How to get your 6.9 to rev

[Oversize]

Done by a PO to bipass the ignition cut-out. Not exactly how I'd do it. In fact I'd be very hesitant to modify something that's from what I hear quite rare and expensive to replace. Note 6.9 stamped into the top of the rotor button:

 

[Tony66_au]

Wow... Dodgy much? LOL

That wire wont carry 1/4 of the voltage once the bypass kicks in.

 

[Michel]

can you please explain?????

what on earth is that?

and why?

 

[Styria]

Mark, I hate to say it, but that is one crappy looking rotor button. I know that they act as a rev limiter, and I also know that they cost a proverbial fortune to buy new. I'm a bit with Michel and Pauline Hanson - please explain ? I have fitted 'normal' rotor buttons to Gleaming Beauty, and have never experienced any problems with over-revving etc. Regards Styria.....

N.B.......well, I've just had another look at your picture - some butchery, even more dodgery as in Tony's words. Is this the ex Black Hands car ?

 

[Oversize]

Yeah I was wondering what bright spark did this and after what Tony said I can hardly see the point!!! Hahahaha!

Yes Styria it's Black Hands old car. I believe this is an early version of a rev and probably by default, speed limiter. As the revs rise, centrifugal forces act against the spring forcing the centre electrode outward, eventually touching the contact at the end of its travel. This contact is earthed, thus grounding the ignition and preventing higher revs. I'd imagine it wouldn't be the best idea on a LPG powered car, cause with a manifold full of gas and the ignition stopping and starting, there's potential for a big backfire... I'd suggest the wire was added in an attempt to prevent the limiter from functioning. I never thought about the voltages involved and I doubt the modifier did either. Even with an adequate wire, I wouldn't think it'd work anyway, as the spring loaded contact looks like it'd still function. Being that electricity is like water and follows the path of least resistance, I'm sure it'd go to ground rather than all the way to the plugs mounted in a hostile environment!

Methinks I'll be carefully removing the solder and thus the bipass wire.

 

[SEL_69L]

Mercedes in their wisdom limit the speed of a 6.9 engine to around 4650 RPM, but I have heard of allegations of up to 5,000 RPM being attained.

The timing chain on an M100 engine is about 1.5 metres in length, and I shudder to think what what may happen if that thing got out of control after sustained high engine revolutions above about 5,000 per minute.

I have seen the results of a combination lack of maintenance and sustained high speeds on a W126 380 engine. It aint pretty! Total destruction.

 

[Tony66_au]

I saw a detonated 4.5 last week, Demolished a valve cover and seized the engine solid.

I offered $200 for the car but he thinks he will do better on Fleabay so I wished him good luck.

So Mark how close to a povvo 4.5 button are they?

Id be tempted to borrow one for a test mate

 

[Styria]

Tony, if I can be so bold as to come in on this - I've never had any problems fitting any old rotor button (good condition, though), and they could well have originated from a 450 engine, although IT HAS BEEN SAID (don't recall where and when) that the angle of the button between 6.9 and 450 is different. I am not sure. Regards Styria

 

[Oversize]

So would MB have determined max revs through calculation only, or killed one intentionally?? If done through calculation, I'm sure they'd have been rather conservative to protect the engines and their reputation.... I remember seeing calculations on max piston speed (and maybe in another thread). The thing I don't understand is how a LS engine with pushrods can rev and yet a MB engine with OHCs and exotic materials cannot.

 

[Tony66_au]

Tony, if I can be so bold as to come in on this - I've never had any problems fitting any old rotor button (good condition, though), and they could well have originated from a 450 engine, although IT HAS BEEN SAID (don't recall where and when) that the angle of the button between 6.9 and 450 is different. I am not sure. Regards Styria

Jump in by all means Herr Styria, Im just speculating.

 

[Tony66_au]

So would MB have determined max revs through calculation only, or killed one intentionally?? If done through calculation, I'm sure they'd have been rather conservative to protect the engines and their reputation.... I remember seeing calculations on max piston speed (and maybe in another thread). The thing I don't understand is how a LS engine with pushrods can rev and yet a MB engine with OHCs and exotic materials cannot.

Often it is down to the Degree of the V and balance or harmonics Mark.

For example the Windsor and Cleveland engines from Ford, The Clevo being a 90 Degree V does not rev as freely as the Windsor and although both come in 302 and 351 displacement they are vastly different engines and designed for different tasks with the Clevo being a torquey monster and the Windsor being a Rev monster.

I built a 351 Cleveland, balanced and blueprinted with Hypertec pistons from the US and a custom cam Forged crank etc etc and although it was very responsive and had torque out the yingyang the bugger still wouldnt rev without harmonics.

We tried it with and without the hypertecs, different flywheels and harmonic balancers and it still didnt like to rev past a certain point so we asked an engine guru and his reply was that the block was never designed for high HP or RPM and was designed for torque and reliability.

My Guess is that the M100's intended purpose is the same, Amazing grunt, smooth operation and flawless reliability.

 

[abl567]

Spot on Tony, after all the M100 was originally designed to power the 600 Grosser and Pullman, very heavy substantial cars requiring loads of torque to keep them moving without high revs spoiling the luxury feel.

 

[Michel]

I can vouch that my M100 on the 690SEL spent a day at the track (the now defunct Oran Park raceway) on or near redline constantly be it revving up or revving down.

It never felt a tired, pressure was constantly up... not a rattle and still running strong until the end.

As long as they are serviced and maintained properly, these are virtually bullet proof (which cannot be said of all Benz engines unfortunately)

 

[Oversize]

Here's some pics of Red Bull's rotor, which is completely different from the standard one. Note that the one and only time I drove her I felt she was lacking power (even for an Aussie), but I'm not sure if it's due to the angle of the non-standard rotor, a stretched timing chain, plugs, injectors, blocked fuel filter, bad fuel, or something else....

 

[Tony66_au]

So is that an M117 rotor?

 

[Styria]

Mark, what about an upside-down pic of Black Hands rotor button - or, if you like, when you have the two side by side (which you can), is the angle different ? I'd be very interested to find out.

Regarding 'revving' the M100 donk, some muffler guy (Lambros was, or is, his name - at Taylor Square) reckoned that a 6.9 is capable of 150 miles an hour. Another story relates to an ex Newcastle guy (Peter Bennett now on the Gold Coast) that had his 6.9 timed by the men in blue at 262 kilometers an hour. That was his story as related to me personally. Regards Styria

 

[Oversize]

Styria, will do. I'd also be quite interested if there's an angle difference and whether it'll effect ignition timing and power.

Is there any place in Australia where there's an open speed limit? Or am I gonna have to head to the salt flats in SA to test the theory....

Speaking of which:

http://www.dlra.org.au/index.htm

 

[Tony66_au]

Salt flats mate, even territory roads are now limited

 

[Oversize]

Ask and ye shall receive! Styria the answer is no; the angles on both rotors appear the same. From the top the original one appears offset, but I'd say that's just to allow for the limiter mechanism. BTW the spring loaded sliding limiter still works. I doubt the bi-pass would be effective as the current will go to ground anyway (path of least resistance). So all the PO did was make a mess of a rare part.... So the only way to bi-pass the limiter is to remove the slider or (better still), replace the rotor with a basic unit. And put the original rotor in the pool room....

 

[Tony66_au]

There ya go, Problem solved nice and easy.

Shows an interesting turn of mind for the person who did the jerry rigged button that was in there, Ive seen some weird work-arounds but this ones a good un lol