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XR4 SPARK PLUG/VALVE ADJUSTMENT TIME

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The time has come for the yearly spark plug change on the xr400. I thought I had it made because I have the motion pro socket for the job this year, boy was I wrong! It was easy to get the socket on the plug but once you loosen the plug the socket gets jammed against the frame when you try pulling the socket off the plug. It took about 2 hours and a water blister on my finger to get that damn plug changed. I used the NGK DPR8Z plug with a .025 gap. Next year I may put in a iridium plug in hopes of it lasting 2-3years without changing it. Plug burned like it should, surprisingly it wasn't rich with my 58/155 jetting with uni filter and everything else stock-830ft elevation.

I blew out the spark plug area with 120psi of air pressure to try to clean some debris out. I blew a nice sized rock out of there! Wouldn't want that falling in the cylinder. It seems impossible not to drop a few grains of sand in the cylinder though when changing the plug. All the moving around of the plug trying to get it out then back in surely pushes a few of the left over sand particles in the cylinder. This really ticks me off. Just a horrible spark plug location. This happened last year too. I am pretty confident once you start the bike and rev it up it just blows any grains of sand out the valves. And the air cleaner surely doesn't stop every grain of sand either but these xr's just keep running! What's your opinion about these problems?

A valve adjustment is next on the list and I can promise you I am not pulling that plug out again! Hopefully I can do it relatively easy without worrying about the plug. Any special tools needed besides the sockets and feeler gauges for a valve adjustment?

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I have not managed to get the spark plug out of my XR400 for quite a while now. I have tried using a Snap-On plug socket but the cylinder head stud seems to be in the way. The standard Honda plug tool is next to useless so when I definitely need to do something with the plug I will have the head off & decoke the head & bore the barrel out to fit the 416 Wiseco piston that I have waiting in my spares box.

As for the valve clearance adjustment, it's very easy to get the engine in the wrong position & the front exhaust adjusted feels as though it's too tight. So just turn the engine over again until all adjusters feel loose. Then use Imperial feeler gauges & not metric as the Imperial ones give much better sizes.

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The spark plug well is a problem. Trailryder has a good tip about adding a cover.

Wash out the spark plug hole. Blow it out. While the old plug is in place, I might loosen it, hold the gas wide open (less vacuum on intake) and kick over the bike to have the air in the cylinder blow out a bit. Then blow out the area again with a compressor.

I have to adjust the valves on my XR400. I might do it today.

Two secrets about valve adjustment and the spark plug.

1) You don't have to remove the plug, you can loosen it to reduce compression.

2) If you're really lazy, use a long non-ratcheting torque wrench to turn the crank the mark. If it is heavy enough it will hold.

I'm going to pull the tank and clean up the spark plug well. Replace the plug while I'm at it.

Valve tips. (There is a full step by step post here.)

Make sure you turn the crank in the proper direction.

Before adjusting any tapet, make sure all 4 are loose. If not turn the crank 360 and try again.

Make sure the comp release is loose.

The MotionPro feelers make the job 100% easier.

Those tapet covers are fragile. Just because you have a 24mm wrench does not mean crank on it.

Edited by Kev_XR

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