Triumph Repair: Bearings?, triumph spitfire 1500, engine cold

Question
Hi Howard,
I bought a 1975 Triumph Spitfire 1500 a few months back. The PO was in the middle of an engine swap project with one that apparently came out of a crashed vehicle. Because of this, I couldn’t hear the engine run before I bought the car. I put everything back together again and it runs and drives, but when the car is underway, a really bad clattering noise come from the engine (and/or gearbox?) under acceleration. I assume the most likely culprits are the bearings in the engine’s bottom end, for which the 1500 is famous. However, there are really two noises, a higher-pitched metallic clattering under light acceleration, then a lower-pitched one that takes over as the car accelerates more. Everything has been checked and adjusted carefully, including carburetor, exhaust, ignition system/ timing etc. The car starts fine, and the clattering noise is much less noticeable when the engine is revved with the car stationary. I have an audio file with the car in motion which I can send you if it'll help to identify the source, but this service apparently only lets me attach image files. I’d appreciate it if you can point me in the right direction on how to confirm the most likely source of the noise(s) before I start ripping the engine out to rebuild it.
Many thanks
Nigel

Answer
Hi Nigel,

In the dealerships we hand to contend with this type of problem at least several times a week so there is a procedure to try to diagnose the noise before tearing down an engine. There is a 100% easy test to see if the noise is a rod or main bearing noise. It is impossible to have and maintain proper oil pressure with even one rod bearing loose enough to knock. So confirm the oil level and hopefully you know what weight oil is in it. If not pull the dipstick and look at it cold. It is obvious when thick oil was added to try to quiet down a bad bearing.

Then start the engine cold and note the oil pressure at idle and at 2000 RPM cold. You should see 30 to 40 PSI at idle and 50 plus at 2000 RPM. Warm the oil up (which takes a little longer then coolant temp to come up) Then with a warmed up engine you should see 25 to 35 PSI at idle and 45 to 70 at cruise speed.

If you see much lower then that you still need to do some more tests. Remove the oil pressure regulator valve and examine the valve and spring and remove the valve cover and run the engine to see if you have oil flow to the rockers. Oil flow to the rockers usually suffers when oil pressure goes away.

You can have upper engine noises that don't show up with any oil pressure changes. Piston slap, Piston pin problems, incorrect head gasket can cause a knocking noise (common on Spitfires) and detonation commonly called ping or valve rattle Neither of which have anything to do with the valves. Detonation can be caused by many things like excess carbon build up in the combustion chambers, low octane fuel or stale gas, Oil in the combustion chamber by the rings or valve guides, wrong heat range spark plugs and the wrong head gasket leaving an edge inside the combustion chamber.

A loose rocker arm or out of adjustment of a valve can make a top end noise but can not be altered by engine load.

loose flywheel bolts or front pulley can give you a deep heave knock too.

A last check with a mechanics stethoscope or a long screwdriver with the handle against one ear can closer pinpoint the location of a noise.

After all that we then decide what needs to be done. Even with a lot of experience hearing engine noises we would never make a decision based on the sound alone.

let me know,

Howard