Author Topic: valve clearance when hot  (Read 827 times)

Offline baz

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valve clearance when hot
« on: 09.06. 2012 21:22 »
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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Re: valve clearance when hot
« Reply #1 on: 10.06. 2012 02:21 »
 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.
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Offline baz

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Re: valve clearance when hot
« Reply #2 on: 10.06. 2012 02:45 »
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

Offline duTch

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Re: valve clearance when hot
« Reply #3 on: 10.06. 2012 02:48 »
Quote
.... 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)
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
Australia

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Re: valve clearance when hot
« Reply #4 on: 10.06. 2012 05:50 »
 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
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7

Online Ted_Flash

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Re: valve clearance when hot
« Reply #5 on: 10.06. 2012 11:20 »
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?
Ted Wilkinson, Ramsbottom, Lancashire
1950 Golden Flash

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Re: valve clearance when hot
« Reply #6 on: 10.06. 2012 13:22 »
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.
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'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
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Offline duTch

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Re: valve clearance when hot
« Reply #7 on: 10.06. 2012 16:03 »
Yup Musky I guess that's kind of what I had in mind by 'loose zero'....and burnt fingers
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
Australia