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CRF450 Valve Clearance Calculator

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my buddy has a 2004 CRF450, and we were checking his valves to see if they needed adjustment. One was just a little bit tight, so we had to figure out what size shim to buy.

We measured his existing shim, and from the formula in the manual, we were able to figure out what size shim would get him to stock specs.

He bought that shim, but he also bought one size smaller. We were curious as to what that would do to his valve clearance (how much looser than spec would we be?). However, being way bad at math, it took me like an hour to figure out what it would end up being (based on the formula in the manual).

So after I finally had the formula down, I made a quick web page here:


You can put in your current valve clearance, your current shim size, and the "what-if" shim size, and it will calculate the estimated valve clearance you would end up with as a result of the "what-if" shim size.

if this has already been done and way old info, sorry for taking your time. I thought it was pretty cool! Now we know what his 2.225 shim would do to his clearance (it would bring it to .30, which is on the loose side of spec, which is .28).

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Let's not make this any harder than it has to be.

If your exh. clearance is .008, you need a shim .003 smaller to make it .011.

You need a smaller shim to increase the clearance.

If your intake is at .004, you need a shim .002 smaller to get it back to .006.

Each shim is one thousanth (is that a word) increment smaller or larger.

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That calculator is cool. It is simple math, but it's alway nice to have a way to double check yourself before you order the wrong pieces/parts. :)

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Here's something I put together a while back:

14901-MBB-000 .0472in 1.20mm

14902-MBB-000 .0482in 1.225mm

14903-MBB-000 .0492in 1.25mm

14904-MBB-000 .0502in 1.275mm

14905-MBB-000 .0512in 1.30mm

14906-MBB-000 .0522in 1.325mm

14907-MBB-000 .0531in 1.35mm

14908-MBB-000 .0541in 1.375mm

14909-MBB-000 .0551in 1.40mm

14910-MBB-000 .0561in 1.425mm

14911-MBB-000 .0571in 1.45mm

14912-MBB-000 .0581in 1.475mm

14913-MBB-000 .0591in 1.50mm

14914-MBB-000 .0600in 1.525mm

14915-MBB-000 .0610in 1.55mm

14916-MBB-000 .0620in 1.575mm

14917-MBB-000 .0630in 1.60mm

14918-MBB-000 .0640in 1.625mm

14919-MBB-000 .0650in 1.65mm

14920-MBB-000 .0659in 1.675mm

14921-MBB-000 .0669in 1.70mm

14922-MBB-000 .0679in 1.725mm

14923-MBB-000 .0689in 1.75mm

14924-MBB-000 .0699in 1.775mm

14925-MBB-000 .0709in 1.80mm

14926-MBB-000 .0719in 1.825mm

14927-MBB-000 .0728in 1.85mm

14928-MBB-000 .0738in 1.875mm

14929-MBB-000 .0748in 1.90mm

14930-MBB-000 .0758in 1.925mm

14931-MBB-000 .0768in 1.95mm

14932-MBB-000 .0778in 1.975mm

14933-MBB-000 .0787in 2.00mm

14934-MBB-000 .0797in 2.025mm

14935-MBB-000 .0807in 2.05mm

14936-MBB-000 .0817in 2.075mm

14937-MBB-000 .0827in 2.10mm

14938-MBB-000 .0837in 2.125mm

14939-MBB-000 .0846in 2.15mm

14940-MBB-000 .0856in 2.175mm

14941-MBB-000 .0866in 2.20mm

14942-MBB-000 .0876in 2.225mm

14943-MBB-000 .0886in 2.25mm

14944-MBB-000 .0896in 2.275mm

14945-MBB-000 .0906in 2.30mm

14946-MBB-000 .0915in 2.325mm

14947-MBB-000 .0925in 2.35mm

14948-MBB-000 .0935in 2.375mm

14949-MBB-000 .0945in 2.40mm

14950-MBB-000 .0955in 2.425mm

14951-MBB-000 .0965in 2.45mm

14952-MEB-000 .0974in 2.475mm

14953-MEB-000 .0984in 2.50mm

14954-MEB-000 .0994in 2.525mm

14955-MEB-000 .1004in 2.55mm

14956-MEB-000 .1014in 2.575mm

14957-MEB-000 .1024in 2.60mm

14958-MEB-000 .1033in 2.625mm

14959-MEB-000 .1043in 2.65mm

14960-MEB-000 .1053in 2.675mm

14961-MEB-000 .1063in 2.70mm

14962-MEB-000 .1073in 2.725mm

14963-MEB-000 .1083in 2.75mm

14964-MEB-000 .1093in 2.775mm

14965-MEB-000 .1102in 2.80mm

14966-MEB-000 .1112in 2.825mm

14967-MEB-000 .1122in 2.85mm

14968-MEB-000 .1132in 2.875mm

14969-MEB-000 .1142in 2.90mm

14970-MEB-000 .1152in 2.925mm

14971-MEB-000 .1161in 2.95mm

14972-MEB-000 .1171in 2.975mm

14973-MEB-000 .1181in 3.00mm

Nice to have hanging on the garage wall. RR.

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I use that all the time. Thanks RR. :)

No problem Fred. Ol' ThumperTalk's a pretty cool place isn't it? :) RR.

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Thanks for sharing. Appreciate the effort you put into the calculator, now I can check my "math" LOL


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