Topic: Valve adjustment lock nut came off

[Bluesoul]

Hey guys and gals, hope you can help me with this.

While riding my 750F2 the other day, I suddenly heard a loud clunking noise coming from the engine. Sounded like valve clearance being way out of spec. Stopped the bike and took off the valve caps. The noise turned out to be a lock nut that came loose, so the adjustment screw turned out and was banging against the cap.
Once I was home I took the engine out and the valve cover off, to my surprise I found the lock nut just laying next to the valve, luckily it didn't fall down the cam chain opening!
There is one thing that worries me a bit though, as the screw turned itself out, the rocker must've slammed against the top of the valve stem. This has caused the edges to be worn away, as you can see on the attached picture. When I turn the adjustment screw in, it only touches the very middle of the valve stem (as you can see, the browner bit in the middle). So I'm wondering if I have to pull the head and install a new valve, or would it be okay to clean it up and just put a new adjustment screw and lock nut in?

[mcpuffett]

Hi Personally i would clean it up and use it as it is  , cheers Mick.

[Dimitri13]

Be glad it didn't loosen up enough to break off the cap :p

[Bluesoul]

Hehe, yeah I bet it could've turned out way worse ;p
Thanks a lot, will order a new screw and gasket, then get it back on the road again!

[dave500]

you might find the end threads in the rocker are burred now and the screw might go very stiff through the last portion of its thread?the valves hard facing where the rocker has contacted the valve tip will be comprimised as well,if the normal contact surface where the screw and valve come together looks ok itll be cool,,you can get away with murder on old tech engines.

[mec]

cause the hole of the rocker arm actuated the valve, perhaps it is a good idea to have a look if the valve stem is bent or not.
if yes, the valve guide could be damaged too.

mec

[Bluesoul]

Thanks guys, I'll take a better look at it this weekend.
If it's only the edges that are worn away, it'll probably be fine. But if the thread or even worse, if the valve stem has any damage, it'll be a bit more work. Will keep you posted about it

[cmouta]

Did you torque the nuts down or go by "feel"?  I just finished a valve job and I did it by feel and this thread makes me nervous!

[70CB750]

With the amount of damage from lose nut on the tappet adjuster, did anybody considered nylocks?

I always check and recheck them, after adjusting,  making sure they are "na krev" as my old man says (bloody tight) but nylocks would work imho.

[Bluesoul]

Did you torque the nuts down or go by "feel"?  I just finished a valve job and I did it by feel and this thread makes me nervous!

Don't want to scare you, but I did do them by feel as well and was pretty sure I torqued them down with sufficient force. Perhaps I'll recheck them next time using a torque wrench, you might want to do the same
Using those nylocks isn't a bad idea indeed, you'd at least be certain they won't come off! Not sure if the thread pitch is standard, but I guess it should be.

[DustyRags]

I haven't done the tappets yet, but that's next on my list- how does one torque those things without letting it spin? Don't you need to have a screwdriver in the end?

[70CB750]

Thats how I do it. 10mm offset wrench and screwdriver.

[MCRider]

I haven't done the tappets yet, but that's next on my list- how does one torque those things without letting it spin? Don't you need to have a screwdriver in the end?

This has been reported here before. in each time it was a result of over-revving. In my case as well. In ordinary conditions nothing out of the ordinary is needed, like nylocks or torque wrenches.

Yes you have to hold the adjuster firmly, I use a stubby screwdriver, while tightening that nut. I use a standard 6" or so 10mm box end wrench.  Then re check your clearance. May take a few attempts to get it right as the adjuster wants to move as you tighten the nut.

I'm interested if the OP over revved his engine?

[Dimitri13]

Mcrider is right. I've only seen a loose locknut from over revving. That's how mine happened.

[Bluesoul]

I'm interested if the OP over revved his engine?

I didn't over rev the engine. I did rev it to about 7-8k rpm, which is about 1k rpm lower than the redline. I think there's really two things that could've caused it, either it was my own fault because I didn't torque it down well enough or there was something with the thread of the screw/nut. I made a few more pictures, the screw does show some damaged thread. I'm not quite sure if it's always been like that or it happened when the nut came off.

Luckily the thread on the rocker arm seems to have no damage at all, so hopefully it'll be an easy fix

[Bluesoul]

An update to this story; I put everything back together with a new adjustment screw/nut and rocker cover gasket. Rode the bike today for 200km at low and higher revs without any issues. Seems like I've been lucky

Thanks everyone for your help!