Re: FIAT cam belt design

["Mark Battley" <m.battley@domain.elided>]

Michael Smith wrote:
>I believe the first mass production use of rubber belt cam drives was on 
>the FIAT 124 when they grafted that twin cam head onto the rather 
>pedestrian pushrod four to create a sports car engine. Clever idea. 

I believe that you are correct, although someone will probably come out of
the woodwork to prove us wrong... a great engine.

>The 
>main problem with cam belts is they are a consumable and people forget to 
>have them serviced periodically. There are lots of advantages to rubber 
>belt cam drives. Unfortunately, the designers of the 164 V6 (actually the 
>Alfa 6 V6) also forgot about serviceability of this component and made the 
>whole thing ridiculously expensive. You can change the cambelt on a Mazda 
>four in about 1.5 hours for $90 plus parts, say $200 tops. By the time you 
>have "done" the 164 cambelt you have spent close to $1,500 including 
>various parts you change "in case they fail later". All prices in Canadian 
>funds out here in the boonies of Western Canada.

Apples and oranges? Comparing a four to a six is not valid - The costs of
doing cam belts changes on most modern, or even not so modern, V6 engines
are scarily high. Partly because of the labour time, and also because there
are usually lots of idler and tensioner pulleys that are "supposed" to be
replaced as a precaution. A few of these at $100-$200 each, a belt (usually
the cheapest part) and a chunk of labour to get everything else out of the
way, and $1000-$2000 is common (at least in $NZ, but our labour costs seem
to be numerically similar to NA), including for many of the Japanese
engines. I had a recent discussion of this with a mechanic friend after
being astounded by hearing the costs from some friends who had had their
Mitsi/Nissan/Mazdas done.

Some fours are very cheap ($NZ 70 for a Fiat Uno 70, labour and parts, the
older DOHC fiats normally aren't much more), others with more stuff in the
way and complicated belt runs can be quite a lot more. It's a longer job on
my Uno turbo, just because of the amount of other stuff in the engine bay.
And don't ask me about the waterpump on that.

Scary belt story - Our Croma (2L Fiat DOHC) was coming up to a supposed
100,000km belt change interval (subsequently I found that there was a
misprint in the Fiat owner's manual and it should be 60,000km....), when the
waterpump went. So I figured I'd do the cambelt at the same time. I couldn't
believe how loose the belt was. It would flop up and down between the
pulleys by about 20-30mm. There wasn't enough tension to turn the tensioner
- It was sliding past the pulley! Actually the belt was in surprisingly good
condition. I just don't know what was keeping it on! Can't remember exactly
but think the new belt + tensioner cost me about $NZ120 ($US55). Last belt
was done by a main dealer when we bought the car, but I have to confess to
my shame that I'd never checked it.

Yes I've had a belt fail on a Fiat 125, so you'd think I'd be more careful!

Mark Battley
Auckland, New Zealand.

1973 Alfa Romeo 2000 GT Veloce
1989 Fiat Uno Turbo 
1989 Fiat Croma
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