The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: Gavin on 21.07. 2011 10:49
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I am rebuilding the iron head on a 51 A10. Can someone tell me the standard size of a valve guide for an A10 iron head... 51 model please? Mine measure .560thou. I am ordering new guides and want to be sure I am getting the correct fit. Thanks.
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Uncle Gavin,
How were the guides measured? With a micrometer? Was the calibration checked?
Did the machinist do the measuring?
O/S guides can be in small increments (0.002"), so initial measurement must be very accurate otherwise the replacement guides you receive could be a Cockus Upus Maximus!
Regards,
Richard
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Hi Ya Niece Richardette, The machinist measured it... with a white cane I believe. So hopefully he had had it re calibrated by the guide dog just before starting time that morning. Because I don't have the sharpest grasp on the intricate details of this little operation, I simply asked if that was just a shade over 1/2" which he assured me was the case... 60 thou over 1/2 inch... that maths seemed to work for me. he even mentioned that he'd like the guides to have about a 3 or 4 thou crush on the head.... sounds so romantic. I recall when my bride had a similar crush on me.
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You must despair of us folk of such little faith!
I should have known better!
Richard (doubting Thomas)
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G'day Gavin,
just went down to shed and measured a spare cast iron guide. It is 0.563", also measured a bronze guide that is +4 thou, it measured 0.567". I know to be true all things should be 25 degrees C when measured, but here right now would be lucky to be 10. My micrometer is reading 1/4 thou big. So to have a 3 to 4 thou crush the hole would have to be 0.560".
You sandgropers are almost as weird as Tasweigians. *eek*
Cheers
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Thanks for the info. I am still waiting for SRM to send the new guides. meanwhile it's been time to touch up some paint work and do some finishing off. So she should be ready for a few miles this summer.