Hi Doug, Three problems jumped out at me.

1. When you break the liner wall
with your new insert, you will creat a flat spot unless you have the capability
to machine the combustion chamber end of the insert EXACTLY to the trochoid
shape. Not going to be easy.

2. Your description of the insert sounds like a
rectangle with radiused corners or full radiused ends. Either case, the
"straight" side of the rectangle will present a "tripper" line that the apex
seal must cross. This may have a tendency to "trip" the seal as it passes and
start a resonance, a chatter, or even break the seal. A large (5,9, even a 15
inch) radius on the "downhill" side of the insert will provide the apex seal a
ramping off effect (two point contact that converges to one point then it's off
the insert and moving totally on the liner wall again). This configuration will
be difficult to match machine. Perhaps the easiest approach is to machine a
round plug set and contoured like Paul L. does the p-port inserts. The liner
end and the outer end can be left round and the portion within the water jacket
can be milled to whatever shape you desire. You still have the problem of
contouring the combustion chamber end. But this would would provide the apex
seal a path onto and off of your insert that is already known to work as
evidenced with ths success of the p-ports already made.

3. Ask Paul L. to check
with his p-port welder about the possibility of excessive heat build-up. It may
be impossible to weld a big glob of stainless steel into the liner where it was
possible to weld in a thin walled tube. The heat required may destroy the
aluminum behind the liner. Also, where the insert plug exits the housing, do it
just like the p-ports. Why reinvent the wheel? ; ) Dave M

Yes I think one would run in difficulty welding in a plug sized chunk of SS.

Paul Lamar


Dave,

Thanks for your thoughts.  This area is very hot, and requires water
flowing around the insert so a technique like Pauls  'weld and bond`
P-port is not going to work. Two plug inserts screwed in with sealant
would be the ideal way to go but that still leaves the existing hole to
plug and then we are back to placing the dual plugs farther out again to
avoid  breaching the existing boss.  The housing is significantly
weakened as well.

Any time the inner liner is breached there will be a need for some
clean-up work to radius the inner edge. This can be seen on any  hole
that Mazda puts into the housing.

Granted about welding problems you are correct but not because of the
mass of the insert. It is not aluminium but stainless 303 which has low
thermal conductivity with weld penetration  measured in tenths of
millimeters.  Agreed the biggest buggaboo is welding anything to the
inner liner, which micro flexes.  Welding causes the metallurgy to
change and become embrittled adjacent to the weld.   Chromium migration
I am told. The best weld IMHO on the P-Port or plug insert would be to
back them out a 0.6mm  and do a fillet weld.  Adding material with a 0.5
mm rod.  I don't have the skill to do this but the guys down the road
do it every day.  Paul has seen their work.

Still the biggest question I have is what effect is there on performance
when the leading apex seal goes over a larger area depression?

Skip how did you do your dual plugs?

Doug in Japan

Hi Doug,
Your "two separate inserts" idea sounds good. The apex seal will thank you : )
Remember to calculate the max stress generated by the pressure of combustion
against the exposed disk area of the insert. This stress needs to be split
between the weld at the liner and the threaded end at the housing's outer
surface The welds you suggest sound like "sealing welds" and may be too small
to take much force so most of the stress will need to be taken with the
threaded end in the aluminum housing. Is the aluminum thick enough there to get
sufficient thread bearing to insure the insert doesn't strip the aluminum
threads and blow out? Sounds like each insert will need to be in the 14 to 16
mm dia range. Do you have a particular spark plug in hand that you can
specifically design around? If so, you could have a 16mm body for the insert
threads and neck the insert down to only what is necessary to provide a spark
access, that would give you the smallest disturbance to the liner (and to gas
by-pass....ie performance). Dave M

--

Dave

Thanks. You mentioned perhaps the biggest reason a housing with leading
dual plugs should be designed from the get go.  That is the force of the
combustion event against the threads.  This explains why the current
housing plug boss design is so robust.  It also explains why there is a
little half moon ridge near the plug holes on the outer housing.
Beefing up the housing to account for loss of strength near the large
breach no doubt.   I suspect but haven't confirmed yet that there is a
stainless boss welded to the outside of the liner near the plug hole.
That would make sense because the flame propagation starts there.  Nut,
screws and bolts !%#`!

Next idea.  Common ground Y shape Siamese twin plugs that fit into the
present 14mm hole.

One less hurtle or one more concern?

Doug in Japan