Valve clearance tolerances

Just got through with the rear cylinder valve clearance checks. Inlets were smack bang in the middle of tolerances, but the exhausts are probably borderline.

I can force the 0.2mm gauge through both of them...but it does require force. However, the 0.18mm gauge slides through with virtually no resistance. Based on this I'm going to guess that they're at about 0.195 or something.

Is this likely to cause any issues for the next few weeks while I'm running it? Probably not going to be doing more than about 60 miles per week at the moment, but I can't afford to have it off the road since the CBR is now going to be laid up while it's worked on, so can only work on it at weekends properly, and my next weekend off is in the middle of January.

It should be fine, 120 miles isnt going to do any damage tbh.

Success!

There was no way I was paying for new shims when I'm hopefully getting rid of the bike in the next few months. With the clearance being borderline, I settled upon a fantastical course of action.

Firstly, shims out. Good good. Then I grabbed a piece of 80 grit sandpaper (I can see your eyes popping out already) and soaked it in WD40. Then I rubbed autosol into the surface.

Following this, I very, very slowly and carefully (and without much pressure) rubbed the shim in a figure-of-eight over this. Due to the soaking and autosol there wasn't much friction, but it was enough to just put some light scratches into the surface of the shims, which would be used as a depth-guide.

After this I took some 80-grit sandpaper (eyes, again!) and scratched up the surface of a piece of scrap aluminium (it was an old soldering-iron holder, so has a nice little protrusion on it that can used as a handle). Autosol went onto the scratched surface, and then the shim was rubbed in a figure-of-eight on it. For a while. Like, 15 minutes. The aluminium had to be periodically scratched up again and more autosol applied, but eventually the surface scratches were gone, and there were only very fine scratches left.

Following this, I took the 80 grit sandpaper (I'm sure you're used to this by now), and scored the inside of the engine to pieces. Kidding. I used it to scratch up the surface of some perspex on an old photo-frame. Autosol went on this. Figure of 8 again.

End result - mirror finish. Rear valve clearances are now 0.21 and 0.21, so I probably took off all of about 0.015mm, but it puts them back in spec and saves me ordering shims. Also, at this small level of lapping it shouldn't cause any problems if the shims are case-hardened. Not bad for an hour's work. Result!

[Sid Squid]

WTF!

You don't want to spend any money so you'll commit a horrible bodge and pass that on to someone else, and detail exactly how you've bodged it - I take it it won't be going in the 'For Sale' section on this web site.

Words fail me.

How's it horrible? A quick flick across the internet shows plenty of people grinding down shims with no problems whatsoever, and most of them have taken off a lot more than I have.

aren't shims made to silly within silly tolerances ? I don't think it was the best idea but if it works, good on you i suppose.

The shims are just pieces of metal made to exact sizes. If they're heat-treated at all then they'll be case-hardened, and case-hardening is going to penetrate the surface for more than the 0.015mm or so that I took off them. That's why I'm not sure how this is a horrible bodge.

If some evidence comes up as to why it's a horrible bodge, I've got 4 shims left over from the old engine, two of which are the same size as the ones that I've lapped, so they can always be swapped back over, but the engine was quite happy running yesterday.

[Spanner Man]

Good afternoon.

I have to agree with Sid on this one. That is a bodge & then some! You would have been better off running with tighter clearances & ordering the correct shims.

There is no way that you could have kept the shim perfectly square during the process, hence it will have a slight taper on it. The bucket wont be sitting squarely on the shim, nor will the shim be sitting squarely in the valve collar. Inevitably premature wear will result.

The internet may be full of tales of success in doing such things. I bet such successes were short term though. Get the correct sized shims & do it properly!


Cheers.

And this is a much more constructive response.

With the amount of material removed, the taper's going to be minute. Where would the unevenness cause wear? The shim? The valve collar? The bucket? If it's on the shim, that shouldn't be a problem; if it wears down more it'll just help with the clearances.

[Spanner Man]

Good afternoon.


Indeed any taper is going to be minimal. However, as the contact area is also pretty minimal, & the load on the bottom of the bucket & the valve collar is pretty high, wear on these items after a relatively short time is a distinct possibility.
Also, if the shim starts to wear rapidly, where is the metal going?
Shims are dead flat for a reason.


Cheers.