1958 A7 cylinder barrels

[A7JAY]

Hi all, my first ever post on here although I've been reading and gaining knowledge for quite some time, my question is, how far potentially could the A7 barrel be taken out to? I know they at +60 atm and I'm thinking I could possibly get some standard 69mm tiger 100 pistons in there, I've not stripped the motor yet so don't know what the compression hight of the BSA pistons are or the pin size for that matter, any help and advice would be appreciated thanks
Jay     

[limeyrob]

I suspect you will have to fit a thick sleeves as the skirts on the barrel may get too thin.  This is one limit on an A10.

[A7JAY]

thanks for the reply sir, I guess I'm just crossing my fingers that I will have enough meat in the spigots to take another 1.5mm out.

[limeyrob]

My A10 is at +60 and the skirts are rather thin but what's really noticeable is that the bores are not central in the skirts so you may need a plan B.  Many years ago I had a piston pick up on a plunger Flash and it took the skirt clean off and dumped it in the bottom end so make sure the piston clearance is generous!

[A7JAY]

ye I always give between 0.005 and 0.0055 clearance

[DAVE BRADY]

Hi,

It is worth investigating this as it prolongs the life of the cylinders.
My wife's A10 is at +80 thou and has run like this for many thousands of miles.  To fit a liner it may need boring to +120 and then the liner would be bored out to standard so several bores needed so increased cost. If the bore ever needs redoing then a liner can be fitted and STD pistons used.
It may be worth asking SRM if they have any ideas as it was from them that we purchased the +80 pistons which I think are Triumph T120 at +20.

Dave.

[A7JAY]

interesting, but aren't the T120 pins smaller than A10 pins?

I'm going to post the same question on the A7/A10 forum and see what those blokes have to say

thanks for you're input chaps 

[DAVE BRADY]

Hi,

They must be the same as the pistons fitted out of the box. I will have look later to see if I can find the box in my archive of labels.

Dave.

[A7JAY]

all the triumph 650 pistons in my graveyard cupboard have 17.5mm pins, according to the Hepolite catalogue A10's have a 19mm pin 😕

[Mark Cook]

For most people a good rebore and new piston would see out their life, I don't expect many will have your mileage, Dave.

Mark

[DAVE BRADY]

Hi,

I checked my archive but could only find a piston ring packet and they are for T120 (71mm bore) at = +0.040.  Sorry, no info. re the pin size.
I have recently fitted new rings as the bore is still within tolerance and should last several thousand miles more if we have enough time to do them.

Dave.

[DAVE BRADY]

Hi,

Just found this on 'British Only Austria".  They may do A7 +0.080 pistons.
Checked our photo library and the larger fin barrels with the plus 80 pistons first appear in 2004.  I will dig out an old MOT to see what mileage has been covered since.

Dave.