From digest.v7.n814 Mon Dec 22 20:40:48 1997
From: Phil Marx <BMW_at_rlc.net>
Date: Mon, 22 Dec 1997 17:14:45 -0500
Subject: Re: 5-Series Engine Change <M50> (Long)

Greg Plassmeyer asked:
>When did the maintanence free engine come to be in the 5 series? I dont
>want >to do any more valve adjustments. And when or if has BMW changed
>from a
>timing belt to a chain?

Mitch Brown responded:
>I know that the '92 525i I had didn't require valve adju$tment$. It was the
>DOHC, and my understanding is that engine used a duplex chain, which is two
>links wide. And that car did NOT have the variable-valve timing.
>
>If I remember right, there's a few changes to the current engine. It's still
>DOHC, and the valves are hydraulic, but they've gone to a simplex chain.
>Apparently it's quieter with no loss of reliability.
>
>Can anybody who is a lot more knowledgeable than me confirm this stuff?!?

I know I've done this before, and there may be a FAQ with this (or should be?) but here goes again:

'91 525i (US) introduced the M50 twin-cam 24-valve engine in the US. It started in the E36 3er in '92 but not in the E30 Cabrio (popular urban legend). Variable valve timing (VANOS) began (US) in '93 with the M50 TU engine for both body styles. This essentially shifted the torque curve down about 800rpm. The original M50 had a single row chain driving the exhaust cam and a single row chain connecting the exhaust to the intake cam. This design remains on M50 TU.

Results of the M50 TU (technical update) revisions are as follows:

• -Improved torque curve, particularly in mid rpm range (esp. for auto. trans)
• -Lower fuel consumption
• -Improved and lower idle speed
• -Lower exhaust emissions
• -Improved engine response
• -Lower engine noise level

The design modification to achieve these revisions were:

• -Introduction of DME M3.3.1 with knock control
• -Increased compression to 10.5:1 (was 10.0:1)
• -Introduction of variable camshaft control (VANOS)
• -Reduced valve stem diameters (6mm vs. 7mm) with single valve springs
• -Reduced weight bucket-type tappets and spring plates
• -New pistons and connecting rods
• -Modified crankshaft vibration damper
• -New hot-film mass air flow sensor
• -New idle speed control

Claims:
Overall internal engine friction and drag torque have been reduced by approximately 15% with average fuel consumption reduced approximately 5% (sounds like the eta of the '90s to me-<g>).

Curiously, the torque/power comparison curves differ slightly between E36/E34.

Most significant improvements from DME 3.1 vs, 3.31:

• -Injection system: sequential (SEFI) vs. individual (CIFI)

  hot wire mass vs. hot-film mass sensor

• -Ignition: Fault monitoring of primary circuit vs. primary and secondary
• -Knock Control: none vs. 2 sensors able to monitor 6cyls. individually
• -Camshaft position sensor: inductive vs. Hall effect sensor
• -VANOS none vs. Ability to alter intake cam timing by 25 degrees

Pistons:
New lightweight, compact pistons (shorter skirt and pin to deck height) with 10.0mm longer connecting rods.

Vibration Damper: Lighter, sheetmetal (axially decoupled) compared to old cast (radially decoupled) design.

Hope that answers even some unasked questions.

• -Phil Marx BMWCCA #6021