Is there a good rule of thumb when to replace the cap and rotor for good preventive maintenance?
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Paul NW Indiana '89 740 Turbo 140,000

I think it would be worth your while to visit the 700/900faq page, scroll down and click on "electrical ignition system" . There is alot of info in there concerning your distributor. You will be glad that you did.


Lawrence

Good grief people!

The cap is like $8-10 bucks and a rotor is less than $5.

Do I hear "cheap" or is that a flock of birds I hear flying overhead...?
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89 245 'loaded' with a Great Pyrenees

Cam-mounted distributor caps are $50.00 +.

Cars equipped with the gear-driven distrubutor (on the front/side) get the inexpensive one: $6.00. In later models, these are common on the Regina-equipped cars.

jp
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Jeff Pierce (Post back with your results... it's what makes this forum work.)

Only Bosch equipped cars get out cheap on that part.
For a Regina cap and rotor you will spend about 60 to 75 dollars.
Not cheap.

Check the prices for the 700/900 with head mounted distributor. Not cheap at all. Very durable though, until the seal leaks...
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67 144, 86 740T, 91 945SE, BMW R69S, R60/2

My 240 had over 150,000 with the original cap and rotor. I replaced it with the correct Bosch and I could not tell any difference.

The maintenance schedule specifies 60k miles. I have found that at 60k, the cap and rotor may be in decent shape or may have fouling oil tracks within, depending on how muc oil escapes the back of the head.

Don't want to make you nervous, but my 1986 740's distributor hall effect went out around 180,000 miles leaving me stranded. As with your 1989, my 1986 has an rpm sensor (hall effect sensor) in the distributor that left me stranded; no pulses, no fuel delivery permitted. So with 140,000 miles, you might want to not only replace cap and rotor, but also the distributor (if you have the coin, since expensive). At the minimum, check the hall connector at the distributor to see that it is not brittle and close to shorting. Also check that the oil seals are keeping oil out of your distributor.

Some have alluded to changing the hall sensor, but would not advise it without a drill press and other tools. Ruin the sensor and your out $70 or so.

Maybe others could give input on this, as maybe my problem was a fluke and they will go forever (it is just a magnetic switch). If you do change the distributor, make sure you change the two "O" ring seals.

Gary

Don't know; I have well over 100K on both of mine.

Every 60,000 miles, but that's assuming you are using OEM (Bosch) or equivalent parts. Cheap stuff from a chain store may not go the distance. Same is true of plug wires, except that Bougicord is the OEM brand, and there have been reports that Bosch replacements are of inferior quality. For the plugs, NGK is the best choice, not platinum, just the cheap regular ones, and the interval is 15-20,000 miles.