Camshafts

[Oversize]

So a mate & I are looking for cam specs for the M100 6.9. So far we’ve found very little info to use as a baseline, or anything to wake up a rebuild project using custom pistons.

Specifically are the Aussie, US & Euro cams any different? Apparently AMG had a special grind & included lightened rockers....

After speaking to a cam grinder who looked at the attached figures, Benz was on the fine line of lobe overlap where positive pulses could interrupt the KJET air meter. This could indicate they were on the border of using exhaust flow to aid the intake. This could suggest they struggled with cylinder filling.

Also of interest is the specs were different for RH & LH cams up to 20k kms to allow for chain stretch. So does that mean they don’t come on song until the engine has done at least 20k kms???

 

[Oversize]

 

[Styria]

Has anyone ever replaced the extra large No. 17 timing chain gauge ? Other than myself, has anyone ever carried out a valve grind and de-coke on a 6.9 litre engine? I have done two, and have also rebuilt at least one 6.3 engine. BTW, they are very different in many aspects. Most publications, or some ga ga carry on tests, merely mention the increased bore size of 4 mms. and forget the rest. Yes, they are very different engines. Regards Styria

 

[Oversize]

Hey Styria well we are well into the process now. All the valves are being replaced on the engine builders recommendation. I believe the heads have been off this engine before & they weren’t thorough during the work undertaken. The cam sprockets were worn & need to be replaced. Most of the guides will be changed too.

Mods will include the custom pistons, blocking the afterburner ports (air injection), headers of my design & possibly a 560 throttle body. After getting all the data it may be custom cams will also be ordered. The builder we have chosen is very fussy & familiar with the Benz engines. Recent work carried out by another builder was deemed to be very sub-standard. You have to remember these are rather complex 1970s supercar engines. They have critical tolerances and are definitely not your average Ford or Holden from the era. They include race car tech designed to last decades and not just a few laps of a track. Even 46 years later you clearly can’t get just anyone to do the work. Indeed, many shops have long since closed their doors.

Given the issue with the cam timing I definitely think it would be better to have adjustable sprockets. If it was setup the way the factory intended, the timing would never be correct during the whole time Colin will have the car! Unless he plans to daily it from this point forward... Far better to have spot on timing & re-adjust where necessary after 20k kms some time in the very distant future. I know a machine shop that can do the work & I may even look at the M119 setup for ideas.

 

[Oversize]

We as per usual I end up answering my own questions even after asking everyone in Facebook land!!

I am now 98% sure all 6.9 cam sets are the same. Apart from any AMG ones that might be floating about... I will be 100% certain when I remove the rocker covers off my Euro probably later this week.

So now we can accurately measure the Aussie ones & see if they’re on the conservative side & if any improvements can be made.

I can definitely say Colin’s car will go better than a Euro. Particularly in conjunction with the other planned mods.

BTW I noticed something interesting about MBs quoted acceleration times. See if you can figure out what I’m taking about....

 

[Oversize]

 

[c107]

We as per usual I end up answering my own questions even after asking everyone in Facebook land!!

I am now 98% sure all 6.9 cam sets are the same. Apart from any AMG ones that might be floating about... I will be 100% certain when I remove the rocker covers off my Euro probably later this week.

So now we can accurately measure the Aussie ones & seem if they’re on the conservative side & see if any improvements can be made.

So no I can definitely say Colins car will go better than a Euro.

BTW I noticed something interesting about MBs quoted acceleration times. See if you can figure out what I’m taking about....

From what you posted looks like they all have the 36/37 camshafts. that would make things easier.

I assume you mean the load of 2 persons in the car for the acceleration sprint? I think that is a standard MB thing. I wonder if they were both big 2 meter tall germans!

 

[Oversize]

Lol spot on! So I wonder if everyone’s been comparing apples with apples? What will a Euro 6.9 do with ONLY the driver, 1/4 tank & no spare, or jack? What does a saving of approx 100kg equate to in extra hp?

 

[Oversize]

The 36/37 cams will be carefully measured to see if any performance gains can be made. It is possible a performance set will be available in the not so distant future.

 

[Oversize]

Confirmed this is my Euro engine with the same cams as an Aussie.

 

[c107]

that's a good finding, and interesting given how different the m117 cams are.
Makes me think the M100 cams are probably optimized for low end torque, which suits the nature of the engine and is also good for emissions.
You could probably get a cam that sacrifices some of that low end torque for higher end power if you wanted. Not sure how much better that would be in the real world though.

 

[Styria]

Well Mark, all I have ever done to 6.9 engines that I have had an association with are the high compression engine in my Gleaming Beauty, and an Astral Silver 6.9 that was purchased by Chris P. now living in WA. I've not heard from him for some time. I carried out Valve Grind and De-Coke on both engines, and in the case of my car I have not experienced any kind of water or oil leaks. That goes back ten years now.

I have changed two components though. Firstly, I installed a genuine 350SL first muffler which is much more shallow and wider than an original 6.9 unit, and I have also replaced the 6.9 rear muffler with a stainless (beautiful quality) straight through Universal muffler. Whilst perhaps I am misled by a fairly raucous exhaust note, I definitely feel that I have gained a more than reasonable amount of horsepower which, in turn of course, translates to additional "ponies". I tend to go the other way to you and Motec - I'd prefer "longer legs" in top gear for more economical cruising, and I have on hand a (2.46 ? 2.2something?) rebuilt differential from a W126 - 500. To my mind, I am satisfied with the standard power output of Gleaming Beauty's Euro engine which is also more economical than the Australian lower compression engine.

Furthermore, just think "more power, more wear and tear' on most components. BTW, I am very interested in the pistons you are having made up. I wonder if you would be prepared to share information. Regards Styria