Weird valve occurance....

[Incubus]

Succubus continues to plague me. The B.

So I installed a replacement head on Succubus to replace the head that had only three spark plug holes. When I torqued the cam holders and checked the valve gap, I found something unexpected.

With the crappy head I just pulled off, the valkve shims were all midrange to get the clearances right. The smallest was a 270. The largest, a 280. But when I put on the replacement head, none of the intake valves have ANY clearances with the shims set as they were in the old head. Meanwhile, the gaps on all of the exhaust valves are very wide, ranging from .019 to .022.

I did not expect plug and play without adjusting the valves, but neither did I expect to have to find a whole bunch of shims over 300 for my exhaust and shims as narrow as - hell, I don't even know, but at least 255 to 260. Until I have a gap I won't know what size shims will fit.

I have been messing with this head all day and I'm tired. Perhaps I am overlooking something simple did or or should have done that would cause the valves to be widely out of adjustment (and yes, I checked to make sure I did not switch the cams).

Any ideas?

Patrick

[BA80]

I'll look and see what came out of there Patrick if I can remember which ones they were. If you can figure what you need I'll see if I can help you out there also.

BTW, if you want to send that head with the busted plug I can get that out and maybe save it if it's not too FUBAR.

[Incubus]

No need, Greg. I wish this forum had an erase function.

I.Am.An.Idiot.

I am especially an idiot because I ride these bikes at speeds of up to 90 mph knowing full well that I am the mechanic.

There is nothing wrong with the head and there is nothing wrong with the valves. There is something wrong with the human component.

I now return you to your regularly scheduled program.

Patrick

[dpotter58]

nope no idiot. own up to it and make us giggle. What did you do? You know we have all done it before right?

[Incubus]

Did you know that the intake valves fit really well in the exhaust valve guides and vice versa? And they look OK in the head, too.

[DAVINCI]

All that work and you didn't lap the valves? tsk...tsk.. It's good practice, insures max compression and if you had lapped them you might have noticed the odd fit of the valve-to-seat?

[dpotter58]

Did you know that the intake valves fit really well in the exhaust valve guides and vice versa? And they look OK in the head, too.

tech tip!!!!!

[Incubus]

Uh, I did lap the valves. I now have eight very clean sealing rings in spots on the head that a valve will never again contact....

At least until I rebuild the head again. Then I may experiment with reverse valve polarity (put 'em in backward).

I have actually lapped them all twice now. I'm telling you, if you discount the fact that the intake valves sank a tiny bit deeper into the head than the exhaust valves (not unusual for bikes of that era), they looked right.

At least I am getting very. very good at breaking down the top end again. Any body have any questions? For about 48 hours I will be an expert...

[BA80]

Did you know that the intake valves fit really well in the exhaust valve guides and vice versa? And they look OK in the head, too.

No......seriously?!...

I think Potter is right, most definitly a tech tip.

[skids]

You wouldn't have had THAT problem with an 80 or 81 model.

[Incubus]

I can take the head off my XS in under an hour. If you do it four or five times over the course of a couple of days, you tend to get real good at it.

So I switched intake for exhaust valves and, amazingly, the exhaust valves immediately came into spec. I only had to adjust one, and that was only from 270 to 275.

Intake was still tight, but no longer slammed shut. I had to switch all four, but they took two 260s and two 265s, so the wear is even.

BTW, when I went to my local Honda dealership to trade out the valve shims (that's right, the Hinda guys do it no charge, the Yamaha guys won't do it at all. Won't sell them to me either. Bastards) they just handed me the shim case and let me help myself. Of note, they had 29mm shims as thin as 200, so I guess this head has a lot of life left.

Patrick