Triumph Repair: oil spraying/odd sounding engine, dual su carbs, head gasket problem

Question
Greetings!  I have a 1973 Spitfire which has a high compression MkIV (1296cc) engine in it.  Some years ago I fitted Euro-spec dual SU carbs and manifold to the engine.  It had been running beautifully until a couple months ago.  The engine now has an odd sound (almost a miss sort of sound), and also has begun spraying oil from somewhere near the mechanical fuel pump (can't quite figure out exactly where) onto and near the starter. I changed the oil/filter, and replaced both the rotor and the distributor cap, but (perhaps not surprisingly) no improvement. I think next I'll check the compression in each cylinder... any insight or guidance would be appreciated!

Answer
Hi Steve,

You are on the right track with the compression test. That is our first test when a car came into a dealership with a miss. Compression needs to be from 135 PSI to 170 PSI with little difference between cylinders. Be sure to hold the throttle open when running the compression tests. If the compression is low on one cylinder you first need to check the valve clearance and then do a "Wet" compression test by squirting several squirts (about a teaspoon) of engine oil from an oil squirt gun into each spark plug hole before running a second compression test.
The second "Wet" test will show higher then the first test but it must not be any higher then 10% to 15% higher. If it is a lot higher, especially on a low tested cylinder, then it is an indication of a piston ring problem. If a cylinder is low and the "Wet" test did not bring it up much, then it is either a valve or head gasket problem.

As for an oil leak, the only way to locate the source of a leak is to wash the engine down and run the engine and with a strong light examine the area for the leak. (Keep in mind that a compression loss due to a ring problem causes excess crankcase pressure which in-turn causes oil leaks.) Run the two different compression tests first.

If the compression tests are ok then look at Ignition as a cause of a miss. If the miss can be noticed at idle do a "cylinder kill" test. By shorting out one spark plug at a time at Idle to note how much RPM drop there is when you kill a cylinder. Do not pull a plug wire to kill a cylinder. This can cause a spark to jump elsewhere causing other problems. A good method is to use a test light pointed probe to probe the rubber plug cover while the alligator clip of the test light is grounded. If your plug wires are resistance wire you should check the ohm reading of each wire with a ohm meter. A rough test is 5 K ohms per foot of wire is usually ok.
clean or replace the spark plugs. Check the point gap (if it has a pointed ignition system) .015" is normal. Check it on all 4 cylinders to test for a bent distributor shaft.

If it only misses at idle and not at higher RPM, let it idle and remove the air filters and with it idling slowly restrict the intake air on one carburetor at a time to see if at any point of restricting air intake, that it smoothes out or speeds up the RPM then you have an intake gasket leak.

Note if there is any tail pipe smoke when you rev the engine and if so, what color is it?
black smoke is excess fuel, Blue smoke is oil and white smoke is either coolant or brake fluid (if it has a brake booster).

let me know,

Howard