Author Topic: Piston markings  (Read 1537 times)

Offline zitman

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Piston markings
« on: 20.03. 2009 17:25 »
Hi all,

Just got the head of my A7SS to replace the head gasket and there is some scoring in the barrels.  My pistons have no markings on the top but are marked with three numbers elsewhere on the pistons:

11603A
413
E-8

The pistons are 67mm diameter at the top and 67.5mm diameter under the oil ring.

Can anyone tell me what "overbore" these are likely to be as I will need to order some pistons and get a rebore sorted.

Ta

Z

Offline MikeN

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Re: Piston markings
« Reply #1 on: 20.03. 2009 20:25 »
Standard bore for an A7 is 66mm.
Yours are 1.5mm oversize.
.040" = 1mm
so if your pistons measure 67.5 then they are plus .060" (or plus sixty).
Do they make them +.080" ?
Mike

Online bsa-bill

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Re: Piston markings
« Reply #2 on: 20.03. 2009 20:30 »
I've seen A10 pistons at +80 allthough some do say barrels are getting thin at this stage, however there may be more meat in A7 barrels at this size ??

All the best - Bill
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

Offline zitman

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Re: Piston markings
« Reply #3 on: 20.03. 2009 22:21 »
Thanks guys, but I thought the A7 Shooting Star was 68mm bore?

Z

Offline dpaddock

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Re: Piston markings
« Reply #4 on: 21.03. 2009 03:46 »
MikeN is correct; 66 mm is the standard bore. Factory listed 0.5  and 1 mm (0.020" and 0.040") oversizes. At 0.060", yours are aftermarket pistons.
Why do you need to rebore?
     David
David
'57 Spitfire


Offline zitman

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Re: Piston markings
« Reply #5 on: 21.03. 2009 10:13 »
Thanks all,

MikeN: Having done yet more research the standard bore IS 66mm.  Sorry for doubting you *smiley4*

David: There is some scoring on the barrels.  The bike is at my mates place at the moment I am heading round later this morning so I will see for myself and measure the pistons again.

Will try to get photos of the scoring and keep you posted.

Cheers

Z



Offline zitman

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Re: Piston markings
« Reply #6 on: 21.03. 2009 20:08 »
Thanks all,

Just measured and the pistons and bores are definitely around the 67.5mm mark so its already on +60.

Got to find out whether +80 is an option and, if so, where I can get some +80 pistons.

I couldn't get photos as the scores are pretty fine so I am taking the barrels to my local British bike expert on Monday to get his opinion.

Z

Offline A10Boy

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Re: Piston markings
« Reply #7 on: 21.03. 2009 21:10 »
If you give it a light "glazebust" or hone you will see how deep they are.
Regards

Andy

1958 Super Rocket
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