Author Topic: Which piston?  (Read 910 times)

Offline conordangel

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Which piston?
« on: 29.06. 2016 13:07 »
G'day all,

I've stripped the head and barrels off dads Golden Flash and found a mildly scored bore and a piston that got hot enough to weld the rings into their grooves! I'm trying to identify this piston, to order a replacement pair. I can't for the life of me find this part number anywhere. Does anyone recognize this piston?

Cheers!

Online RichardL

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Re: Which piston?
« Reply #1 on: 29.06. 2016 14:25 »
Welcome to the forum. Can we get an introduction, perhaps?
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Offline coater87

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Re: Which piston?
« Reply #2 on: 29.06. 2016 15:09 »
 Hi,

 This might not be as simple as just a new set of pistons.

 It is going to depend on cylinder wall condition, and current size of said cylinder bores.

 I dont know how many engines you have done, or your experience level at this kind of thing. But the cylinder walls wear larger over the course of miles. Your walls are also scored, so depending upon bore size and damage, you might be able to get by with a hone and a new set of pistons.

 If they are in tough shape, might have to have cylinders bored over-sized and then buy new plus sized pistons to go with them.

 Then, you need to figure out how or why we welded a piston tight. *conf*

 More pictures, we love pictures! *smile*

 Lee
Central Wisconsin in the U.S.

Offline Topdad

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Re: Which piston?
« Reply #3 on: 29.06. 2016 15:29 »
Taken the words out of my mouth , lee. pistons don't just do that theres got to be a more sinister reason I'm afraid. Whizz of the barrels and measure the bores accurately or get a machine shop to do it ,then plan accordingly, best of luck
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Offline duTch

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Re: Which piston?
« Reply #4 on: 29.06. 2016 16:46 »

 If it's any help, Parts list for '49-'53 shows #67-304: A10....Piston complete(up to 1951), Casting numbers are apparently one number away (I thought it went the other way *conf*)
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
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Online muskrat

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Re: Which piston?
« Reply #5 on: 29.06. 2016 21:41 »
G'day conordangel.  *welcome*.
All of the above. 67-304 is 6.5:1 compression from 1950.
Give us an intro over in http://www.a7a10.net/forum/index.php?board=13.0
Where abouts r u in this big island.
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Offline conordangel

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Re: Which piston?
« Reply #6 on: 30.06. 2016 05:10 »
This is the right side piston, which is by far the worse of the two. A friend pointed out that the piston is clearly worn at four areas, evenly spaced around the piston, why is that?

I've also discovered, from the restoration paperwork (from 1988) that the bores were resleeved back to standard size. Does this mean if a hone isn't enough, we can go to the +0.020" oversize pistons? Or is re-resleeving the way to go?

Cheers!

Offline conordangel

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Re: Which piston?
« Reply #7 on: 30.06. 2016 05:15 »
Having great difficulty posting photos for some reason. No idea how to shrink the file size to under 1500KB!?

Adm edit: see "Forum info & help"

Online Triton Thrasher

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Re: Which piston?
« Reply #8 on: 30.06. 2016 06:45 »
This is the right side piston, which is by far the worse of the two. A friend pointed out that the piston is clearly worn at four areas, evenly spaced around the piston, why is that?


If the piston and bore were new and that happened, then the clearance was probably too small.

If not new, then the piston got too hot, through detonation/weak mixture/ignition timing, or labouring along at too-low rpm.


Offline conordangel

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Re: Which piston?
« Reply #9 on: 30.06. 2016 07:31 »
Piston damage!

Offline conordangel

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Re: Which piston?
« Reply #10 on: 30.06. 2016 07:38 »
More piston damage

Offline a10gf

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Re: Which piston?
« Reply #11 on: 30.06. 2016 08:27 »
Looking like you got an interesting job :O)

Such piston damage, could starving of oil \ low oil pressure also be a cause?

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Offline BSA_54A10

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Re: Which piston?
« Reply #12 on: 30.06. 2016 09:22 »
This is the right side piston, which is by far the worse of the two. A friend pointed out that the piston is clearly worn at four areas, evenly spaced around the piston, why is that?

I've also discovered, from the restoration paperwork (from 1988) that the bores were resleeved back to standard size. Does this mean if a hone isn't enough, we can go to the +0.020" oversize pistons? Or is re-resleeving the way to go?

Cheers!

Because the barrels were bored incorrectly.
To do them properly you need to clamp the barrel top & bottom and take very small cuts.
Shop used to doing car blocks usually mount them wrong then take off too much each pass and don't do enough honing.
It is called a 4 square defect, google it for the long detailed description.

You can bore A 10's out to +.080" if you are using low compression pistons. so at + 020" you have a long way to go before resleeving is needed.
First thing to do is find a workshop who knows what they are doing , cleaning up the bores then working out which oversize pistons to fit and finally finishing the barrels to suit the pistons.
Bike Beesa
Trevor

Offline BSA_54A10

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Re: Which piston?
« Reply #13 on: 30.06. 2016 09:30 »
From the photos that is not overheating, it is a bad rebore done way too tight .
Unless you go to a shop that does a lot of air cooled engines most idiot moron boring machine operators bore the barrels to water cooled engine clearences and even worse a lot of them will bolt it down from the head and not from the barrel flange resulting with a bore that is too tight and not square on to the crank.
Bike Beesa
Trevor

Offline Butch (cb)

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Re: Which piston?
« Reply #14 on: 30.06. 2016 13:18 »
Barrels are reported as already resleeved which I think will likely limit max oversize you can go, though +020 should surely be fine.
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