The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: bonny on 18.06. 2010 16:51

Title: cast iron or aluminium ?
Post by: bonny on 18.06. 2010 16:51
which do you think is better for everyday commuting ? a cast iron or aluminium cylinder head ? i have both though the ally one needs a bit of work before i could fit it . is the cast iron one more robust in everyday use ? 
Title: Re: cast iron or aluminium ?
Post by: trickytree on 18.06. 2010 17:14
I cant comment on "A" series heads but of all the motorcycles I have ever owned they have all had ally heads and not one of them has fell in two while riding it. A valve seat fell out of my 500 Morini while in Austria once but then Morinis are Italian and as the electrics were working at the time so I supose the bike thought it owed me one.
Title: Re: cast iron or aluminium ?
Post by: mike667 on 18.06. 2010 20:17
what on the bike always worked pretty good 4 me
Title: Re: cast iron or aluminium ?
Post by: muskrat on 18.06. 2010 20:35
G'day Bonny,
                     Alloy heads, besides being much lighter, disperse heat better. Hence the use on the more sporty models.
Cheers
Title: Re: cast iron or aluminium ?
Post by: Rocket Racer on 19.06. 2010 01:52
my understanding is that the early small fin iron heads run hot, but the latter big fin ones are fine for normal use.
The other variables being engine state of tune and climate.
My cast iron B33 is bullet proof, but in a fairly low state of tune and I dont live in a very hot climate.
I'd use the head that needs less $$$ spending unless the looks matter. certainly for commuting.
Title: Re: cast iron or aluminium ?
Post by: Brian on 19.06. 2010 02:11
Technically a alloy head would be better for the reasons Muskrat has mentioned but in reality it doesnt matter that much unless you want to start exploring the outer ends of the bikes performance. The iron head will perform and last perfectly well so use it unless you want to spend the money repairing your alloy one.

As for the story that small fin heads run hot, a load of rubbish, old wives tale. Maybe if you put 10-1 pistons in or something like that but under normal use they are perfectly ok. Mine have been subjected to some very harsh conditions and I havent had any top end troubles yet. My plunger A10 (and the A7) regularly gets ridden in the summer on days up in the 40 plus degree C's, usually reasonable distances and always at 65mph or round abouts and it (they) havent given me any trouble (yet). Mind you the bottom end has just crapped itself on the A10 but thats another story.
Title: Re: cast iron or aluminium ?
Post by: Big Nick on 22.06. 2010 21:05
i use a cast iron one and use the bike for commuting
Title: Re: cast iron or aluminium ?
Post by: beezalex on 22.06. 2010 21:28
The only times I've had trouble with my small fin iron head was when really spanking my plunger A10...and I mean either steep mountain climbs that go on for miles at full throttle (trying to hold 70) or going flat out at 80+.  What happens is the exhaust valve clearances open up and she starts to detonate through the exhaust.  One night while riding with some buddies, mostly on triples and Hinckleys I actually pushed her to the ton but after a few seconds of that, she lost power and shot three-foot flames out of the exhaust.   *eek*

I would also surmise that none of this would happen with my bike if it didn't have 8.5:1 pistons in it.  I would prolly stay around 7:1 with an iron head.
Title: Re: cast iron or aluminium ?
Post by: mike667 on 22.06. 2010 23:20
and shot three-foot flames out of the exhaust.   *eek*


Nice - wish i'd been there 4 that Alex!
Title: Re: cast iron or aluminium ?
Post by: Big Nick on 23.06. 2010 22:05
Alex top man !