Author Topic: +80 Chronometric  (Read 1429 times)

Offline spyke

  • Dorset, England
  • A's Best Friend
  • ***
  • Join Date: May 2009
  • Posts: 135
  • Karma: 0
+80 Chronometric
« on: 12.09. 2009 20:52 »
Hi chaps,

I dont know if its not the done thing to have two questions on different subjects in one post but here goes, someone let me know if its frowned on .
1.Anybody got thoughts on the use of +80 pistons in a fairly low tuned motor.My thick flange barrels are a worn +60 and the cost of sleeving and boring is a bit out of my budget.
2.What number chronometric/s will give me the right speed reading on my A10.Dont give a monkey whether its the correct one for the model and year etc .Im going to have a look at a couple next week and I dont want to by the wrong one.

Cheers Spyke
A10 spitfire style

Richard

  • Guest
Re: +80 Chronometric
« Reply #1 on: 12.09. 2009 21:58 »
Spyke
I have had 80thou pistons in my S/R for some time actually I am on my second set due to a tolerence mistake by a well known firm (shhh dont tell rocketman) and have had no problems since the second set and have covered a few thousand miles but I think you would have to be sure you do not leave the bore walls to thin, dont ask me how to check that as I have no idea but if I am right BSA only recommended going to 60 thou oversize. But most people I have spoken to seem to think that 80 thou should be ok. It should give you about 680 to 700 cc which is probably why my S/R goes so well.
2:1 I beleive but there is left and right hand rotation and you will have to wait for mor knowledgable persons to advise on that, but a good source for repairs and or replacements would be David Woods in the UK (do a google search)
Richard

Offline trevinoz

  • Newcastle, N.S.W. Australia.
  • Wise & Enlightened
  • *
  • Join Date: Jul 2006
  • Posts: 2877
  • Karma: 67
Re: +80 Chronometric
« Reply #2 on: 12.09. 2009 22:05 »
Spyke,
            I guess with the barrel you will have to toss a coin. I have seen pistons listed somewhere at 100 thou os so I suppose anything is possible. It will be interesting to hear from anyone who has bored their cylinders over +60.
As to the speedo, if you are running standard gearing and have standard drive gears in your gearbox, you need a speedo calibrated to 1450 revs per mile or thereabouts. The number is usually printed on the face but with old speedos, anything can be inside.
Trev.

Offline trevinoz

  • Newcastle, N.S.W. Australia.
  • Wise & Enlightened
  • *
  • Join Date: Jul 2006
  • Posts: 2877
  • Karma: 67
Re: +80 Chronometric
« Reply #3 on: 12.09. 2009 22:10 »
Richard,
               good to hear that +80 is successful. Back in the good old days, +40 was the maximum available and then resleeve.
 Trev.

Offline coater87

  • Wise & Enlightened
  • *
  • Join Date: Jul 2008
  • Posts: 1181
  • Karma: 6
Re: +80 Chronometric
« Reply #4 on: 12.09. 2009 22:31 »
 Spyke,

 I have seen some awful things done to motors. I did them myself mostly back when I thought the world revolved around going 1/4 mile as fast as possible.

 But in this case, the BSA budget being tight for you as it is for me, before I had this bored to +80, I would look into a re-sleeve really well- not for right now, but for later. Make sure that by going out to +80 you are not taking so much from the bores that a re-sleeve is no longer possible. These barrels are hard to come by, and saving some now but costing a fortune later is not saving at all.

 Richard has had no problems at +80, so I would say give it a try as long as a good sleeve is still do-able next major rebuild.

 Lee
Central Wisconsin in the U.S.

Offline rocket man

  • Valued Contributor
  • ****
  • Join Date: Mar 2009
  • Posts: 466
  • Karma: 2
Re: +80 Chronometric
« Reply #5 on: 12.09. 2009 23:25 »
hi Richard ive seen what you've put s..m its ok everybody makes mistakes
i had mine rebored to plus 80s as well  and when i sent it to srm i had it
re-sleeved no problem so there must be  enough meat on them

Offline BSA_54A10

  • Wise & Enlightened
  • *
  • Join Date: May 2008
  • Posts: 1983
  • Karma: 32
    • BSA National
Re: +80 Chronometric
« Reply #6 on: 13.09. 2009 12:17 »
Standard and + 20's get machine from the same sized blanks.
+40 & +60 get machined from the same size but naturally larger blanks.
There is enough meat in the barrels to go +80 and possibly even + 100 as the bores are a long way apart.
Bike Beesa
Trevor

Offline trevinoz

  • Newcastle, N.S.W. Australia.
  • Wise & Enlightened
  • *
  • Join Date: Jul 2006
  • Posts: 2877
  • Karma: 67
Re: +80 Chronometric
« Reply #7 on: 13.09. 2009 22:10 »
Yes Trevor, the bores are a long way apart but there is not much meat between the bores and the outside.
Trev.

Offline dpaddock

  • NC, USA
  • Valued Contributor
  • ****
  • Join Date: Jul 2006
  • Posts: 429
  • Karma: 5
Re: +80 Chronometric
« Reply #8 on: 14.09. 2009 13:10 »
To what diameter are the bores opened for re-sleeving?

David
David
'57 Spitfire


Online muskrat

  • Global Moderator
  • Wise & Enlightened
  • **
  • Join Date: Jul 2009
  • Posts: 8170
  • Karma: 106
  • Lake Conjola NSW Oz
    • Shoalhaven Classic Motorcycle Club Inc
Re: +80 Chronometric
« Reply #9 on: 14.09. 2009 14:31 »
G'day all,
            Just had mine re-sleeved. $360AU. 2mm wall thickness of sleeve = 74mm = +.160" with the remaining cylinder skirt 2mm thick. I have seen barrels with the skirt machined off and the new sleeve is now the skirt.
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7