The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: muskrat on 13.03. 2016 20:55
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G'day all.
Instead of topic http://www.a7a10.net/forum/index.php?topic=10429.0;topicseen changing direction.
An A7 head will fit onto an A10 without modification safely as long as flat top pistons are used. The combustion chamber is best chamfered to match the A10 bore, then higher comp pistons can be used.
I have 10.5:1 pistons in my A10 with a 54 SS head on thick flange barrels. With thin flange barrels 8.5:1 pistons would be the safe limit.
Cheers
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Doesn't anyone feel disturbed that the few remaining alloy A7 heads are being butchered to fit Gold Flashes?
cheers
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I didn't think there was shortage of A7 ally heads, either single or 'twin carb' versions. Or is it people hoarding them?
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I put a A7 head onto my A10 barrels, & as Musky said I chamfered the head to suit..
Chamber on left done ... chamber on right to go...
Also had new Valves, valve seats & head decked..
no problems with mine.. *smile*
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I had fit a twincarb A7 alloyhead on my first A10 race projekt three years ago.
There are no modifications need when fit 8.5 pistons.
The smaler bore is like a little squish and I will see this as an advantage.
The gap between the pistoncrown and the head is best in the range of 1.2 to 1.4mm fully fit with gasket.
cheers Klaus
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Hi All,
It doesnt always work like that Klaus *warn* *warn*
John
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Can someone say what advantage there is to using an A7 head on an A10? Is it just, "Hey, I got one of those on the shelf!"?
Richard L.
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Hi All,
It doesnt always work like that Klaus *warn* *warn*
John
Hi John,
I had used hight domed JP pistons and it worked with this.
May be the flat ones doesn't.
cheers Klaus
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Can someone say what advantage there is to using an A7 head on an A10? Is it just, "Hey, I got one of those on the shelf!"?
Richard L.
Typically A7SS alloy heads are in better condition than the A10 alloy ones. And often they happen to be what is available.
My race sidecar runs an A7 head, but as it had been radius'ed comparably to an A10... I only realised when I checked the casting numbers.
Twin port A7SS heads are more common for the earlier years. for those who want bragging rights (with racing carbs fitted *yeah*)
Valve springs, collets and valve collars differ between A7 and a10 alloy motors and cannot be mixed up as the collars have a different taper which isnt always evident until the collets shatter *eek* and the motor goes off song
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Hi all, I finally registered, haha...good forum this is. A long time brit biker, some actually run from time to time.
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So an A7 head will also have smaller porting and valves, how much nicer will that make it run?
I assume one wouldn't be doing this as a top end performance mod?
Roland Pike and other early researchers found increases in power sometimes with smaller porting and what might seem like obvious obstructions were actually helpful in mixing and power production.
My example is the Goldstar port step was found to be good for noticeable gain. The 1-1/2" GP was bigger than the as finished port, so when they opened the port , and removed this 'step' to match they lost power....
And of course the first thing done by most was to cut out the port to match the carb size for 'better flow'..when the opposite seemed to be the end effect. Talk about counter intuitive!.... *eek*
I can't say what current tuning practice is off hand, perhaps the Eddie Dow tuning tips booklet might offer more.
What's been the experience here, are there any performance changes noticed when this is done?
An interesting topic, thanks.
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Hi all, I finally registered, haha...good forum this is. A long time brit biker, some actually run from time to time.
........................
So an A7 head will also have smaller porting and valves, how much nicer will that make it run?
I assume one wouldn't be doing this as a top end performance mod?
What's been the experience here, are there any performance changes noticed when this is done?
An interesting topic, thanks.
Bodger Welcome to the forum!
My A7 head had already been heavily doctored and needed a lot of remedial work, so not much help in determining the implication of fitting a stock head.
However the A7SS head is still a performance head (albeit for a 500) and there is a lot to be said for small ports as they have higher velocity gas flows so more effective at lower openings.
For a road motor I would not be rushing to port and big valve.
I didnt have that choice but it wasnt an issue as my head is now as tuned as it can be without major effort running dual 10TT9's on methanol.
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Oh, thanks Rocket!
I have a 52 A7ss 23xx that was perhaps a dealer/factory flat tracker as it has been leaned on: light flywheel, polished as well, triplex chain (std..I thought it was duplex std) and lightened and polished rockers, and a 357 cam, and a rigid frame.
It has a Daytona gearset as well, stamped as...so who knows, maybe even raced at Daytona...or not, but it came from some local west coast racers associated with a dealer who was said to have grumbled that the brothers who I bought it from ($150 in 1968) should have given it back to him etc...it was in a pile with a rigid frame, a rear wheel spooled front wheel, and smelled of Castrol.
It also came with a B series frame without the passenger loops.
I bought an A7SS head at a swap , the engine came with an iron head.
Now I should look more closely and measure ports and valves.
And as a flat tracker with the 50's known mods it may have been in the 40+ hp range..or not.
So yours...with Methanol?! and say 14:1 compression, yipes, 50+ hp then ?
For your road race outfit?
What crank and rods?
Since I'm new here I can't (yet) ask for pikkies, but.......