OT: timing belts

From: Gordon JC Pearce <gordon_at_gjcp.net>
Date: Sun Dec 26 04:35:48 2004

Chad Fernandez wrote:
> Gordon JC Pearce wrote:
>
>> Well, that's just down to stupidity.
>
>
> That's called an interference engine.

Yes, I know some small Vauxhall/Opel engines don't run interference.

>> 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...
>
> Do these engines sit transversely in a front wheel drive (fwd) car? Most
> cars here are fwd, and have the engines positioned transversely. A lot
> of times you will have to disconnect at least one of the engine mounts
> and lift the engine up. Also, since it's bound to be an overhead cam
> engine, the accessorys will have to come off.

The Volvo engines are inline, and in the case of the 240 there's *loads*
of room to get in about it. On both of those it's just a case of taking
the fanbelt off, taking the belt cover off, locking the engine at TDC
(there's a hole thoughtfully provided in the crank, covered by a bolt in
the block) and then changing the belt. On the Citroens, however...

It's transverse, and you can barely get a reputable credit card between
the cover and the inner wheelarch (particularly on the XM). However,
you can jack the car with its hydraulics, prop it up nice and high, and
remove the driver's (right, in this country) wheel, and get at it all
through the wheelarch.

The only one I've ever had to remove an engine mounting to do was a
Nissan Micra, where whichever way you go at it, the belt cover is
blocked by the top mounting. Silly design.

>> As to why we use timing belts, well... The problem with timing chain
>> designs is that the chains wear and go slack.
>
> I don't know too much about chains used with overhead cams, but on push
> rod engines this doesn't happen until many miles are on the vehicle.

Because pushrod engines typically have very short chains. Compare them
with the miles of chain used in Volvo B27 engines (2- and 7-series V6,
Renault 30, Delorean)!

> The only problem I've had with a chain, actually was the top timing
> gear, not the chain itself. It was on my 69 Buick LeSabre. The top
> gear was aluminum with nylon or plastic teeth. They stripped off, while
> on the highway. This happened in 1995, so the car was about 26 years
> old, with 100K miles on it. I thought the gear design was dumb, but I
> assume it was done for sound or vibration purposes. I know GM may not
> rank very high with the Europeans on the list, but it's one of my
> favorite cars that I've owned.

Yeah, as I think I said in another post, the Essex V6 used in old Fords
had fibre teeth. You can replace the gear set with an all-steel one but
it's hellish noisy.

> I did have belt problems once on my 1982 Dodge with a 2.2L engine. I
> got it wet in the snow, since I plowed into a snowbank, with the plastic
> cover off. I had a heck of a time getting it back into position, after
> it skipped. I didn't really know how to get the belt around the
> tensioner, cam pulley, and crank pulley with out throwing the timing
> off. I was probably sick and tired of working on the car, in the cold,
> and ran out of patience.

Argh. Yes, a lot of engines seem to need a special tool to move the
tensioner.

Interestingly enough, the aircooled flat four in my Citroen GSA has two
little holes blanked off by rubber plugs in the outer fan cowling, so
you can slacken and retighten the tensioner locknuts. Apparently you do
this every 10,000 miles.

Gordon.
Received on Sun Dec 26 2004 - 04:35:48 GMT