Top overhaul was my highest priority until the clutch slave blew which led to a total clutch rebuild.
Spark plugs from cylinders 2 and 3 were comparatively sooty despite my efforts to optimize carburetor mixture and the engine was running a bit too hot for comfort. Let's be an optimist and list possible causes:
1. Head gasket no longer sealing properly between cylinders
2. Manifold gasket leak
|Materials - head, manifold and valve cover|
gaskets + valve seals
|rocker arm cover off|
|push rods clearly labeled as they came off|
|cylinder head off|
combustion chambers > ports
|rocker arm, valve springs and studs|
|cylinder head components|
|Pistons, rings and bores showed no signs|
of major wear after cleaning
|valves were clearly labeled while dismantling|
slight lapping of valves before reassembly
Unfortunately this head has not been modified for unleaded fuel use and could not find a source for hardened exhaust valve seats locally ;( Since I did not want to risk parts getting lost, everything was reassembled. Hardened valve seats = back job to be pursued ASAP!
|new valve seals installed, cylinder head|
cleaned and ready for mounting as
new head and manifold
Thermostat blanking sleeve
It is so typical in the tropics for uninformed mechanics to take off the thermostat as a cure all for overheating problems. So I did some research and found this information at Mini Spares:
Removal of the thermostat helps reduce engine temperature, however a thermostat blanking sleeve should be fitted to maintain correct coolant circulation to the entire head. Failure to do so will cause overheating around numbers 3 and 4 combustion chambers with obviously disastrous results. When the blanking sleeve is used, it is also necessary to blank off the by-pass hose (not found on late heads) between the head and water pump.
Fortunately some local Mini enthusiasts already knew this and a blanking sleeve was sourced locally. But the thermostat cover was practically welded by rust. Since the studs and cover were not available locally, it had to be coaxed out out patiently...
|...finally it gave up|
|1/2" water plugs unavailable|
instead we used a bypass hose with a 9/16"
piece of metal from a bolt stuck in the middle
Given the proximity between the water pump and the cylinder head, the water pump had to come off. Fortunately it was already one of those late deep/cast impeller type in good condition ;)
|new gasket + blanking sleeve|
Not quite - change oil + fit a new filter...
Valve/tappet clearances (.012") had to be set using the rule of 9 -
as pictured above, valve 4 fully open (most compressed spring) valve/tappet 5 is adjusted, thus 4 + 5 = 9, 1 + 8 = 9, 2 + 7 = 9 and so on...
Fiddled with the carburetor mixture, checked contact point gap and ignition timing with a strobe. The Mini is now running better (cooler) than ever and no more sooty spark plug electrodes.
I am now searching for a competent local machine shop that can fit hardened exhaust valve seats and use stainless steel bolts/studs for the thermostat cover. Maybe that machine shop can also help me with the clutch lever arm + plunger? Wishful thinking ;)