In the 1950's I seem to recall having the head of the Seven surface
ground to raise the CR but cannot remember how much was taken off.
At that time you could also buy alloy high CR heads but they were above my
I remember experimenting by fitting two amal motorcycle carbs, which
worked well and then bought an adapter to fit a twin choke Stomberg from a
Ford V8. I also recall hearing that one could change things such that the
exhaust ports became the inlets and 4 Amals could be fitted.
Colin Chapman (Lotus) was into A7's at the time and sold various mods to
improve braking and handling including a split front axle.
Cars were fun in those days.
Donald, South Uist
Instead of playing with engine tuning take the trafficators off, this
will add another 5 mph to it. <bg>
Visit the new Model Engineering adverts page at:-
Not tried welding on an Austin seven head but a friend of mine used to
raise the compression ratio on Talbot heads by adding weld with cast
iron rods and then machining. You have to heat the head to almost red
hot first to reduce thermal shock.
Early Austin seven heads were not very good and didnt have enough meat
to skim. The later, 1937 onwards, head gave a higher compression
ratio (5.8 : 1 instead of 4.9 : 1) and you can take up to 1/16 inch
off the surface. I used one of these on my special for road use.
Better still is to get hold of the head from an Ulster, Nippy, or
Speedy which can have up to 1/8 inch machined off. These have the
advantage that it will still be acceptable to the VSCC if applicable.
The alloy heads made post war are best if you can find one.
There you go then Charles, there should be a pile of old Reliants to look
through in Long Eaton, with just light shotgun damage & a few bloodstains.
umm, cast iron ones are best in my experience for welding cast iron. lol, in
all seriosnes, get some Murex cast iron rods, and warm them gently in the
oven before you use them (shhh i wont tell if you dont lol) also pre heat
the whole (or as much as possible) of the job as this will reduce the
tendency of cracking due to thermal shock, then weld away to your hearts
content, but DO NOT use anything to cool it with when you have finished, or
you may find yourselve with more problems than you started with.
Hope this is of some help
From the Keyboard of Tim Bird
Visit my updated website @ www.timbird.net
Welding is not my forte. Anything that gets hot enough to hurt me is not
really my thing. I have a little Clarke gasless mig for emergency repairs
but avoid using it like the plague. Everything I try and weld turns into
little lumps of pigeon crap which may or may not stick to the job. The usual
advice with cast iron is get it as hot as possible before welding and let it
cool slowly afterwards. Your chances of ending up with a cracked head are
fairly high though and I wouldn't entertain it personally. Someone else may
have better advice.
Dave Baker - Puma Race Engines (www.pumaracing.co.uk)
Welding cast iron can be a b***ch. Problem areas for a used castings
1/ oil in the pores - even baking for hours at 300 deg C doesn't
always get it out
2/ lack of tensile strength. When the weld pool solidifies it
obviously shrinks and the surrounding material is too weak in
tension. Often a repaired casting may look sound, but fails parallel
to the weld in the heat affected zone.
Nickel rods seem to be best, and as soon as the pool solidifies in
needs to be peened to relieve the stresses. Best to work in small
areas distributing the thermal stress.
Can you not machine a flat on the combustion chamber, and fix a
suitably shaped piece of cast iron with bolts? If you want to increase
the compression ratio why not skim it, or modify the piston crowns ?
The material needs to be added around the base side of the spark plug
to reduce the volume over the cylinder. Skimming may work up to a
point but you've still got the plug in the middle of the cylinder.
Another thing I remember is that you have to be careful when raising the
CR too much because the two bearing crank deflects at high revs and you
could end up with the middle pistons hitting the head.
Changing to a three bearing block and crank was not a solution because
introducing the third bearing weakened the crank and these later engines
were no good for souping up because of that.
Donald, South Uist
the problem of welding bits inside the combustion chamber is that the
burning pattern of the fuel combustion will not be even...thus will shorten
the life of the engine,,it will also end up pinking a the raised weld will
glow hot as the engine heats up thus ignighting the fuel mixture before the
normal piont of ignition ei if the spark occures 8degrees before top dead
centre then it will end up at any point between 12 to 8 degrees tdc (top
dead center) this will then end up causing failer of the bigends ,,bores etc
combustion chambers are designed to keep the combustion presser even over
the top of the piston as much as possible thus giving equal pressure all
around the top of the piston so as not to push to hard on one side which
will cause exccessive waer in one side of the rings and bore,,
another problem is that if you weld abit into the combustion chamber then
you can loose power as the fuel burns quicker at one end before the othe
thus the presser caused by the ignition is thus weakend,,
the only save method is to get the head scimmed,, obut whether u need one
mill or less depends on the engine,,
get a presser guage and put it in place of the sparkplug and turn over the
engine will allow you find out your pressent combustion level..but on this
type of engine i would not raise it to increase the power as it will end up
(as some one else on here said) dammage the main bearings and possibly
break the crank
if you want abit more power why not change the engine?? these rear wheel
drives are very easy to do
a diff. opt. iff head not cracked is heat head hot then fill wit
brazeing rod. down side is cannot be welded with nickel rod after a
brass sinkes in and will mess up further welding. :rolleyes
View this thread: http://www.rcgroups.com/forums/showthread.php?threadid5090
It can work and is done on American cast iron heads by drag racers.
The weld material is used to fill the combustion chamber and is then
ground out to get the desired shape and volume.
I read about it recently but can't remember where, but IIRC the head
is heated to a dull red color and held at this temperature. Cast iron
rod is used to build up the combustion chamber and the head is then
slowly cooled in wood ash, vermiculite or wrapped in a thermal blanket
In some cases this technique is even used to relocate sparkplug holes.
Hope this helps.
On Thu, 24 Mar 2005 22:43:49 +0000, Charles Ping
recently but can't remember where, but IIRC the head
I think this was done to some Cleveland pro stock engines, the heads
only had to survive a few runs though. They relocated the plug and
with hand finished piston crowns got 14:1. it has probably been done
to every other type of engine raced in prostock before they used
furnace brazing iron heads was common enough, Swaymar used to chop a
chunk out of Cologne heads and put a new bit in to give three ports
and people used them on road engines!!!!!!!!!!
why not have Arias knock up four pistons.
Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here.
All logos and trade names are the property of their respective owners.