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The manual advises to replace spark plugs every 10km/200hr. Has anyone found that necessary? For similar plugs in aircraft, we change them when they're out of tolerance, but not based on hours.

I replace the spark plugs every 15000 km. Didn't have any problem.

From the Owners Manual, Page 150. This is of course referring to the original military spark plugs. If you have converted to the civilian ignition with conventional spark plugs, your mileage will vary.

Yes, that is the manual I was referring to -- I guess I should have quoted the chapter and verse.

The question was: what are people's actual experiences with practical replacement intervals?

I converted to the civilian ignition with Perrtronix, then to PinzSSI and have been using NGK BP6RES plugs with both. I replace them every 5000 miles since they are relatively inexpensive. They never look very worn. Hope this helps.

I'm looking for experiences from people running the original military-style plugs.

Thanks, though.

I think it is very good to keep the gap of the spark plug electrodes at the given gap of 0,6 - 0,7 mm. Spark plug gap widens through the time in service and the elctrodes are getting round as well, so they should get shaped from time to time and as long as the engine works fine I don`t replace them - the mileaqge of my 710M is now 10200 km´s since refurbishing in 1998.

I think it is useful to keep the plugs in proper gap and shape - as the gap widens it will stress the ignition system.

On my Dodge WC52 I have the spark plugs in since I bought it 1988 and they haven´t been new at that time. The Dodge is running with ordinary spark plugs.

Thanks, heinz, that's the kind of data I was looking for. Likely the original replacement interval presumed military budget service.