M120 cams in a M104? - PeachParts Mercedes-Benz Forum

Mighty190 · #1 07-22-2017, 06:49 PM

Just a thought I had the other day. Do the cams swap between engines? How do the specs compare? I've been wanting to build a 2.8L m104.945 that's a bit peppier than stock. Its my understanding that m120 cams do not phase as much as the m104 and that would actually be nice for building something high compression and playing with cam timing beyond stock.

Anyone know anything about that before I go down the rabbit hole on researching this?

These are some links I've found on M104 cams

http://www.catcams.co.uk/acatalog/Mercedes_M104.html
http://www.peachparts.com/shopforum/performance-paddock/308869-m104-engine-specs.html

duxthe1 · #2 07-22-2017, 07:24 PM

The right head on a 120 is a standard 104 head. I'd be surprised if the cams weren't also standard 104 parts but I'm curious what your research turns up. I just built a .980 using a late exhaust cam as an intake cam with a functional 20 degree advancer. The gains aren't life changing but if you're building a motor from scratch I'd definitely go for some custom cam work. Feel free to ask any questions that come to mind.

MAG58 · #3 07-22-2017, 10:06 PM

The two intake cams are reverse rotation compared to the exhaust cams and engine rotation. That will complicate your swap.

whipplem104 · #4 07-23-2017, 02:03 PM

Pretty sure they will not work. The reverse rotation does change the timing of the valves in rotation and there would not really be a lot of need to do something bigger for the m120 engine. It really puts out less power per cylinder. They were only like 389hp.
And again.. I think that your time and money could be spent way better than anything with camshafts. Even used parts and gaskets etc. Buying a 3.2l engine or a 3.6 would be cheaper most likely.

Mighty190 · #5 07-23-2017, 07:49 PM

I'm specifically looking at doing a 2.8 engine. I have a 3.6 in a car right now. I really just want to see if I can make something that revs up a bit better than stock with used parts that are easily available. I think it could be fun to mill and port the head a little and stick the biggest "stock" cams in it.

Both the cams can't be reverse rotation. The m120 spins the same way as the m104. It would make sense that the right side would use similar if not the same cams. A reason I think they may have a different pattern is the m120 has the twice the displacement so it doesn't need as much help making low end tourque so maybe there are cams that favor rpm or mid range power. That said the 6 liter is said to be developed from a m104.98x. I wonder if that's a coincidence or Mercedes saved development costs buy basing the 6L M120 head design on a standard M104 and just used the same cams.

duxthe1, how did you get the exhaust cam on the intake side? Aren't the base circles different diameters? Also I measured a few cams I have and the intake from a M104.98x seems to have a lot more lift than the M104.99x cams. Seems like paring that intake with a later exhaust cam in the late head would be a good combo if M120 is no different.

duxthe1 · #6 07-23-2017, 08:46 PM

I don't think any of the 120 cams are reverse rotation, just in opposite order on the left side. The only difference I could imagine would be one side cams are slightly longer due to the bore spacing cant be shared for the #1 and #7 cylinders so one is offset to the rear a bit. I'd bet its the left side since that's already the oddball and how the V8 engines are set up too.

There is a 4mm difference in base circle, but that means only 2mm has to be made up and I accomplished that with the valve job. Had about .5mm to spare. Cam had to be drilled in the flange at an obtuse angle to get an oil feed for the advancer. Thread just below about it and the head work done to my 104.980.

As far as the best stock cams... they are all pretty much the same excepting the 3.6 which even then I think only one side is a little different. All of the intakes are 9.5mm lift with 180 degrees duration @2mm and all of the exhaust cams are 9.5mm lift with 197 degrees duration @2mm. By subbing an exhaust cam for my intake I picked up 17 degrees duration.

Mighty190 · #7 07-24-2017, 10:14 AM

I wonder what's up with the .99 cams I have then because my measuremetns would put the .5mm out of spec and they don't look very worn and multipule lobes were right on 9mm. The C36 intake cam is the unique one. I saw that when I did the head gasket. I should've had it sent out and measured so I could share the specs but I'm actually picking up another 3.6 engine here in a bit so I could it with that too haha.

But that makes sense with the valve job. If I were to do a swap like that I don't know if I would try to retain the vvt.

whipplem104 · #8 07-24-2017, 07:00 PM

It still does not matter what direction they turn. The cam timing is different than a inline 6.
In a v engine the cylinders on one bank are not phased the same way as in an inline engine.
I thought I remembered the intake cams the chain wrapped under but that might be some other engine.
But look into it.

MAG58 · #9 07-25-2017, 10:27 PM

Quote:

Originally Posted by duxthe1

I don't think any of the 120 cams are reverse rotation, just in opposite order on the left side.

I'm pretty sure M120 intake cams spin backwards...

duxthe1 · #10 07-25-2017, 10:52 PM

Indeed they do. Been a long time since I had one apart.

Mighty190 · #11 07-28-2017, 09:43 AM

Interesting. I wonder if that effects how the profile is ground. As far as I am aware cam profiles are not directional and if they are that would be some kind of first. Guess this does mean the cam phaser works the opposite way.

Roncallo · #12 10-29-2017, 07:55 PM

Looking at those cams on the M120 engine it should be clear that both intake cams spin one way and both exhaust cams spin the other way. And I would assume they do the same thing as the 104. Therefore there is a good possibility that the left and right cams are the same, providing there is a spacer on the left side. Based on rated HP of the 3 liter 104 and the 6 liter 120 it does not appear that there is HP to be gained if they do fit. I have no access to EPC from this computer but a parts number lookup might shed some light on this.

97 SL320 · #13 10-30-2017, 05:41 PM

Both M104 cams turn clockwise from the front with chain over top of both. The M120 chain loops under the intake cam ( CCW rotation ) on it's way to the other bank.

The real question would be are the exhaust cams different lift / duration? On a M104 It is possible with slight mods to install the exhaust cam into the intake side for a bit more lift. If the M120 exhaust cam was bigger than the M104, something could be gained.

Roncallo · #14 10-30-2017, 09:50 PM

Quote:

Originally Posted by 97 SL320

Both M104 cams turn clockwise from the front with chain over top of both. The M120 chain loops under the intake cam ( CCW rotation ) on it's way to the other bank.

The real question would be are the exhaust cams different lift / duration? On a M104 It is possible with slight mods to install the exhaust cam into the intake side for a bit more lift. If the M120 exhaust cam was bigger than the M104, something could be gained.

This is depressing. I did one of these about 8 years ago. Could swear it was an over under arrangement. Had to check some You Tube videos. Sure enough the 104 is both over.

Cauf61 · #15 12-23-2021, 05:57 AM

Quote:

Originally Posted by duxthe1

I don't think any of the 120 cams are reverse rotation, just in opposite order on the left side. The only difference I could imagine would be one side cams are slightly longer due to the bore spacing cant be shared for the #1 and #7 cylinders so one is offset to the rear a bit. I'd bet its the left side since that's already the oddball and how the V8 engines are set up too.

There is a 4mm difference in base circle, but that means only 2mm has to be made up and I accomplished that with the valve job. Had about .5mm to spare. Cam had to be drilled in the flange at an obtuse angle to get an oil feed for the advancer. Thread just below about it and the head work done to my 104.980.

As far as the best stock cams... they are all pretty much the same excepting the 3.6 which even then I think only one side is a little different. All of the intakes are 9.5mm lift with 180 degrees duration @2mm and all of the exhaust cams are 9.5mm lift with 197 degrees duration @2mm. By subbing an exhaust cam for my intake I picked up 17 degrees duration.

Hello I know this is an old topic but great info anyway. I found this info on the 103 and 104.980 cams. Made some notes on it. What is your opinion. Could this be correct ?