, from the front of the furthest forward to the rear of the furthest back.

4. What is the valve angle on the heads?

6. Does anyone have physical measurements of the valves themselves? I think I've found valve diameter, but not length or stem diameter.

7. How strong are the crankshafts known to be? Can they handle a couple thousand more RPM than stock? Specifically the crankshaft, and none of the other rotating assembly. This would be the hardest part for me to find a suitable replacement for ($$$).

8. Are there any well-known issues I should be aware of in relation to oiling or cooling?

Would having a spare intake manifold help you? I just happen to have one on my trophy wall. The measurement top to bottom of the mounting flange is 595mm.

One side of the V12 is an M104 motor. Same valves, same head, it should have the same dimensions you are looking for info on. The big differences include the M104 block is cast iron and that the M120 carries a mirror image M104 block in tandem.

I would expect the stock crank to meet your needs. It's alloy block that should turn out to be your limiting factor.

-CTH

A spare intake manifold might help. I could get all of the measurements I need, get it scanned for a CAD drawing, and design a new intake manifold from that. I might have to cut it up to get inside shape/measurements of the runners though. What would your asking price be?

I'll try to get information from the M104 on valve/valve spring sizing and specs, but it seems possible that the M120 didn't use the same hardware, considering how many changes in valve sizes the M104 itself went through.

I'm hoping that an exhaust cam will bolt in place of an intake cam, so I can set the lobe separation angle and spin them both in the same direction. This will also make it much easier when dealing with having them reground, either through base circle reduction or welding and reprofiling. From there I can either work on new tensioners, or a conversion to timing belt. The water pump will be replaced to move it out of the way. New flanges will be cut and an electric remote mount pump will be used, this would help with redesigning chain guides or converting to belt.

The crank is my main concern. The only possibility of an upgrade would be billet.

I've seen that crank, it's impressive. I don't think you'll have a problem if you're only going for 2x HP from stock.

Share your finalized CAD diagrams with us when the smoke settles and the intake is yours for the price of shipping. It's heavy. I bet a 30HP gain would be gotten by 3D print of the manifold in a suitable plastic.

-CTH

The first step is sourcing an M120. Ebay has a few for sale for ~$4000. There are also 2 complete cars within 4 hours of me for less than the cost of an engine on ebay, but neither owner is very receptive to questions.

I've done enough searching to find off-the-shelf parts to replace a lot of the weak points of the M120 at a small fraction of the cost of buying actual M120 parts, so sourcing a high mileage engine isn't out of the question.

Gone are the days of 1500$ s600 and 600sel cars that owners just want to see go away. -cth

I think I saw a few in Bay Area Pick n Pulls back in the day. I once found a rust free 280SE 4.5 that had just showed up. Got the rear axle out during lunch time. I also saw a intact un crashed XJ12 once.

I'm hopefully picking up a car Monday for $2300. Fairly low miles, in good shape, with electric/ECU issues. I have a spare MS3Pro sitting around, I would just need to order another harness to get it wired and fired assuming that it is indeed an ECU problem.

Doing some digging, I just want to confirm that an M104 exhaust cam will fit physically (ignore the gear/sprocket) into an M104 passenger side head. The firing order should be correct, and the head is technically a standard M104 head on that side.

I want to buy a spare camshaft for measurements to look into having custom cams made. This camshaft could potentially be shipped off and the odds of it going back into the engine are very low, so I want to make sure I get a spare.

I now have the car in my possession and it is running. There are some electrical problems, but I plan on getting those out of the way before diving into the build.

Edit: Since I now own the car so my questioning has greatly shifted, and because this forum seems pretty dead, I'll probably end this thread here.
Maybe I'll document the build somewhere.

:2thumbsup

One thing you will want to consider is do you want the center sump M120 like from the W140' or the Forward type sump like from the R129 SL's. Center sump oil pans are cheep. SL forward sump pans are going for $700+. And to change over you need the upper and lower pan, the pump and the baffles. Might as well get a short block.

Or I can just convert to dry sump. Lots of OEM cars coming with dry sumps now so they're not too hard to find. I could fabricate a pan and pickup easily enough, especially if mid sump pans are cheap enough that I could find a reasonable spare.

I'm far more in favor of doing labor and fabrication than spending money. I've done my share of big power on the extreme cheap.

I've already ordered the harness to convert my S600 to use my spare MS3Pro so I can start tearing out enough emissions equipment to gain room for header fabrication. I'll measure clearance for various pan types while I'm down there.

Yes the center sump will be a lot cheaper and I do know one guy that modified his pump inlet to work with the forward sump. Pay attentions to the baffles, they are different, I'm not sure what the difference is.

There may be a guy in FL making dry sump conversions for the M120. At least he makes a lot of other stuff so worth checking him out.

https://www.gooichimotors.com/m120-v12-parts

I've looked into Goochi, but decided they're a bit unreasonable because of their love of titanium.