Author Topic: A7 head with 1 1/16 inlet???  (Read 1984 times)

Offline 900triple

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A7 head with 1 1/16 inlet???
« on: 15.05. 2012 23:40 »
Hi all,

I'm probably not going to enjoy the answers but I still need put out of my misery...

30 years ago I acquired a small pile of A7 bits which included an AA7 engine (1951). 25 years later I thought it would be a good idea to haul the engine and random bits out from underneath the bench and build a bike. And - quite remarkably - I've more or less done that. A standard looking but very non standard plunger A7 emerged, eventually. Now after a prolonged  and herculean effort I'm at the final finishing stages and tonight I started to fit the carb. The engine has always been in one piece all these years and last year Rob Wardle rebuilt it completely for me  *smile*

When I measured the carb - 1" - and then the inlet I found that the inlet hole is 1 1/16" (27mm). Consternation, as this is A10 terrritory. I cannot find anywhere a reference to a 1 1/16" inlet A7 head.

Seems that this lovely rebuilt engine has an A10 head???  *sad2*

Before I pull the head off can anyone make my day and tell me that BSA did indeed make a cast iron, single carb 1 1/16" inlet diameter head for the A7? Is there a way I can check for sure that it is an A7 or A10 head without taking the head off?

Does anyone have a good supply of valium they can deal me with?

Will I be able to sleep tonight?

Answers please on a  postcard...

Alan  *help*




Offline duTch

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Re: A7 head with 1 1/16 inlet???
« Reply #1 on: 16.05. 2012 00:06 »
Can't do the Vallium, though It was quite fun on the one occasion I had to for 'chop-chop', I can tell you what you want to hear but would have to maybe lie and won't blatantly do that either :! :!
   My alloy head has the part# cast into the underside of the inlet tract, and would expect the same of an iron head ????,if not there, somewhere?
     My guess is that someone has opened up the hole to fit a bigger carb and a smaller one fitted after for some reason, but I've been wrong before (once in grade 2- yeah sure)!
   Can't comment on performance, if it is A10,as i have a feeling i read somewhere the combustion chamber is a different shape  ????but reckon it'd run ok anyway, just put a bigger carb on with suitable jetting? I'm sure someone has a better idea, good luck, duTch
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
Australia

Offline Beezageezauk

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Re: A7 head with 1 1/16 inlet???
« Reply #2 on: 16.05. 2012 10:15 »
Hi Alan,

On checking my data I've found that the only A7's to use a 1 1/16 carb were the 1952-54 A7 and A7 Star Twin models but the carbs on these were AMAL T10TT9's.

That just leaves the A10 heads as you suspected with a more conventional 1 1/16 carb.

Like Dutch mentioned, I can't see any problem by using the head you've got provided an appropriate carb is fitted and set up ok.  No doubt more knowlegable folk on this forum could advise further on this.

I wouldn't be surprised if there weren't loads of these bikes running around with the wrong heads fitted and the owners are non the wiser!!

Beezageezauk.

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Re: A7 head with 1 1/16 inlet???
« Reply #3 on: 16.05. 2012 10:24 »
Do a compression test.
If you get a number over 120 PSI then you are in the home straight.
Fitting a 1" carb on a 1 & 1/16 " manifold will not really cause you any grief unless you are trying for a standing 1/4 mile record.
Bike Beesa
Trevor

Offline muskrat

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Re: A7 head with 1 1/16 inlet???
« Reply #4 on: 16.05. 2012 11:35 »
G'day Alan,
               1951 A7 head has 67-381 cast under the manifold which is part # 67-380. Mine also has an upside down Q on top of the manifold.
A A10 will have 67-251 or 67-966 cast as above.
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
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Muskys Plunger A7

Offline 900triple

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Re: A7 head with 1 1/16 inlet???
« Reply #5 on: 16.05. 2012 18:55 »
Thanks for your comments...feeling a wee bit better now. Looks as if I need to suck it up and see how it runs...when it eventually runs that is.

And check the casting number. Watch this space!

Alan

Offline 900triple

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Re: A7 head with 1 1/16 inlet???
« Reply #6 on: 16.05. 2012 19:17 »
Well...I've just checked the casting and guess what? 67-381!!!! The correct head for the engine even after 61 years. I feel like I've won the lottery. Now I need to get hold of a 1 1/16" carb and crack on with it.

From ecstasy to depression to ecstacy again. Welcome to the world of building up old incomplete piles of sh1t.

I'm away to play in my shed - cheers

Alan   *wave*

Offline 900triple

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Re: A7 head with 1 1/16 inlet???
« Reply #7 on: 16.05. 2012 20:04 »
And guess what? When your lucks in, its in!

Having a trawl through a seperate box of bits I've found the carb (Monobloc) I need. Even better with the Monobloc on this head the normal version with the float bowl on the nearside (L/H) does not fit but this one has the bowl on the offside (R/H). Cannot believe it.

Now need to research the inetrnals required. Anyone give me a head start with jet sizes?

Is it too late to put on a lottery ticket for tonight?

I'm gonna sleep happy tonight... *smile*

Alan

Offline muskrat

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Re: A7 head with 1 1/16 inlet???
« Reply #8 on: 16.05. 2012 20:45 »
 Great stuff Alan. Don't mention lottery. Sat night I was 1 number off winning 2.5 MILLION. Still got enough to get a new trailer  *yeah*, hit a tree with the old one on Sun *angry*.
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7

Offline trevinoz

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Re: A7 head with 1 1/16 inlet???
« Reply #9 on: 16.05. 2012 22:21 »
Alan,
          A RH monobloc would most likely be a 689 which would be getting a little large as they range from 1-1/8" to 1-3/16".

 Trev.

Offline 900triple

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Re: A7 head with 1 1/16 inlet???
« Reply #10 on: 16.05. 2012 22:35 »
Hi Trev,

Absolutely spot on - the carb is a 689 and measures 28.5mm which makes it a 1 1/8". To be honest its close enough for me as a 0.75mm step is neither here nor there and given the bike is being built for road riding it shouldnt affect performance. Saves me a few bob and a lot of hassle trying to find one at 27mm.

Well spotted - this forum must be the most knowledgeable on the net. Is there anything you lot dont know (apart from next weeks lottery numbers that is...).

Cheers

Alan

Offline gavinoz

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Re: A7 head with 1 1/16 inlet???
« Reply #11 on: 17.05. 2012 06:01 »
Hi,

Beezageezauk quoted "On checking my data I've found that the only A7's to use a 1 1/16 carb were the 1952-54 A7 and A7 Star Twin models but the carbs on these were AMAL T10TT9's.'

The service manual (A7&A10, 49-53) I have just got says A7 Star Twin used

Type 276FD/1DBH,      Choke size 1",       Engine end size 1 1/16"

Gavinoz



Rigid A7S, 57 A10 in pieces
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Offline Beezageezauk

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Re: A7 head with 1 1/16 inlet???
« Reply #12 on: 17.05. 2012 17:29 »
Yes,  A7 Star Twins also had other carbs fitted but the T10TT9 was the only one with a 1 1/16 choke size.  Some had 15/16 some 7/8 and some had 1inch chokes.

Or was it common practice for BSA to use a carb with 1inch choke on a 1 1/16 inlet manifold?

Alan:-  It's always a bit hit and miss trying to set up a carb for a different model for which it was not intended.  You might need to experiment with main jet sizes to set your carb up.  I would start with a 3 1/2 cutaway on the throttle valve, a 30 pilot jet, somewhere around a 290 main jet if you're running with an air filter or a 400 main jet without.  Needle on position number 3.

These main jet sizes are those quoted for A10's so might be a bit high for an A7.

I might be able to lend you a selection of main jets for testing purposes.  Let me know if I can help.

Beezageezauk.



Offline 900triple

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Re: A7 head with 1 1/16 inlet???
« Reply #13 on: 17.05. 2012 23:01 »
Hi Beezageezauk,

400 main jet? I was planning on a 240 based on the research I've done - but maybe that would be with a filter. I'm planning not to use the filter. May take you up on your kind offer - I've a small collection full of main jets and if it wasn't for the rain and COLD tonight I'd be out checking to see whats available there first.

I hate this Scottish weather...but that's off topic.

Cheers

Alan


Offline duTch

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Re: A7 head with 1 1/16 inlet???
« Reply #14 on: 18.05. 2012 03:57 »
Good it's working for you 900...x3
  Of topic but can't resist, Musky you have to earn points for hitting a tree with a trailer- would've thought there'd be something in front to muster it out out of target zone *smile*
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
Australia