From a point at sea, to the circles of your mind, this is Bill:
I want to renew the timing belt on my 740, with the B230E engine. I
purchased a Haynes manual this morning and don't find it all that clear. It
keeps jumping about round the different models. Does anyone know if I have
interpreted the manual correctly that you don't need a tension checker when
replacing the belt, you just trust the automatic tensioner to get it right.
Are the timing marks in the sprockets/casings easy to identify?. To be
honest I haven't looked at the engine with the manual in hand yet, that
comes tomorrow, weather permitting. I'm sure it will all become clear once I
start.
If you've done a timing belt on any other car before you won't have
any trouble with this one. The most difficult part is loosening the
crank pulley - easiest way is to put a socket and T-bar on it with an
extension tube braced against something solid, and then briefly
operate the starter motor.
The tensioner is spring loaded to take the slack up - once this is
done you clamp it with a nut so it can't move; then turn the engine
over a couple of times by hand, loosen and re-clamp. After 500 miles
loosen and re-clamp it again - there's a hole in the cover to make
this easy. It's often a good idea to replace the tensioner with the
belt - it's not expensive.
Also note, that you can lever back the tensioner against it's spring
easily enough with a bar of some sort (once the clamp nut is loosened,
obviously), and then you will see a hole in which you can slip a nail
to retain it in this position while you replace the belt. Remove the
clamp nut entirely and the whole tensioner can be pulled off while
it's like this.
The only sprocket wheels you need to get aligned are the crank and
camshaft ones; the intermediate one doesn't matter on this model. The
marks on the wheels are easy enough to find, but the marks on the case
that they align with are not necessarily obvious. If in doubt, put
your own marks on with tippex (typing correction fluid) before you
remove the old belt.
I have used the following method without needing to find any marks:
before you remove the old belt, put a couple of daps of tippex on the
edge of each sprocket, so that the dabs overlap onto the edge of the
belt. Make each dab exactly co-incide with a tooth. Now remove the old
belt, and, by counting the teeth between dabs, mark the new belt with
tippex so that it matches the old one. When you fit the new belt, line
up the tippex dabs and the sprockets will be in the same alignment as
with the old one. Even if the sprockets get turned, it's just a matter
of matching the dabs, and it will be OK.
Another method I read about on here a while ago, but have not yet
tried myself: Before loosening the tensioner and removing the old
belt, slit it longways with a Stanley knife, turning the engine as you
go, so the you have two half-width belts. Loosen the tensioner and
remove the front part of the old belt. Fit the new belt half on. Cut
the other old half off. Fit new belt fully.
BTW, this model is a non-interference engine, which means that pistons
and valves can never come into contact with each other - rotating the
crankshaft is OK when the belt is off.
Finally, regarding the Haynes manual - the one with the blue cover is
a retrograde step by Haynes; it is poorly set out, confusing, and not
particularly comprehensive. Have a look on eBay to see if you can get
a copy of the older black covered book - it is much more informative
and covers 740 and 760 models up to 1989. I got mine for about 4 quid.
--
Stewart Hargrave
A lot faster than public transport
For email, replace 'SpamOnlyToHere' with my name
