Recently took a 1969 850cc head off and found a few shims lurking under the exhaust vale springs. Checked on valve shimming on the net and whilst I can understand what's happening I'd appreciate anyone's thoughts on how to check what thickness of shims are needed. Posts on the net are very unclear and/or need specialist tools.
Posted 13 January 2020 - 04:39 AM
I've not come across them but they did sorta fit them for a short time, from about 75-ish to 80-ish.
When I say 'sorta fitted' I note that in the parts book, the quantity needed is " A/R ", meaning " As Required ". I'll have more of a look later, but it appears that these are not always fitted and I'd say, are only fitted in order to gain a certain fitted Spring poundage.
Posted 20 January 2020 - 04:08 AM
Thanks Moke Spider. The shims were all on the exhaust valves: my suspicions were only raised when I noted that one of them appears to be a collapsed cup washer indicating none dealer works.The only reference I have found is in relation to motor bike engines as an adjustment following longer term value seating (ie valve seating getting lower in the head due to numerous grindings)..
I did check the height of the collet from the valve spring seat with all the valves in (but not the springs) and held in place so they were fully shut. Seems that the shims approximate to the difference in this distance between valves. Of course that could just be coincidence!
Hope you're doing OK with the fires mate.
Posted 20 January 2020 - 04:46 PM
I've had a look through a few documents of the era and I can't see any reference to them, other than in one of the parts book with an 'A/R', but no technical description.
Certainly what you've measured here makes sense. Personally, I'd look for a spring with additional height to make up the difference or look for shorter valves. Depending on how thick the shims are, it could be asking for trouble - as you've seen !
Cheers for your well wishes re: the fires. I have been meaning to put up a post in Chit Chat. Where I actually live, we've been quite lucky as they well missed us. Certainly some have copped it very bad. The scale of it is mind boggling though. We've just had about 4 - 5 days of light rain, first in months and that's cleared the smoke that had been hanging around most days, for nearly 2 months. But that's Summer in Australia. Now the fires are more or less out of the way, next we have the Cyclones and then flooding yet to come. Oh, the joy.
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