Author Topic: Broken piston rings.  (Read 831 times)

Offline v8ivor

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Broken piston rings.
« on: 26.10. 2015 20:31 »
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.
 

Online RichardL

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Re: Broken piston rings.
« Reply #1 on: 26.10. 2015 21:34 »
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.
Plan on signing up for the world-wide 2020 DISTINGUISHED GENTLEMAN'S RIDEon September 27, 2020 (if it's not cancelled and we are free to move about by then). Watch website at https://www.gentlemansride.com for details.

Offline v8ivor

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Re: Broken piston rings.
« Reply #2 on: 31.10. 2015 22:51 »
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.

Offline duTch

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Re: Broken piston rings.
« Reply #3 on: 31.10. 2015 23:40 »

 
Quote
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 *smile*.

 
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
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Online bsa-bill

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Re: Broken piston rings.
« Reply #4 on: 01.11. 2015 09:29 »
Quote
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.
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Online Triton Thrasher

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Re: Broken piston rings.
« Reply #5 on: 01.11. 2015 12:53 »
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.

Offline v8ivor

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Re: Broken piston rings.
« Reply #6 on: 01.11. 2015 14:11 »
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.

Offline v8ivor

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Re: Broken piston rings.
« Reply #7 on: 01.11. 2015 14:31 »
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 ? )

Online bsa-bill

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Re: Broken piston rings.
« Reply #8 on: 01.11. 2015 14:58 »
Quote
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

Quote
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 *????*

Quote
, 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


All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Online Triton Thrasher

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Re: Broken piston rings.
« Reply #9 on: 01.11. 2015 15:10 »
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.

Online Greybeard

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Re: Broken piston rings.
« Reply #10 on: 01.11. 2015 17:54 »
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!  :o

Offline duTch

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Re: Broken piston rings.
« Reply #11 on: 01.11. 2015 21:53 »

 
Quote
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;
 
Quote
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...? *smile*


 
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
Australia