To fire the engine you need good compression, good spark and good air and fuel mixture.
It helps if you have some tools such as a compression tester, resistance and volt meter, strobe light and gas analyser to do the job, but it is not necessary to get it going.
Compression.
Take the key out of the ignition, find the starter handle and try to turn the engine over. Watch your thumbs as the compression may kick back. It should be difficult to turn at every half revolution and once over the hump turn easily. A standard Javelin engine has a ratio of compression of about 7. This means the pressure at the top of the stroke should be about 7 bar or 7x15 psi. Modified engines may be higher at 160 psi. Teach your muscle memory what this feels like by turning over a few different engines. If you do not get four equal compressions then diagnose using the guide that follows.
Spark.
Remove all spark plugs and move the spark leads so that when you push the plug back into them the plug rests touching the metal of the engine so that you can see any spark going across the plug gap (which you might want to check is 25 thou).
Switch on the ignition and see you get a good white spark at all four plug gaps. This is best done in poor lighting. Experience should teach you the colour and sound of a good spark. Diagnosis later!
Timing.
Take off the rocker covers checking there is some oil, but no water in them. Turn the engine slowly until you get a spark on front right (viewed looking at engine) No 1 cylinder. Try to turn the push rods on this cylinder which should both be free. The foremost rod is the exhaust and should have 6 thou of clearance. The one next to it is the inlet with only 3 thou. Teach yourself how this feels by rattling the rod. More later!
Also check the spark occurs exactly on the timing mark on the flywheel. There should be three marks. 1 line 2 indicates top dead centre for firing cylinders 1 and 2. 3.4 is for cylinders 3 and 4 and is directly opposite or 180 deg. There is also a mark at 12 deg before TDC for setting the valve timing. You can do a rough check of valve timing by seeing if the inlet valve starts to lift at this 12 BTDC mark.
Check ignition spark timing against the TDC marks (or ones you have put on the crank pulley) and at the same time check push rod rattle at TDC, for all four cylinders. Diagnosis later.
Fuel.
By now you should be able to smell fuel. Does it smell fresh? Old fuel loses its volatility. Manually pump the petrol pump. Do you hear squishing and then get resistance? Are there any drips of petrol outside the carb? Does the choke operate fully on both sides? Diagnosis later!
Fire Up.
Put the plugs and leads back. No need yet for the rocker cover as we want to check oil feed to rockers. Check everything clear of fan. Pull choke out, press starter. Switch off. Check oil feed.
Set tappets.
Having seen how many experienced Jowett people incorrectly set tappets not only I but JCL recommends this technique.
March 1953 Item No. 131. Tappet Adjustment, Solid Type – Javelin and Jupiter
To clarify the instructions on tappet adjustment the following notes are issued. It is extremely important in view of the fine adjustment required that:
1. With the engine COLD the inlet clearance is set to 0.003" (0.076 mm) and the exhaust to 0.006" (0.152 mm) these dimensions being measured between the end of the valve stem and the rocker.
2. Ensure that the tappet being adjusted is riding on the base circle of the cam and NOT on the initial portion of the cam-quietening ramp.
Adjustment should be made to tappets according to the table shown below:
Setting Position of Engine, Valve to be Adjusted Pulley position of TDC mark on pulley (hour hand of clock)
Number 1 Exhaust valve fully open , Number 2 Exhaust , 8:30
Number 1 Inlet valve fully open , Number 2 Inlet , 3:30
Number 3 Inlet valve fully open , Number 4 Inlet , 9:30
Number 3 Exhaust valve fully open , Number 4 Exhaust , 2:30
Number 2 Exhaust valve fully open , Number 1 Exhaust , 8:30
Number 2 Inlet valve fully open, Number 1 Inlet , 3:30
Number 4 Inlet valve fully open, Number 3 Inlet , 9:30
Number 4 Exhaust valve fully open , Number 3 Exhaust , 2:30
See chassis number plate on bulkhead to identify cylinder numbers.
To understand what you are doing look at the valve timing diagram in the maintenance manual. Figure 29 page 25. Normally I use the position of the opposing valve lift rather than marks on the crankshaft but you can use the timing disc and stick on crank pulley as a check on your procedure. Note these two diagrams are mirror images because one measures position of TDC mark on pulley at event, the other position on a rotating shaft of TDC mark on timing case when event occurs. You are effectively setting the inlet valves for 1 and 2 cylinder at 3:30(clock position on the crank pulley) 120.5 deg before TDC and exhaust valves for 1 and 2 cylinder at 8:30(clock position) 252.5 deg after TDC. Cylinders 3 and 4 are opposite on the clock, remember, so 9:30 inlet and 2:30 exhaust.
Compression diagnosis.
With ignition switched off and plugs screwed in correctly, turn the engine over listening for air escaping noise. You can do this better with a helper and a couple of feet of plastic pipe held to your ear. With the tube down the oil filler you may hear a slow escape as you reach TDC but it should not be rush out, showing that all compression is lost. You should hear no escaping when listening inside each carburettor throat or out of the exhaust pipe. Sure you will get a noise on the inlet and exhaust stroke, but a leak is a distinctive sound. Such a test can best be done using a modified spark plug feed from a compressed air line. If the engine has been running then examination of the spark plug or inside the combustion chamber with an endoscope should show the cause which may be worn bores or broken rings, pitted valves or leaking head gasket.
Ignition diagnosis.
I was assured that the distributor cap and leads were good, but the resistance meter showed that 4 of the 5 leads were open circuit and not approximately 5000 ohms. Luckily a spare set was available but a new ignition coil end had to be fitted. Spark problem solved except one of the spark plug ends required the screw cap on the spark plug to be removed, just to be different!
But of course, there are many other reasons for poor starting as the Jowett species has its own symptoms and each individual makes up even more. Javelins were originally positive earth so the ignition coil needs to be fitted appropriately. The electrons need to be going from core of plug to tip, which can be tested using a pencil lead and a keen eye. This is colourfully illustrated on JowettTalk.
Most people rely on the + and – symbols on the coil, but coils with CB could come from a negative earth vehicle! On a standard Javelin the + goes to the Contact Breaker.
The infamous tracking rotor arms have caught many out, so it is a good idea to carry a known good spare.
Points gap should be initially set to 15thou , check you get a good spark there. If not the capacitor may be at fault. You can get bouncing points or bad leads to them and the earth strap can fray as it is fragile. Tracing electrical faults is best done with a meter. Do not be surprised if poor starting traces back to the earth on the battery or engine, high resistance ignition switch or fuse, poor battery or high resistance feed from the battery. You can check some of this by looking at the voltage between the feed to the coil and the engine block and making sure it does not drop below 10 volts when the starter is operating.
Feed me.
Jowetts are very particular about their diet, but they are also very poor at getting it right. Carburettors do wear and are infrequently maintained. The float needle valves invariably leak petrol, resulting in rich mixture, so get some new ones and fit the washer above them. I have seen many Jowett Carbs with no gasket between top of float chamber and carb body. Disaster on the diet!
The throttle spindles wear, causing excess air intake and weak mixture. Carbs are often poorly fitted to the manifold resulting in air leakage. Leaks can occur in the air pipe to the pintle valve attached to the oil filler cap. That valve too can misbehave. So use your trusty stethoscope (plastic pipe) to hear for these leaks. Worst of all the seals in the balance pipe can fail with clouds of smoke coming out the patient’s rear.
The petrol pump too can cause malaise, with diaphragm, valve and wear problems. Check you get about 30 to 40 inches of pressure using some plastic pipe on output of pump when hand priming.
The choke strangler flaps may not be closing fully. Set the LHS (as viewed by passenger) choke strangler flap to close fully slightly in advance of the RHS choke strangler flap. The natural spring twist in the actuating cross rod will permit the RHS choke strangler flap to fully close, thus ensuring that both flaps are fully closed. Reverse instructions for LHD car.
Always learning.
You never know it all with a Jowett. They are a constant source of enjoyment for the diagnostician.