Valve clearance

Hello all, I've been lurking on here for a while and have finally run into a question that I was not easily able to anwer using the search feature. I would like to thank everyone who has helped me so far that doesn't even know they have helped me. There is a wealth of information on here and I have been able to get all my questions answered by using the search function, except this one...

I was checking my valve clearances and I have an exhaust valve that I think is tight. When I check the clearance with the cam lobe directly opposite the valve I have .09mm clearance, if the cam is rotated slightly off (maybe 10 degrees or so) then it checks between .15mm and .2mm. So my question is am I right in thinking that I need to replace the shim for that valve? I have a few more parts I need to order from Chacal (awesome service btw ) and if I need a shim I would like to add that to my order.

 

Only one is tight?

Otherwise, intakes at .11mm~.15mm; exhausts at .16~.20mm?

The lobe should be pointing straight up at 90 degrees from the surface of the shim; if that's where you're measuring the .09mm at then it's the gap you use to calculate from. Ten degrees of rotation will start to put you on the "ramp" of the lobe, hence the tighter reading.

If it's at .09mm, then going "down" two shim sizes from what's in there will put you in spec at .19mm.

 

BigFitz, I just want to make sure I understand.

When you say "straight up" don't you mean 180 degrees? When you say 90 degrees....it would be at, say 3 o'clock or 9 o'clock, whereas 180 degrees would be at 12 o'clock.

Not trying to be a smart guy....just want to make sure I'm understanding the correct way to do this (I recently checked mine at 180 degrees from the apex of the cam lobe).

 

Me to, the manuals do say 180 degrees!! Could be a typo on by Fitz.

 

I said "90 degrees from the SURFACE of the shim."

If the shim were perfectly horizontal, the lobe would be sticking straight up. That's 90 degrees.

The lobe IS at 180 degrees from the centerline of the valve, yes. But it's easier to see and visualize the 90-degree angle between the SURFACE of the shim and the direction of the cam lobe.

No typo.

I can post a diagram if it would help.

 

I don't get it! The readings are taken with the lobe located 90° to the shim where the gap from cam to shim should be the greatest (allowing the valve to close and stay closed for a specified period of time)....he got a reading of .09mm.

Then when he rotates the cam 10° and begins to get on the "ramp" his readings actually increase instead of decrease..... from .09mm to .15mm & .2mm.

Shouldn't the gap be decreasing as the lobe comes closer to pressing on the shim to open the valve?

 

Sorry, I misread the numbers.

However-- it matters not.

Did you ever take a good close look at the camshafts on these bikes?

They're only precise where they need to be; otherwise they're all kind of lumpy-bumpy like an Indian cast brass lamp.

If you start jockeying the cam around to where you get the biggest reading possible, you won't correctly shim the valve.

If you follow the book, you will get it right. Quoting: "The proper position of the cam when measuring the valve clearance is with the cam lobe directly opposite the valve lifter." (XJ650G factory manual, page 11, paragraph 4.) Straight up from the surface of the shim. I'll find a diagram.

 

That makes sense....thanks!

 

Yes, I was surprised that only one was out of spec. However there was evidence on the screw heads for the side cover that they had been remved before so I may have gotten lucky and have a PO that actually maintained their bike.... I'm not going to hold my breath though

Yes that is exactly what is happening.

Thank you Fitz, you just answered my question. Looks like I am ordering a shim. It was actually a bit of an accident that I even took the readings with the cam off position. I pulled the shim out to see what size it was and after I put it back in I wanted to check the clearance again and somehow didn't get it back to the proper position when I checked it at first. After I repositioned the cam I was able to duplicate my readings. After I got the strange readings I started todoubt my insoection technique and wanted to verify it with the masses/

 

Now that you all have it straight in your minds, read this;

<http://kopcicle.multiply.com/journal/item/19/Suck_Squeeze_Bang_Blow_>


On a number of cams that I have measured, the lowest part of the base circle is not always opposite of the peak lift point. This was done using a degree wheel and dial indicator, accurate to a tenth on each dial.
They varied from none to .0015 inch. ( ?? mm )
Since the factory is concerned with long life, and not peak performance, the clearances given can be fudged a little on either end, without dire consequences, in my opinion. Tighter clearances will give greater duration, and looser will give noisier valve rattle. You decide for your bike. CZ

 

"Fudge" 'em tight for long enough on the exhausts and you'll burn one.

I've found that following the factory recommended maintenance procedures and intervals on these bikes produces longevity, reliability AND performance. Yamaha knew what they built, and they told us the proper way to maintain it. All we need to do is pay attention.