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66' Spitfire Head #792273 12/07/19 5:41 pm
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Richard Phillips Offline OP
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Did BSA use the small valve head in 66' with the GP Carbs and high compression pistons.
Thanks,
Richard

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Re: 66' Spitfire Head [Re: Richard Phillips] #792291 12/07/19 9:37 pm
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Allan Gill Offline
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Gary would know better but I believe all spitfires had the big valve head, the later spitfires has the initial part of the port chamfered to meet up with the 32mm Concentric. There is a service sheet showing the modification on the BSAoc UK website. I’m not sure but I think Lightning’s also had the 30mm big port/valve head for 66 also. Pistons 10.5:1?


beerchug
Re: 66' Spitfire Head [Re: Richard Phillips] #792298 12/07/19 10:14 pm
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Richard Phillips Offline OP
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Thanks Allen.
I’m planing on a spitfire hornet special. The bottom end is finished I have a choice of big valve or small valve head, to pair up with GP Carbs, ET ignition not sure on the pistons compression yet.
I know you were a proponent of small valve heads. What direction would you take.

Re: 66' Spitfire Head [Re: Richard Phillips] #792299 12/07/19 10:20 pm
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Adam M. Offline
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Are you going to use it on the road?
If yes, small port head, if just racing big port head.

Re: 66' Spitfire Head [Re: Adam M.] #792304 12/07/19 11:04 pm
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Allan Gill Offline
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Originally Posted by Adam M.
Are you going to use it on the road?
If yes, small port head, if just racing big port head.


I’d use the small port in either instance, I’ve had 9k on a small port head with much more torque than the large port, they might even work better with the GPs Than the big port. I would even stick with the small valves, it’ll keep the bottom end more tractable.

A lot of people forget that super rocket heads were same size valves and ports or smaller. Same cc’s but no slower and known for their torque.


beerchug
Re: 66' Spitfire Head [Re: Richard Phillips] #792325 12/08/19 5:53 am
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Mark Parker Offline
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Heads are fairly easy to come by and also to swap between so experimenting with a couple could soon find what's best for what you want. If you run the 10-1 or 10.5-1 pistons this gives more options, and improves the power spread. Small valve/small port may be an advantage on a low compression engine, and stock maximum flow is not much different, around 112cfm with a bell on the port for both valve sizes, but at low-mid lift, which is important, flow may be greater with the bigger valve.

And my experiments with a small valve on an enlarged oval port limited it to around 130cfm, the bigger 40.5mm later BSA valve allowed over 150cfm. On a 30mm oval port 140+cfm is possible with the 40.5mm valve. The factory must have had around 128-130cfm on their best race tuned 650s which gave around 66hp.

To preserve a totally stock look, I'd use the bigger BSA valves and GP carbs and oval port the head for better flow and a nicer wider power spread. Even with a carb off it looks stock, so making it perform nicer for riding I think is worthwhile.


mark
Re: 66' Spitfire Head [Re: Allan Gill] #792369 12/08/19 6:19 pm
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Adam M. Offline
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Originally Posted by Allan Gill
, I’ve had 9k on a small port head with much more torque than the large port, they might even work better with the GPs


You weren't worrying about rods?
I closed my tachometer once on second gear, remembered about rods and back off at once. smile

Re: 66' Spitfire Head [Re: Adam M.] #792386 12/08/19 8:49 pm
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Allan Gill Offline
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Originally Posted by Adam M.
Originally Posted by Allan Gill
, I’ve had 9k on a small port head with much more torque than the large port, they might even work better with the GPs


You weren't worrying about rods?
I closed my tachometer once on second gear, remembered about rods and back off at once. smile


Nope, the battered original rods were fine to 8000, the rods from Thunder are a lot beefier.


beerchug
Re: 66' Spitfire Head [Re: Richard Phillips] #792409 12/08/19 10:43 pm
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Nick H Offline
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How to identify large or small port head, say in an eBay photo? True that the small port won't have the connection between the intakes?


1966 BSA Lightning
(2) 1967 Triumph "Choppa"s
1974 Indian ME125
Re: 66' Spitfire Head [Re: Richard Phillips] #792412 12/08/19 10:50 pm
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Allan Gill Offline
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Some do and some don’t. 50 years on and a lot can happen to anything.

Small ports have part number cast in front of the right inlet valve, inside the rocker area. Later heads have the part number between the ports. Also the small ports are noticeably thicker around the port on inlet.


beerchug
Re: 66' Spitfire Head [Re: Richard Phillips] #792614 12/11/19 4:39 pm
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Nick H Offline
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Thanks Allan, good to know. You have so much knowledge, I used to think you were a "grey beard"!
If anyone has a nice "small port" A65 head to sell, please PM me.


1966 BSA Lightning
(2) 1967 Triumph "Choppa"s
1974 Indian ME125
Re: 66' Spitfire Head [Re: Nick H] #792627 12/11/19 6:48 pm
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Allan Gill Offline
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Originally Posted by Nick H
Thanks Allan, good to know. You have so much knowledge, I used to think you were a "grey beard"!
If anyone has a nice "small port" A65 head to sell, please PM me.


It’s getting grey.... slowly. I used to just have too much time on my hands... now I have more projects but not so much time to do them.

I do have a head, but with postage etc you’d be better buying one from the states, most of the ones I have, come from there originally and there seems to be a lot more available.


Also worth noting that all (unless modified) 68-466 heads will have 5/16” rear studs, if using on a later engine these will need opening out to 3/8” easy enough to do as the original hole will guide the drill down if you use all sizes in between, just make sure any fash is cleaned up afterwards.


beerchug
Re: 66' Spitfire Head [Re: Richard Phillips] #792637 12/11/19 8:26 pm
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Mark Parker Offline
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There are photos of a small port head here:

The cast in valve seats are smallish, fitting a valve any bigger than 42mmwould need new seats.

https://www.eBay.com.au/itm/BSA-A65-Lightning-Cylinder-Head-With-Rockers/254344053393?hash=item3b38164291:g:QPoAAOSwFKldZzy0


mark
Re: 66' Spitfire Head [Re: Richard Phillips] #792639 12/11/19 8:42 pm
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Allan Gill Offline
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The 38mm valves do work perfectly well on a 650 though Mark.


beerchug

Moderated by  Allan Gill, Jon W. Whitley 

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