Valve Clearance/Adjustment Questions???

[Mr. Neutron]

Hey, All!!!

I'm replacing the cam chain on my '06 YZ450F. I checked the valve clearances while I've got things this far apart, and it brings up a few questions I have. I did do some searching, using "valve clearance", and "valve adjustment", but didn't find an answer to what I was looking for.....?

I pulled a lifter & 1 shim on the left intake valve (all my intake valves have what I consider "low" clearances: a *loose* .0035"). The last digit on my shim is hard to read, but looks kinda like a number 6. It mics out to .0695", which essentially converts to 1.76mm (using .03937 as the convert factor).

Does the factory use valve shims of different values other than the .05mm increments mentioned in the manual? As far as I know, the valves have not been adjusted in 60+ hours, so I'm assuming I have a "factory" valve shims. The manual does give an example of rounding up or down, if a shim's last digit is 0, 1, 2, 4, 5, 6, 8, or 9. But it also states that "Pads are available in 0.05 mm increments." ?

By my way of reasoning, I should buy some shims one .05mm (.0019") increment thinner for my intake valves, to gain some more clearance. This would then put my clearance towards the high end of the .0039"-.0059" tolerance zone, if my calculations are good, correct? Are there maybe aftermarket shims out there made in other than .05mm increments? It'd be nice to have the clearance more in the middle of the range.....

Also, I read about a lot of folks here that never adjust their valves in, say, 100 or more hours of service. My bike actually starts really easy, and runs great (much faster than the rider goes..... ). Given these things, and knowing how the previous owner was GREAT about changing the oil & filter, and keeping the air filter clean & oiled, it surprises me to have my intake clearances at the low end of the spectrum. Anyone else have a similar experience? I know that the cams are in the correct position, the piston is at TDC, & etc., so I'm really certain good measurements were taken.....

Jimmie

[mlynn450]

Check OEM parts for honda crf450r in the parts section here. I believe they sell smaller increments in shims.

[grayracer513]

What you have is a head that is still exactly as it was built:

Service shims are only available in increments of .05 mm, (and, yes, Honda does sell them in .025 mm increments) but the factory has access to shims in increments of .01 mm. With these, they build the heads as close to the minimum clearance as possible. Why? Because tighter is better.

Smaller valve clearance means less impact on the cam, lifters, valves, and seats, and gets marginally more out of the cam grind to boot.

If you found a shim that is marked 176, that's what it is. And if your intake clearance is .10-.11 across the board, that means it hasn't moved since it was put together. Be happy. It's supposed to be like that.

[Mr. Neutron]

Thanks, Guys!

I eventually used the words "valve shims", or valve pads" and finally found info like you posted in a SEARCH...... Sorry about that..... ?

Hmmm. Yesterday afternoon, myself and a friend of mine couldn't read that last digit on the shim pad, so I miked it and converted my inch readng to 1.76mm. ? At that time, this was a surprise to me, since I thought shim pads were only offered in .05mm increments (per the manual, and a Yamaha parts fiche I looked at.....). Thus, I assumed all shim pads would have a last digit of either "5" or "0"...... My bad there; after I posted this, I still kept searching, and eventually read an old post by Grayracer513 about the subject..... I just didn't understand that their assemblers get a variety of shim pads we consumers don't get (from Yamaha, anyway....).

Thanks for the info on the factory setting the valves at the "tight end" of the clearance range, Grayracer513! ?*Technically*, my intake valves may be just slightly out of spec. Like I said above, the clearance is a loose .0035", but an .004" shim won't go. Do you think those few tenths of clearance I'm lacking aren't worth worrying about? I personally think it's simply the sorta thing I need to keep an eye on, but no new shims are needed now..... The bike only has 62 hrs. on it, starts & runs great, & etc.......

BTW, cam chain showed no signs of kinking, or undue wear, that my (admittedly poor ) eyes could see..... This cam chain job seems like a fairly straightforward job to do, especially with all the info & help from this forum..... Thanks, You All!!!

Jimmie

[grayracer513]

*Technically*, my intake valves may be just slightly out of spec. Like I said above, the clearance is a loose .0035", but an .004" shim won't go. Do you think those few tenths of clearance I'm lacking aren't worth worrying about? ? I personally think it's simply the sorta thing I need to keep an eye on, but no new shims are needed now.....

My deal is that if it's in spec, it's in, and if it's not, it needs to be adjusted. However, I do see your point. And with that in mind, you may be even closer than you think, since the reality is that the minimum clearance in English is not .004", it's .003937". Hair splitting, and if an .004" "won't go", it may be tighter than that, but still, it's looser than .0035", right? The truth is that it's a little silly to think you can really take measurements that precisely with a feeler gauge in the first place, but that's what we have to work with.

So it's up to you. I might go buy the next smaller service shim and slide it in there (like replacing the 176 with a 175), or I might get lazy and leave it, but you will have the caps off while changing the chain anyway, so how hard would it be?

[Streamline]

I know this is an old post but I had the exact same issue, I had the factory shims except for 1 and just went for the mid clearances. My only problem is that I can't get TDC as it looks as though I may be a tooth off on the cam chain. I have 7 "links" (as the manual shows) in between the 2 dots but 1 dot is not at the top, it's over a bit. So I'm not sure if I should mess with it or not?

[grayracer513]

I have 7 "links" (as the manual shows) in between the 2 dots but 1 dot is not at the top, it's over a bit. So I'm not sure if I should mess with it or not?

That's not how you time the cams.

https://www.thumpertalk.com/forum/showthread.php?p=7467845#post7467845