Tutorial, Petrol engine setting up

For all you petrol heads out there.
Most of these are generic to our series Landrover.
Areas covered are.
Engine
Spark
Fuel
All are interconnected when we are looking for a good smooth running engine.

We will start with the engine and I will try and keep it simple.
Engine
Compression, if you have a compression tester check all cylinders, they should be similar or the same. If not you could try a squirt of oil in through the plug hole and see if the reading goes higher. If it does it shows the piston rings are not sealing as good as they should, if the reading doesn’t go up but still shows low it’s possibly your valves not seating properly. Burnt out valves, decoke required, too tight valve clearances ect. A cylinder leak test will pin point the trouble

It is pointless proceeding to tune an engine which has a known mechanical flaw like a poor cylinder.
Check your valve clearances, do not be tempted to have them too tight, when checking with your feeler gauge rotate the push rods between your fingers, ( this checks for bent push rods ) if they are bent and you adjust the gap at the widest part the rod can rotate and reduce the gap to nothing potentially holding the valve off its seat. I have also seen the rocker arms with indentations in them causing the top of the valve to rebate into the rocker. Replace if so.
If you are still having problems with your valve clearances and want to look for work, check the Camshaft rollers and slides, I have also seen the rollers with flats pots on them.
Assuming the engine is ok on we go.




Ignition

Starting with the ignition Coil, make sure the wires are the correct way around on the Plus and minus, minus to the points, usually the wiring has different ends to stop this happening. You can do a resistance check on the primary and secondary ( Use manual for spec )

Ignition leads, if you have a meter check the resistance in all HT leads as a rule of thumb 10K ohms is the norm but can go up to about 20 depending on the design of the leads. The higher the reading the more likely its going to fail.

Distributor cap, you shouldn’t be tempted to scrape the inner contacts, this causes a larger gap for the spark to jump, it should look like new and no visible cracks or lines between segments.
( usually caused by tracking of the sparks )
The centre contact should push in and spring back out.

Rotor Arm
With some insulated pliers remove the King lead ( centre coil Lead ) from the distributor cap, Remove the distributor cap, point the king lead at the rotor arm (get someone to crank the engine) there should be NO Spark, if it does replace the Rotor arm.

Distributor / Points
New points only stay accurate for 12hrs of running, there shouldn’t be any pitting on the two surfaces. Set the points gap or dwell angle (dwell angle is more accurate)
Hold the rotor arm spindle and try and physically move the rotor arm spindle sideways, it shouldn’t move side to side, if it does your dwell will never be accurate. There also should be a lube pad running against the shaft to lube the heel of the points.



Distributor mechanical advance
Hold the rotor arm which is still located on the distributor shaft, twist the rotor arm, it should rotate slightly and spring back. This is checking your bob weights, if it rotates and stays the springs are off, if it doesn’t move at all it’s seized. This movement is essential for performance and economy.

Vacuum advance.
A simple check, disconnect the small bore pipe from the manifold side and suck on it, With dist cap removed watch for the points base plate rotating slightly ( this is also essential for economy and performance ). You should be able to create vacuum, if you can’t the diaphragm might be holed.

Spark Plugs
The gap on all plugs should be the same and correct, too small and you don’t get a full burn, too large and the spark might want to track ( it will take the easiest path ) the centre electrode should be prominent and still have a flat end and look as if it had a file across it. Old plugs can look rounded. If you have had a Carb flooding problem the plugs might look black and oily, they will not spark properly. ( Clean properly or replace )

Ignition Timing
It's better using a strobe light for this, set the basic timing at idle with vacuum pipe disconnected.
Now rev the engine to 2000 rpm and check for the mechanical advance, it should be noticeable, add the vacuum pipe and check again at 2000 rpm and it should read even more advanced, continue revving and it should continue to advance.

Carb / Manifold
Engine running
Use some WD40 and spray the inlet manifold area and base of the carb, if the engine revs go up it’s leaking in air (repair it)
All ok. On we go

Engine not running.
Air filter clean and ok.
Webber/ Zenith type. Not SU or HIF

If you are going to tinker with the CO screw look to where the screwdriver flats are and count the number of turns in, ( go gentle don’t force the screw too tight it can snap off the tip) ok, remember the number then turn it back to where it was.
Look at the butterfly spindle it also should rotate but have little or no up/down movement. Check the throttle for full operation, push the accelerator pedal full down and check linkage, adjust if needed.
When operating the throttle linkage look down the top of the Carb and check the accelerator pump is working, you should see a small squirt of petrol.

Engine running
Normal operating temperature
At idle turn the CO screw in slowly till the revs peak (stop)
Re- adjust the idle with the idle screw (bring the revs back down). Re adjust the CO screw to achieve the sweet spot peak revs.( continue this process until you cant see any improvement )
At this point the engine is running too weak to perform when driving. Turn the CO screw out at least one full turn and rev the engine.
Road test.
If it seems not to want to pull away using full throttle but seems to pull better as you reduce throttle its still running weak, rotate the CO screw one full turn out again. All going well you should be near to where the original position was unless the carb has been adjusted to mask another problem.
Still got carb problems you might need to overhaul it and check all jets main, float height etc. A CO meter is obviously the best method of adjusting a Carb. With all of the above in good order the colour of the spark plug can guide you to engine running too rich or weak. There are plenty spark plug colour charts ( Light tan is good )

I have tried to keep it brief, there is a lot more in depth trouble shooting which I wont go into today.
I hope this helps.

thats all very pretty but its not entirly accurate and some of the test described can lead to failure of expensive componets.
taking a plug lead off while cranking the injun can cause damage to electronics on some engines.
using a strobe is not always the best way to time an engine as the timing marks are in the same place regardless of fuel used or attitude operated at and we wont mention any of teh other countless parameters than make timing marks no more that a guide to initial start up.
if you don't have access to a rolling road then timing by ear is the next best thing.

and if you have a +ive earth series then connecting the coil up as stated will be arse about face

thats all very pretty but its not entirly accurate and some of the test described can lead to failure of expensive componets.
taking a plug lead off while cranking the injun can cause damage to electronics on some engines.

Click to expand...

I Agree that’s why it’s steered around the Landrover petrol engine, not many black boxes on them that I recall.
Take all above in the context of a series 2 / 3 petrol 4 cylinder. The principles apply to others though.

Superb stuff!