Should the spark plug cap 'snap' on?

10 replies to this topic
  • jcm3

Posted March 09, 2010 - 10:52 AM


I had a helluva time starting my 2001 YZ426 over the weekend, and found that either:
- the plug was fouled (probably not, it was only a month old)
- the spark plug cap was not securely fastened

I swapped out the plug, and when I pulled it off, it didn't seem like it was fully seated.

When I was buttoning it back up, it seemed like the spark plug cap wire had to be 'just right' for it to seat down all the way, and I also noticed that the cap didn't snap on like it does on all of the other bikes I have owned, or the way it does on a car spark plug. It just seems like it pushes on, but doesn't really give any indication that it is all the way down except that you can't push it any farther.

Is this by design, or should I feel more of a click or a snap when it connects?

I'll have to keep a better eye on it.

  • grayracer513

Posted March 09, 2010 - 12:06 PM


It should engage firmly; snap into place, if you will. You may want to replace it.

  • mxdirtking

Posted March 10, 2010 - 07:58 AM


I just adjusted my valves and when putting the spark plug cap on it really didn't slap on or click but it runs fine.

  • jcm3

Posted March 10, 2010 - 10:37 AM


Thanks guys.

I assume that it probably doesn't really click onto the end of the spark plug itself as a car does, but is held into place more by the tight fit of the rubber cap into the valve cover.

I'll keep a good eye on it.

  • grayracer513

Posted March 10, 2010 - 10:55 AM


No, it snaps onto the end of the plug by virtue of a spring clip, independent of the rubber boot. As I said, you should replace it.

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  • jcm3

Posted March 10, 2010 - 12:17 PM


$70??? Yikes.

  • anthony72

Posted March 10, 2010 - 12:28 PM


Pinch the female tight on aplication? Idk iv had to change my wire in a bike that's only been started 5 times befor. I supose it should only be close enough to conduct, I guess check it like u would a choke

  • Clint12

Posted March 11, 2010 - 06:44 AM


did my plug last night (2002 yz426) and it did "snap in place" I'm thinking you should replace it

  • Birdy426

Posted March 11, 2010 - 08:12 PM


If you have to replace the cap. you may want to think about the coil on cap mod. You can find coils from an R1 in a salvage yard for a couple of bucks. Be sure you get the connector, too.

  • Polar_Bus

Posted March 12, 2010 - 03:56 AM


About a year ago when I removed my plug cap, I observed a lot of moisture and some debris that got down inside the plug cavity, i'm not sure if I did not have my rubber cap seated perfectly tight, but my sparkplug was rusted to $hit, and was difficult to remove. Now, I use anti-seeze on the spark plug threads, and I seal the rubber boot with die-electric grease where it seals to the top of the head. I just recently removed my plug and now it looks mint.. just a heads up.

  • jcm3

Posted March 16, 2010 - 03:14 PM


So, one of the parts guys down at Pasadena Yamaha is pretty cool. I didn't want to order one if I didn't need one, but special orders have to be paid up front and can't be returned.

So, he ordered one for me without charging me if I agreed to pay the $10 restocking fee if I didn't end up wanting it.

The plug doesn't snap on like a car spark plug or my son's PW50 for that matter, but rather feels kind of like if you push a nut that is slightly too big onto some threads. It pushes on, and you can feel it contacting the threads as it goes over them. I think you probably know what I mean.

I tested the new one, and went home and verified that mine is ok. But, it's hard to feel with the plug down as far under the valve cover as it is, so I had to turn and push it. Then, I could feel it going on as it should, so I think it's fine.

I didn't want to pay $100-ish if my spark plug cap was ok, and couldn't really get a good feeling about how it was supposed to feel until I compared it to a new one.

Just an FYI in case this post comes up in a future search.

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