peculiar valve migration...

when I first got my hands on my Seca almost three years all the valves were plenty tight (.05 or .1mm pretty much across the board)
At that time I adjusted them, cleaned the carbs, bench synced and set the pilot mix by ear both with great care and as much precision as can be had by those methods.
I'm rather forgetful of facts and figures by nature so I tend to establish a methodology and stick with it. I write things down and follow procedures step by step. As such it didn't really occur to me until this evening (third valve inspection) that every time except the first I have had to swap only one shim. Furthermore it's always the same shim (my #4 intake) that goes from high side of tolerance (.20-.25) to tighter than spec (tonight was worse than usual, the .05 feeler was a TIGHT fit, would barely drag through)

what gives? any thoughts? my best SWAG is something carb related causing that one to predetonate from time to time, hammering that valve but would think i'd notice...

 

Are these metric numbers or fractions of inches you're talking?

Spec is .11mm~.15mm for the intakes, and .16mm~20mm for the exhausts.

If you're saying that you have an intake valve that's going from .20mm down to .05mm, then you might want to investigate.

Valves don't just pound into their seats, they also stretch if overheated. Guessing, I'd say you might have a lean condition of some sort in #4.

You said "bench sync" and "set the pilot mix by ear" did you vacuum sync?

Have you run a compression test lately?

Something's amiss in that #4 hole.

 

yeah millimetric.
I looked at the plugs and they show all four consistent and a touch on the lean side.

never done a vac sync on this bike.
compression test was done long ago. worth investigating.
Tune by ear is your standard "set the idle as low as it will stay running, adjust mixture to bring idle up, set idle down again, repeat, repeat, repeat" after having bench sync'd by dropping bb's simultaneously and confirming with feelers.

My plan for sunday is, in the following order:
install correct shim
compression test
confirm carbs are clean and bench sync'd
vacuum sync
check mix on all four combined with EGA for grins
consider for the dozenth time, getting a color tune plug.
install fresh plugs
drink beer

almost resorted to grinding a shim (yes I know what I'm doing, hold my beer, I'll show ya) but a buddy came through and picked it up from a shop with a pool across town.

 

Ya know, if you have access to an EGA, those little plugs on the bottom of your exhaust pipes are there for exactly that purpose... and I have a copy of the Yamaha EGA manual that applies to the XJs if you need specs...

 

It's possibe that the #4 intake valve has a manufacturing defect and you'll just have to keep an eye on it.

 

I have the mac 4-1 it came that way from the PO along with an airbox that was all busted.(botched drilling or something) Otherwise I would have stock intake and exhaust. I'm a pod guy by circumstance not nature.
Since getting that big ol diagnostic cabinet it's crossed my mind more than once to drill some holes in the exhaust, weld on appropriate nuts and install stainless set screws or something, effectively fabbing the taps.
Also if I ran a straight pipe rather than my "muffler" I could just probe all the way up it and into one header at a time.

I'll poke around with it some on sunday and see what comes of it. I would be interested in those specs but I'm not sure how much still applies with all the mods.

TimetoRide, such as? you say manufacturing defects my ears perk right up.

 

It would appear that you are getting wear in the one valve, and since they are not turned from billet, that particular valve got some bad material in it, or wasn't heat treated correctly, or the initial valve angle was cut wrong (I'm starting to guess here) This also applies to the valve seat.

 

hmm... all make equal sense, and I suppose it could be leaner than the rest as fitz threw out. Golly, if it's only good for ANOTHER 30k miles I'm gonna want my hunnert dolla back.

 

Please share both your shim grinding experiences and your beer ... Sure they will rotate in use but only when not under load, the top side is the wearing side, the underside is just in compression and as I understand it the nitriding is only for wear resistance, the impact strength will come from the through hardening ... as long as the grinding process doesn't introduce excess heat it should be ok ... any takers?

 

get the mag table CLEAN AS F*#k. Slap it down with a piece of scrap or two that are thinner than your target finish thickness. Position the pieces of scrap to trap it as the grinding wheel will try to squirt it out. no biggy except that in doing so it will ride up on a piece of grit and now ya done ground it lop sided.

Heat control. lots of coolant if ya have it. with or without, many tiny fast passes. 1/4" or less stepover and no more than two tenths (0.0002") step down. Feel free to just pause off the work from time to time, ie when stepping down after a set of passes be lazy about it. A dull barely visible spark should be ok, most of the heat goes with the spark and you're running coolant. Heat in the part should soak fine into the table. Fat, bright, near yellow sparks, no good, don't do that for a full set of passes and take a lighter step on the next set.
The shims are around 1 1/8" across. 1/4" step over means at least 5 passes before stepping down.
Taking say a 270 shim down to 250 is about .0078" of material to remove.
Stepping down two tenths at a time (that may even be too heavy) means about 40 steps down... times 5 swipes per step... bring a book...

Only grind one side, IE the number side so no-one ever mistakes it for that size again. Even though I always mic 'em anyway.

Minimum clean-up one side, measure, CLEAN THE TABLE and go for finish.

Pretty straight forward surface grinding really.

Once done to finish dimension run a file around the outside edge (If you haven't put in your time as a deburr boy have someone that knows how to use a file do it) or maybe if you're real careful with a smallish belt sander. You need SOME edgebreak but for our yammies ALMOST none will do.

Now DEMAGNETIZE the sh*t out of it. Lap with 1 or 2000 grit on glass or granite for grins. clean and install, ground side down. could even get fancy with an acid pen and mark the new size. I'd just write it in the notebook of clearances and currently installed shims.

The entire shim/bucket and valve all rotate WHILE the cam is pushing them due to a bit of angle on the cam grind. Basically the cam makes contact of center and pushes it round and round so the valve never hits the same spot on the seat. If they did they'd be much more prone to scoring since the tiniest imperfection would grow and grow.

Bare in mind this all will take half to a full hour depending on which shim you're starting with and how much you're taking off. If the mechanic on the other side of town is at his shop where he has his shim pool then drive there with a beer or three for him.
If it's friday night, everyone is closed for the weekend and you were hoping to get tuned up saturday morning, shakedown ride saturday afternoon and a nice long ride sunday AND you have a surface grinder in your back pocket then by all means, crack a cold one and go to town.

I'm a LITTLE surprised this site doesn't have a thread for fabrication chat like TCU but I can also understand not wanting it to balloon up the way I perceive that site has.

 

Grinding Valve Adjustment Shims is NOT a recommended practice.

The only "Site-recommended" practice for Adjusting Valve Clearances is removing the Out-of-specs Adjustment Shim and REPLACING that Shim with a Yamaha Valve Shim of the correct thickness to bring the Adjustment within proper specifications.

There are Dangers associated with altering the Valve Clearances by Lifting the Shim with "Shim Stock", ... and altering the Shim Disc by Grinding-off material from the Shim Disc.

(I suppose if you are a highly-experienced Professional Machinist, with access to proper Precision Machine Tools, ... you've got the requisite qualifications to Machine a few thousandths off a Hardened Metal Disc with the precision required for such work.)

 

Shims are usually heat treated and end up with hardness on the outer surfaces leaving the inner material softer (case hardening). When these are ground you end up with the softer inner material now on the surface. It can now deform and be pounded flatter. This will cause the valve adjustment to go out of spec. Be vewy, vewy careful.

 

Hey Budd, thanks for that, very comprehensive rundown, I'm going to give it a whirl, I have access to a surface grinder, but you didn't share the beer

I'd also agree with Rick, this is not something you do in your garage with an angle grinder.

JF, do you know what the base material is? Perhaps we can fab up new shims from 4150 or similar? As I understand it they are through hardened using normal heat treatment (heat and quench) then nitrided for surface hardness.

 

I heard the same size shim is also at the Volvo dealership - but how can you beat $7.00 shims from Len ??

 

yeah like I said. there are people that can do it.
it can be done.
I ain't WORTH doing.
except in very unusual circumstances. (IE you have the tools and need it done NOW and just can't wait, even then swap for the right one per JFstew's point on stress relief of the case hardening.)

As it is I took a few spare shims to work friday, made some calls and had a buddy run 5 minutes off his normal delivery route to pick it up. The cost?
"you owe me two of your unused shims"
oh darn. I'd have easily paid $10 to dodge the ordeal of setting up and baby sitting that grinder.
As I type this the bike is on the lift with the covers off waiting to cool so I can touch the beast.

 

Here's how to get the Shims you NEED for the ones you got that need replacing.

Measure the Clearances.
Pull the Shims needing others.
Do the Math. Twice. Get it right.
Have a list with the Shims you NEED in your left pocket along with your Shims.
Head-over to the Closest YAMAHA Shop or BUSY Shop that services Yamaha's.
On the way over stop at Dunkin Donuts.
Get four large Iced Coffee's ... Black; with Creams and Sugar -- on-the-side.
(Having a sweet-looking Babe carrying the Coffee's is a HUGE plus.)

Just head right-on-in to the Shop Area.

"I'm adjusting the valves on my own bike. So, I know how hard you guys are working. I brought-over Vanna White with Iced Coffee's to order.
Her's my old shims and a list of the ones I need. How am I doing so far?"

You only need one guy who wants a Iced Coffee and you go home with the Shims you need.

 

you're a genius Rick.
I'm trying that one.
By the way... works at the dentists office too.