Back to computing topic ... Re: OT: timing belts

[Computer Collector Newsletter]

Ummm, I started the off-topicness here, so I'll try to end it by putting
forward these questions:
- What is the most odd computer you've encountered in a car's drivetrain?
- What is the largest computer you've fit into a car?
- What is the computer that gave Jay a flat tire en route to VCF East this
year?

--- Gordon JC Pearce <gordon at gjcp.net> wrote:

> Joe R. wrote:
> >    The '68 chevy didn't use a timing belt, it used a timing chain. Just
> > like all the REAL American cars! Personally I wish they all still did. I
> > hate these stupid rubber timing belts! All they're good for is generating
> > revenue for the delaers when they slip or break and you end having to buy
> > half of a new engine or a new car.
> 
> Well, that's just down to stupidity.  A new timing belt costs a tenner 
> at the most and even on an absolutely evil b*st*rd of an engine to work 
> on (step forward, Citroen XM 2.5TD, not nearly as nice an engine as the 
> CX 25DTR) it takes at worst a couple of hours to fit.  I can do Volvo 2- 
> and 3-series belts in about half-an-hour...
> 
> It's cheap, it's important, and it's something you can easily do at 
> home.  Got to be a bit careful with diesels, though - sometimes you need 
> a locking tool to stop the pump moving.  I change them on any car I buy 
> as a mere matter of course - think of it as (and here is where we swerve 
> briefly ot ON-topic) similar to pulling all the boards from a classic to 
> make sure the power supply isn't putting out the wrong voltage, the 
> first time you power it up.
> 
> As to why we use timing belts, well...  The problem with timing chain 
> designs is that the chains wear and go slack.  This means you either 
> need complicated hydraulic tensioners (like on the Peugeot/Renault/Volvo 
> B27/B28 V6 as fitted to Volvos 260s, Renault 30s, Deloreans and the 
> like, or Maserati V6es as fitted to Citroen SMs, or Triumph Stag V8s - 
> all notorious for timing chain failures), or just allow the chain to 
> slop about once it's worn (pretty much every other OHV chain-driven 
> engine).  The problem with that is that if there is a lot of slack in 
> the chain, the position of the cam shaft (and hence the valve timing, 
> and on most OHV engines the ignition timing) can be out by as much as 5 
> degrees.  If you've ever fitted a timing belt or chain to a car one 
> tooth out (ummm, nope I've *never* managed to do that, then wonder why 
> the engine was really quiet but down on power) you'll know how much of a 
> difference that can make.  Now imagine that instead of being "out" by a 
> fixed amount, it's randomly flapping backwards and forwards plus or 
> minus 5 degrees...
> 
> Of course, the Ford Essex 3 litre V6 in my Scimitar solves the problem 
> by having no belts or chains at all - just two big gears.  The large 
> gear uses fibre teeth which wear after a few hundred thousand miles, but 
> that's another story....
> 
> Gordon.
> 


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