So, I'm putting together a 12A for Improved touring racing - stock ports - no porting allowed.



I pulled apart my existing motor and found a broken side seal and a broken apex seal along with a few broken corner seals.



This motor was a Mazda reman that I bought in 94. Put about 20k street miles on it and then used it for 2.5 seasons of IT racing.



I was expecting the housings to look really bad, but they actually look pretty good - virtually zero chrome flaking, no deep groove from the seal corner.



But there are visible chatter marks all along the housings. They feel totally smooth except in one small area, near the edge of the housing.



So, my questions are:



1. How do you assess chatter marks - how bad is too bad? How much will this affect top end power? I'm tempted to re-use the housings, but I am not sure how much performance I'll be giving up. Pic's attached.



2. I've been revving to about 8-8.5k - using stock apex seals. Is that why the chatter marks are there?



3. I'm wondering about carbon seals, but concerned they won't last long before requiring a rebuild. Also heard that they chip easily. Do I need carbon seals to prevent damage to the housings at 8.5k? Ceramics are not an option.



[attachment=44580:general_marks.jpg]

[attachment=44581:marks_ne...ug_holes.jpg]

[attachment=44582:close_up_plug_hole.jpg]

[attachment=44583:uneven_part.jpg]





Thanks,

Neil

 

The chatter marks will increase wear on carbon seals, so if you have some used ones on hand I would put them in. I would not buy new and use them in these housings. In new housings and proper premix, the seals and new housings will last for years of racing. I would put the steel seals in these housings.



New springs. Break the edges of the seals with a diamond file. The over 8,000 RPM with lots of heat gets the chatter marks going. The steel seals can bounce over the hump at hight speed. It never gets better with time. Run one ounce of a good synthetic 2 cycle top oil in each gallon of fuel, even when running the stock OMP. If the OMP is still used, then I would not run a synthetic in the sump. Perhaps Valvolene racing 40 or 50 wt. When the center of the seal gets hotter than the edges, it bows slightly and drags more in the center scoring the area around the plug holes as shown. You need to run richer all around to get the EGTs as low as possible.



The carb may have needles that have a spring inside them. I replace that spring with a bit of tubing from the inside of a Bic pen, to make the needle rigid. The rubber tip on the needle is fine. Then you can run a bit more fuel pressure and a bit higher float level to go richer. A piece of hose over the bowl vent run up a few inches higher into the air cleaner will help with cutting out in corners. I don't know if that is legal. There are other mods for the stock carb, that are no doubt not legal.



Get the EGTs into the 1600s at the top and more power will be yours. They lean out and go flat at the top with the stock carb. From years in the IMSA racing stocks series.



Lynn E. Hanover