The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: spyke 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
-
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
-
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.
-
Richard,
good to hear that +80 is successful. Back in the good old days, +40 was the maximum available and then resleeve.
Trev.
-
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
-
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
-
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.
-
Yes Trevor, the bores are a long way apart but there is not much meat between the bores and the outside.
Trev.
-
To what diameter are the bores opened for re-sleeving?
David
-
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