The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: Humble Pie on 20.10. 2010 15:58

Title: Which A10 Iron Head do I need ?
Post by: Humble Pie on 20.10. 2010 15:58
ok , I want to run a iron head on my 63 A10 ( originally an alloy head ) it is an SR motor,,what iron head will work best for this ?

Do I have to change pistons?

Thanks
Title: Re: Which A10 Iron Head do I need ?
Post by: bonny on 20.10. 2010 19:25
i'd imagine you'd have to drop the compression ratio a bit with an iron head as the iron head couldn't get rid of the extra heat as quickly.
Title: Re: Which A10 Iron Head do I need ?
Post by: trevinoz on 20.10. 2010 21:46
The question is, why?
A Golden Flash head will do if you can find one.
You shouldn't have to change pistons as plenty of A10s were upgraded to high compression in the old days with no ill effects.
Trev.
Title: Re: Which A10 Iron Head do I need ?
Post by: bonny on 21.10. 2010 00:09
can i ask why you want to run an iron head on what is otherwise a reasonably high performance engine ? my bike came with an iron head when i bought it ( it actually turned out to be an a7 head) i did pick up an alloy head but money and time constraints mean i can't fit it yet, the only advantage i can think of is an iron head will make for a quieter engine compared to an alloy headed one.
Title: Re: Which A10 Iron Head do I need ?
Post by: Humble Pie on 21.10. 2010 01:09
don't need a performance motor and just want something that will last

Motor needs a rebuild ( just cause it has been sitting so long ) it's a good clean motor

and I'm just odd like that :)
Title: Re: Which A10 Iron Head do I need ?
Post by: Rocket Racer on 21.10. 2010 03:58
You can run any A10 iron head and if you happen to have flat top pistons, could even run an a7 iron head if you wanted.
being a late motor you would find the early small fin heads would look a bit odd! but excluding the very early long stroke heads you can run whatever (big fin) head you fancy.
The iron A7 heads wont like any raised piston crowns on your a10 without reshaping.
Nothing wrong with the alloy heads either, these days worth considering fitting hardened valve seats whatever your preference if you want longevity with lead free fuels.

We're all a bit odd  ;) we ride old beesa's!
Title: Re: Which A10 Iron Head do I need ?
Post by: iansoady on 21.10. 2010 11:50
I wonder how much real, as opposed to theoretical, performance advantage is given by the alloy head? My iron-headed Flash seems quite brisk off the mark, and is certainly at least as fast in both acceleration and top speed terms as the Velo Venom it replaced*, as well as offering a more relaxed back-roads ride. But that's in real world conditions, not on a timing strip.

*Surprisingly, it also seems to handle better (at least up to 70 mph or so) - I used to get a distinct wriggle on white lines / road grooves on the Velo whilst the Flash is rock steady. Suspension, bearings etc on both in good condition. On looking at the frame, the BSA does have a much more rigid looking structure whereas the Velo frame is very obviously derived from the rigid.

No doubt howls of protest from Velo owners but again this is my experience of 2 specific bikes.
Title: Re: Which A10 Iron Head do I need ?
Post by: Humble Pie on 21.10. 2010 13:34
Yeah,I figure sell the alloy head ,,find a good Iron one,,ebay seems to have pistons now and then so should be good.  Any difference in the push rods between Alloy and Iron ? and can I use the 357 Cam without issue ?

Also what head casting # do I want to look for for late iron head ?
Title: Re: Which A10 Iron Head do I need ?
Post by: brackenfel on 21.10. 2010 19:20
Hi Ian,
No howls of protest but what tyres did you have on the Velo?? My Viper shod with a mix of modern profile Avons ( AM20 / AM21 Super Venom) is rock steady whatever you do to it & will surprise much more modern or "sportier" bikes on the bends..
I've bought some AM26's for the A10 for when it's back together. The rear one is already on (just), the front one will follow it. The perfectly good SM Mk2 that was on the back has been taken by the good mate who helped me get the Roadrider on  - he loves them, I don't...

As for iron heads, I bought mine with one & have no immediate plans to change it.. Seems fast enough to me & is a lot quieter....

Cheers,
Adrian
Title: Re: Which A10 Iron Head do I need ?
Post by: Humble Pie on 21.10. 2010 21:30
but wait there's more ,,questions that is.  Can I use the 67-206 Rocker box on the Iron head or are alloy and iron rocker boxes not interchangeable ?
Title: Re: Which A10 Iron Head do I need ?
Post by: trevinoz on 21.10. 2010 21:36
You can use the rocker box but valve springs, valves and colletts are different.
357 cam will work but the smaller Flash valves will hamper performance.
A Rocket engine looks so much better than a Flash engine due to the alloy head.
Trev.
Title: Re: Which A10 Iron Head do I need ?
Post by: Rocket Racer on 22.10. 2010 00:20
357 cam will work but the smaller Flash valves will hamper performance.
A Rocket engine looks so much better than a Flash engine due to the alloy head.
Trev.

Trev,
while I too prefer the weight benefits of an alloy head and prefer the top end benefits of big valves and a hot 357 cam, these are subjective preferences. There is a lot to be said for both softer cams and the torque of smaller valves if the rider wants a "nice" ride. For a roadster, I would happily run a small valve head, but again all down to personal preference and riding requirement.
Tim
Title: Re: Which A10 Iron Head do I need ?
Post by: iansoady on 22.10. 2010 10:21
Hi Ian,
No howls of protest but what tyres did you have on the Velo?? My Viper shod with a mix of modern profile Avons ( AM20 / AM21 Super Venom) is rock steady whatever you do to it & will surprise much more modern or "sportier" bikes on the bends..

Cheers,
Adrian

Adrian,

In fact my Velo had similar tyres to yours and the BSA is on Avon SMs! As I say, it is only my experience and it could be there are factors I am unaware of. The Velo was fine on well surfaced twisty bends (and as you say would keep up with much more modern bikes although being left in the dust on the straights) but it was the longitudinal grooves that made it wriggle - not enough to be frightening but certainly noticeable.

I wonder whether the more compliant modern tyres were a contributor. I am currently rebuilding the A10 wheels and had intended to replace the SMs with something a bit more modern but am now inclining towards keeping them as they're fine on dry roads and I do not intend to use it much in the wet having had my fill of long miserable soggy journeys over the last 40+ years. The Hinckley Tiger is far more comfortable in these conditions.
Title: Re: Which A10 Iron Head do I need ?
Post by: brackenfel on 22.10. 2010 14:27
Hi Ian,
My A10 hasn't been far enough to make comparisons.. Sadly I bought it about a year ago with the intention of riding it and about a month later the "sorting" started.. One thing led to another & it's still off the road.

I too try & avoid the wet, it's just that I don't like the squarish section on the SMs as you can feel it if you get too near the edge. Can't make a comparison between the Velo & A10 yet but I'm looking forward to doing so!!
I keep the Velo tyres pretty hard, I must contact Avon & see what pressures they recommend for the AM26 on te A10..

All the best,
Adrian
Title: Re: Which A10 Iron Head do I need ?
Post by: Humble Pie on 22.10. 2010 14:30
ok then :) so what would be the correct # on the head I'm looking for :D

Have some SR cases I'll trade for one
Title: Re: Which A10 Iron Head do I need ?
Post by: chaterlea25 on 22.10. 2010 16:45
Hi, Humble Pie,
Just my opinion here, I would stick to the alloy head that you have already!, I'm presuming this is for the 63 SR engine you asked about (am I mistaken?).
Or have you more than one project on the go??
 I cant see the reasoning to opting for an iron head over alloy????

I am very interested in a (very good) set of late SR cases, DA10R xxxx
If someone has an iron head for you perhaps we could make a 3 way deal?

I have an earlier (RR)alloy head available, its still on an engine so I havn't examined it closely yet

Regards
John O R
Title: Re: Which A10 Iron Head do I need ?
Post by: Humble Pie on 22.10. 2010 17:15
I'm set on what I want to do ,,yes it is the 63,, I have 59 CA10R 83XX cases and Cam  ( 59 SR )