timing chain engine idle question

[Mike Wattam <MikeWattam@domain.elided>]

Hi Ben

Timing chains can be changed with the engine in the car, it is necessary to
have good access to the front of the engine so hood off and radiator out
plus grille, before you start.

It is not necessary to renew the chain guides if there is no excessive wear
of the wearing surfaces, and they are not hard/broken.  You should expect
to see grooves in them from the chain links, but the rollers should still
be well clear of the wearing surfaces.

It is not necessary to renew the chain tensioners if the rubber pads are
not excessively grooved as above, also check the fit of the piston in the
housing.  If they are loose near the end of their travel, oil will leak out
to the detriment of the engine bearings and possibly chain tension.

Check all sprockets for wear.  This is best done with a new chain, wrapping
it around the sprocket and checking for 'lift' at mid-point, then carefully
examine the tooth profiles to make sure both sides of all teeth are
symetrical.  If you are unsure about this unscientific method, a visit to a
motorycle repair shop where you will find experts in this checking.

Suggested parts list;

156056  camshaft tab washer (2)
149789  camshaft sprocket (2)*
145840  chain cover seal
145839  "
144666  "
UKC3344 front oil seal
151089  chain tensioner (2)*
151277  tensioner travel restrictor (2)
148115  chain guide plate*
147907  "
149452  "
145416  "
143257  crankshaft sprocket (2)
145275  sprocket shim (as required)

Repair operation manual is essential!

Regarding the idle problem, from what you say you have the auto gearbox in
your car.  When cold, the Stag does tend to suffer from nil torque below
1,200 rpm, and this is made much worse by either incorrect timing or a most
likely a weak fuel mixture.  So check the following;

Engine in good condition, not smoking badly or using excessive oil
Correct ignition timing, points correctly adjusted and no excessive free
play on distributor spindle or two base plates below points
distributor cap and rotor arm both in A1 condition
Spark plugs good, correctly gapped, HT cables fittedd to correct plugs
vacuum hoses to distributor in good condition, no leaks, vacuum unit
working (suck on hose with distributor cap off and no movement = split
diaphragm, a common problem)
plug lead resistance within limits
air leak at carburettor base adaptor - 'O' ring perished or air leaking
past nut at top
no oil in carburettor dash-pots
perforated carburettor diaphragms
air intake hot/cold valve not working - with engine running but cold,
remove hose from valve on top front of filter casing, when a distinctly
audible 'clonk' should be heard as the valve opens.  Check in the opposite
sense when engine is really hot.
air leaks from other hoses, check by removing oil filler cap when hesitancy
in engine spped denotes all is working OK with no leaks.
finally, have an emissions test and hopefully this will reveal a weak
mixture, in which case re-adjust both carburettors to rechen mixture but
still within design limits.  Note a weak mixture does NOT save fuel.

Please let me konw if any of the above needs clarification.

Mike Wattam
Chairman - Triumph Stag Register