Author Topic: A10 plunger,cylinder head advice  (Read 908 times)

Offline Topdad

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Re: A10 plunger,cylinder head advice
« Reply #15 on: 25.07. 2024 11:12 »
My modestly tuned A10 as large inlet vales in an iron head ,comp at 8.25  and a 357 cam ,lovely motor lots of low down grunt and pulls easily with a acouple of teeth bigger engine sprocket ,so I'd say stick with your iron head
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Offline Von datoh

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Re: A10 plunger,cylinder head advice
« Reply #16 on: 25.07. 2024 14:36 »
Topdad that sounds exactly where I’d like my engine to be!,when you say large inlet valves is that standard with your head?or did you fit bigger? Out of interest what carb are you running as well ? Thanks In advance
Somerset
A10 plunger

Offline Topdad

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Re: A10 plunger,cylinder head advice
« Reply #17 on: 26.07. 2024 12:04 »
No sent to SRM who fitted bigger valves and guides they told me the iron head can take bigger valves than an ally one , the carb was a new concentric of the shelf job but can't remember number .think its a 3 tooth bigger engine sprocket pulls it without a blip up hills and 2 up
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Offline Von datoh

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Re: A10 plunger,cylinder head advice
« Reply #18 on: 26.07. 2024 14:45 »
I will look into that didn’t know you could fit larger valves to the iron head,how do you find that 357 cam not to “peaky” I wondered if that be ok for road use didn’t want to shift the power to high up the reverse range ?
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A10 plunger

Online limeyrob

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Re: A10 plunger,cylinder head advice
« Reply #19 on: 26.07. 2024 16:58 »
Your bike would have left the factory with a 67-334 cam which would suit its original compression ratio and broad torque delivery.  The 67-356 is a later step up in power but keeps the low end torque.  I have a 356 in my '59RR.  The 357 is the last cam with the most power, there is some debate (on-going?) about whether this is "peaky", opinions vary.  My take would be that in most engines when the power is upped by a cam it ups the power in the higher rev range by helping the engine breath better at high revs, at mid range and low range there's not much difference.
So if you intend to keep the bike in the upper rev ranges then you will feel the improvement from the 357, but if not then its not a benefit.  A10s are not a high revving bike and certainly with a Golden Flash the great pleasure is opening the throttle at 30 mph in top and pulling up to 70 without a gear change.  If you look at period road tests they are not much bothered by 1/4 mile or 0-60 but they talk a lot about 30-50 and acceleration in top gear from low speed.  Its a different riding style which about getting into top and staying there.  If you are riding with a manual A/R this makes sense.
I did a lot of miles on a tuned (10.5:1) A65 and it was very revvy and peaky.  I liked it but I liked the gentle power of a softly tuned A10 too, it was more relaxing and comfortable.  If you want power and revs in a BSA just get a twin carb A65, they are fast, cheaper than A10's and there's plenty about. Don't spoil an A10 trying to make it into the A65 you should have bought.
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Online JulianS

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Re: A10 plunger,cylinder head advice
« Reply #20 on: 26.07. 2024 20:47 »
My iron head A10 has 7.25:1 pistons and a 357 cam which I find gives better low down power than the 356.

Fitted with Road Rocket valves with springs/collars etc to suit from Ebor Bikes, the springs are much better quality and last longer than the commonly supplied ones.

https://eborbikes.com/

Anyone seen or know anything about the Apachie cam which has been added by hand to the attached US bulletin?

Online limeyrob

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Re: A10 plunger,cylinder head advice
« Reply #21 on: 26.07. 2024 23:28 »
Very interesting, thanks for posting!  That 358 cam holds the exhaust open a lot longer.  I suspect that works well with a long open pipe?  Also interesting that you are getting good bottom end power with a low comp and 357 cam.  I was not sure about that so built my engine with a 356, time will tell whether I made the right call.  Mine is 8 1/2 : 1 (or could be 9) with a single 30mm Concentric and RR ally head.
Slough 59 GF/SR

Offline Von datoh

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Re: A10 plunger,cylinder head advice
« Reply #22 on: 27.07. 2024 00:48 »
Great reply’s from people thanks for sharing your experience and advice.The plan is to build the plunger project with the best parts I can (utilising later engine parts if better),I bought it as a pile of bits and have been assembling parts as I go.My idea is not to make it something it’s not I think it’s got a beautiful look the a10 engine,and an a65 was not currently what I wanted anyway.Thanks again all:)
Somerset
A10 plunger

Online chaterlea25

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Re: A10 plunger,cylinder head advice
« Reply #23 on: 27.07. 2024 12:35 »
Hi All,
The 357 cam is in no way "peaky"
Bottom end power is very smooth,
My SR will pull from tickler without problems.
The difference is that you get a good surge  of power at about 4k RPM.
Mine has a 2 into 1 pipe and Goldie type silencer, SS system that came from Armours and a 30mm Mikuni

John
1961 Super Rocket
1963 RGS (ongoing)

Offline muskrat

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Re: A10 plunger,cylinder head advice
« Reply #24 on: 27.07. 2024 22:47 »
G'day John.
I find the same with my A7 plunger recently rebuilt with 357, A7SS head with 932 carb and straight through pipes. Plonks along well but gets a kick in the pants at about 4K.
I'll have to wait till later in the day for a ride, it's snowing (only light) at the moment!
Cheers
'51 A7 plunger, '57 A7SS racer now a A10CR, '78 XT500, '83 CB1100F, 88 HD FXST, 2000 CBR929RR ex Honda Australia Superbike .
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Muskys Plunger A7