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Dave Martin
Dave Martin
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1970 a65 barrels
#809685 05/20/20 9:31 pm
Joined: Nov 2017
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Would like to know how far you can bore the cylinders without causing problems?
This would be on a 1970 a65.

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Re: 1970 a65 barrels
Regi #809696 05/20/20 10:15 pm
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+60 is fine with 99% of barrels
Pistons of that size are readily obtainable.

The barrels vary quite a lot, some are offset to one side considerably.
I've run a set at +0.100 with no problems but i had the guy who bored it
move the centre on one side over a bit.

The factory said max +40

Re: 1970 a65 barrels
Regi #809774 05/21/20 8:28 am
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Nick, the factory probably never would have guessed that folk would still be using their bikes 50+ years later and thought anything bigger than 0.040” would be a waste of time.


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (undergoing restoration)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

Re: 1970 a65 barrels
Regi #809835 05/21/20 4:27 pm
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Thank you both for your thoughts on this.I had in the past been told that at 60 over you would have head gasket troubles,but hope that wont be the case hear.

Re: 1970 a65 barrels
Regi #809853 05/21/20 6:38 pm
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Get the barrel skimmed or rather checked for flatness and you shouldn’t have any gasket issues


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (undergoing restoration)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

Re: 1970 a65 barrels
Regi #809958 05/23/20 12:25 am
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After market mobs like MCS in the 'states made pistons for A65's up to +0.100 back in the day.
They made some nice stuff, good forged pistons, offset pin versions etc.


Moderated by  Allan G, Jon W. Whitley 

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