BSA Owners' Club Forum

The BSA Workshop => Twins => Topic started by: Bess on 19 February, 2017, 18:15:01

Title: A65 Piston advice
Post by: Bess on 19 February, 2017, 18:15:01
I'm at a point where I need to buy new pistons for our latest A65 projects, I have a Lightning my son a Thunderbolt. I have read plenty of horror stories of what to and what not to buy. What make should I buy and would fitting 7:1 ratios be a better option for less vibration etc. ?
Title: Re: A65 Piston advice
Post by: STAR TWIN on 20 February, 2017, 14:51:00
Advice I received from a very reputable engine builder is don't go above 7.5:1 for normal road use and current rather dismal petrol. With any engine I build now, I go for the lowest available compression ratio pistons. Modern petrol has a considerably lower octane ratio than was available when our bikes were new. You may be OK with a higher compression ratio if you always use premium petrol. However it isn't always available. You try getting some North or West of Perth for instance. I take it everyone uses premium petrol in their BSAs. If not, why not?
Title: Re: A65 Piston advice
Post by: JulianS on 20 February, 2017, 16:20:09
My alloy head A10 is on GPM 8.75:1 pistons. Goes fine on ordinary grade fuel no additives. Tried premium grade and it does not seem to make any difference. Have not tried supermarket petrol.

Tried it on 7.25;1 new hepolites and definate drop in power felt.

The new hepolite rings were very poor quality and had not bedded in over 1000 miles. Some dealers who sell the new hepolite pistons will not sell the new hepolite rings because of the poor quality, they fit Italian rings.

So next time I need pistons it will be either GPM or new old stock real Hepolites.

Iron head A10 pinked a lot on GPMs.
Title: Re: A65 Piston advice
Post by: Bess on 01 March, 2017, 10:03:40
Thanks for the info guys. Went with what SRM recommended in the end....
Title: Re: A65 Piston advice
Post by: STAR TWIN on 01 March, 2017, 14:23:54
Would be interested to know what SRM recommended.
Title: Re: A65 Piston advice
Post by: Bess on 01 March, 2017, 15:08:09
They recommended the pistons they use on their rebuilds.

Inside of the piston casting is the name AERCO, the rings are stamped AE and on the box "BSA piston and genuine Hepolite made in England piston".

Found this on the web  https://www.enginepartsuk.net/ae

 Best wishes...