345: Intermittent low oil pressure & ticking

[Keith F]

1973 SII 345, 10W-30 oil, occasional puff of smoke on hot start.

Occasionally while driving sustained highway speeds (~2800 - 3000 RPM) I get an audible tick coinciding with the mechanical oil pressure gauge dropping from a steady 40 PSI to a fluttering 30 PSI (gauge needle looks like it's vibrating).

This will happen maybe two or three times during a 120 mile drive. It lasts around 1 minute. If I let off the accelerator while at speed, the tick does not stop.

If I pull off an exit, it stops ticking when the RPMs drop, so I haven't been able to trace the origin of the noise.

Last time it occurred, I pulled off the next exit and added a quart of oil. The symptom reoccured within 30 miles, so I don't believe it was related to oil level.

Any thoughts? Thanks.

[GregF]

Keith, most owners of 345s are running one quart over full all the time. Fill the engine at an oil change so that it is at the full mark and then add one additional quart. When that has gone down to the pan, pull the dipstick and see where the level is. Etch this new line on the dipstick and refill it any time it gets to the original full mark. The problem is that at sustained highway speeds, engine oil is not getting back to the pan in quantity enough for the oil pump to keep pressure up. The oil passsages that are the furthest away get shorted on oil, typically lifters on the right rear of the engine start ticking.
I would try to solve this quickly as I had a 72 SCout II 345 that actually broke its exhaust valve off and dropped it into the cylinder when the ticking was occuring; jamming the engine to a quick halt at 70 MPH. IH said that the oil problem shouldn't have caused the valve to break at 13,000 miles and wouldn't repair the engine until a letter from a lawyer quickly convinced them to repair it for free rather than fight it.
Greg