valve lash adjustment query

YamahaRick · Full Member Joined: Dec 01, 2008 Posts: 85

would like some feedback on what others are doing as far as valve adjustment on the 650's. i'M REALLY OLD SCHOOL AND LIKE TO RUN MY VALVES A LITTLE BIT LOOSER THAN THE SPECS for free revving. Sorry bout the caps but I hate re typing. Any suggestions on what is best for these engines?

tacoswild · Posted: March 17, 2009, 1:35 am Post subject: Re: valve lash adjustment query

Running them looser means the valves stay closed more than stock I think. Beyond me what effect that has.

The previous owner of my bike (he had it for 20 years) told me to go one thou looser than the manual on both valves, or at least a loose slip fit if you do the stock feelers. I tried it, ran okay but sounded pretty different. I ended up putting it back to a loose fit on the stock .003 and .006 size feelers.

Another member here mentioned that yamaha changed their recommendation at some point to .004 from .003 but I haven't been able to find anything in the service notes or tech bulletins available online to confirm that. Might have to give it a try.

YamahaRick · Full Member Joined: Dec 01, 2008 Posts: 85

Well The old wisdom is that running them a little looser reduces valvetrain loading a little bit and lets the engine rev a little free-er thereby adding a lil horsepower. It may not rev higher that you can measure, but you can sometimes feel a noticeable inprovement in how fast it gets there. Conversely a liittle snugger on the valves gives you a lil more torque. but it wont rev as fast. Not major amounts of either but this is engine voodoo from the likes of Smokey Yunick, Carroll Shelby and Mickey Thompson from the golden years of Hot Rodding and a 10th of a horsepower as a lot even back then. Hell it still is! Thanks for the tip. I'm gonna leave it @ 4 and 6.

xsjohn · Posted: March 17, 2009, 11:04 am Post subject: Re: valve lash adjustment query

My original Yamaha manual says .0025 on the intakes for the later models.......probably an attempt to quiet the intakes.......not good I believe......a slightly simi snug 4 is best.....even with my oilers on the intake 5 can get tappy......at .0025 the valve tips won't last.....

xsjohn

pumps · Posted: March 17, 2009, 2:53 pm Post subject: Re: valve lash adjustment query

Why do you suppose it is called "lash"?

yamaman · Posted: March 17, 2009, 3:06 pm Post subject: Re: valve lash adjustment query

According to Wiki:
"Backlash - the clearance between mating components"

en.wikipedia.org/wiki/...gineering)

pumps · Posted: March 17, 2009, 6:12 pm Post subject: Re: valve lash adjustment query

Very interesting. I wouldn't have thought to check wikipedia. My son wiki's everything.

tacoswild · Posted: March 17, 2009, 8:14 pm Post subject: Re: valve lash adjustment query

Seems the gap allows oil in there but does it also account for some heat related change? If so, I wonder why we set this cold.

penn71911 · Posted: March 17, 2009, 8:21 pm Post subject: Re: valve lash adjustment query

Actually, I set mine 3 and 5 HOT... no logic to it, that's what it took to keep mine quiet. no ill effects so far in about 10,000 miles

jayel · Posted: March 17, 2009, 8:23 pm Post subject: Re: valve lash adjustment query

tacoswild wrote:

Seems the gap allows oil in there but does it also account for some heat related change? If so, I wonder why we set this cold.

so you don't burn your fingers to start with.... then if you were going to set them hot, how hot is hot enough? easier to set at a easily obtainable cold temp range

penn71911 · Posted: March 17, 2009, 8:30 pm Post subject: Re: valve lash adjustment query

" so you don't burn your fingers to start with.... "

Very Happy

Good point... The reason I started doing it hot, the tappping was driving me insane, setting them at spec... After riding it home one day, about 13 miles, I decided to see if I could tighten it up a bit...

I tend to think of the specs as a general guideline... more than a rule... ya know...

xsjohn · Posted: March 17, 2009, 8:33 pm Post subject: Re: valve lash adjustment query

Been there with you guys a hundred times at least....till you get a bit more oil back there one way or the other just suffer........ Laughing

xsjohn

YamahaRick · Full Member Joined: Dec 01, 2008 Posts: 85

Good suggestions all. I like to do valves hot since well, thats how we run'em.
Back in the good old day(haha) you would alwways be given a cold and hot spec. so it was easier to guestimate. Splitting the 2 always seemed to be just right, except for me who likes a little on the loose side. Except for htis bike. Does the clatter out the exhaust make anyone else feel homicidal? Besides Penn and me that is.
So John, I set a snug 4 and 6 Warm, not hot so I'll give it another shot tomorrow. May try 4 & 6 hot, and then if thats not good enuff, I'll go 3 & 5 hot. Can't see the 25 thou John. That is too damn tight and I believe restrict rpm to some degree not to mention the tips like you said. Not a good idea.
SO tell me more about these mysterious "oilers"

tacoswild · Posted: March 17, 2009, 10:55 pm Post subject: Re: valve lash adjustment query

I manage to set the clutch and cam tensioner hot without losing my fingers but yeah I see what you mean about cold being more repeatable than hot.

I'm curious if these tiny changes in valve lash can have much effect at all on the valve timing. I'm hoping not, want to play around without worry.

Looked at my manual for the specs of the stock 71 cam. Intake lobe is described as 39.88mm the long way with a base circle diameter of 32.19mm. If I'm figuring it right that's a difference of 7.79mm between fully open and closed. Now here's a question mark for me, is the rocker symmetrical? Does 7.79mm of lift at the cam end mean the other end moves the valve 7.79mm too? I don't know the answer to that but if the valve is moving 7.79mm that makes the stock 0.076mm of lash seem pretty insignificant. Less than 1% of it's travel and changes to that lash are only going to be fractions of that 1%. Seems like it would be very tough to affect the valve timing by even 1 degree with any sane adjustment.

tacoswild · Posted: March 18, 2009, 5:38 pm Post subject: Re: valve lash adjustment query

Having slept on this I'm not so certain now about my conclusion. I'm thinking today that it's irrelevant how much the valve moves at full open. That stock 0.076mm of lash is very small so at the point where the cam starts ramping up away from the base circle it might not take much rotation one way or another to move the rocker that small a distance.

Only way to know for sure would be to get out a degree wheel and dial indicator and do the whole valve timing routine at different valve lash settings. The description in the manual of that routine is what got me started thinking about this in the first place. You're supposed to set the valve lash to a special setting to check the valve timing, 0.012" front and back iirc

woodman · Full Member Joined: Oct 12, 2008 Posts: 256

John, whats this top end oiler youre talking about ? First Ive heard about it.

woodman · Full Member Joined: Oct 12, 2008 Posts: 256

Found it

nj1639 · Posted: March 18, 2009, 9:06 pm Post subject: Re: valve lash adjustment query

xsjohn wrote:

My original Yamaha manual says .0025 on the intakes for the later models.......probably an attempt to quiet the intakes.......not good I believe......a slightly simi snug 4 is best.....even with my oilers on the intake 5 can get tappy......at .0025 the valve tips won't last.....

xsjohn

Hey John,
Can you be a bit more specific with those valve clearance numbers? Are you talking .04mm for intake and .06mm for exhaust or what? .004 inches / .006 inches ? I'm lost.

yamaman · Posted: March 18, 2009, 9:30 pm Post subject: Re: valve lash adjustment query

Good reading here! Pretty sure that John is talking inches! Cheers

www.motorcycleproject....clear.html

tacoswild · Posted: March 18, 2009, 10:23 pm Post subject: Re: valve lash adjustment query

Interesting page and the guy seems to know what he's a talking about but I don't think it makes sense. He says:

Quote::

Valve clearance is just another form of cushion. Steep flank = less ramp = more clearance. On the other hand, shallow flank = more ramp = less clearance.

How does the empty space of the valve lash qualify as a cushion? It's not going to soften anything. To me all that gap can do is make you miss the very smallest movement of the rocker. It needs to move across that gap before the valve starts moving at all. If you make the gap bigger the rocker is going to be moving faster by the time it hits the valve tip. That means harder, not softer to my way of thinking. His conclusion seems backwards.

xsjohn · Posted: March 18, 2009, 10:41 pm Post subject: Re: valve lash adjustment query

nj1939.......was talking inches..........004 intake and .006 exhaust ........later ones too...

tacowild.......would suppose the space is also for some oil to get in there.....glad I got some extra oil back there on mine......the click used to pester me but I no longer hear anything.....

xsjohn

xsleo · Posted: March 20, 2009, 4:20 pm Post subject: Re: valve lash adjustment query

I think that when the engine is fully warmed up and running the clearance will be near zero clearance, at least in theory. It would be very hard to set them that way.
The designers of an engine know this, so they adjust the settings to account for the expansion of the parts in the valve train between when the engine is cold, and at operating temperture.
Changing the clearance will effect the timing slightly, tighter will advance, looser will retard. It will also effect the lift, tighter =more, looser = less. It may effect duration the smae way, tighter= longer, looser = shorter.
Will the average rider on the average bike notice these minor changes, I doubt it. On a highly tuned racer with a highly tuned rider then maybe.

pumps · Posted: March 20, 2009, 11:22 pm Post subject: Re: valve lash adjustment query

Tried setting my intakes at 004 and they were pretty noisy. 006 was good on the exhausts but went with 002/ intakes as the book says.

gggGary · Full Member Joined: Jan 07, 2009 Posts: 114

Well I just got a Yamaha service book for the 82 83 models.
Valve lash
intake .0024" .06mm
Exhaust .0059" .15mm

the rockers have a 1 to 1.21 ratio so the valves open 20% further than the cam lift minus lash.
couple of things factor into valve lash. especially on production equipment there is a lot of set and forget it so the lash setting has to last for a long time. The lash tends to decrease over time as the valve seats erode. On this bike living under those aluminum bells a valve with a lot of lash sure does ring.

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