Hi,

I have a cylinder head and wanted to install larger valves. I was
hoping that someone could give me some info on the general procedure,
most importantly, can I do it myself at home or do I need an
engineering place to do part of it?

Do I have to replace/cut the valve seat?

It's a 12g940 Mini head with 1 5/16ths inch inlet valves. I want to
increase the size of the inlet valves to 1.4inch (as in the MG Metro
which uses the same 12g940 head casting but is fitted with the 1.4
valves as standard.

Cheers,
Dave

It would likely be cheaper and work better to swap the head. Maybe a
rebuilder will take you old head in as a core and give you a good price
on a rebuilt?

I swapped the head on my old 1275 for one with the larger valves. If I
remember right, the internal passages are larger as well to handle the
increased valve flow. (this was on a late 60's vintage, things might
have changed)

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's

Skirrow wrote:

This is pretty much a machine shop job - it's possible to do at home, but
only with an investment in tools well beyond the cost of having it done for
you. To make this work, you need to have the valve seat cut larger to suit
the new valve size, you need to have top and bottom cuts to blend the new
seat (the old "three angle valve job"), and you really need to smooth out
and open up the bowl under the valve at least, to gain an advantage from the
larger valve. If you have a cylinder head rebuilder do it, they will do a
regular valvejob and refit the valves for you, but they probably won't do
any of the flowing and blending work.

You know of Minispares, of course - check out their website for
remanufactured and prepared heads. When I was racing Mini's a few years
ago, I did my first heads myself, then just bought them - cheaper in the
long run!

Cheers, Brian


"Skirrow" <daveskirrow (AT) btinternet (DOT) com> wrote

In article <_11ab.71629$PD3.4748729 (AT) nnrp1 (DOT) uunet.ca>,
Brian <brian.evans@mci%%%.com> wrote:
I'd say keep it in the 'family' and check out Dave Baker at Puma
Racing who posts here. Seem to remember he's a wizard with A Series heads.

--
*Fax is stronger than fiction *

Dave Plowman dave.sound (AT) argonet (DOT) co.uk London SW 12
RIP Acorn

Thanks fellas, I've looked at heads from Minispares etc but the prices
are far to much for me which was why I fancied having a go myself.
I've read and re-read David Vizard's "Tuning the A-series engine" and
I'm ready to spend hours in the garage with a dremel enlarging,
de-shrouding, porting and so on to Vizard's specifications. It just
seemed a shame to do it on a head with standard valves.

What would I use to cut the valve seat if I decided to do it myself?
And what other tools would I need aside from the usual head rebuild
stuff?

Perhaps I'll just get a head of an MG Metro (already with the larger
valves fitted) and grind that to the Vizard specs.

"Skirrow" <daveskirrow (AT) btinternet (DOT) com> wrote

snip
You are right, a good option is to get an MG Metro head if you can find one.
However there is a 'cheat' I heard about 30 years ago. First, get the valve
seats recut for the larger valves. You then have seats that are wider than
the lands on the valves. Then put some engineering blue on the valves and
drop them into their new seats (you need the guides in of course). Take out
the valves and you now have the dimensions of the new seats marked out in
blue. The unmarked material needs to be removed. You may find the Dremel
very slow - you need a decent flexible drive to attach to your meaty mains
drill. Not expensive but get a good one as mine ran its bearings very
quickly. Or do you have a pillar stand for your drill? This will give you a
nicely vertical valve throat - just put a grinding stone of suitable size in
the drill and bring it down into the throat. By this time you will have
removed the old guides so you can do all the Vizard-style port shaping, for
which you will need the flex drive. The advice about 3-angle ports is
important but you have the Vizard book so you won't forget that. If you must
cut the seats yourself you will need the correct cutters but not worth
buying them so find a decent machine shop.
This approach is not ideal but I used it on a 1098 Sprite head in 1972 and
it easily blew my mate's Spitfire into the weeds. Later on though the head
cracked between 2 seats so you might want to have it tested before you
invest all that time.
If this is for road use you can get away with standard valve guides.
Apparently they last longer than the bronze ones, although the latter are
much better for sustained high revs as in racing.

In article <RAdab.2419$I9.2028 (AT) newsfep4-winn (DOT) server.ntli.net>,
Les Rose <**lesrose@**ntlworld.com> wrote:
For information, B&Q have a rotary cutter under their PPPro range which
sort of replaces the Rotozip, and this includes a flexible drive. It's
also a router. The motor is 500 watts plus so should be up to the job.
I've not used it for this sort of work, but it looks like it should be
suitable in a DIY sense. Not sure about the price, as I got the older one
at clearance time for about 50 quid.

--
*Suicidal twin kills sister by mistake.

Dave Plowman dave.sound (AT) argonet (DOT) co.uk London SW 12
RIP Acorn

Skirrow wrote:


Not the first to tell you this but Swap the head for a Metro one much
easier, fitting bigger valves is major work even with the right seat
cutters and a high speed die grinder.

Skirrow wrote:


Standard A+ head is MUCH better than the average modified A series,
same goes for the carb and manifd.

sp4mtrap (AT) hotmail (DOT) com (-AD-) wrote in
news:MPG.19d3953790c0c791989b5a (AT) news (DOT) cis.dfn.de:

Sorry to hijack the thread - whats the advantage of a bronze guide?
Is it worth using when trying to build a bulletproof, reliable and slightly
more powerful 1257gt based engine?

I ask as I'm about to rebuild a head, and it badly needs new guides (
<http://www.raromachine.com/mini/engi...20Strip%20014-
small.jpg> )- thought it already has hardened seats!

splam