Spark plug removal??

Ok, I must be missing something here. I've had my 98 YZ400F for a few weeks now and absolutely love it. Today I was going to change my spark plug just to get a new fresh one in there because I'm not sure how old the current one is. Well I got the spark plug cap off, and I have no idea how to get the plug out. It's pretty deep in that hole, so did the bike come with a special spark plug wrench or something. None of my spark plug wrenches really even came close to reaching it and it can't be that hard to get out the plug. Do I need to get a special spark plug wrench or am I missing something here? Excuse me if I sound like a complete idiot and am totally missing something obvious (most likely). Anyways, thanks for the help. Also any other tips or things to watch out for on my 98 YZ400? The bike's in great shape and has been maintained great. Just got finished changing the oil and cleaning the air filter, I'm thinking about picking up one of those stainless steel oil filters from Scotts and saving some money in the long run and maybe getting better filtration with the stell filter. Thanks again.


98 YZ400F

Yep, the bike came with a deep well plug wrench. Go to your Yamaha dealer and buy one. I have no idea how much they are.

A normal 5/8" automotive plug socket will work provided you have a swivel or "wobbler" (and ratchet, extension, hands and arms etc.).

Most two stroke plugs are larger, a 13/16" works for them and is way too big to even fit in the access hole on your thumper. Also, a thumper can go on the same plug longer, IMO, horrible jetting and funky CDI problems notwithstanding :)

Don't bother with the Scott's filters, I often reuse my stock ones until the rubber seals look suspect, so IMO the limiting factor are those things, not the filter, and the Scott’s I looked at didn’t appear to have appreciably different rubber seals. Relatively speaking the stock filters are a bargain, then.

They are also made of steel, but are not stainless, and I’m not sure what you need that for. Anyway just backwash them with something, make sure there aren’t any holes in the mesh and that the rubber seals look good and put ‘er back in.

You’ve got your hands on a great bike, BTW, probably the best 3+ year old dirt bike you can get.

Keep in mind when changing the spark plug, dirt and debris can be down in and around the spark plug. When you pull it out, all of that dirt, sand, etc....will fall into the cylinder. I noticed that it was a problem when I did my top end and went to pull the plug. Blow it out with some compressed air before removing the plug or use the ole lungs to do it. Hope this helps. A standard 5/8 plug wrench will work fine. Just have a swivel like suggested. :)

I have to reply again to say that MotoStyle makes a very important point, one that I probably should have mentioned (thanks Mr. Style).

I’ll add that there is a small hole in the cylinder head on the right side, just above the barrel or cylinder that serves as a drain of sorts for the spark plug access hole (or cavity or whatever). After you yank the boot (or before, sometimes you can make the boot pop off :) ) you can blow air into this hole and force any debris out the top of the head cover BEFORE you take out the plug.

A good tip.

those stainless steel oil filters are great because the holes in the filter are much smaller than the stock filter so it traps much more dirt than the stock filter ever could. I highly recomend them

Originally posted by yzf:

those stainless steel oil filters are great because the holes in the filter are much smaller than the stock filter so it traps much more dirt than the stock filter ever could.

That’s what I was told too. The only thing that bothers me about that is that if the holes are smaller the filter might flow less. Different bike, but KTM will not recommend their use in the RFS due to concerns about less flow, and supposedly will not honor the warranty on bikes that use them.

Just some food for thought.

Here is some neat little spark plug tid bits. I keep a spare plug under my tail light lense, it fits in there snug and water tight :) . I keep a 3" woobler rachet extension in one side of the swing arm access hole, and the socket in the other side and pop the covers back in. They have not fallen out yet! I just make sure I have my 3/8 rachet in my camel back and the multi tool to pull the seat, lense cover and tank off. I have never had to change the plug on the trail yet, but I know I can if I have to.

Also, once the plug is loose, good luck getting it out. I use a retriever magnet tool, but can grab it with my multi tool if I had to on the trail.

>The Scotts performance web site actually

>claims that they flow more oil

>than the OEM paper filters.

> John

Interesting since the stock filter is wire mesh as well. Maybe it says this for filters in general but not necessairily the YZ filters?

Hick, I would have had a whole bunch of dirt and sand making it's way through my valves and valve train if I hadn't removed that dirt beforehand. I think most of us think that since there is a rubber boot to protect the plug, there shouldn't be dirt and debris down in there. WRONG. Dirty water and mud can penetrate the boot seal and when the water dries up from the heat of the motor, what's left? DIRT.

Thanks for the praise Hick. Just another helpful tip from a Thumper owner and long time MX'er.

Mr. Style

The Scotts performance web site actually claims that they flow more oil than the OEM paper filters.


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