Porting Your Cylinder Head For Power
Dyno tests in the days of racing Zephyrs, showed the Zephyr
head could be worked very satisfactory and with installation of extra
carburation and headers could come very close to Raymond Mays performance at
far less cost with the better heat retaining characteristics of cast iron.
The Mklll head (213E) with matching manifolds is the best
head marked with an “H” above the intake flange for High compression. Zephyr
and Zodiac Mklll's have the same head. The Mklll head marked with an “L”
resembles a Mkll head. When installing this head on the earlier motors, use the
Mklll rocker gear, pushrods and oil feed pipe. If running a standard cam, the
block face of earlier Mkll and Mkl blocks are often left free of the valve
reliefs that are standard in Mklll block deck faces. However, I do recommend
these reliefs are ground in with a porting tool as mentioned in the engine
build article as this will allow for higher lift cams, valve float and valve
unshrouding for extra flow. Use the Mklll head gasket as a guide for the relief
and do not go within 60thou of the top ring groove area of the piston
at TDC.
Here are some porting web sites that give tips on general
porting.
http://www.sa-motorsports.com/diyport.shtm
http://www.mondellotwister.com/ArtHeadPort.htm
http://www.mondellotwister.com/ArtPtngAtHme.htm
The basic idea is the same regardless of the type of 4
stroke OHV engine.
I would also recommend a 3-angle valve seat to be cut into
the head and inserts for unleaded are a matter of preference (we have a link in
our FAQ section regarding this topic).
The exhaust port and D plate should be slightly larger than
the head exhaust port to stop reversion which fouls the combustion mixture,
more so in long duration cams. Do match the intake manifold and gasket to the
intake port. I recommend a 60-80 grit sand roll finish to the intake manifold
and intake ports to help keep fuel in suspension. However, there is an
advantage to keeping the combustion chamber and exhaust port polished smooth to
retard carbon build up.
There are some minor extra details in our Engine build up
article on this site as well.
The above article shows (Practical Motorist September
1963-writer Alan Witney) the installation of double valve springs, I found
Triumph 2000 inner springs were a good mock up though minor machining for the
spring seat on the head is a worthwhile step often over looked. However as
detailed in the Engine build write up on this site, new stock single Ford
springs work to 7000rpm with stage 3 cams .To much spring pressure can be a bad
thing leading to excess cam and lifter wear as well as accelerated rocker shaft
wear.
Below is a 150mm bench grinder with a 1/8-die grinder cable
attachment. This was $55NZ at K-Mart. I have seen them at varying prices at
other suppliers. The attachment has spanners supplied and is useful for fine
work around valve guides and under the valve seat. It also has lots of torque
with the flywheel effect of the grinding stones. Do pre-lube the cable with
3in1 oil from time to time.
The below stones are Japanese made ones and are 1/8 shaft
size. Get good quality ones, as they are not always glued onto the shafts
correctly. These were $9NZ for the set on the white card at a Mitre 10 Handy
man store. The other stones are 1/4 to 6mm stones, which are useful for
combustion chambers and for removing minor cuts left behind from the carbide
cutter. The carbide cutter next to the white ball stone, goes for around $60NZ,
get the best quality one you can afford and it will cut through old cast iron
like a knife through butter. Do keep the power tool moving in a circular
direction all the time. These are available in different shapes and shaft
lengths. Make sure you get "double cut" and not ones meant for alloy.
The sanding drums were $10NZ for what you see there and are handy for
finishing. Use CRC or Auto trans fluid etc for keeping the drums from clogging.
I used the below 500w power drill for most of my porting
with the carbide cutter and it worked fine. Now in New Zealand, good
inexpensive electric die grinders are hard to come by, if you go with air,
you need at least a 2.5HP compressor with a large 40L tank. I would also
recommend one with a front exhaust on the hand piece to keep the work area
clean. I myself prefer electric.
This is my secret: I get the smallest, slimmest router for
woodwork I can find. These have ample wattage (the one shown has 830w) and are
usually variable speed. They are also use to side loading. My one was $89NZ and
came with a 2-year warranty and replacement bushes. I also have found a slimmer
400w one.
As you can see from the below picture, the router easily
slips out of its frame to make for a very useable tool. Ebay is also a good
place to find die grinders, check voltage in your county
though! (Keep an eye out for a Makita copy of 240-300w).
SAFETY
Make sure you wear very good eye protection. I would
recommend a flip top shield instead of goggles as I have brushed metal
filings into my eyes while washing up that have been in my hair/eyebrows. Not
fun when they rust!
Ear plugs/muffs plus a throwaway paper dust mask is also
recommended as well as good lighting. Make sure the head is well supported and
I use an earth leakage protector on electric tools. These go for $29NZ and
are plugged in at the WALL end.
Disclaimer:
The advice and guidelines given in these articles are given in good faith.
The owners and managers of the Galeforce Zephyr site will take no
responsibility for any injuries or loss sustained while carrying out the
described tasks and procedures or any consequences arising. Please read
the Safety First
Article