The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: baz on 09.06. 2012 21:22
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further to an earlier post and out of curiosity i checked my valve clearance today whilst my engine was very hot and i found they were very slightly bigger than when the engine was cold,i only checked the exhaust valves but i assume the inlet clearance would be bigger aswell,the engine is a 650 with alloy head and normal steel push rods,i had always been led to believe the clearance closes when the engine heats up? ........baz
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G/day Baz,
I know it closes up in the cafe. My "hot" might be a bit warmer than most would get. 10.5:1, 105 octane, 2 x 30mm flat slides, straight through reverse cone meggas, 7500 rpm up Little Forest Hill. Barely made the last 1/4 mile, stalled at top. Let cool for 3 beers and she was good as gold. Did the same on way home (due to 3 beers) so I quickly took the covers off (ouch hot, ouch hot) and it took a good 1/8 turn to free the ex tappets and the inlet were zero clearance. When cold gave them an extra 2 and 4thou, not happened since. Most books will give bigger clearances for racing.
Cheers
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Ive not had the chance to thrash the hell out of my one yet ive got to wait until monday when i can get it MOTd (ive only been out round the local factory estate),just fitted new rings so i'll have to break them in but then i will give it hell thats what these bikes were built for and if it goes bang i'll build it better next time i have my tappets set at 10thou in and 12thou out ,i just hope the old overheating problem has gone cheers baz
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.... good as gold. Did the same on way home (due to 3 beers)
Sounds like an ad for our local midstrength??-not me.!!
Musky, how you reckon would it be if you just set them loose-zero at hot?? (Apart from burnt fingers)
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G'day Dutch, I would still like a coupla thou at pipe blueing hot. By the time you get it all organized it would have dropped 20-50 degrees.
Cheers
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I'd guess that the major factor in differences in valve clearances as the engine heats up would the material the push rods are made of, due to their length? So with a hot running engine you would be better off with steel pushrods rather than dural?
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Yes Ted your right, I use dural. Lots of other things as well, like if you used those alloy barrels on ebay would change the settings. It's a suck n see sort of thing with any motor that deviates from factory standard.
Cheers
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Yup Musky I guess that's kind of what I had in mind by 'loose zero'....and burnt fingers