Author Topic: Fuel pressure shim thickness  (Read 168 times)

daantjie

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Fuel pressure shim thickness
« on: 29 January 2021, 12:05 PM »
Hi guys

With regards bumping up fuel pressure at the main pressure regulator valve in the fuel distributor, I cannot seem to find a definitive range with regards to thickness and bar increase.  In  the M100 engine manual it says that 0.1mm equates to 0.2 bar, but what I am seeing online makes this number seem too heavy, in that most sources say that for example 0.5mm shim will give you 0.3 bar, as opposed to 1 full bar if we go by what is in the engine manual.

What gives :o?
Daniel
1977 450 SEL 6.9 - Astralsilber

s class

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Re: Fuel pressure shim thickness
« Reply #1 on: 30 January 2021, 12:05 AM »
I rebuild these FDs professionally, and if everything is working correctly, you should expect approx 0.1 to 0.2 bar change per 0.1mm.  It is also dependent on the shape and condition of the seal at the end of the pressure piston, and the thickness of the copper washer under the head of the regulator.
« Last Edit: 30 January 2021, 12:08 PM by s class »

'76 6.9 Euro, '78 6.9 AMG, '80 280SE, '74 350SE, '82 500SEL euro full hydro, '83 500SEL euro full hydro , '81 500SL

daantjie

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Re: Fuel pressure shim thickness
« Reply #2 on: 30 January 2021, 08:14 AM »
I rebuild these FDs professionally, and if everything is working correctly, you should expect approx 0.1 to 0.2 bar change per 0.1m.  It is also dependent on the shape and condition of the seal at the end of the pressure piston, and the thickness of the copper washer under the head of the regulator.

Thanks Ryan I'll get tinkering and see what transpires, cheers!
Daniel
1977 450 SEL 6.9 - Astralsilber

raueda1

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Re: Fuel pressure shim thickness
« Reply #3 on: 30 January 2021, 03:27 PM »
I rebuild these FDs professionally, and if everything is working correctly, you should expect approx 0.1 to 0.2 bar change per 0.1m.  It is also dependent on the shape and condition of the seal at the end of the pressure piston, and the thickness of the copper washer under the head of the regulator.

Thanks Ryan I'll get tinkering and see what transpires, cheers!
I ended up using trial-and-error, probably for the reasons Ryan mentions.  The cumulative effect of all that is substantial.  Took me about 4 tries before I got it right.  Good luck!
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0