Broken piston rings.

[v8ivor]

Hi Fellas,
I just lifted the barrels on my 52 A10 rebuild  and found the top rings broken. Does anyone know how to identify the pistons so as I can get a new set ? They are +40 and there is very little coke build up, just a little scorching on the sides of the pistons and next to no ridging. I'm wondering if the wrong rings were fitted or they were not correctly gapped. Also the con-rods are non magnetic with a bright nickel colour.
 

[RichardL]

If you know your pistons are +40, that should be all you need to know, unless they are some crazy custom piston not originally built for an A10. They are not rare. Andrew (Beezermacc) appears to have them at 29.90 GBP ( https://sites.google.com/site/priorymagnetos/barrels-pistons-etc ), but most of the major suppliers should also have them (SRM, Draganfly, C&D, etc.). Whoever you get them from, you can double-check with them that their stock of +40s will work for you.


Richard L.

[v8ivor]

Thanks Richard,
I think I will hone them and take a chance on a set of rings ( Try the new rings in the bores and see what gap I've got ) BTW Both broken top rings have a small ridge on them, so the most part of the ring that fits in the piston grove is sloppy and the tiny bit that extends past the width of the piston is the same size as the grove, so I wondered if the rings were worn before they broke ? Also do you know if those shiny rods were standard ?
Keep the rubber side down !
Ivor.

[duTch]

 

BTW Both broken top rings have a small ridge on them, so the most part of the ring that fits in the piston grove is sloppy and the tiny bit that extends past the width of the piston is the same size as the grove, so I wondered if the rings were worn before they broke ?

  Fair likelihood I say


A10/7 Conrods are aluminium Alloy as stock, so no magnetism to be expected, shiny 'nickel colour' kinda comes with them .

 

[bsa-bill]

If you know your pistons are +40, that should be all you need to know,

Hi guys - not nit picking you post Richard, I just want to know from any passing guru if that is the case and  a bit more about rings, so here goes (probably stuff I should or maybe once knew)

1. I had in mind that I've seen new rings like v8ivor described (stepped) - maybe a zen moment
2. I thought that rings were not always swappable between different manufacturers similar pistons, or is there a standard groove width and depth.
3. I've had tapered rings that I have great difficulty telling which way they are tapered, the instructions always state which way up they go, not a lot of help when up is not defined.

[Triton Thrasher]

Yes, some top rings have a step within the groove. Step faces upwards, if I remember correctly.

Rings on both pistons breaking in service sounds less likely than the home mechanic breaking them when fitting the barrels.

[v8ivor]

Thankyou for confirming that I have the correct rods. And it also sounds feasible that the rings were broken by the re-builder, becauseof the lack of coke, however, I have posted an update today.

[v8ivor]

There was no ridging at the top of the bores, it was just a little coke, but the ring gap was around 62 thou ( Maybe the wrong rings ? )

[bsa-bill]

Yes, some top rings have a step within the groove. Step faces upwards, if I remember correctly.

Thanks for that TT, so I'm not completely loopy - yet

Rings on both pistons breaking in service sounds less likely than the home mechanic breaking them when fitting the barrels.

Yep, something I've never managed to do, of course you can't be sure of the last time

, but the ring gap was around 62 thou

Way to much even allowing for new ideas such as this from US via Ebay at http://www.ebay.co.uk/itm/BSA-A10-piston-RINGS-pre-unit-650-twin-Hastings-STD-Standard-ring-set-USA-made-/361355194871

"The new industry standard for British motorcycles is to gap the rings at .020 / New independent lab tests and studies (in the USA and England) show that any gap between .024 to .010 is efficient, and does not show more oil loss than normal gaping at .010 to .014 or does not show any less engine performance, or any extra loss of compression.
I understand that this information might be difficult to accept or understand because the way we have been doing things for the last 80 years but all the rings that are coming out of the USA (Hastings) are using this standard and the gap spec is .020 / JCC and Hepolite are also using this standard"

interesting and certainly would take some out some of the first journey after rebuild jitters

[Triton Thrasher]

There was no ridging at the top of the bores, it was just a little coke, but the ring gap was around 62 thou ( Maybe the wrong rings ? )

Anyone better at sums than me is welcome to correct me, but that looks like the gap you might see if the rings were meant for a 20 thou smaller bore.

[Greybeard]

There was no ridging at the top of the bores, it was just a little coke, but the ring gap was around 62 thou ( Maybe the wrong rings ? )

JUST A LITTLE COKE??? Can we keep drug references out of this forum! 

[duTch]

 

1. I had in mind that I've seen new rings like v8ivor described (stepped) - maybe a zen moment
2. I thought that rings were not always swappable between different manufacturers similar pistons, or is there a standard groove width and depth.
3. I've had tapered rings that I have great difficulty telling which way they are tapered, the instructions always state which way up they go, not a lot of help when up is not defined.

 Bill I had the same thought re;(1), but then I realised he said;
 

so the most part of the ring that fits in the piston grove is sloppy and the tiny bit that extends past the width of the piston is the same size as the grove,

, which is stepped the other way round to what I had in mind...so I guess that means VERY worn rings*conf*?

  Also concur with points noted (2) &(3)... in case (2), I guess 'accurate user judgment' will generally suffice...?