Author Topic: A10 Over Compression Rebuild  (Read 459 times)

Offline Mzungumark

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A10 Over Compression Rebuild
« on: 20.03. 2016 16:55 »
 Hi there,

So, I got this '57 A10 that suffered over compression due to some nugget putting together what they thought were the best bits from two engines, even cut and Gas welded two Push Rods together to make one the right length!

Now, I am originally from just down the road from Small Heath myself, Redditch actually, the home of Royal Enfield. However, I now live in Uganda and as you can imagine, we are not exactly tripping over A10 parts here...

If anyone can make it easy for an old soldier to understand, I'd appreciate help in what ratio parts I need to get this old girl back on the road.

How do I tell, by just looking, which ratio Pistons I have? Got both short and long Cylinders, short one is a wright off, cracked and has a piece of barrel missing. I can't imagine it would be salvageable. Long Cylinder is good, sleeves badly scored though. Crank is true but will need grinding to the first oversize Shells (.25?). Con rods look fine, but I don't know if they were from the short or long block.

The bike was a rolling chassis with the engine in two big buckets when I got it. So I'm only guessing that the long Cylinder was on when it went pop.

So what do you think?


Online trevinoz

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Re: A10 Over Compression Rebuild
« Reply #1 on: 20.03. 2016 20:24 »
Do you know which crank you have? A7 rods are 6", A10 around 6.5".
Big end shells increase by .010",  e.g. .020", .030".
If the bores are bad you will have to rebore and fit new pistons.

Offline Rocket Racer

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Re: A10 Over Compression Rebuild
« Reply #2 on: 20.03. 2016 22:28 »
How do I tell, by just looking, which ratio Pistons I have? Got both short and long Cylinders, short one is a wright off, cracked and has a piece of barrel missing. I can't imagine it would be salvageable. Long Cylinder is good, sleeves badly scored though. Crank is true but will need grinding to the first oversize Shells (.25?). Con rods look fine, but I don't know if they were from the short or long block.
Mark,
 the long vs short barrel and rod comments suggest you have a blend of A7 and A10 parts as the A10's all had common rod and barrel lengths, only fundementally differing in flange thicknesses and big end diameter.
So you do need to confirm you have a small or large journal crank. What is the big end diameter approximately?

The only barrel I've ever scrapped had the flanges blown off. Sleeving and welding can recover most and if not the fins are useful for repairing other barrells.
Do you know what diameter the badly scored barrel is? they can go out to an absolute maximum of 72.5 if never previously resleeved.


The most commonly fitted repro pistons would be the 7.25 flat tops which are chinese made hepolites.
Higher compression pistons require better fuels and less suitable for small journal thin flange '57 motors unless its a super rocket that typically had a special transitional crank by 57. (assuming you have the correct crank...)

What parts are you missing?
A good rider periodically checks all nuts and bolts with a spanner to see that they are tight - Instruction Manual for BSA B series, p46, para 2.
New Zealand

Offline BSA_54A10

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Re: A10 Over Compression Rebuild
« Reply #3 on: 22.03. 2016 10:36 »
Reddich is the home of the Bantam I will have you know
Bike Beesa
Trevor

Offline shuswapkev

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Re: A10 Over Compression Rebuild
« Reply #4 on: 24.03. 2016 12:49 »
most of the cylinders I have used have had the lowers bits broken off...

I have just had sleeves fitted...
  here in oz we can get sleeves of near any size from diesel fitters...  I just turn them down as they are very thick...( diesel)
I paid $25.00 each for my A10 sleeves