Valve Seals?

[Schming]

I'm not a cocky youngster, I'm a young whipper-snapper.

And I promise I'll never surface grind a shim as long as my friendly neighborhood dealer keeps swapping with me.

Old Age and Treachery, Always, will overcome youth and skill

[crazy steve]

...Does Yamaha give any such measurments in the big shop manual?...

Sorta kinda....

Basically, they tell you to check the guide bore and stem diameter, do the math and see if you're still within allowable clearance. They do give a max on the guide bore at 7.1 mm, or .280", and list stem diameter at 7 mm. Max allowable clearance is .004" on the intakes, .005" exhaust. OEM spec is about half of that.

[TomB]

Another thing I do with machine availability ....make my own guides, though not for the XS so far, I've made guides for old Triumphs. As already said side forces on the valves are greatly reduced as the buckets take that, the old Triumphs used to get huge front and back wear from rocker action. My XS guides have shown little signs of wear.

Another one to watch for is the wear limit sizes given by factory manuals, I dunno what the Yam manuals are like but I was asked to look at the valves of a Suzuki GSXR750 a couple of years ago, the valves were well down on size against the manual so the mechanic had bought new valves to go in, they turned out to be the same size as the used ones, I checked out the stem diameter all the way along the used valves' lengths, the unworn but ground diameter was the same as where the valve went up and down in the guide, so it was unworn, the manual sizes were cobblers.

That is the way to check for stem wear, check the polished/worn area against the ground but unused area, this will usually mean up near the collet grooves and down where some carbon may have to be cleaned off near the valve head.

Steve quotes 4 and 5 thou for intake and exhaust valve stem clearances, if you try wiggling the stems about in a guide with this much clearance it'll seem to be an horrific amount of play, not saying Steve is wrong, simply that 4 and 5 thou is a lot, and the valves will work Ok with that amount of clearance so don't go scrapping good valves/guides when you're gobsmacked by how rattly they can be.
I got to the point of cylindrically grinding a few thou off reamers to machine guides for worn valves, the valve stem is bloody tight to get through the guide at the unworn top but a nice fit once in.

CZ. I don't mark my shims, I don't really care what size they are, I simply grind off what needs to come off that shim when checked with feeler gauges, I dunno what size I'd go down to but if I got anywhere worrying about how thin they're getting I think valve seat reccession would be more of a worry

You guys fill your own teeth as well? Heh, Heh, Heh...

HAHAHAHA! If I was a Dentist I would I'm an Engineer so I grind my own shims

PS, when I havn't had access to a grinder it is possible using a bit of hand skill, a bucket full of patience, and some decent 60 grit Wet +Dry emery on a flat surface, to polish a few thou off shims, keep mic'ing the shims up to maintain flatness, then polish the shim on 800 grit.

Sorry if I waffled on



.

[CaptonZap]

Another thing I do with machine availability ....make my own guides, though not for the XS so far, I've made guides for old Triumphs. As already said side forces on the valves are greatly reduced as the buckets take that, the old Triumphs used to get huge front and back wear from rocker action. My XS guides have shown little signs of wear.

Another one to watch for is the wear limit sizes given by factory manuals, I dunno what the Yam manuals are like but I was asked to look at the valves of a Suzuki GSXR750 a couple of years ago, the valves were well down on size against the manual so the mechanic had bought new valves to go in, they turned out to be the same size as the used ones, I checked out the stem diameter all the way along the used valves' lengths, the unworn but ground diameter was the same as where the valve went up and down in the guide, so it was unworn, the manual sizes were cobblers.

That is the way to check for stem wear, check the polished/worn area against the ground but unused area, this will usually mean up near the collet grooves and down where some carbon may have to be cleaned off near the valve head.

Steve quotes 4 and 5 thou for intake and exhaust valve stem clearances, if you try wiggling the stems about in a guide with this much clearance it'll seem to be an horrific amount of play, not saying Steve is wrong, simply that 4 and 5 thou is a lot, and the valves will work Ok with that amount of clearance so don't go scrapping good valves/guides when you're gobsmacked by how rattly they can be.
I got to the point of cylindrically grinding a few thou off reamers to machine guides for worn valves, the valve stem is bloody tight to get through the guide at the unworn top but a nice fit once in.

CZ. I don't mark my shims, I don't really care what size they are, I simply grind off what needs to come off that shim when checked with feeler gauges, I dunno what size I'd go down to but if I got anywhere worrying about how thin they're getting I think valve seat reccession would be more of a worry


HAHAHAHA! If I was a Dentist I would I'm an Engineer so I grind my own shims

PS, when I havn't had access to a grinder it is possible using a bit of hand skill, a bucket full of patience, and some decent 60 grit Wet +Dry emery on a flat surface, to polish a few thou off shims, keep mic'ing the shims up to maintain flatness, then polish the shim on 800 grit.

Sorry if I waffled on



.

Howdy Tom,
I think Steve misplaced a decimal, since .1 mm equals .003937 inches, and .0004 to .0005 sounds about right in my experience. That would equate to about 2 to 3 thou at the head, without going into the trig tables.

When you ground the bent valve, (from a different thread),
how bent was it? Did you take the same amount off of the seat and the shim? Or just make up the difference in the shim after you put it back together?

Don'tcha just love machine tools?

CZ

[skids]

Way to go, Tom.
Then I dip it in battery acid and use it like a pen and print the thickness on the ground side. Let it set for a few minutes, rinse it off, and presto, indelible marking. Until the next time you grind it.

CZ

Really a good idea

[TomB]

Howdy Tom,
I think Steve misplaced a decimal, since .1 mm equals .003937 inches, and .0004 to .0005 sounds about right in my experience. That would equate to about 2 to 3 thou at the head, without going into the trig tables.

CZ

not saying Steve is wrong, Tom

But you did



But it would account for why it seemed a lot, but seriously, valves can be very sloppy and work perfectly Ok.

How bent was the valve we ground? as I said they were all slightly lifted off the valve seats so maybe double the usual valve clearance, grinding this much off the head of the valve affects the shims little and the basic valve head shape little, you're basically regrinding the angles back on. I'm guessing all the folk saying throw the valve away in the other thread are none engineers coz its standard engineering practice in engineering, when working in a contract toolmaking shop I've ground marine engine valves for customers.

As I said, I've done 80 odd K miles on these valves.