The New And Improved Unofficial R65 Forum V2
Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: Bill Conquest on December 16, 2011, 01:07:18 AM
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Hi - Can anyone give me the settings for the valves and any words of wisdom or guidance? Thanks, Bill
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There was a service bulletin released that changed the recommended valve clearance that was stated in the repair manual. I attached a copy of the said bulletin.
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Full history of published valve clearance settings that I've read in print:-
78 - 80 owners manual inlet .004" Ex .006"
81 - owners manual inlet .002" Ex .008"
Mar 82 Service bulletin inlet .004" Ex .008"
Most people go with the revised bulletin settings but Snowbum recommends larger clearances specifically for the R45/65. I think inlet .006" Ex .010" Don't know why R45/R65's should be different to other airheads but he must have a reason. I'm going to ask him one day when I've figured out a plausible theory.
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From what I've seen personally, the R65 engine runs hotter than the larger displacement bikes .
That may explain the need for an increased valve clearance, just my personal theory, may very well be wrong too .
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The valve stems on the R45/R65 are 7mm, and the stems on the R80/R100 of the same time period are 8mm diameter. So, there is also more mass in the larger bikes' valves. I run mine at a 'generous' .004/.008 - I guess they're actually more like .005/.009. you can run them at .006/.010 but I do definitely notice significantly more noise then, and it is just enough to irritate me.
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I knew about the thinner valve stems but couldn't see how that would have any bearing on valve clearances or the possibility of increased valve seat recession that might dictate the wisdom of larger clearances.
Could smaller valve seats recess faster ? Can't see that as mine have zero recession as far as I can tell.
The only real difference I can see between R45/R65 and other airheads in the valve gear is the length and geometry of the pushrods.
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0.004 and 0.008 on both my R65s. A little bit o' BMW music ain't bad. ;)
Monte
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Thanks everyone -looks like .004 - .008 is the consensus. There was a write up of the process of checking the valves on the forum somewhere, does anyone know where it was?
Thanks, Bill
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Six and ten is news to me - never heard that before. I've been running them like the other airheads at four and eight. I'm also very curious why the Bum would recommend the larger tolerance.
A problem with wider gaps is pounding of the tappets that eventually flattens them out.
I wonder if the R65s run hotter and thus the valves need more rest time on the seats to cool down?
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... I wonder if the R65s run hotter and thus the valves need more rest time on the seats to cool down?
Street talk is that BMW changed the valve lash specs on the exhaust valve due to excessive heat contributing to exhaust valve recession.
The additional 0.002" of exhaust lash adjustment permits the valve to remain on the valve seat for just a nano second longer, thereby permitting a greater transfer of valve heat to the valve seat where it can be absorbed and dispersed.
So they say...
Monte
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It is a bit of a tradeoff - larger gap for valve lash also puts the point of contact with the pushrod a little further along the point of the cam, where the acceleration profile is a little less gentle. This can make for more harshness as far as valvetrain acceleration goes, with slightly greater mechanical stress due to the harder initial acceleration. On the other hand, slightly longer closure time does give the valves ever so slightly longer to dissipate heat against the valve seat. The major benefit of lead in the fuel (when it was in the fuel, that is) was the formation of microscopic "welds" where some lead would melt and be re-harden - the cooling process transferring a greater amount of heat energy into the valve seat&head as a consequence. Without lead in the fuel to form these minute solder joints to help expedite the cooling process, it pays to keep the valve lash at the full accepted distance. But, like with anything in this world, a good thing can also be taken too far!
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I know it's relative to ambient temperature so those who ride in southern latitudes will run hotter but I don't buy the running hotter than other airheads theory. Give or take a couple of barrel finns (and barrels don't get as hot as the heads) R45/R65's have the same cooling surface area as an R100. So you'd think they would run cooler. Mine certainly does.
Like most people I'm using .004" and .008" and I'm not suggesting anyone do differently but for those who want to theorise on Snowbum's reasoning here's something I read which although related to nhmaf's comments on acceleration rams is probably going to seem counter intuitive.
"camshaft ramp and valve clearance are inversely related"
read about it here
http://www.motorcycleproject.com/motorcycle/text/cows-clear.html
Mild camshafts need small valve clearances and cams with a steeper profile need larger clearances. R45/R65 cams are certainly not the same as the other airheads even if the cam timing timing is nominally the same. So maybe Snowbums comments are something to do with the the fact that our cams are different.
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Uncharacteristically, Snowbum did not say why he suggested those clearances.