In the two previous blogs I described the dyno configuration as well as quality control testing. From time to time I had to stop quality control testing and perform endurance testing instead.
In the case of the Valiant the schedule was:
- Run the engine for 9,5 hours at various lengths of time and loads to bed the rings and bearings in and then run it for half an hour at full throttle to measure the output in terms of power and torque at various speeds.
- Now run the engine at speeds of 1 600, 2 000, 2 400, 2 800, 3 200 and 3 600 r/min for 10 hours at each speed under full throttle. (The revs are changed by adjusting the dynamometer load.)
- At the end of this cycle the total time taken will be 60 hours. The oil and various filters are now changed, as well as the spark plugs and distributor points.
- The above cycle plus service procedure is now repeated another seven times to give a total of 480 hours of full-throttle running.
On the Valiant engine bore wear was minimal, but the big-end bearings had to be replaced at 240 hours. However, we later found a different brand of bearing shells that lasted the full 480 hours.
Endurance testing is very tedious. You cannot let the engine out of your sight for long. You have to be ready to stop the engine at the first sign of trouble or else face a disaster. On two occasions an oil leak started a fire in the spill pan underneath the engine. This had to be stopped before it got out of hand.
You also have to listen for unusual noises, because a failed bearing could very quickly cause a complete engine breakdown. By the time I conducted my first endurance test I had an assistant; an old mechanic we called Pop. Once, during an endurance run, I thought I could hear a bearing knock, and Pop agreed, so we stopped the engine, dropped the sump, and inspected the bearings shells, but could not find anything to account for the knock. The second time it happened we removed our shoes, walked around the engine to feel the vibration in the concrete and decided it was only an imaginary knock.
The dynamometer was also used to try and solve a mystery. After three years I left the dyno cell, and Pop was promoted to dyno operator. I was promoted to resident engineer for the engine assembly plant. Soon after I started in the new position Valiant engines started to fail a few thousand miles after being sold. I saw a number of these failed engines but they were usually so wrecked that all the evidence was gone. We suspected that some machining operation wasn’t being checked correctly, leading to the wrong tolerance. We built-up an engine using parts that were rejected by quality control because of incorrect dimensions and punished it for days at full throttle on the dyno. We hoped it would break and give us a clue, but it never did. We never found the cause and the spate of breakages stopped as suddenly as it started.
