The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: wardleybob on 12.05. 2016 07:19

Title: Re: a10 pistons
Post by: wardleybob on 12.05. 2016 07:19
Hi is there sutch a thing as plus 80.thou pistons? If so where do you get them for a A 10.
Title: Re: a10 pistons
Post by: beezermacc on 12.05. 2016 08:36
I managed to acquire a pair, but it is a few years ago, from SRM.
Title: Re: a10 pistons
Post by: ellis on 12.05. 2016 13:36
Wow 80.thou, Wouldn't that make the cylinders too weak ?

ELLIS
Title: Re: a10 pistons
Post by: bsa-bill on 12.05. 2016 13:50
Quote
Wow 80.thou, Wouldn't that make the cylinders too weak ?

I've heard that mentioned as a possible factor in deciding if going for a rebore out to +80 or fitting liners to bring them back to original.
I went for liners but there is an argument that liners might weaken the barrels also, so you pays your money and makes your choice.
I've had no issues at all with liners, it is a more expensive option of course
Title: Re: a10 pistons
Post by: Klaus on 12.05. 2016 15:33
The bore for a liner is 73mm to fit in. Pistons plus 8 are 72mm. I know there are AMC Pistons with a SDT bore 72mm only 1958 for the US Market they will fit but also hard to find.

Whats about a set of new Pistons made by your own spezification? I gues it is nealy the same price as fit 2 liners and a set of new SDt pistons. And I am sure the qualtity is much better as aftermarked pistons.
Use an Airfilter and the pistons will stay the double time and milage.

cheers Klaus
Title: Re: a10 pistons
Post by: Greybeard on 12.05. 2016 15:37
Use an Airfilter and the pistons will stay the double time and milage.

That's good news; I have an air filter.  *smile*
Title: Re: a10 pistons
Post by: muskrat on 13.05. 2016 12:55
I have one low mileage +70 piston if it's any use to anybody. http://www.a7a10.net/forum/index.php?action=dlattach;topic=10630.0;attach=31972;image
Title: Re: a10 pistons
Post by: nimrod650 on 13.05. 2016 18:07
 try paul on 01964 529070  east yorkshire uk he has loads of a10 spares incl new liners and pistons
Title: Re: a10 pistons
Post by: mikeb on 16.05. 2016 12:06
I've been through this recently and ended up with a pair of JP 0665 - 8:1CR for my super rocket, mailed directly from the manufacturer in Aus. You can also find them online. they were the only +080s I could find (I called or emailed many places, almost sourced some mondial 9.5:1 -google it). the JPs fitted without much trouble (one of the clips was tight) and now in service but only 500 miles so too early to pass comment, other than at 8:1 they don't pink at all whereas the old hepolite 9:1 pinked on anything stepper than a judder bar.
I read lots of threads about how someones JPs had violently exploded and someone elses doubled the weight on their engine thereby unbalancing the bike and shaking it off the road etc etc. When i weighed them (with rings and pins) they were 2 to 3g heavier than the old +060 hepolites (with rings and pins), and well matched between the two. some people say the rings are rubbish and they are only a single piece oil ring - you could do better on that. but most of the oil appears to be staying in the engine so far. an engineer (and a65 owner) who helped me had a number of positive reports on JPs tho also found some variability in some batches. the other option was a resleeve so what is there to lose? (don't answer that RR!)
Title: Re: a10 pistons
Post by: BSA_54A10 on 17.05. 2016 10:01
I have used a lot of JP's without any problems, provided I toss the rings.
I have had this out with him numerious times.
Don't know where he gets them from but every one I know who has fitted them has had massive problems bedding them in
Title: Re: a10 pistons
Post by: Rocket Racer on 24.05. 2016 07:00
Barrels that havent been resleeved can take up to +100 if the bores are parallel.
+80's can be hard to find, I have a set of 10.5:1 on the shelf.

I'd be looking to flycut pistons that big to keep the weight down. Heavier pistons do take the balance factors in the wrong direction so also expect to have to balance the crank.

I've seen thin flanged barrels that have taken significant abuse before the flanges let go with 10.5:1 pistons on +100.

its the flange thickness thats going to let you down.

Mike, I'm very pleased your +80 JP's have hung together, they may be on my avoid like the plague list but in your case they have coped with running in so  *wink2*