Silver7

Could someone possibly explain to me what is causing this groove at the beginning and end of this primary port? I'm not sure if its the corner seal or the side seal causing this wear pattern. I am also up for suggestions on what can possibly be done to salvage the housing. If the side seal is scratching the port then I am tempted to port out just a hair further and bevel the end of the port so that it makes a smooth transition back to the housing surface. If the corner seal is causing this then I might be in trouble.



The engine ran fine but then I started loosing compression because the RA apex seal springs were weakening. I took the motor apart just to replace the apex seal springs with stock mazda springs and this is what I found. I will be investigating the cause sometime during this week but I thought I'd post a pic and maybe get some ideas first.

Barry Bordes

What does the compression side of the plate look like? If it also has a groove I would guess too tight a clearance on the side seals.



This is what mine looked like from running .002" clearance.

Lynn E. Hanover

The mark is from the trailing end of each side seal dropping into the port. That will round the end of the seal off and drop compression. It is possible to get good life from this situation, by: raising the top outside of the port opening a bit, so that the seal comes back onto the iron from inside to outside. This lifts the seal up before the end can hit the port opening.



Also: radius and polish the closing line a bit. And where that mark is, reduce the surface a thousandth or so over about 1/4". Just follow the line above the port. If the engine has not run very long on new side seals, just turn them over to get rid of the rounded corners. Do the same at the bottom of the port where the similar mark is. This damage happens at low RPM where the seal ends have time to drop into the port. In racing "J" ports I port ouboard until the leading end of the seals is just supported all the way across the port opening. If you assemble the pieces to spin a rotor around on this iron you can ink up the path with a Majic Marker and put a scribe into the end of a side seal groove and turn the rotor and crank to scribe the path of the trailing end of the seal. The scribe will fall off of the port edge.



The trailing end falling off is OK if done as above. Never port out so far that the leading end falls off. The iron is ruined then.



A tight .002" is OK for the street. A tight .001" is OK for a NA weekend machine. An All out NA road racer I use zero clearance. So long as the seals and the corner seal will pop back up when depressed, that is enough.



Lynn E. Hanover

Lynn E. Hanover

The deeper wear pattern across both TDCs is a function of the engines geometry. In some of the side seals path it is being dragged side ways across the iron, but at the two TDCs it is moving in line, like a knife blade trying to cut something. So, much more side seal moves across that iron than any other iron in the engine, so it wears more. The hot side wears more as the hotter metal is more easily worn away. While side seal end clearance has no affect on this, you can reduce the wear slightly by breaking the leading corner of the side seal about one thousandth with a diamond file on assembly, and run a synthetic 2 cycle premix top oil.



So if you drag a knife blade down your leg while held at 90 degrees to your leg, it may not cut your skin.

(like shaving each morning) However, if you drag that blade in line with your leg, you get cut.



Another of lifes unit pressure problems.



Lynn E. Hanover

Silver7

Lynn - Thanks for the explanation. I finally caught up with Judge Ito today and he explained in person some of the things you discussed. I now have a better understanding of what is happening and what can be done to correct the port.