When I bought my Mk IV mechanically is was in very good condition but I
decided to do a pretty extensive mechanical overhaul with the main
objectives being to install an Overdrive and get the engine as near as I
could to Mk 3 spec.. I have a few comments that my be of interest
Crank case vent.
I replace the single Stromberg with two HS2 from a Mk 2 spit and an
inlet
manifold from a Mk 3. I connected the rocker cover vent to the PCV valve on
the manifold and also ran a tee off to the carbon canister . So now the oil
vapor is sucked into the inlet manifold and also the gas tank is under
slight vacuum as per the original Mk IV set up
Rocker shaft oiling
I initially installed the extra line which roots oil from the engine oil
gallery to the rockers. But I found that there was too much oil going to
the shaft. This resulted in a puff of oil smoke when the engine started up
because the excess oil is getting down the valve guides when the engine is
stopped. The Spit doesn't have the little "O" rings on the valve stems to
stop this which other cars do. If you are thinking of putting this line on
to prevent the front of the rocker shaft being starved of oil then block
the normal oil feed off.
Distributor timing
I had a battle to try to mimic the advance curve of a UK spec MK3. I
bought 2 distributors off E Bay from Mk2 and 3 cars and eventually got a
system that got close to the UK spec. The thing that puzzles me is that I
could not get full advance on any of the distributors. I would have
thought that as the springs weaken with age you should get to full
advance at lower revs but this was not the case. None of the distributors
was capable of giving the full advance that the ROM states. A finished up
with a distributor from a Mk 2 on which I fitted a vacuum advance from a Mk
3. I'm a little concerned about pre detonation since I can only get 91
octane and I don't know whether these octane boosters I use really does any
good.
Alternator
I fitted a DelCo 65 amp alternator to get away from having to pay a high
price for a recon Lucas unit. It is OK but it doesn't drop out of
regulation at idle. This means that the idle speed is effected by the
electrical load, i.e head light on or off. On modern cars the computer
controls the idle speed irrespective of alternator load but of course this
is not the case on the Spit. It's not a great problem but it might better
to use a lower output alternator which will drop out at idle.
Exhaust system
I fitted a Double S exhaust system ( two pipes out the back) and it
sounds
great but it is a little to noisy and I can't hear the engine when the soft
top is down... which is always the case as I haven;t got a soft top. Bear
this is mind if you are thinking of going this route.
Overdrive.
You have to get one of these. I have now a single rail box with a J type
overdrive. I can keep up with the traffic on the free way easy, here in
South California that means 75 to 80 mph, without exceeding 4000 rpm. But
the problem is the car is so damn small that the SUV hulks just don't see
me. When tip I have is that if you are going this route you need to fit a
speedo from a 1500. The 1500 speedo turns 1000 per mile whereas the Mk IV
speed turns 1184. I, for one, didn't realize that the 1500 had a different
count speedo
Stuart Greenwood
sagreenwood@earthlink.net
San Diego Ca
Triumph TR8, Stag and Spitfire Mk IV
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