Rotary Engine build Blog

12A, Colorado Rotary Engine shop, vintage racing 12A

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7 Min Read

Rotary Engine REbuild / refresh 12A vintage racecar

Vintage Rotary Engine rebuildRotary Engine Shop in Colorado | We have customers that still run the 12A engine in their vintage race cars.

 
Why? Because these smaller motors are tough.
 
Do the right maintenance, use the proper process when building them, with solid cooling systems, these motors will last for years.
 
One of our builds from 2017 came in for some TLC. Here we have a 12A motor with a street port, weber carb, header, upgraded oiling system and larger radiator / electric cooling fan.
 
Here is a pic of that motor when it was built in the winter of 2017, lapped housings, FD stationary gears, polished rotor housings, etc.
 
12A vintage racing engine buildThis motor was built with the combination of two older 12A's to make one good one. Lucky for the owner, he brought me two motors that were out of automatic rotary engined cars.
 
Why is this preferable? Because these motors were not beat on as hard as a MT car would have been back in the 70/80's.
 
We mixed and matched the best components to build a solid motor.
 
After 6 years of racing in the Rocky Mountain Vintage racing club here in Colorado, we did a compression test and recommended that the motor come out and be freshened up.
 
Good thing too. The first thing that we look at is how it comes apart, fortunately it came apart as it should have with normal wear on bearings. Everything looked good with the exception of the apex seals, closer examination showed us that taking it apart was very good in terms of preserving the life of the rotor housings.
 
The rotor housings were showing early signs of wear on their outer edges. This is due to the apex seals bending. Because I have been involved with this car / motor from the beginning, once we got the camera mounted in the car for analysis (several years ago), I was shown that the car would sputter on the top end pulling down the long straights. Getting a camera saved this motor from self destruction. I can't emphasize enough how important this is, drivers feedback isn't as reliable as looking at real data.
 
12A engine in for rebuildSure enough, the car was running out of fuel on full pulls. I encouraged them to bring it in and let me evaluate the fuel system and make adjustments. This type of driving (avoiding the issue) caused the motor to go lean (only for a few seconds) and creating high combustion temperatures, thus the bending of apex seals. Two years ago, we modified the fuel system with larger fuel lines, proper venting and enlarging the float bowl of the weber carb. The motor pulled hard and we had the camera to verify down the long straights of road course racing by looking at the gauges at that critical moment.
 
Please note: Using a camera like our Cambox visor cam is a critical piece of hardware for us builders, especially when cars like this do not have data logging ECU's. Details matter.
 
What else did we find?
 
Rotary Engine Shop ColoradoA couple of things, the oil pump was needing replacement, these things wear out, pretty normal. The rotor bearings were needing replacing (with new competition race bearings) and of course replacing all the seals, springs and oil control rings. It was noted that is was spitting oil residue back through the carb (early sign of needing a refresh).
 
The motor is back together with new seals, springs, etc. and ready to be dropped back in the car.
 
These motors like fuel, they like being in their happy temperature zone (water 185-195, oil 195-205F) in order to make meaningful power. Build them right and they will last.
 
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Topics:   12A, Colorado Rotary Engine shop, vintage racing 12A

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