YZ426 strangest oil leak ever....

[stevensj13]

Okay guys. I bought a YZ426. There is a little hole on the cylinder/head on the right side (kick start side) of the engine, and the bike will spit a bit of oil out of said hole almost sequentially. It shoots far enough to touch the exhaust and sometimes hit your boot... does anyone know what that hole is for? I can provide pics if need be. The bike doesnt smoke, and has plenty of compression/power. Is that a breather or something? or is it safe to tap the hole and thread it for a bolt? I just dont want boiling oil on my leg, I dont mind adding a bit of oil to compensate for a leak or something, I just dont wanna burn the shit out of my leg!

[capt justin]

I think that hole leads to the spark plug and it is used to help clean that area before one removes the plug (compressed air in hole), and it lets any water out that get in around plug boot

[bblueox]

I have a 2003 YZ450 that had a similar issue. On my 03 the manual compression relief has been removed,(they switched to the auto compression relief that year) they used the head casting from the previous year so the void for the compression relief is plugged with a small cap. Anyway, my head vent tube had been pinched which caused the pressure in the head to build up and pop the cap off and spew oil. In other words, make sure your head is venting properly, hope this helps.

[MX Tuner]

Some of the YZ's have a bolt with a sealing washer that plugs a hole in the oil delivery passage going to the cams. This bolt goes into the head sideways right in front of the external oil pipe near the back of the head. Is this bolt missing? Some models have a ball bearing tapped into the hole to plug it.

If the spark plug well drain hole was pumping oil out that fast, it would have to have a bad oil leak at the valve cover gasket and possibly a loose spark plug.

[grayracer513]

Some of the YZ's have a bolt with a sealing washer that plugs a hole in the oil delivery passage going to the cams. This bolt goes into the head sideways right in front of the external oil pipe near the back of the head. Is this bolt missing? Some models have a ball bearing tapped into the hole to plug it.

If the spark plug well drain hole was pumping oil out that fast, it would have to have a bad oil leak at the valve cover gasket and possibly a loose spark plug.

The 1/4" hole in the center of the right side of the head is the plug well drain. You may also be missing the bolt that retains the decompression shaft, which would be up on the right side of the head, behind the exposed end of the shaft.

[stevensj13]

It has manual decompression if that matters. Here is a picture of the head. The hole is dead center of the pic, not by the decomp lever. Is it okay to plug that hole? or is it important for pressure release or something like that?

[grayracer513]

Don't plug it. That's the drain for the plug well. If you plug it, water, oil, and debris will accumulate around the spark plug, and the pressure increase under the plug boot may pop the spark plug wire off every so often.

Fix the oil leak at your cam cover by replacing the gasket, and be sure your plug is torqued to 14 ft/lb.

[glenn77]

Grayracer513 is right. Same thing happened to my 2011 YZ450f. The gasket was leaking and the oil comes out of that hole that is a drain hole for the spark plug well. Easy and cheap fix.

[stevensj13]

Could i take the cam cover off and add some gasket sealer to the gasket and mating surfaces to cure the leak if thats my problem? I have 2 tubes of make a gasket and gasket sealer that I havent use

[grayracer513]

No. Unless you want it to keep leaking. See your other post:

https://www.thumpertalk.com/forum/showthread.php?t=1029742

[stevensj13]

Yeah. I guess I'll order a gasket from my local Yamaha shop