I recently read an article in the May Thunder Press by Kip Woodring who writes the Motorhead Memos. This guy knows his shit and does his research. (Note: The last time I looked Thunder Press did not have the May archives posted yet. But I’m sure you can find a copy at your local bike shop.) The article was about spark plugs. The thing that intrigued me about the article was that it was mainly about the advantages of Iridium plugs. I’ve been looking for a set for about 6 months, but didn’t want to pay the $20-$25 a pop for them. The two main reasons I wanted to change the plugs are; 1) the low amount of voltage required to spark these things. Might come in handy with a close to dead battery, or if you still have a generator or kicker. 2) The life span. Some estimates are that Iridium plugs will outlast the engine. I’ll do a update in 20 years to answer that one. A month ago I found a source that got me some for $9 apiece so I got four.
The main part of Kip’s article was the way that a spark plug dissipates heat from your engine, a fact that totally escaped my old brain. I’d try to explain it, but I would recommend that you read his article if that sort of thing interest you. With the stock plugs my 96” in 90-degree heat would run about 250 on the oil and 350 on the rear head. That’s pretty normal for a 96”. Since I was going to Bakersfield where 90 degrees is a cold spell, it was a good time for a test. The Iridium plugs have been in for a month, but it hasn’t been hot enough here to notice a difference. BTW, here’s a good Cross-Reference for Harley spark plugs.
0:dark thirty. 53 degrees. Head south down 101,east over the pass and into the deserts of Bakersfield. 200 miles and the sun is just rising. Perfect, no traffic the whole way. It’s now about 70 degrees. Oil temp never broke 200. Normal op. temp is 230 by HD specs. Go to the business meeting. Blah, blah, blah… frigggin meeting's over, get the hell outta here. It’s now somewhere between 90 and 100 degrees. Perfect weather for my test. I go about 100 miles and stop to check temps. I also stopped so Dave and I could get a cold drink and check out the little restaurant in Cholame that has all the James Dean memorabilia. Yes, Dave made it down there as he mentioned in his last post. Ya know, it’s one thing to drop everything and ride 100 miles when a Brother is down or needs a hand. But 100 miles in the heat just for the company… it’s much appreciated. That’s something few would understand. Thanks. So I check temps: oil 235, a drop of 15-25 degrees from normal. Rear head, 285, a drop of 65 degrees. I should say that I run Lucas synthetic motorcycle oil also. It may be a combination of the two, but the Iridium spark plugs definitely made a difference I could measure. If you can drop a few degrees off you engine temp by swapping spark plugs, it might be worth looking into.
Even though these plugs should last for I have no damn idea how long, there is a reason I bought four for a two cylinder. For one, they’re hard to find and usually need to be ordered in. And reason number two, the important reason; the second set went to a Brother for his birthday.
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