Doing your own valve shims.

[Pete.]

A lot of people service their own bikes but many don't feel confident about tackling valve shims. I have always done my own but it's not a job I like and it's also easy to make a mistake when you're trying to measure, record, calculate what shims go where. Some time ago I wrote a simple tool in Excel, with help from a couple of guys on 200mph.org, to make the whole process less painful.

1. First put in the in and ex clearances, then print it out. Take it to your engine and write the clearances in the 'measured clearance' boxes as you measure them. Refer to your bike's manual on how to measure the valve clearances but basically you get the inlet & exhaust lobes for that cylinder pointing at 10 and 2 o'clock so you're measuring under the camshaft base circle with a feeler gauge.

If your clearances come within the range specified in your manual, you're done, put the bike back together and ride

2. If any are out, you're going to have to change some shims. Some bikes (like yammy XJ/XS) you can remove the shims from the top of the buckets with a special tool. More modern bikes have shims under the buckets to keep the valvetrain light. For these you have to remove the cams, refer to your manual for how. Remove the shims and write the sizes down in the boxes marked 'installed shim'. If you have a vernier or micrometer, use that to measure the shims as they can occasionally be printed wrongly.

3. Now go back to the PC and put all the stuff you have measured in the spreadsheet and it will tell you what size shims you need for each of the valves that are out.

4. Here's the clever bit: Print the sheet out again once all the data is in the boxes. There's a very good chance that some of the shims you have removed from the valves that were out of spec, will go into other places in the head to bring the clearances back in. All you do is sort through the shims and drop them onto the boxes on the printed sheet marked 'shim required'. You can fiddle about with them so that you use as many of your stock shims as possible, and have to pay for fewer replacements. Replacement shims are about £3-4 each from places like wemoto.

Always replace the shims with the printed side towards the bucket, to stop the printing being rubbed off by the cam or the valve stem. Once you have your shims all sorted, replace the cams and torque them to the amount specified in your manual.

Finally, re-check your clearances to make sure you haven't made a mistake


Click here for an excel viewer if you don't have excel installed.

Click the image below to download the shim calculator tool

https://peterrimmer.myby.co.uk/images/shimcalc.gif
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[garyd]

Excellent info
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CRF230 all you need

[leatherpatche...]

Nice one, thanks.