The BSA A7-A10 Forum

Technical (topic titles must be descriptive) => A7 & A10 Engine => Topic started by: baz on 09.06. 2012 21:22

Title: valve clearance when hot
Post by: baz 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
Title: Re: valve clearance when hot
Post by: muskrat 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.
Cheers
Title: Re: valve clearance when hot
Post by: baz 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
Title: Re: valve clearance when hot
Post by: duTch 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)
Title: Re: valve clearance when hot
Post by: muskrat 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
Title: Re: valve clearance when hot
Post by: Ted_Flash 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?
Title: Re: valve clearance when hot
Post by: muskrat 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.
Cheers
Title: Re: valve clearance when hot
Post by: duTch 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