From digest.v7.n93 Tue Aug 12 00:01:20 1997
From: "Brett Anderson" <Bretta_at_webspan.net>
Date: Tue, 12 Aug 1997 00:34:27 -0400
Subject: M3 over rev problem

I can't resist this one, a temporary exit from self imposed exile..........

As I am currently in the process of repairing an M3 overrev, and had another towed in today, I only have one thing to say. If you buy a stick, learn to drive it before you race it. I have over 10 years of club racing, including 3 years of sponsered production car racing, I screwed up plenty of shifts, but never managed to let out the clutch in the wrong gear.

I agree that the M(S)50 is very susceptible to a problem that many other cars would ride through without a problem, but this is the price you pay for performance.

There are 2 sure fire solutions to this problem, BMW could easily introduce either one at a cost so low that it would not even need to be passed on to the final sticker price.

Solution number 1, dish the pistons to convert the engine from an interferance style to a free running style, so the valves cannot physically touch the pistons, even if the timing chain breaks.

Solution number 2, significantly increase the valve spring strength and compression rate.

Problems and advantages with these solutions: Number 1:
Problem, Compression ratio of around 8.5 :1, severe power loss over current design.
Advantage, car will run great on 87 octane, no need for knock sensors

Number 2:
Problem, greatly increased friction , greatly reduced horsepower as a result
Advantage, no more damage from mis shifts

As you can see, the advantages of solutions of the problem are not even close to the disadvantages. How many of you M3 owners would buy the car for $40+ K if it had the same power as a 318i ?

This problem is not strictly related to M3's, and definately not to pre 10/95 M3's, I have seen it , at least once, in every M50 vehicle, the fact that BMW decided to harden the valve retainers to a greater rate has nothing to do with the cause or prevention of the problem. Increasing the hardness of the retainers , at best, will stop the valves sinking about 1 mm further through the caps, which they will only do during severe punishment such as constantly bouncing the engine off the rev limiter, or an over rev situation, the valve travel in these engines is 7 mm, at 3 mm, the valve will hit the piston, so 1 mm more or less is going to do nothing to change the situation.
Fact is , manufacturers make running production changes all the time, none of these are an admission of a problem, merely an improvement on design. Should we recall all pre 97 E38's because they have thumb wheels for the heater fan control, and the later cars have rocker switches, I mean, afterall, the thumbwheels could cause arthritis...right

Whilst I sympathise with those M3 owners that have had large repair bills, having seen these engines, and spoken to many of the drivers, I have no reason to consider the repairs should be covered by warranty.

What it all comes down to is a persons ability to control their actions. An M3 transmission does not slide smoothly into second gear at 90 MPH, it does not grind either, but it does go in harder than it would into 4th. Stop asking BMW to pay for your mistakes, and take responsibility for your own actions.

Brett Anderson

BMW and ASE Master Technician