Spark Plugs

[BobZ]

I've been searching for spark plug brands and numbers suitable for my '78 R100S and haven't had much luck. What are you guys currently using?

[20774]

The original rider's manual for my '78 R100/7, which includes the R100S, says to use the Bosch W225 T30 plug. Check Snowbum's page near the bottom for conversion:

http://bmwmotorcycletech.info/sparkplugs.htm

That would be Bosch W5DC or NGK BP7ES...both non-resistor type.

[markaz]

Check ebay. There were lots of NOS Bosch T30 plugs there for reasonable prices last I looked.

[doktortim]

I bought up a bunch of genuine original German Bosch W5DC plugs several years ago. May as well have spec if you can. The NGK equivalent non-resisters are well proven to do the job just fine.

Last I heard you can still get the W5DC in the BMW dealer box, but do check the code on the plug itself. WR's have been found in W boxes.

There is no longer any such thing as a Bosch non-resister plug from any of the FLAPS.

[Darryl Cainey]

Every Auto Parts Stores have conversion charts for sparkplugs.

I took my Bosch plug number and bought the NGK equivolent, sold in sets of 2.

Much cheaper, bike runs great, change plugs once a year, 513,000 miles and counting!

[BobZ]

Thanks for the replies. I am trying to avoid mail order, I'll try the auto store equivalent.

[longridgebuilder]

NGK are excellent plugs and readily available at most auto part stores. And they're reasonably priced.

[bmweuro]

What ever you do, do not use Champion plugs. They have a slightly different thread pitch and once you use them you are stuck with them. If you try and replace it with a Bosch or NGK after the fact they will strip out.

[jforgo]

What ever you do, do not use Champion plugs. They have a slightly different thread pitch and once you use them you are stuck with them. If you try and replace it with a Bosch or NGK after the fact they will strip out.

Funny you should mention that; I had trouble with using Champion glow plugs in a diesel. After their relatively short life was over, the chambers had to be reamed for Bosch plugs to fit. Never had that trouble, nor the short life, wth Bosch or Beru. What's up with Champion?

[bmweuro]

Funny you should mention that; I had trouble with using Champion glow plugs in a diesel. After their relatively short life was over, the chambers had to be reamed for Bosch plugs to fit. Never had that trouble, nor the short life, wth Bosch or Beru. What's up with Champion?

I don't know why Champion is different. Maybe in the old days where everything was cast iron it wasn't an issue.

[doktortim]

I don't know why Champion is different. Maybe in the old days where everything was cast iron it wasn't an issue.

It was an issue to me back in the 60's when I used Champions in Chevys and Fords. They were junk then and the only thing I have done with Champions since is remove them when ever and where ever found.

[jad01]

So, here I am in the garage checking the valves... pull the plugs to rotate to TDC, and with this thread in mind take a look at the plug numbers, only to find... Bosch WR7DC. How did that happen? In any event, I had a good set of W7DC on-hand and swapped them out (I'm using the leads from Motorrad Elektrik w/NGK 5-ohm resistor caps). That said, the plugs were a good color and otherwise looked fine- the bike has been running well, so I guess I'm lucky there.

[Stan_R80/7]

Not to discourage any paranoia about not having the correct resistance plug, but the difference is not significant. My '78 R80/7 came with resistor plugs when I bought it in '89. The plug specified by parts suppliers showed only the resistor plug. The bike ran great with OEM points, condenser, plugs and wires with resistor plugs.

Since I can now easily get non-resistor plugs, those are in the bike now. I can't tell any difference. The resistance in the spark gap is so high the plug and wire resistance is insignificant. The 'resistor' spark plugs have some resistance added to cut down on radio (electromagnetic) interference from the plug and wires that causes problems with modern electronics. If I were more an electronics 'gadgeteer', resistor plugs would be used again.

The correct heat range, however, is important and can be found from spark plug manufacturers for your '78 R100S. Euromotoelectrics calls out the Bosch W5DC plug for the R100 S, or there is the NGK equivalent BP7ES http://www.ngksparkplugs.com/part_fi...=3538&type=reg. I found the NGK plugs easier to buy than Bosch. YMMV.

[20774]

Stan -

You're probably right, but adding resistance in a situation where the ignition system might be compromised due to other unknown issues (corrosion in the coil tower, spark plug wire breaking down, etc.), might put the bike in a situation where it would misfire or not start. Since we can get the right part, it's best to use it rather than throw another variable into the mix. $0.02 deposited!