rocker shaft set or "grub" screws

Sorry wiggly, to cut to the chase , I done the rocker spindle job, did it make any difference? No. And I used grub screws. These old singles make a noise 👍.

Hi Guzziman 

Motor will have to come out to get the rocker cover off. There's just not enough clearance.

If the Kedo tappet screws you're referring to are the flat ball ones (also known as elephant foot) then, the tips of the valves have to be in good flat condition to achieve a decent outcome, which is lots less noise. And they do work well, I can vouch for that. If you have less than 5k miles since the rebuild, I'm guessing your valve tips haven't yet been dented by the standard tappet screws. 

(Edit: The noise is due to the fact that with dented valve tips, you end up with clearances greater than spec, despite the correct feeler fitting the gap. Reason being you can't accurately measure what is now a curved gap with a flat feeler. )

Mini diagram to illustrate:       )l)        The first bracket is your tappet screw, then the feeler, then second bracket is your dented valve tip.

With Kedo flat balls in place the clearance cannot be 'checked' at intervals since there's no way that I found to get the feeler in between the flat ball and the valve tip, so you re-set each time. Easy enough but I made a device to achieve the desired 36 and 54 degrees of rotation to reach the 0.1mm and 0.15mm clearance. Kedo don't supply it. It can be eyeballed fairly well, but I went all OCD on making up a tool. 

I googled SR500 grub screw fix and not much comes up frankly. I think papawheelie was the last known person to do the fix on the old forum and he posted some great pics. His approach was to beef up the area on the rocker cover where the grub screws went first with some ali welding then insert helicoils into the new material to take the grub screws then thread-lock them down if I remember properly. 

It was always seen as a fix worth doing. Maybe an alternative is a 400 head/rocker cover. I don't know if that's been explored/tested. Worth looking into. 

Hope it goes well. This may be of some use.

www.xt500.co/rocker-shaft-question-t3353.html

You'll understand immediately when you fit them, but the snug fit of flat-ball surface to (hopefully) flat valve tip plus the viscosity of your oil makes it impossible to force the blunt edge of a feeler between the two. (Maybe customise a feeler by filing the tip to a razor edge?)

Hence you can't 'check' what the clearance is once fitted. But when you you set the clearance (by reference to Kedo's fitting instructions supplied,) you close the screw down to zero clearance, then back off by 36 degrees to arrive at 0.1mm inlet likewise back off by 54 degrees to arrive at 0.15mm clearance on the exhaust valve. Holding a piece of card with 36 and 54 degree angles drawn on it will enable correct setting. 

(The pitch of the thread being 1mm, hence a full turn of the screw makes for a 1mm clearance.)

The grub screw fix was not required on 400s (maybe not the earliest of 400s but anything later,) because yamaha redesigned the head to avoid this exact issue. 

There are plenty of Youtube videos where XT owners post clips of 'before' and 'after' grub screw fix to show the difference in top end noise. I guess it all comes down to how badly the motor needs the fix as to the audible difference. 

I'm pretty sure in the thread linked in my earlier reply, someone mentions whether their motor needed grub screws both ends of each rocker or just one end, and why. (Teledan you'll recall used to frequent the old SR forum.) I think the guy means side not size in the link below.

www.xt500.co/grub-screw-why-from-top-size-t5032.html

Yes, you're exactly right about using a feeler for the initial set up and that's what I did when I first fitted them. Immediately after, I tried to introduce a feeler gauge which is when I realised that at the next service interval they'd need to be re-set rather than checked due to the sheer inability to get the feeler in there. 

(I didn't want to go backing the screw right off as you risk losing the flat ball part of the adjuster in your motor! Besides which, the little flat ball sticks like a bugger to the valve tip and dislodging it, so you can get the feeler in there, risks disaster.)

That was when my fevered brain devised the degree tool, which sadly I cant show you as I have no pics of it now, and the bike and all the tools were sold a little while ago due to my arthritis. It was ingenious (if I say so myself,) and worked to perfection, but a piece of card with the angles drawn on will work fine too.