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Valve Clearance and shims

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birdyboy
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Valve Clearance and shims

Post by birdyboy on Thu 17 Jun 2010, 7:38 am

Have any of you done this for yourselves? Is it something I am doing wrong or is it a bit hit & miss on judging the clearance with feelers? I'd have thought that the measured clearances would all have been greater than the specified clearance sizes but for me they have all shown to be smaller - does this make sense to anyone or have I done the first step wrong? Many thanks.


Last edited by birdyboy on Thu 17 Jun 2010, 7:45 am; edited 1 time in total (Reason for editing : spelling)
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eternally_troubled
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Re: Valve Clearance and shims

Post by eternally_troubled on Thu 17 Jun 2010, 9:22 am

I haven't done this but others have and with relative success.

I'm guessing that you are at the 48,000 mile service point.

It is quite possible that the valve clearances are less than the specified distance - this would mean that you need to change your shims for thinner ones. As the valve body wears the valve seat the valve will 'move' upwards, closing the gap betwen the bucket/shim and the cam lobe.

When you check the clearances you are checking that this gap is *wide* enough and hasn't closed up to nothing. If there is no (or too little) gap the valve may not seat properly (as it is being pushed off the seat by the cam lobe) and will not make good thermal contact with the seat, meaning that it gets too hot and burns out.

Looking on the bright side - assuming your measurements are correct - you have just made an important discovery about how your engine is wearing and are in good position to fix it (ie. buy and install the right size shims :)
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birdyboy
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Good news

Post by birdyboy on Thu 17 Jun 2010, 4:04 pm

That makes good sense. Thanks for taking the time to reply. I just bought the bike which has only done 21k miles, (supported by old MOT cert's), but service history is unknown which is why I'm going over it with a fine tooth comb.
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birdyboy
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All done.....

Post by birdyboy on Sun 20 Jun 2010, 4:49 pm

Glad to say that all shims sorted and bike started second press of the button. As long as you don't rush, take reasonable care, it's well within the average DIY'ers capability. Establishing the starting clearance is also a little hit and miss with feeler's, but don't try to get too precise as replacement shims only come in 0.025mm increments anyway so you have to round up or down to the nearest size, (unless you can use one of the shims you just took out of course).

Only kit I had to buy was a micrometer (Screwfix £15) in order to measure the shims that came out. Also keep in mind that some of the shims you take from one tappet can be used to correct the clearances for other valves so you don't need to buy a whole set. Many dealers will also do part exchange for the old shims you have but can't use. I have an XL spreadsheet which I put together to help simplify sizing the replacements. Just email me and I will gladly send to you if of use. birdyboy@onetel.com


Last edited by birdyboy on Mon 28 Jun 2010, 10:03 pm; edited 1 time in total (Reason for editing : spelling)
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ashcroc
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Re: Valve Clearance and shims

Post by ashcroc on Sun 20 Jun 2010, 4:54 pm

Don't forget to write the size on the shims with a marker pen. It makes it a whole lot easier to find the right size next time when their floating around in your tool box.
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birdyboy
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Shim sizes

Post by birdyboy on Sun 20 Jun 2010, 5:03 pm

Don't worry - got that base covered. Used an old CD case and stuck the shims to the inside of the case under a strip of masking tape, then on the outside of the case stuck another piece of tape next to each shim with the measured size... Look's quite slick and is easy to refer to.
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Specialistpea
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Re: Valve Clearance and shims

Post by Specialistpea on Sat 26 Jun 2010, 3:44 pm

I did this a while ago and found that the sizing of the replacement shims you can buy is limited. I ended up putting most of the original shims back in again as the tolerence was lower than the nearest replacement I could get. If you havce not already taken them out. measure them and leave them in situ till you have checked with your bike shop etc about replacements available.
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johnlodge47
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May I have a copy od your spreadsheet, please?

Post by johnlodge47 on Tue 07 Jan 2014, 7:45 am

Thanks for the kind offer on the forum.
Cheers,
John

@birdyboy wrote:Glad to say that all shims sorted and bike started second press of the button.  As long as you don't rush, take reasonable care, it's well within the average DIY'ers capability.  Establishing the starting clearance is also a little hit and miss with feeler's, but don't try to get too precise as replacement shims only come in 0.025mm increments anyway so you have to round up or down to the nearest size, (unless you can use one of the shims you just took out of course).

Only kit I had to buy was a micrometer (Screwfix £15) in order to measure the shims that came out.  Also keep in mind that some of the shims you take from one tappet can be used to correct the clearances for other valves so you don't need to buy a whole set.  Many dealers will also do part exchange for the old shims you have but can't use.  I have an XL spreadsheet which I put together to help simplify sizing the replacements.  Just email me and I will gladly send to you if of use.  birdyboy@onetel.com
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ceejay
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Re: Valve Clearance and shims

Post by ceejay on Sun 25 Feb 2018, 4:06 pm

Resurrecting this ancient thread but I have a related question regarding shim increments... I have just measured my valve clearances again, taking my time to be as accurate as possible... which turns out was pointless because as posted above it seems shims are only available in 0.025mm increments.

Anyway I have existing shims stamped "198" and "192". Do I assume those shims are 1.975mm and 1.925mm respectively? Seems an odd way to mark them (rounding one up and the other down) but a good session of googling suggests shims in those actual sizes (198 and 192) are unobtainable.

For the record I have done about 15000 miles since my last clearance check and it appears they have all closed up about 0.02mm. With the increments the shims are available in  I may have to set my exhaust valve clearances to 0.25mm (the lower and of the spec) because it's either that or 0.28mm (outside the higher end). Seems a bit annoying given they are likely to close up with use and go out of spec pretty quickly again. Guess I will just have to do an early valve clearance check.. or would setting them to 0.28mm be a terrible idea?

(Maybe just me but I find checking valve clearances on the CB500 a bit of a pain compared to other vehicles!)

Or am I over analysing?!  Very Happy
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ceejay
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Re: Valve Clearance and shims

Post by ceejay on Mon 26 Feb 2018, 10:24 am

Found some answers I think ... Honda 7.5mm shims marked 198 are 1.975mm and shims marked 192 are 1.925mm and so on.

Also, thinking about it, I will go with setting my exhaust valve clearances nearer the .25mm lower end as oppose to .28mm even though they are likely to close with use because:

1. that is within spec (obviously) and you have to assume that some engineer would be counting on the fact that clearances will be set to the lower end only to reduce with use and this is okay. Given clearances reduced by approx 0.02mm in 15,000 (pretty hard) miles it is unlikely there will close up enough to ride the cam lobes full time or anything major like that during the next 15,000 miles.

2. I won't have to worry about the valves not opening enough.

Also I probably am over analysing and I should just set them within spec and stop thinking about it too much  Cool
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Grarea
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Re: Valve Clearance and shims

Post by Grarea on Mon 26 Feb 2018, 1:52 pm

I have absolutely no idea what you are talking about.
(I clearly need to think about mine)
But, I think you are thinking plenty.
If you over think things, you can feel safe in the knowledge that you have thought more than you need to. You have then made a decision based on knowledge.

Much better than underthinking in my view.
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Crash- Elmit
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Re: Valve Clearance and shims

Post by Crash- Elmit on Mon 26 Feb 2018, 10:45 pm

To those that have undertaken this task have you noticed any performance/fuel ecomomy differences?
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ceejay
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Re: Valve Clearance and shims

Post by ceejay on Tue 27 Feb 2018, 4:49 pm

Much better than underthinking in my view.

I do a lot of underthinking too unfortunately! Very Happy


To those that have undertaken this task have you noticed any performance/fuel ecomomy differences?

Depends how much they are out by, if they are out a long way then you'd probably hear it as well as notice a performance difference when set right. With mine I doubt I'd feel the difference because they are not out by much. Also immediately after I tend to change the oil and sync carbs so if there is a slightly different feel I wouldn't know what bit caused it!

There is actually nothing difficult about doing valve clearances on the bike, it is just time consuming (at least when you are slow with mechanical stuff like me!). Bearing in mind some bikes it's a case of simply removing a side valve cover and adjusting with a screwdriver (20 min job) the process involves tank off, coolant out, thermostat off, sub air filter off, valve cover off, plugs out then if you actually need to change any shims timing chain tensioner off then the actual camshafts themselves and buckets out to get to them.

If you do need different shims anywhere and you are not a/near a garage you will likely have to order them and wait for their arrival before putting it all back together (unless you want to go through the process twice). And even if, like me, you opt to wait I still put the cam shafts back and valve cover on just to stop any dust etc landing there while it's sitting.

And all that to not notice any difference haha... but gives me piece of mind at least
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Crash- Elmit
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Re: Valve Clearance and shims

Post by Crash- Elmit on Tue 27 Feb 2018, 10:13 pm

My bike ha sdone over 100000 miles without the valve clearences ever being done but I don't have any problems with the bike so have left it alone. I use mine all year round so can't strip it and leave it until replacement shims arrive and don't fancy doing it twice

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